/* $OpenBSD: channels.c,v 1.442 2024/12/05 06:49:26 dtucker Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * This file contains functions for generic socket connection forwarding.
 * There is also code for initiating connection forwarding for X11 connections,
 * arbitrary tcp/ip connections, and the authentication agent connection.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 *
 * SSH2 support added by Markus Friedl.
 * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
 * Copyright (c) 1999 Dug Song.  All rights reserved.
 * Copyright (c) 1999 Theo de Raadt.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/un.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif

#include <netinet/in.h>
#include <arpa/inet.h>

#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <netdb.h>
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#include <stdarg.h>
#ifdef HAVE_STDINT_H
# include <stdint.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>

#include "openbsd-compat/sys-queue.h"
#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "ssherr.h"
#include "sshbuf.h"
#include "packet.h"
#include "log.h"
#include "misc.h"
#include "channels.h"
#include "compat.h"
#include "canohost.h"
#include "sshkey.h"
#include "authfd.h"
#include "pathnames.h"
#include "match.h"

/* XXX remove once we're satisfied there's no lurking bugs */
/* #define DEBUG_CHANNEL_POLL 1 */

/* -- agent forwarding */
#define NUM_SOCKS       10

/* -- X11 forwarding */
/* X11 port for display :0 */
#define X11_BASE_PORT   6000
/* Maximum number of fake X11 displays to try. */
#define MAX_DISPLAYS  1000

/* Per-channel callback for pre/post IO actions */
typedef void chan_fn(struct ssh *, Channel *c);

/*
 * Data structure for storing which hosts are permitted for forward requests.
 * The local sides of any remote forwards are stored in this array to prevent
 * a corrupt remote server from accessing arbitrary TCP/IP ports on our local
 * network (which might be behind a firewall).
 */
/* XXX: streamlocal wants a path instead of host:port */
/*      Overload host_to_connect; we could just make this match Forward */
/*      XXX - can we use listen_host instead of listen_path? */
struct permission {
        char *host_to_connect;          /* Connect to 'host'. */
        int port_to_connect;            /* Connect to 'port'. */
        char *listen_host;              /* Remote side should listen address. */
        char *listen_path;              /* Remote side should listen path. */
        int listen_port;                /* Remote side should listen port. */
        Channel *downstream;            /* Downstream mux*/
};

/*
 * Stores the forwarding permission state for a single direction (local or
 * remote).
 */
struct permission_set {
        /*
         * List of all local permitted host/port pairs to allow for the
         * user.
         */
        u_int num_permitted_user;
        struct permission *permitted_user;

        /*
         * List of all permitted host/port pairs to allow for the admin.
         */
        u_int num_permitted_admin;
        struct permission *permitted_admin;

        /*
         * If this is true, all opens/listens are permitted.  This is the
         * case on the server on which we have to trust the client anyway,
         * and the user could do anything after logging in.
         */
        int all_permitted;
};

/* Used to record timeouts per channel type */
struct ssh_channel_timeout {
        char *type_pattern;
        int timeout_secs;
};

/* Master structure for channels state */
struct ssh_channels {
        /*
         * Pointer to an array containing all allocated channels.  The array
         * is dynamically extended as needed.
         */
        Channel **channels;

        /*
         * Size of the channel array.  All slots of the array must always be
         * initialized (at least the type field); unused slots set to NULL
         */
        u_int channels_alloc;

        /*
         * 'channel_pre*' are called just before IO to add any bits
         * relevant to channels in the c->io_want bitmasks.
         *
         * 'channel_post*': perform any appropriate operations for
         * channels which have c->io_ready events pending.
         */
        chan_fn **channel_pre;
        chan_fn **channel_post;

        /* -- tcp forwarding */
        struct permission_set local_perms;
        struct permission_set remote_perms;

        /* -- X11 forwarding */

        /* Saved X11 local (client) display. */
        char *x11_saved_display;

        /* Saved X11 authentication protocol name. */
        char *x11_saved_proto;

        /* Saved X11 authentication data.  This is the real data. */
        char *x11_saved_data;
        u_int x11_saved_data_len;

        /* Deadline after which all X11 connections are refused */
        time_t x11_refuse_time;

        /*
         * Fake X11 authentication data.  This is what the server will be
         * sending us; we should replace any occurrences of this by the
         * real data.
         */
        u_char *x11_fake_data;
        u_int x11_fake_data_len;

        /* AF_UNSPEC or AF_INET or AF_INET6 */
        int IPv4or6;

        /* Channel timeouts by type */
        struct ssh_channel_timeout *timeouts;
        size_t ntimeouts;
        /* Global timeout for all OPEN channels */
        int global_deadline;
        time_t lastused;
};

/* helper */
static void port_open_helper(struct ssh *ssh, Channel *c, char *rtype);
static const char *channel_rfwd_bind_host(const char *listen_host);

/* non-blocking connect helpers */
static int connect_next(struct channel_connect *);
static void channel_connect_ctx_free(struct channel_connect *);
static Channel *rdynamic_connect_prepare(struct ssh *, char *, char *);
static int rdynamic_connect_finish(struct ssh *, Channel *);

/* Setup helper */
static void channel_handler_init(struct ssh_channels *sc);

/* -- channel core */

void
channel_init_channels(struct ssh *ssh)
{
        struct ssh_channels *sc;

        if ((sc = calloc(1, sizeof(*sc))) == NULL)
                fatal_f("allocation failed");
        sc->channels_alloc = 10;
        sc->channels = xcalloc(sc->channels_alloc, sizeof(*sc->channels));
        sc->IPv4or6 = AF_UNSPEC;
        channel_handler_init(sc);

        ssh->chanctxt = sc;
}

Channel *
channel_by_id(struct ssh *ssh, int id)
{
        Channel *c;

        if (id < 0 || (u_int)id >= ssh->chanctxt->channels_alloc) {
                logit_f("%d: bad id", id);
                return NULL;
        }
        c = ssh->chanctxt->channels[id];
        if (c == NULL) {
                logit_f("%d: bad id: channel free", id);
                return NULL;
        }
        return c;
}

Channel *
channel_by_remote_id(struct ssh *ssh, u_int remote_id)
{
        Channel *c;
        u_int i;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c != NULL && c->have_remote_id && c->remote_id == remote_id)
                        return c;
        }
        return NULL;
}

/*
 * Returns the channel if it is allowed to receive protocol messages.
 * Private channels, like listening sockets, may not receive messages.
 */
Channel *
channel_lookup(struct ssh *ssh, int id)
{
        Channel *c;

        if ((c = channel_by_id(ssh, id)) == NULL)
                return NULL;

        switch (c->type) {
        case SSH_CHANNEL_X11_OPEN:
        case SSH_CHANNEL_LARVAL:
        case SSH_CHANNEL_CONNECTING:
        case SSH_CHANNEL_DYNAMIC:
        case SSH_CHANNEL_RDYNAMIC_OPEN:
        case SSH_CHANNEL_RDYNAMIC_FINISH:
        case SSH_CHANNEL_OPENING:
        case SSH_CHANNEL_OPEN:
        case SSH_CHANNEL_ABANDONED:
        case SSH_CHANNEL_MUX_PROXY:
                return c;
        }
        logit("Non-public channel %d, type %d.", id, c->type);
        return NULL;
}

/*
 * Add a timeout for open channels whose c->ctype (or c->xctype if it is set)
 * match type_pattern.
 */
void
channel_add_timeout(struct ssh *ssh, const char *type_pattern,
    int timeout_secs)
{
        struct ssh_channels *sc = ssh->chanctxt;

        if (strcmp(type_pattern, "global") == 0) {
                debug2_f("global channel timeout %d seconds", timeout_secs);
                sc->global_deadline = timeout_secs;
                return;
        }
        debug2_f("channel type \"%s\" timeout %d seconds",
            type_pattern, timeout_secs);
        sc->timeouts = xrecallocarray(sc->timeouts, sc->ntimeouts,
            sc->ntimeouts + 1, sizeof(*sc->timeouts));
        sc->timeouts[sc->ntimeouts].type_pattern = xstrdup(type_pattern);
        sc->timeouts[sc->ntimeouts].timeout_secs = timeout_secs;
        sc->ntimeouts++;
}

/* Clears all previously-added channel timeouts */
void
channel_clear_timeouts(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;
        size_t i;

        debug3_f("clearing");
        for (i = 0; i < sc->ntimeouts; i++)
                free(sc->timeouts[i].type_pattern);
        free(sc->timeouts);
        sc->timeouts = NULL;
        sc->ntimeouts = 0;
}

static int
lookup_timeout(struct ssh *ssh, const char *type)
{
        struct ssh_channels *sc = ssh->chanctxt;
        size_t i;

        for (i = 0; i < sc->ntimeouts; i++) {
                if (match_pattern(type, sc->timeouts[i].type_pattern))
                        return sc->timeouts[i].timeout_secs;
        }

        return 0;
}

/*
 * Sets "extended type" of a channel; used by session layer to add additional
 * information about channel types (e.g. shell, login, subsystem) that can then
 * be used to select timeouts.
 * Will reset c->inactive_deadline as a side-effect.
 */
void
channel_set_xtype(struct ssh *ssh, int id, const char *xctype)
{
        Channel *c;

        if ((c = channel_by_id(ssh, id)) == NULL)
                fatal_f("missing channel %d", id);
        if (c->xctype != NULL)
                free(c->xctype);
        c->xctype = xstrdup(xctype);
        /* Type has changed, so look up inactivity deadline again */
        c->inactive_deadline = lookup_timeout(ssh, c->xctype);
        debug2_f("labeled channel %d as %s (inactive timeout %u)", id, xctype,
            c->inactive_deadline);
}

/*
 * update "last used" time on a channel.
 * NB. nothing else should update lastused except to clear it.
 */
static void
channel_set_used_time(struct ssh *ssh, Channel *c)
{
        ssh->chanctxt->lastused = monotime();
        if (c != NULL)
                c->lastused = ssh->chanctxt->lastused;
}

/*
 * Get the time at which a channel is due to time out for inactivity.
 * Returns 0 if the channel is not due to time out ever.
 */
static time_t
channel_get_expiry(struct ssh *ssh, Channel *c)
{
        struct ssh_channels *sc = ssh->chanctxt;
        time_t expiry = 0, channel_expiry;

        if (sc->lastused != 0 && sc->global_deadline != 0)
                expiry = sc->lastused + sc->global_deadline;
        if (c->lastused != 0 && c->inactive_deadline != 0) {
                channel_expiry = c->lastused + c->inactive_deadline;
                if (expiry == 0 || channel_expiry < expiry)
                        expiry = channel_expiry;
        }
        return expiry;
}

/*
 * Register filedescriptors for a channel, used when allocating a channel or
 * when the channel consumer/producer is ready, e.g. shell exec'd
 */
static void
channel_register_fds(struct ssh *ssh, Channel *c, int rfd, int wfd, int efd,
    int extusage, int nonblock, int is_tty)
{
        int val;

        if (rfd != -1)
                (void)fcntl(rfd, F_SETFD, FD_CLOEXEC);
        if (wfd != -1 && wfd != rfd)
                (void)fcntl(wfd, F_SETFD, FD_CLOEXEC);
        if (efd != -1 && efd != rfd && efd != wfd)
                (void)fcntl(efd, F_SETFD, FD_CLOEXEC);

        c->rfd = rfd;
        c->wfd = wfd;
        c->sock = (rfd == wfd) ? rfd : -1;
        c->efd = efd;
        c->extended_usage = extusage;

        if ((c->isatty = is_tty) != 0)
                debug2("channel %d: rfd %d isatty", c->self, c->rfd);
#ifdef _AIX
        /* XXX: Later AIX versions can't push as much data to tty */
        c->wfd_isatty = is_tty || isatty(c->wfd);
#endif

        /* enable nonblocking mode */
        c->restore_block = 0;
        if (nonblock == CHANNEL_NONBLOCK_STDIO) {
                /*
                 * Special handling for stdio file descriptors: do not set
                 * non-blocking mode if they are TTYs. Otherwise prepare to
                 * restore their blocking state on exit to avoid interfering
                 * with other programs that follow.
                 */
                if (rfd != -1 && !isatty(rfd) &&
                    (val = fcntl(rfd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
                        c->restore_flags[0] = val;
                        c->restore_block |= CHANNEL_RESTORE_RFD;
                        set_nonblock(rfd);
                }
                if (wfd != -1 && !isatty(wfd) &&
                    (val = fcntl(wfd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
                        c->restore_flags[1] = val;
                        c->restore_block |= CHANNEL_RESTORE_WFD;
                        set_nonblock(wfd);
                }
                if (efd != -1 && !isatty(efd) &&
                    (val = fcntl(efd, F_GETFL)) != -1 && !(val & O_NONBLOCK)) {
                        c->restore_flags[2] = val;
                        c->restore_block |= CHANNEL_RESTORE_EFD;
                        set_nonblock(efd);
                }
        } else if (nonblock) {
                if (rfd != -1)
                        set_nonblock(rfd);
                if (wfd != -1)
                        set_nonblock(wfd);
                if (efd != -1)
                        set_nonblock(efd);
        }
        /* channel might be entering a larval state, so reset global timeout */
        channel_set_used_time(ssh, NULL);
}

/*
 * Allocate a new channel object and set its type and socket.
 */
Channel *
channel_new(struct ssh *ssh, char *ctype, int type, int rfd, int wfd, int efd,
    u_int window, u_int maxpack, int extusage, const char *remote_name,
    int nonblock)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int i, found = 0;
        Channel *c;
        int r;

        /* Try to find a free slot where to put the new channel. */
        for (i = 0; i < sc->channels_alloc; i++) {
                if (sc->channels[i] == NULL) {
                        /* Found a free slot. */
                        found = i;
                        break;
                }
        }
        if (i >= sc->channels_alloc) {
                /*
                 * There are no free slots. Take last+1 slot and expand
                 * the array.
                 */
                found = sc->channels_alloc;
                if (sc->channels_alloc > CHANNELS_MAX_CHANNELS)
                        fatal_f("internal error: channels_alloc %d too big",
                            sc->channels_alloc);
                sc->channels = xrecallocarray(sc->channels, sc->channels_alloc,
                    sc->channels_alloc + 10, sizeof(*sc->channels));
                sc->channels_alloc += 10;
                debug2("channel: expanding %d", sc->channels_alloc);
        }
        /* Initialize and return new channel. */
        c = sc->channels[found] = xcalloc(1, sizeof(Channel));
        if ((c->input = sshbuf_new()) == NULL ||
            (c->output = sshbuf_new()) == NULL ||
            (c->extended = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_set_max_size(c->input, CHAN_INPUT_MAX)) != 0)
                fatal_fr(r, "sshbuf_set_max_size");
        c->ostate = CHAN_OUTPUT_OPEN;
        c->istate = CHAN_INPUT_OPEN;
        channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, 0);
        c->self = found;
        c->type = type;
        c->ctype = ctype;
        c->local_window = window;
        c->local_window_max = window;
        c->local_maxpacket = maxpack;
        c->remote_name = xstrdup(remote_name);
        c->ctl_chan = -1;
        c->delayed = 1;         /* prevent call to channel_post handler */
        c->inactive_deadline = lookup_timeout(ssh, c->ctype);
        TAILQ_INIT(&c->status_confirms);
        debug("channel %d: new %s [%s] (inactive timeout: %u)",
            found, c->ctype, remote_name, c->inactive_deadline);
        return c;
}

int
channel_close_fd(struct ssh *ssh, Channel *c, int *fdp)
{
        int ret, fd = *fdp;

        if (fd == -1)
                return 0;

        /* restore blocking */
        if (*fdp == c->rfd &&
            (c->restore_block & CHANNEL_RESTORE_RFD) != 0)
                (void)fcntl(*fdp, F_SETFL, c->restore_flags[0]);
        else if (*fdp == c->wfd &&
            (c->restore_block & CHANNEL_RESTORE_WFD) != 0)
                (void)fcntl(*fdp, F_SETFL, c->restore_flags[1]);
        else if (*fdp == c->efd &&
            (c->restore_block & CHANNEL_RESTORE_EFD) != 0)
                (void)fcntl(*fdp, F_SETFL, c->restore_flags[2]);

        if (*fdp == c->rfd) {
                c->io_want &= ~SSH_CHAN_IO_RFD;
                c->io_ready &= ~SSH_CHAN_IO_RFD;
                c->rfd = -1;
                c->pfds[0] = -1;
        }
        if (*fdp == c->wfd) {
                c->io_want &= ~SSH_CHAN_IO_WFD;
                c->io_ready &= ~SSH_CHAN_IO_WFD;
                c->wfd = -1;
                c->pfds[1] = -1;
        }
        if (*fdp == c->efd) {
                c->io_want &= ~SSH_CHAN_IO_EFD;
                c->io_ready &= ~SSH_CHAN_IO_EFD;
                c->efd = -1;
                c->pfds[2] = -1;
        }
        if (*fdp == c->sock) {
                c->io_want &= ~SSH_CHAN_IO_SOCK;
                c->io_ready &= ~SSH_CHAN_IO_SOCK;
                c->sock = -1;
                c->pfds[3] = -1;
        }

        ret = close(fd);
        *fdp = -1; /* probably redundant */
        return ret;
}

/* Close all channel fd/socket. */
static void
channel_close_fds(struct ssh *ssh, Channel *c)
{
        int sock = c->sock, rfd = c->rfd, wfd = c->wfd, efd = c->efd;

        channel_close_fd(ssh, c, &c->sock);
        if (rfd != sock)
                channel_close_fd(ssh, c, &c->rfd);
        if (wfd != sock && wfd != rfd)
                channel_close_fd(ssh, c, &c->wfd);
        if (efd != sock && efd != rfd && efd != wfd)
                channel_close_fd(ssh, c, &c->efd);
}

static void
fwd_perm_clear(struct permission *perm)
{
        free(perm->host_to_connect);
        free(perm->listen_host);
        free(perm->listen_path);
        memset(perm, 0, sizeof(*perm));
}

/* Returns an printable name for the specified forwarding permission list */
static const char *
fwd_ident(int who, int where)
{
        if (who == FORWARD_ADM) {
                if (where == FORWARD_LOCAL)
                        return "admin local";
                else if (where == FORWARD_REMOTE)
                        return "admin remote";
        } else if (who == FORWARD_USER) {
                if (where == FORWARD_LOCAL)
                        return "user local";
                else if (where == FORWARD_REMOTE)
                        return "user remote";
        }
        fatal("Unknown forward permission list %d/%d", who, where);
}

/* Returns the forwarding permission list for the specified direction */
static struct permission_set *
permission_set_get(struct ssh *ssh, int where)
{
        struct ssh_channels *sc = ssh->chanctxt;

        switch (where) {
        case FORWARD_LOCAL:
                return &sc->local_perms;
                break;
        case FORWARD_REMOTE:
                return &sc->remote_perms;
                break;
        default:
                fatal_f("invalid forwarding direction %d", where);
        }
}

/* Returns pointers to the specified forwarding list and its element count */
static void
permission_set_get_array(struct ssh *ssh, int who, int where,
    struct permission ***permpp, u_int **npermpp)
{
        struct permission_set *pset = permission_set_get(ssh, where);

        switch (who) {
        case FORWARD_USER:
                *permpp = &pset->permitted_user;
                *npermpp = &pset->num_permitted_user;
                break;
        case FORWARD_ADM:
                *permpp = &pset->permitted_admin;
                *npermpp = &pset->num_permitted_admin;
                break;
        default:
                fatal_f("invalid forwarding client %d", who);
        }
}

/* Adds an entry to the specified forwarding list */
static int
permission_set_add(struct ssh *ssh, int who, int where,
    const char *host_to_connect, int port_to_connect,
    const char *listen_host, const char *listen_path, int listen_port,
    Channel *downstream)
{
        struct permission **permp;
        u_int n, *npermp;

        permission_set_get_array(ssh, who, where, &permp, &npermp);

        if (*npermp >= INT_MAX)
                fatal_f("%s overflow", fwd_ident(who, where));

        *permp = xrecallocarray(*permp, *npermp, *npermp + 1, sizeof(**permp));
        n = (*npermp)++;
#define MAYBE_DUP(s) ((s == NULL) ? NULL : xstrdup(s))
        (*permp)[n].host_to_connect = MAYBE_DUP(host_to_connect);
        (*permp)[n].port_to_connect = port_to_connect;
        (*permp)[n].listen_host = MAYBE_DUP(listen_host);
        (*permp)[n].listen_path = MAYBE_DUP(listen_path);
        (*permp)[n].listen_port = listen_port;
        (*permp)[n].downstream = downstream;
#undef MAYBE_DUP
        return (int)n;
}

static void
mux_remove_remote_forwardings(struct ssh *ssh, Channel *c)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        struct permission *perm;
        int r;
        u_int i;

        for (i = 0; i < pset->num_permitted_user; i++) {
                perm = &pset->permitted_user[i];
                if (perm->downstream != c)
                        continue;

                /* cancel on the server, since mux client is gone */
                debug("channel %d: cleanup remote forward for %s:%u",
                    c->self, perm->listen_host, perm->listen_port);
                if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
                    (r = sshpkt_put_cstring(ssh,
                    "cancel-tcpip-forward")) != 0 ||
                    (r = sshpkt_put_u8(ssh, 0)) != 0 ||
                    (r = sshpkt_put_cstring(ssh,
                    channel_rfwd_bind_host(perm->listen_host))) != 0 ||
                    (r = sshpkt_put_u32(ssh, perm->listen_port)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        fatal_fr(r, "channel %i", c->self);
                }
                fwd_perm_clear(perm); /* unregister */
        }
}

/* Free the channel and close its fd/socket. */
void
channel_free(struct ssh *ssh, Channel *c)
{
        struct ssh_channels *sc = ssh->chanctxt;
        char *s;
        u_int i, n;
        Channel *other;
        struct channel_confirm *cc;

        for (n = 0, i = 0; i < sc->channels_alloc; i++) {
                if ((other = sc->channels[i]) == NULL)
                        continue;
                n++;
                /* detach from mux client and prepare for closing */
                if (c->type == SSH_CHANNEL_MUX_CLIENT &&
                    other->type == SSH_CHANNEL_MUX_PROXY &&
                    other->mux_ctx == c) {
                        other->mux_ctx = NULL;
                        other->type = SSH_CHANNEL_OPEN;
                        other->istate = CHAN_INPUT_CLOSED;
                        other->ostate = CHAN_OUTPUT_CLOSED;
                }
        }
        debug("channel %d: free: %s, nchannels %u", c->self,
            c->remote_name ? c->remote_name : "???", n);

        if (c->type == SSH_CHANNEL_MUX_CLIENT) {
                mux_remove_remote_forwardings(ssh, c);
                free(c->mux_ctx);
                c->mux_ctx = NULL;
        } else if (c->type == SSH_CHANNEL_MUX_LISTENER) {
                free(c->mux_ctx);
                c->mux_ctx = NULL;
        }

        if (log_level_get() >= SYSLOG_LEVEL_DEBUG3) {
                s = channel_open_message(ssh);
                debug3("channel %d: status: %s", c->self, s);
                free(s);
        }

        channel_close_fds(ssh, c);
        sshbuf_free(c->input);
        sshbuf_free(c->output);
        sshbuf_free(c->extended);
        c->input = c->output = c->extended = NULL;
        free(c->remote_name);
        c->remote_name = NULL;
        free(c->path);
        c->path = NULL;
        free(c->listening_addr);
        c->listening_addr = NULL;
        free(c->xctype);
        c->xctype = NULL;
        while ((cc = TAILQ_FIRST(&c->status_confirms)) != NULL) {
                if (cc->abandon_cb != NULL)
                        cc->abandon_cb(ssh, c, cc->ctx);
                TAILQ_REMOVE(&c->status_confirms, cc, entry);
                freezero(cc, sizeof(*cc));
        }
        if (c->filter_cleanup != NULL && c->filter_ctx != NULL)
                c->filter_cleanup(ssh, c->self, c->filter_ctx);
        sc->channels[c->self] = NULL;
        freezero(c, sizeof(*c));
}

void
channel_free_all(struct ssh *ssh)
{
        u_int i;
        struct ssh_channels *sc = ssh->chanctxt;

        for (i = 0; i < sc->channels_alloc; i++)
                if (sc->channels[i] != NULL)
                        channel_free(ssh, sc->channels[i]);

        free(sc->channels);
        sc->channels = NULL;
        sc->channels_alloc = 0;

        free(sc->x11_saved_display);
        sc->x11_saved_display = NULL;

        free(sc->x11_saved_proto);
        sc->x11_saved_proto = NULL;

        free(sc->x11_saved_data);
        sc->x11_saved_data = NULL;
        sc->x11_saved_data_len = 0;

        free(sc->x11_fake_data);
        sc->x11_fake_data = NULL;
        sc->x11_fake_data_len = 0;
}

/*
 * Closes the sockets/fds of all channels.  This is used to close extra file
 * descriptors after a fork.
 */
void
channel_close_all(struct ssh *ssh)
{
        u_int i;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++)
                if (ssh->chanctxt->channels[i] != NULL)
                        channel_close_fds(ssh, ssh->chanctxt->channels[i]);
}

/*
 * Stop listening to channels.
 */
void
channel_stop_listening(struct ssh *ssh)
{
        u_int i;
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c != NULL) {
                        switch (c->type) {
                        case SSH_CHANNEL_AUTH_SOCKET:
                        case SSH_CHANNEL_PORT_LISTENER:
                        case SSH_CHANNEL_RPORT_LISTENER:
                        case SSH_CHANNEL_X11_LISTENER:
                        case SSH_CHANNEL_UNIX_LISTENER:
                        case SSH_CHANNEL_RUNIX_LISTENER:
                                channel_close_fd(ssh, c, &c->sock);
                                channel_free(ssh, c);
                                break;
                        }
                }
        }
}

/*
 * Returns true if no channel has too much buffered data, and false if one or
 * more channel is overfull.
 */
int
channel_not_very_much_buffered_data(struct ssh *ssh)
{
        u_int i;
        u_int maxsize = ssh_packet_get_maxsize(ssh);
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_OPEN)
                        continue;
                if (sshbuf_len(c->output) > maxsize) {
                        debug2("channel %d: big output buffer %zu > %u",
                            c->self, sshbuf_len(c->output), maxsize);
                        return 0;
                }
        }
        return 1;
}

/* Returns true if any channel is still open. */
int
channel_still_open(struct ssh *ssh)
{
        u_int i;
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_MUX_LISTENER:
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_RDYNAMIC_OPEN:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_ZOMBIE:
                case SSH_CHANNEL_ABANDONED:
                case SSH_CHANNEL_UNIX_LISTENER:
                case SSH_CHANNEL_RUNIX_LISTENER:
                        continue;
                case SSH_CHANNEL_LARVAL:
                        continue;
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_RDYNAMIC_FINISH:
                case SSH_CHANNEL_X11_OPEN:
                case SSH_CHANNEL_MUX_CLIENT:
                case SSH_CHANNEL_MUX_PROXY:
                        return 1;
                default:
                        fatal_f("bad channel type %d", c->type);
                        /* NOTREACHED */
                }
        }
        return 0;
}

/* Returns true if a channel with a TTY is open. */
int
channel_tty_open(struct ssh *ssh)
{
        u_int i;
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_OPEN)
                        continue;
                if (c->client_tty)
                        return 1;
        }
        return 0;
}

/* Returns the id of an open channel suitable for keepaliving */
int
channel_find_open(struct ssh *ssh)
{
        u_int i;
        Channel *c;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL || !c->have_remote_id)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_RDYNAMIC_OPEN:
                case SSH_CHANNEL_RDYNAMIC_FINISH:
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_MUX_LISTENER:
                case SSH_CHANNEL_MUX_CLIENT:
                case SSH_CHANNEL_MUX_PROXY:
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_ZOMBIE:
                case SSH_CHANNEL_ABANDONED:
                case SSH_CHANNEL_UNIX_LISTENER:
                case SSH_CHANNEL_RUNIX_LISTENER:
                        continue;
                case SSH_CHANNEL_LARVAL:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_X11_OPEN:
                        return i;
                default:
                        fatal_f("bad channel type %d", c->type);
                        /* NOTREACHED */
                }
        }
        return -1;
}

/* Returns the state of the channel's extended usage flag */
const char *
channel_format_extended_usage(const Channel *c)
{
        if (c->efd == -1)
                return "closed";

        switch (c->extended_usage) {
        case CHAN_EXTENDED_WRITE:
                return "write";
        case CHAN_EXTENDED_READ:
                return "read";
        case CHAN_EXTENDED_IGNORE:
                return "ignore";
        default:
                return "UNKNOWN";
        }
}

static char *
channel_format_status(const Channel *c)
{
        char *ret = NULL;

        xasprintf(&ret, "t%d [%s] %s%u %s%u i%u/%zu o%u/%zu e[%s]/%zu "
            "fd %d/%d/%d sock %d cc %d %s%u io 0x%02x/0x%02x",
            c->type, c->xctype != NULL ? c->xctype : c->ctype,
            c->have_remote_id ? "r" : "nr", c->remote_id,
            c->mux_ctx != NULL ? "m" : "nm", c->mux_downstream_id,
            c->istate, sshbuf_len(c->input),
            c->ostate, sshbuf_len(c->output),
            channel_format_extended_usage(c), sshbuf_len(c->extended),
            c->rfd, c->wfd, c->efd, c->sock, c->ctl_chan,
            c->have_ctl_child_id ? "c" : "nc", c->ctl_child_id,
            c->io_want, c->io_ready);
        return ret;
}

/*
 * Returns a message describing the currently open forwarded connections,
 * suitable for sending to the client.  The message contains crlf pairs for
 * newlines.
 */
char *
channel_open_message(struct ssh *ssh)
{
        struct sshbuf *buf;
        Channel *c;
        u_int i;
        int r;
        char *cp, *ret;

        if ((buf = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        if ((r = sshbuf_putf(buf,
            "The following connections are open:\r\n")) != 0)
                fatal_fr(r, "sshbuf_putf");
        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL)
                        continue;
                switch (c->type) {
                case SSH_CHANNEL_X11_LISTENER:
                case SSH_CHANNEL_PORT_LISTENER:
                case SSH_CHANNEL_RPORT_LISTENER:
                case SSH_CHANNEL_CLOSED:
                case SSH_CHANNEL_AUTH_SOCKET:
                case SSH_CHANNEL_ZOMBIE:
                case SSH_CHANNEL_ABANDONED:
                case SSH_CHANNEL_MUX_LISTENER:
                case SSH_CHANNEL_UNIX_LISTENER:
                case SSH_CHANNEL_RUNIX_LISTENER:
                        continue;
                case SSH_CHANNEL_LARVAL:
                case SSH_CHANNEL_OPENING:
                case SSH_CHANNEL_CONNECTING:
                case SSH_CHANNEL_DYNAMIC:
                case SSH_CHANNEL_RDYNAMIC_OPEN:
                case SSH_CHANNEL_RDYNAMIC_FINISH:
                case SSH_CHANNEL_OPEN:
                case SSH_CHANNEL_X11_OPEN:
                case SSH_CHANNEL_MUX_PROXY:
                case SSH_CHANNEL_MUX_CLIENT:
                        cp = channel_format_status(c);
                        if ((r = sshbuf_putf(buf, "  #%d %.300s (%s)\r\n",
                            c->self, c->remote_name, cp)) != 0) {
                                free(cp);
                                fatal_fr(r, "sshbuf_putf");
                        }
                        free(cp);
                        continue;
                default:
                        fatal_f("bad channel type %d", c->type);
                        /* NOTREACHED */
                }
        }
        if ((ret = sshbuf_dup_string(buf)) == NULL)
                fatal_f("sshbuf_dup_string");
        sshbuf_free(buf);
        return ret;
}

static void
open_preamble(struct ssh *ssh, const char *where, Channel *c, const char *type)
{
        int r;

        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN)) != 0 ||
            (r = sshpkt_put_cstring(ssh, type)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0) {
                fatal_r(r, "%s: channel %i: open", where, c->self);
        }
}

void
channel_send_open(struct ssh *ssh, int id)
{
        Channel *c = channel_lookup(ssh, id);
        int r;

        if (c == NULL) {
                logit("channel_send_open: %d: bad id", id);
                return;
        }
        debug2("channel %d: send open", id);
        open_preamble(ssh, __func__, c, c->ctype);
        if ((r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "channel %i", c->self);
}

void
channel_request_start(struct ssh *ssh, int id, char *service, int wantconfirm)
{
        Channel *c = channel_lookup(ssh, id);
        int r;

        if (c == NULL) {
                logit_f("%d: unknown channel id", id);
                return;
        }
        if (!c->have_remote_id)
                fatal_f("channel %d: no remote id", c->self);

        debug2("channel %d: request %s confirm %d", id, service, wantconfirm);
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_REQUEST)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_cstring(ssh, service)) != 0 ||
            (r = sshpkt_put_u8(ssh, wantconfirm)) != 0) {
                fatal_fr(r, "channel %i", c->self);
        }
}

void
channel_register_status_confirm(struct ssh *ssh, int id,
    channel_confirm_cb *cb, channel_confirm_abandon_cb *abandon_cb, void *ctx)
{
        struct channel_confirm *cc;
        Channel *c;

        if ((c = channel_lookup(ssh, id)) == NULL)
                fatal_f("%d: bad id", id);

        cc = xcalloc(1, sizeof(*cc));
        cc->cb = cb;
        cc->abandon_cb = abandon_cb;
        cc->ctx = ctx;
        TAILQ_INSERT_TAIL(&c->status_confirms, cc, entry);
}

void
channel_register_open_confirm(struct ssh *ssh, int id,
    channel_open_fn *fn, void *ctx)
{
        Channel *c = channel_lookup(ssh, id);

        if (c == NULL) {
                logit_f("%d: bad id", id);
                return;
        }
        c->open_confirm = fn;
        c->open_confirm_ctx = ctx;
}

void
channel_register_cleanup(struct ssh *ssh, int id,
    channel_callback_fn *fn, int do_close)
{
        Channel *c = channel_by_id(ssh, id);

        if (c == NULL) {
                logit_f("%d: bad id", id);
                return;
        }
        c->detach_user = fn;
        c->detach_close = do_close;
}

void
channel_cancel_cleanup(struct ssh *ssh, int id)
{
        Channel *c = channel_by_id(ssh, id);

        if (c == NULL) {
                logit_f("%d: bad id", id);
                return;
        }
        c->detach_user = NULL;
        c->detach_close = 0;
}

void
channel_register_filter(struct ssh *ssh, int id, channel_infilter_fn *ifn,
    channel_outfilter_fn *ofn, channel_filter_cleanup_fn *cfn, void *ctx)
{
        Channel *c = channel_lookup(ssh, id);

        if (c == NULL) {
                logit_f("%d: bad id", id);
                return;
        }
        c->input_filter = ifn;
        c->output_filter = ofn;
        c->filter_ctx = ctx;
        c->filter_cleanup = cfn;
}

void
channel_set_fds(struct ssh *ssh, int id, int rfd, int wfd, int efd,
    int extusage, int nonblock, int is_tty, u_int window_max)
{
        Channel *c = channel_lookup(ssh, id);
        int r;

        if (c == NULL || c->type != SSH_CHANNEL_LARVAL)
                fatal("channel_activate for non-larval channel %d.", id);
        if (!c->have_remote_id)
                fatal_f("channel %d: no remote id", c->self);

        channel_register_fds(ssh, c, rfd, wfd, efd, extusage, nonblock, is_tty);
        c->type = SSH_CHANNEL_OPEN;
        channel_set_used_time(ssh, c);
        c->local_window = c->local_window_max = window_max;

        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "channel %i", c->self);
}

static void
channel_pre_listener(struct ssh *ssh, Channel *c)
{
        c->io_want = SSH_CHAN_IO_SOCK_R;
}

static void
channel_pre_connecting(struct ssh *ssh, Channel *c)
{
        debug3("channel %d: waiting for connection", c->self);
        c->io_want = SSH_CHAN_IO_SOCK_W;
}

static void
channel_pre_open(struct ssh *ssh, Channel *c)
{
        c->io_want = 0;
        if (c->istate == CHAN_INPUT_OPEN &&
            c->remote_window > 0 &&
            sshbuf_len(c->input) < c->remote_window &&
            sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
                c->io_want |= SSH_CHAN_IO_RFD;
        if (c->ostate == CHAN_OUTPUT_OPEN ||
            c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                if (sshbuf_len(c->output) > 0) {
                        c->io_want |= SSH_CHAN_IO_WFD;
                } else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                        if (CHANNEL_EFD_OUTPUT_ACTIVE(c))
                                debug2("channel %d: "
                                    "obuf_empty delayed efd %d/(%zu)", c->self,
                                    c->efd, sshbuf_len(c->extended));
                        else
                                chan_obuf_empty(ssh, c);
                }
        }
        /** XXX check close conditions, too */
        if (c->efd != -1 && !(c->istate == CHAN_INPUT_CLOSED &&
            c->ostate == CHAN_OUTPUT_CLOSED)) {
                if (c->extended_usage == CHAN_EXTENDED_WRITE &&
                    sshbuf_len(c->extended) > 0)
                        c->io_want |= SSH_CHAN_IO_EFD_W;
                else if (c->efd != -1 && !(c->flags & CHAN_EOF_SENT) &&
                    (c->extended_usage == CHAN_EXTENDED_READ ||
                    c->extended_usage == CHAN_EXTENDED_IGNORE) &&
                    sshbuf_len(c->extended) < c->remote_window)
                        c->io_want |= SSH_CHAN_IO_EFD_R;
        }
        /* XXX: What about efd? races? */
}

/*
 * This is a special state for X11 authentication spoofing.  An opened X11
 * connection (when authentication spoofing is being done) remains in this
 * state until the first packet has been completely read.  The authentication
 * data in that packet is then substituted by the real data if it matches the
 * fake data, and the channel is put into normal mode.
 * XXX All this happens at the client side.
 * Returns: 0 = need more data, -1 = wrong cookie, 1 = ok
 */
static int
x11_open_helper(struct ssh *ssh, struct sshbuf *b)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_char *ucp;
        u_int proto_len, data_len;

        /* Is this being called after the refusal deadline? */
        if (sc->x11_refuse_time != 0 &&
            monotime() >= sc->x11_refuse_time) {
                verbose("Rejected X11 connection after ForwardX11Timeout "
                    "expired");
                return -1;
        }

        /* Check if the fixed size part of the packet is in buffer. */
        if (sshbuf_len(b) < 12)
                return 0;

        /* Parse the lengths of variable-length fields. */
        ucp = sshbuf_mutable_ptr(b);
        if (ucp[0] == 0x42) {   /* Byte order MSB first. */
                proto_len = 256 * ucp[6] + ucp[7];
                data_len = 256 * ucp[8] + ucp[9];
        } else if (ucp[0] == 0x6c) {    /* Byte order LSB first. */
                proto_len = ucp[6] + 256 * ucp[7];
                data_len = ucp[8] + 256 * ucp[9];
        } else {
                debug2("Initial X11 packet contains bad byte order byte: 0x%x",
                    ucp[0]);
                return -1;
        }

        /* Check if the whole packet is in buffer. */
        if (sshbuf_len(b) <
            12 + ((proto_len + 3) & ~3) + ((data_len + 3) & ~3))
                return 0;

        /* Check if authentication protocol matches. */
        if (proto_len != strlen(sc->x11_saved_proto) ||
            memcmp(ucp + 12, sc->x11_saved_proto, proto_len) != 0) {
                debug2("X11 connection uses different authentication protocol.");
                return -1;
        }
        /* Check if authentication data matches our fake data. */
        if (data_len != sc->x11_fake_data_len ||
            timingsafe_bcmp(ucp + 12 + ((proto_len + 3) & ~3),
                sc->x11_fake_data, sc->x11_fake_data_len) != 0) {
                debug2("X11 auth data does not match fake data.");
                return -1;
        }
        /* Check fake data length */
        if (sc->x11_fake_data_len != sc->x11_saved_data_len) {
                error("X11 fake_data_len %d != saved_data_len %d",
                    sc->x11_fake_data_len, sc->x11_saved_data_len);
                return -1;
        }
        /*
         * Received authentication protocol and data match
         * our fake data. Substitute the fake data with real
         * data.
         */
        memcpy(ucp + 12 + ((proto_len + 3) & ~3),
            sc->x11_saved_data, sc->x11_saved_data_len);
        return 1;
}

void
channel_force_close(struct ssh *ssh, Channel *c, int abandon)
{
        debug3_f("channel %d: forcibly closing", c->self);
        if (c->istate == CHAN_INPUT_OPEN)
                chan_read_failed(ssh, c);
        if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
                sshbuf_reset(c->input);
                chan_ibuf_empty(ssh, c);
        }
        if (c->ostate == CHAN_OUTPUT_OPEN ||
            c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                sshbuf_reset(c->output);
                chan_write_failed(ssh, c);
        }
        if (c->detach_user)
                c->detach_user(ssh, c->self, 1, NULL);
        if (c->efd != -1)
                channel_close_fd(ssh, c, &c->efd);
        if (abandon)
                c->type = SSH_CHANNEL_ABANDONED;
        /* exempt from inactivity timeouts */
        c->inactive_deadline = 0;
        c->lastused = 0;
}

static void
channel_pre_x11_open(struct ssh *ssh, Channel *c)
{
        int ret = x11_open_helper(ssh, c->output);

        /* c->force_drain = 1; */

        if (ret == 1) {
                c->type = SSH_CHANNEL_OPEN;
                channel_set_used_time(ssh, c);
                channel_pre_open(ssh, c);
        } else if (ret == -1) {
                logit("X11 connection rejected because of wrong "
                    "authentication.");
                debug2("X11 rejected %d i%d/o%d",
                    c->self, c->istate, c->ostate);
                channel_force_close(ssh, c, 0);
        }
}

static void
channel_pre_mux_client(struct ssh *ssh, Channel *c)
{
        c->io_want = 0;
        if (c->istate == CHAN_INPUT_OPEN && !c->mux_pause &&
            sshbuf_check_reserve(c->input, CHAN_RBUF) == 0)
                c->io_want |= SSH_CHAN_IO_RFD;
        if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
                /* clear buffer immediately (discard any partial packet) */
                sshbuf_reset(c->input);
                chan_ibuf_empty(ssh, c);
                /* Start output drain. XXX just kill chan? */
                chan_rcvd_oclose(ssh, c);
        }
        if (c->ostate == CHAN_OUTPUT_OPEN ||
            c->ostate == CHAN_OUTPUT_WAIT_DRAIN) {
                if (sshbuf_len(c->output) > 0)
                        c->io_want |= SSH_CHAN_IO_WFD;
                else if (c->ostate == CHAN_OUTPUT_WAIT_DRAIN)
                        chan_obuf_empty(ssh, c);
        }
}

/* try to decode a socks4 header */
static int
channel_decode_socks4(Channel *c, struct sshbuf *input, struct sshbuf *output)
{
        const u_char *p;
        char *host;
        u_int len, have, i, found, need;
        char username[256];
        struct {
                u_int8_t version;
                u_int8_t command;
                u_int16_t dest_port;
                struct in_addr dest_addr;
        } s4_req, s4_rsp;
        int r;

        debug2("channel %d: decode socks4", c->self);

        have = sshbuf_len(input);
        len = sizeof(s4_req);
        if (have < len)
                return 0;
        p = sshbuf_ptr(input);

        need = 1;
        /* SOCKS4A uses an invalid IP address 0.0.0.x */
        if (p[4] == 0 && p[5] == 0 && p[6] == 0 && p[7] != 0) {
                debug2("channel %d: socks4a request", c->self);
                /* ... and needs an extra string (the hostname) */
                need = 2;
        }
        /* Check for terminating NUL on the string(s) */
        for (found = 0, i = len; i < have; i++) {
                if (p[i] == '\0') {
                        found++;
                        if (found == need)
                                break;
                }
                if (i > 1024) {
                        /* the peer is probably sending garbage */
                        debug("channel %d: decode socks4: too long",
                            c->self);
                        return -1;
                }
        }
        if (found < need)
                return 0;
        if ((r = sshbuf_get(input, &s4_req.version, 1)) != 0 ||
            (r = sshbuf_get(input, &s4_req.command, 1)) != 0 ||
            (r = sshbuf_get(input, &s4_req.dest_port, 2)) != 0 ||
            (r = sshbuf_get(input, &s4_req.dest_addr, 4)) != 0) {
                debug_r(r, "channels %d: decode socks4", c->self);
                return -1;
        }
        have = sshbuf_len(input);
        p = sshbuf_ptr(input);
        if (memchr(p, '\0', have) == NULL) {
                error("channel %d: decode socks4: unterminated user", c->self);
                return -1;
        }
        len = strlen(p);
        debug2("channel %d: decode socks4: user %s/%d", c->self, p, len);
        len++; /* trailing '\0' */
        strlcpy(username, p, sizeof(username));
        if ((r = sshbuf_consume(input, len)) != 0)
                fatal_fr(r, "channel %d: consume", c->self);
        free(c->path);
        c->path = NULL;
        if (need == 1) {                        /* SOCKS4: one string */
                host = inet_ntoa(s4_req.dest_addr);
                c->path = xstrdup(host);
        } else {                                /* SOCKS4A: two strings */
                have = sshbuf_len(input);
                p = sshbuf_ptr(input);
                if (memchr(p, '\0', have) == NULL) {
                        error("channel %d: decode socks4a: host not nul "
                            "terminated", c->self);
                        return -1;
                }
                len = strlen(p);
                debug2("channel %d: decode socks4a: host %s/%d",
                    c->self, p, len);
                len++;                          /* trailing '\0' */
                if (len > NI_MAXHOST) {
                        error("channel %d: hostname \"%.100s\" too long",
                            c->self, p);
                        return -1;
                }
                c->path = xstrdup(p);
                if ((r = sshbuf_consume(input, len)) != 0)
                        fatal_fr(r, "channel %d: consume", c->self);
        }
        c->host_port = ntohs(s4_req.dest_port);

        debug2("channel %d: dynamic request: socks4 host %s port %u command %u",
            c->self, c->path, c->host_port, s4_req.command);

        if (s4_req.command != 1) {
                debug("channel %d: cannot handle: %s cn %d",
                    c->self, need == 1 ? "SOCKS4" : "SOCKS4A", s4_req.command);
                return -1;
        }
        s4_rsp.version = 0;                     /* vn: 0 for reply */
        s4_rsp.command = 90;                    /* cd: req granted */
        s4_rsp.dest_port = 0;                   /* ignored */
        s4_rsp.dest_addr.s_addr = INADDR_ANY;   /* ignored */
        if ((r = sshbuf_put(output, &s4_rsp, sizeof(s4_rsp))) != 0)
                fatal_fr(r, "channel %d: append reply", c->self);
        return 1;
}

/* try to decode a socks5 header */
#define SSH_SOCKS5_AUTHDONE     0x1000
#define SSH_SOCKS5_NOAUTH       0x00
#define SSH_SOCKS5_IPV4         0x01
#define SSH_SOCKS5_DOMAIN       0x03
#define SSH_SOCKS5_IPV6         0x04
#define SSH_SOCKS5_CONNECT      0x01
#define SSH_SOCKS5_SUCCESS      0x00

static int
channel_decode_socks5(Channel *c, struct sshbuf *input, struct sshbuf *output)
{
        /* XXX use get/put_u8 instead of trusting struct padding */
        struct {
                u_int8_t version;
                u_int8_t command;
                u_int8_t reserved;
                u_int8_t atyp;
        } s5_req, s5_rsp;
        u_int16_t dest_port;
        char dest_addr[255+1], ntop[INET6_ADDRSTRLEN];
        const u_char *p;
        u_int have, need, i, found, nmethods, addrlen, af;
        int r;

        debug2("channel %d: decode socks5", c->self);
        p = sshbuf_ptr(input);
        if (p[0] != 0x05)
                return -1;
        have = sshbuf_len(input);
        if (!(c->flags & SSH_SOCKS5_AUTHDONE)) {
                /* format: ver | nmethods | methods */
                if (have < 2)
                        return 0;
                nmethods = p[1];
                if (have < nmethods + 2)
                        return 0;
                /* look for method: "NO AUTHENTICATION REQUIRED" */
                for (found = 0, i = 2; i < nmethods + 2; i++) {
                        if (p[i] == SSH_SOCKS5_NOAUTH) {
                                found = 1;
                                break;
                        }
                }
                if (!found) {
                        debug("channel %d: method SSH_SOCKS5_NOAUTH not found",
                            c->self);
                        return -1;
                }
                if ((r = sshbuf_consume(input, nmethods + 2)) != 0)
                        fatal_fr(r, "channel %d: consume", c->self);
                /* version, method */
                if ((r = sshbuf_put_u8(output, 0x05)) != 0 ||
                    (r = sshbuf_put_u8(output, SSH_SOCKS5_NOAUTH)) != 0)
                        fatal_fr(r, "channel %d: append reply", c->self);
                c->flags |= SSH_SOCKS5_AUTHDONE;
                debug2("channel %d: socks5 auth done", c->self);
                return 0;                               /* need more */
        }
        debug2("channel %d: socks5 post auth", c->self);
        if (have < sizeof(s5_req)+1)
                return 0;                       /* need more */
        memcpy(&s5_req, p, sizeof(s5_req));
        if (s5_req.version != 0x05 ||
            s5_req.command != SSH_SOCKS5_CONNECT ||
            s5_req.reserved != 0x00) {
                debug2("channel %d: only socks5 connect supported", c->self);
                return -1;
        }
        switch (s5_req.atyp){
        case SSH_SOCKS5_IPV4:
                addrlen = 4;
                af = AF_INET;
                break;
        case SSH_SOCKS5_DOMAIN:
                addrlen = p[sizeof(s5_req)];
                af = -1;
                break;
        case SSH_SOCKS5_IPV6:
                addrlen = 16;
                af = AF_INET6;
                break;
        default:
                debug2("channel %d: bad socks5 atyp %d", c->self, s5_req.atyp);
                return -1;
        }
        need = sizeof(s5_req) + addrlen + 2;
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN)
                need++;
        if (have < need)
                return 0;
        if ((r = sshbuf_consume(input, sizeof(s5_req))) != 0)
                fatal_fr(r, "channel %d: consume", c->self);
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN) {
                /* host string length */
                if ((r = sshbuf_consume(input, 1)) != 0)
                        fatal_fr(r, "channel %d: consume", c->self);
        }
        if ((r = sshbuf_get(input, &dest_addr, addrlen)) != 0 ||
            (r = sshbuf_get(input, &dest_port, 2)) != 0) {
                debug_r(r, "channel %d: parse addr/port", c->self);
                return -1;
        }
        dest_addr[addrlen] = '\0';
        free(c->path);
        c->path = NULL;
        if (s5_req.atyp == SSH_SOCKS5_DOMAIN) {
                if (addrlen >= NI_MAXHOST) {
                        error("channel %d: dynamic request: socks5 hostname "
                            "\"%.100s\" too long", c->self, dest_addr);
                        return -1;
                }
                c->path = xstrdup(dest_addr);
        } else {
                if (inet_ntop(af, dest_addr, ntop, sizeof(ntop)) == NULL)
                        return -1;
                c->path = xstrdup(ntop);
        }
        c->host_port = ntohs(dest_port);

        debug2("channel %d: dynamic request: socks5 host %s port %u command %u",
            c->self, c->path, c->host_port, s5_req.command);

        s5_rsp.version = 0x05;
        s5_rsp.command = SSH_SOCKS5_SUCCESS;
        s5_rsp.reserved = 0;                    /* ignored */
        s5_rsp.atyp = SSH_SOCKS5_IPV4;
        dest_port = 0;                          /* ignored */

        if ((r = sshbuf_put(output, &s5_rsp, sizeof(s5_rsp))) != 0 ||
            (r = sshbuf_put_u32(output, ntohl(INADDR_ANY))) != 0 ||
            (r = sshbuf_put(output, &dest_port, sizeof(dest_port))) != 0)
                fatal_fr(r, "channel %d: append reply", c->self);
        return 1;
}

Channel *
channel_connect_stdio_fwd(struct ssh *ssh,
    const char *host_to_connect, int port_to_connect,
    int in, int out, int nonblock)
{
        Channel *c;

        debug_f("%s:%d", host_to_connect, port_to_connect);

        c = channel_new(ssh, "stdio-forward", SSH_CHANNEL_OPENING, in, out,
            -1, CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
            0, "stdio-forward", nonblock);

        c->path = xstrdup(host_to_connect);
        c->host_port = port_to_connect;
        c->listening_port = 0;
        c->force_drain = 1;

        channel_register_fds(ssh, c, in, out, -1, 0, 1, 0);
        port_open_helper(ssh, c, port_to_connect == PORT_STREAMLOCAL ?
            "direct-streamlocal@openssh.com" : "direct-tcpip");

        return c;
}

/* dynamic port forwarding */
static void
channel_pre_dynamic(struct ssh *ssh, Channel *c)
{
        const u_char *p;
        u_int have;
        int ret;

        c->io_want = 0;
        have = sshbuf_len(c->input);
        debug2("channel %d: pre_dynamic: have %d", c->self, have);
        /* sshbuf_dump(c->input, stderr); */
        /* check if the fixed size part of the packet is in buffer. */
        if (have < 3) {
                /* need more */
                c->io_want |= SSH_CHAN_IO_RFD;
                return;
        }
        /* try to guess the protocol */
        p = sshbuf_ptr(c->input);
        /* XXX sshbuf_peek_u8? */
        switch (p[0]) {
        case 0x04:
                ret = channel_decode_socks4(c, c->input, c->output);
                break;
        case 0x05:
                ret = channel_decode_socks5(c, c->input, c->output);
                break;
        default:
                ret = -1;
                break;
        }
        if (ret < 0) {
                chan_mark_dead(ssh, c);
        } else if (ret == 0) {
                debug2("channel %d: pre_dynamic: need more", c->self);
                /* need more */
                c->io_want |= SSH_CHAN_IO_RFD;
                if (sshbuf_len(c->output))
                        c->io_want |= SSH_CHAN_IO_WFD;
        } else {
                /* switch to the next state */
                c->type = SSH_CHANNEL_OPENING;
                port_open_helper(ssh, c, "direct-tcpip");
        }
}

/* simulate read-error */
static void
rdynamic_close(struct ssh *ssh, Channel *c)
{
        c->type = SSH_CHANNEL_OPEN;
        channel_force_close(ssh, c, 0);
}

/* reverse dynamic port forwarding */
static void
channel_before_prepare_io_rdynamic(struct ssh *ssh, Channel *c)
{
        const u_char *p;
        u_int have, len;
        int r, ret;

        have = sshbuf_len(c->output);
        debug2("channel %d: pre_rdynamic: have %d", c->self, have);
        /* sshbuf_dump(c->output, stderr); */
        /* EOF received */
        if (c->flags & CHAN_EOF_RCVD) {
                if ((r = sshbuf_consume(c->output, have)) != 0)
                        fatal_fr(r, "channel %d: consume", c->self);
                rdynamic_close(ssh, c);
                return;
        }
        /* check if the fixed size part of the packet is in buffer. */
        if (have < 3)
                return;
        /* try to guess the protocol */
        p = sshbuf_ptr(c->output);
        switch (p[0]) {
        case 0x04:
                /* switch input/output for reverse forwarding */
                ret = channel_decode_socks4(c, c->output, c->input);
                break;
        case 0x05:
                ret = channel_decode_socks5(c, c->output, c->input);
                break;
        default:
                ret = -1;
                break;
        }
        if (ret < 0) {
                rdynamic_close(ssh, c);
        } else if (ret == 0) {
                debug2("channel %d: pre_rdynamic: need more", c->self);
                /* send socks request to peer */
                len = sshbuf_len(c->input);
                if (len > 0 && len < c->remote_window) {
                        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                            (r = sshpkt_put_stringb(ssh, c->input)) != 0 ||
                            (r = sshpkt_send(ssh)) != 0) {
                                fatal_fr(r, "channel %i: rdynamic", c->self);
                        }
                        if ((r = sshbuf_consume(c->input, len)) != 0)
                                fatal_fr(r, "channel %d: consume", c->self);
                        c->remote_window -= len;
                }
        } else if (rdynamic_connect_finish(ssh, c) < 0) {
                /* the connect failed */
                rdynamic_close(ssh, c);
        }
}

/* This is our fake X11 server socket. */
static void
channel_post_x11_listener(struct ssh *ssh, Channel *c)
{
        Channel *nc;
        struct sockaddr_storage addr;
        int r, newsock, oerrno, remote_port;
        socklen_t addrlen;
        char buf[16384], *remote_ipaddr;

        if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
                return;

        debug("X11 connection requested.");
        addrlen = sizeof(addr);
        newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
        if (c->single_connection) {
                oerrno = errno;
                debug2("single_connection: closing X11 listener.");
                channel_close_fd(ssh, c, &c->sock);
                chan_mark_dead(ssh, c);
                errno = oerrno;
        }
        if (newsock == -1) {
                if (errno != EINTR && errno != EWOULDBLOCK &&
                    errno != ECONNABORTED)
                        error("accept: %.100s", strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }
        set_nodelay(newsock);
        remote_ipaddr = get_peer_ipaddr(newsock);
        remote_port = get_peer_port(newsock);
        snprintf(buf, sizeof buf, "X11 connection from %.200s port %d",
            remote_ipaddr, remote_port);

        nc = channel_new(ssh, "x11-connection",
            SSH_CHANNEL_OPENING, newsock, newsock, -1,
            c->local_window_max, c->local_maxpacket, 0, buf, 1);
        open_preamble(ssh, __func__, nc, "x11");
        if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0 ||
            (r = sshpkt_put_u32(ssh, remote_port)) != 0) {
                fatal_fr(r, "channel %i: reply", c->self);
        }
        if ((r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "channel %i: send", c->self);
        free(remote_ipaddr);
}

static void
port_open_helper(struct ssh *ssh, Channel *c, char *rtype)
{
        char *local_ipaddr = get_local_ipaddr(c->sock);
        int local_port = c->sock == -1 ? 65536 : get_local_port(c->sock);
        char *remote_ipaddr = get_peer_ipaddr(c->sock);
        int remote_port = get_peer_port(c->sock);
        int r;

        if (remote_port == -1) {
                /* Fake addr/port to appease peers that validate it (Tectia) */
                free(remote_ipaddr);
                remote_ipaddr = xstrdup("127.0.0.1");
                remote_port = 65535;
        }

        free(c->remote_name);
        xasprintf(&c->remote_name,
            "%s: listening port %d for %.100s port %d, "
            "connect from %.200s port %d to %.100s port %d",
            rtype, c->listening_port, c->path, c->host_port,
            remote_ipaddr, remote_port, local_ipaddr, local_port);

        open_preamble(ssh, __func__, c, rtype);
        if (strcmp(rtype, "direct-tcpip") == 0) {
                /* target host, port */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->host_port)) != 0)
                        fatal_fr(r, "channel %i: reply", c->self);
        } else if (strcmp(rtype, "direct-streamlocal@openssh.com") == 0) {
                /* target path */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0)
                        fatal_fr(r, "channel %i: reply", c->self);
        } else if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
                /* listen path */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0)
                        fatal_fr(r, "channel %i: reply", c->self);
        } else {
                /* listen address, port */
                if ((r = sshpkt_put_cstring(ssh, c->path)) != 0 ||
                    (r = sshpkt_put_u32(ssh, local_port)) != 0)
                        fatal_fr(r, "channel %i: reply", c->self);
        }
        if (strcmp(rtype, "forwarded-streamlocal@openssh.com") == 0) {
                /* reserved for future owner/mode info */
                if ((r = sshpkt_put_cstring(ssh, "")) != 0)
                        fatal_fr(r, "channel %i: reply", c->self);
        } else {
                /* originator host and port */
                if ((r = sshpkt_put_cstring(ssh, remote_ipaddr)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)remote_port)) != 0)
                        fatal_fr(r, "channel %i: reply", c->self);
        }
        if ((r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "channel %i: send", c->self);
        free(remote_ipaddr);
        free(local_ipaddr);
}

void
channel_set_x11_refuse_time(struct ssh *ssh, time_t refuse_time)
{
        ssh->chanctxt->x11_refuse_time = refuse_time;
}

/*
 * This socket is listening for connections to a forwarded TCP/IP port.
 */
static void
channel_post_port_listener(struct ssh *ssh, Channel *c)
{
        Channel *nc;
        struct sockaddr_storage addr;
        int newsock, nextstate;
        socklen_t addrlen;
        char *rtype;

        if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
                return;

        debug("Connection to port %d forwarding to %.100s port %d requested.",
            c->listening_port, c->path, c->host_port);

        if (c->type == SSH_CHANNEL_RPORT_LISTENER) {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "forwarded-tcpip";
        } else if (c->type == SSH_CHANNEL_RUNIX_LISTENER) {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "forwarded-streamlocal@openssh.com";
        } else if (c->host_port == PORT_STREAMLOCAL) {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "direct-streamlocal@openssh.com";
        } else if (c->host_port == 0) {
                nextstate = SSH_CHANNEL_DYNAMIC;
                rtype = "dynamic-tcpip";
        } else {
                nextstate = SSH_CHANNEL_OPENING;
                rtype = "direct-tcpip";
        }

        addrlen = sizeof(addr);
        newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
        if (newsock == -1) {
                if (errno != EINTR && errno != EWOULDBLOCK &&
                    errno != ECONNABORTED)
                        error("accept: %.100s", strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }
        if (c->host_port != PORT_STREAMLOCAL)
                set_nodelay(newsock);
        nc = channel_new(ssh, rtype, nextstate, newsock, newsock, -1,
            c->local_window_max, c->local_maxpacket, 0, rtype, 1);
        nc->listening_port = c->listening_port;
        nc->host_port = c->host_port;
        if (c->path != NULL)
                nc->path = xstrdup(c->path);

        if (nextstate != SSH_CHANNEL_DYNAMIC)
                port_open_helper(ssh, nc, rtype);
}

/*
 * This is the authentication agent socket listening for connections from
 * clients.
 */
static void
channel_post_auth_listener(struct ssh *ssh, Channel *c)
{
        Channel *nc;
        int r, newsock;
        struct sockaddr_storage addr;
        socklen_t addrlen;

        if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
                return;

        addrlen = sizeof(addr);
        newsock = accept(c->sock, (struct sockaddr *)&addr, &addrlen);
        if (newsock == -1) {
                error("accept from auth socket: %.100s", strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }
        nc = channel_new(ssh, "agent-connection",
            SSH_CHANNEL_OPENING, newsock, newsock, -1,
            c->local_window_max, c->local_maxpacket,
            0, "accepted auth socket", 1);
        open_preamble(ssh, __func__, nc, "auth-agent@openssh.com");
        if ((r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "channel %i", c->self);
}

static void
channel_post_connecting(struct ssh *ssh, Channel *c)
{
        int err = 0, sock, isopen, r;
        socklen_t sz = sizeof(err);

        if ((c->io_ready & SSH_CHAN_IO_SOCK_W) == 0)
                return;
        if (!c->have_remote_id)
                fatal_f("channel %d: no remote id", c->self);
        /* for rdynamic the OPEN_CONFIRMATION has been sent already */
        isopen = (c->type == SSH_CHANNEL_RDYNAMIC_FINISH);

        if (getsockopt(c->sock, SOL_SOCKET, SO_ERROR, &err, &sz) == -1) {
                err = errno;
                error("getsockopt SO_ERROR failed");
        }

        if (err == 0) {
                /* Non-blocking connection completed */
                debug("channel %d: connected to %s port %d",
                    c->self, c->connect_ctx.host, c->connect_ctx.port);
                channel_connect_ctx_free(&c->connect_ctx);
                c->type = SSH_CHANNEL_OPEN;
                channel_set_used_time(ssh, c);
                if (isopen) {
                        /* no message necessary */
                } else {
                        if ((r = sshpkt_start(ssh,
                            SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0 ||
                            (r = sshpkt_send(ssh)) != 0)
                                fatal_fr(r, "channel %i open confirm", c->self);
                }
                return;
        }
        if (err == EINTR || err == EAGAIN || err == EINPROGRESS)
                return;

        /* Non-blocking connection failed */
        debug("channel %d: connection failed: %s", c->self, strerror(err));

        /* Try next address, if any */
        if ((sock = connect_next(&c->connect_ctx)) == -1) {
                /* Exhausted all addresses for this destination */
                error("connect_to %.100s port %d: failed.",
                    c->connect_ctx.host, c->connect_ctx.port);
                channel_connect_ctx_free(&c->connect_ctx);
                if (isopen) {
                        rdynamic_close(ssh, c);
                } else {
                        if ((r = sshpkt_start(ssh,
                            SSH2_MSG_CHANNEL_OPEN_FAILURE)) != 0 ||
                            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                            (r = sshpkt_put_u32(ssh,
                            SSH2_OPEN_CONNECT_FAILED)) != 0 ||
                            (r = sshpkt_put_cstring(ssh, strerror(err))) != 0 ||
                            (r = sshpkt_put_cstring(ssh, "")) != 0 ||
                            (r = sshpkt_send(ssh)) != 0)
                                fatal_fr(r, "channel %i: failure", c->self);
                        chan_mark_dead(ssh, c);
                }
        }

        /* New non-blocking connection in progress */
        close(c->sock);
        c->sock = c->rfd = c->wfd = sock;
}

static int
channel_handle_rfd(struct ssh *ssh, Channel *c)
{
        char buf[CHAN_RBUF];
        ssize_t len;
        int r, force;
        size_t nr = 0, have, avail, maxlen = CHANNEL_MAX_READ;
        int pty_zeroread = 0;

#ifdef PTY_ZEROREAD
        /* Bug on AIX: read(1) can return 0 for a non-closed fd */
        pty_zeroread = c->isatty;
#endif

        force = c->isatty && c->detach_close && c->istate != CHAN_INPUT_CLOSED;

        if (!force && (c->io_ready & SSH_CHAN_IO_RFD) == 0)
                return 1;
        if ((avail = sshbuf_avail(c->input)) == 0)
                return 1; /* Shouldn't happen */

        /*
         * For "simple" channels (i.e. not datagram or filtered), we can
         * read directly to the channel buffer.
         */
        if (!pty_zeroread && c->input_filter == NULL && !c->datagram) {
                /* Only OPEN channels have valid rwin */
                if (c->type == SSH_CHANNEL_OPEN) {
                        if ((have = sshbuf_len(c->input)) >= c->remote_window)
                                return 1; /* shouldn't happen */
                        if (maxlen > c->remote_window - have)
                                maxlen = c->remote_window - have;
                }
                if (maxlen > avail)
                        maxlen = avail;
                if ((r = sshbuf_read(c->rfd, c->input, maxlen, &nr)) != 0) {
                        if (errno == EINTR || (!force &&
                            (errno == EAGAIN || errno == EWOULDBLOCK)))
                                return 1;
                        debug2("channel %d: read failed rfd %d maxlen %zu: %s",
                            c->self, c->rfd, maxlen, ssh_err(r));
                        goto rfail;
                }
                if (nr != 0)
                        channel_set_used_time(ssh, c);
                return 1;
        }

        errno = 0;
        len = read(c->rfd, buf, sizeof(buf));
        /* fixup AIX zero-length read with errno set to look more like errors */
        if (pty_zeroread && len == 0 && errno != 0)
                len = -1;
        if (len == -1 && (errno == EINTR ||
            ((errno == EAGAIN || errno == EWOULDBLOCK) && !force)))
                return 1;
        if (len < 0 || (!pty_zeroread && len == 0)) {
                debug2("channel %d: read<=0 rfd %d len %zd: %s",
                    c->self, c->rfd, len,
                    len == 0 ? "closed" : strerror(errno));
 rfail:
                if (c->type != SSH_CHANNEL_OPEN) {
                        debug2("channel %d: not open", c->self);
                        chan_mark_dead(ssh, c);
                        return -1;
                } else {
                        chan_read_failed(ssh, c);
                }
                return -1;
        }
        channel_set_used_time(ssh, c);
        if (c->input_filter != NULL) {
                if (c->input_filter(ssh, c, buf, len) == -1) {
                        debug2("channel %d: filter stops", c->self);
                        chan_read_failed(ssh, c);
                }
        } else if (c->datagram) {
                if ((r = sshbuf_put_string(c->input, buf, len)) != 0)
                        fatal_fr(r, "channel %i: put datagram", c->self);
        } else if ((r = sshbuf_put(c->input, buf, len)) != 0)
                fatal_fr(r, "channel %i: put data", c->self);

        return 1;
}

static int
channel_handle_wfd(struct ssh *ssh, Channel *c)
{
        struct termios tio;
        u_char *data = NULL, *buf; /* XXX const; need filter API change */
        size_t dlen, olen = 0;
        int r, len;

        if ((c->io_ready & SSH_CHAN_IO_WFD) == 0)
                return 1;
        if (sshbuf_len(c->output) == 0)
                return 1;

        /* Send buffered output data to the socket. */
        olen = sshbuf_len(c->output);
        if (c->output_filter != NULL) {
                if ((buf = c->output_filter(ssh, c, &data, &dlen)) == NULL) {
                        debug2("channel %d: filter stops", c->self);
                        if (c->type != SSH_CHANNEL_OPEN)
                                chan_mark_dead(ssh, c);
                        else
                                chan_write_failed(ssh, c);
                        return -1;
                }
        } else if (c->datagram) {
                if ((r = sshbuf_get_string(c->output, &data, &dlen)) != 0)
                        fatal_fr(r, "channel %i: get datagram", c->self);
                buf = data;
        } else {
                buf = data = sshbuf_mutable_ptr(c->output);
                dlen = sshbuf_len(c->output);
        }

        if (c->datagram) {
                /* ignore truncated writes, datagrams might get lost */
                len = write(c->wfd, buf, dlen);
                free(data);
                if (len == -1 && (errno == EINTR || errno == EAGAIN ||
                    errno == EWOULDBLOCK))
                        return 1;
                if (len <= 0)
                        goto write_fail;
                goto out;
        }

#ifdef _AIX
        /* XXX: Later AIX versions can't push as much data to tty */
        if (c->wfd_isatty)
                dlen = MINIMUM(dlen, 8*1024);
#endif

        len = write(c->wfd, buf, dlen);
        if (len == -1 &&
            (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK))
                return 1;
        if (len <= 0) {
 write_fail:
                if (c->type != SSH_CHANNEL_OPEN) {
                        debug2("channel %d: not open", c->self);
                        chan_mark_dead(ssh, c);
                        return -1;
                } else {
                        chan_write_failed(ssh, c);
                }
                return -1;
        }
        channel_set_used_time(ssh, c);
#ifndef BROKEN_TCGETATTR_ICANON
        if (c->isatty && dlen >= 1 && buf[0] != '\r') {
                if (tcgetattr(c->wfd, &tio) == 0 &&
                    !(tio.c_lflag & ECHO) && (tio.c_lflag & ICANON)) {
                        /*
                         * Simulate echo to reduce the impact of
                         * traffic analysis. We need to match the
                         * size of a SSH2_MSG_CHANNEL_DATA message
                         * (4 byte channel id + buf)
                         */
                        if ((r = sshpkt_msg_ignore(ssh, 4+len)) != 0 ||
                            (r = sshpkt_send(ssh)) != 0)
                                fatal_fr(r, "channel %i: ignore", c->self);
                }
        }
#endif /* BROKEN_TCGETATTR_ICANON */
        if ((r = sshbuf_consume(c->output, len)) != 0)
                fatal_fr(r, "channel %i: consume", c->self);
 out:
        c->local_consumed += olen - sshbuf_len(c->output);

        return 1;
}

static int
channel_handle_efd_write(struct ssh *ssh, Channel *c)
{
        int r;
        ssize_t len;

        if ((c->io_ready & SSH_CHAN_IO_EFD_W) == 0)
                return 1;
        if (sshbuf_len(c->extended) == 0)
                return 1;

        len = write(c->efd, sshbuf_ptr(c->extended),
            sshbuf_len(c->extended));
        debug2("channel %d: written %zd to efd %d", c->self, len, c->efd);
        if (len == -1 && (errno == EINTR || errno == EAGAIN ||
            errno == EWOULDBLOCK))
                return 1;
        if (len <= 0) {
                debug2("channel %d: closing write-efd %d", c->self, c->efd);
                channel_close_fd(ssh, c, &c->efd);
        } else {
                if ((r = sshbuf_consume(c->extended, len)) != 0)
                        fatal_fr(r, "channel %i: consume", c->self);
                c->local_consumed += len;
                channel_set_used_time(ssh, c);
        }
        return 1;
}

static int
channel_handle_efd_read(struct ssh *ssh, Channel *c)
{
        char buf[CHAN_RBUF];
        ssize_t len;
        int r, force;

        force = c->isatty && c->detach_close && c->istate != CHAN_INPUT_CLOSED;

        if (!force && (c->io_ready & SSH_CHAN_IO_EFD_R) == 0)
                return 1;

        len = read(c->efd, buf, sizeof(buf));
        debug2("channel %d: read %zd from efd %d", c->self, len, c->efd);
        if (len == -1 && (errno == EINTR || ((errno == EAGAIN ||
            errno == EWOULDBLOCK) && !force)))
                return 1;
        if (len <= 0) {
                debug2("channel %d: closing read-efd %d", c->self, c->efd);
                channel_close_fd(ssh, c, &c->efd);
                return 1;
        }
        channel_set_used_time(ssh, c);
        if (c->extended_usage == CHAN_EXTENDED_IGNORE)
                debug3("channel %d: discard efd", c->self);
        else if ((r = sshbuf_put(c->extended, buf, len)) != 0)
                fatal_fr(r, "channel %i: append", c->self);
        return 1;
}

static int
channel_handle_efd(struct ssh *ssh, Channel *c)
{
        if (c->efd == -1)
                return 1;

        /** XXX handle drain efd, too */

        if (c->extended_usage == CHAN_EXTENDED_WRITE)
                return channel_handle_efd_write(ssh, c);
        else if (c->extended_usage == CHAN_EXTENDED_READ ||
            c->extended_usage == CHAN_EXTENDED_IGNORE)
                return channel_handle_efd_read(ssh, c);

        return 1;
}

static int
channel_check_window(struct ssh *ssh, Channel *c)
{
        int r;

        if (c->type == SSH_CHANNEL_OPEN &&
            !(c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD)) &&
            ((c->local_window_max - c->local_window >
            c->local_maxpacket*3) ||
            c->local_window < c->local_window_max/2) &&
            c->local_consumed > 0) {
                if (!c->have_remote_id)
                        fatal_f("channel %d: no remote id", c->self);
                if ((r = sshpkt_start(ssh,
                    SSH2_MSG_CHANNEL_WINDOW_ADJUST)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->local_consumed)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        fatal_fr(r, "channel %i", c->self);
                }
                debug2("channel %d: window %d sent adjust %d", c->self,
                    c->local_window, c->local_consumed);
                c->local_window += c->local_consumed;
                c->local_consumed = 0;
        }
        return 1;
}

static void
channel_post_open(struct ssh *ssh, Channel *c)
{
        channel_handle_rfd(ssh, c);
        channel_handle_wfd(ssh, c);
        channel_handle_efd(ssh, c);
        channel_check_window(ssh, c);
}

static u_int
read_mux(struct ssh *ssh, Channel *c, u_int need)
{
        char buf[CHAN_RBUF];
        ssize_t len;
        u_int rlen;
        int r;

        if (sshbuf_len(c->input) < need) {
                rlen = need - sshbuf_len(c->input);
                len = read(c->rfd, buf, MINIMUM(rlen, CHAN_RBUF));
                if (len == -1 && (errno == EINTR || errno == EAGAIN))
                        return sshbuf_len(c->input);
                if (len <= 0) {
                        debug2("channel %d: ctl read<=0 rfd %d len %zd",
                            c->self, c->rfd, len);
                        chan_read_failed(ssh, c);
                        return 0;
                } else if ((r = sshbuf_put(c->input, buf, len)) != 0)
                        fatal_fr(r, "channel %i: append", c->self);
        }
        return sshbuf_len(c->input);
}

static void
channel_post_mux_client_read(struct ssh *ssh, Channel *c)
{
        u_int need;

        if ((c->io_ready & SSH_CHAN_IO_RFD) == 0)
                return;
        if (c->istate != CHAN_INPUT_OPEN && c->istate != CHAN_INPUT_WAIT_DRAIN)
                return;
        if (c->mux_pause)
                return;

        /*
         * Don't not read past the precise end of packets to
         * avoid disrupting fd passing.
         */
        if (read_mux(ssh, c, 4) < 4) /* read header */
                return;
        /* XXX sshbuf_peek_u32 */
        need = PEEK_U32(sshbuf_ptr(c->input));
#define CHANNEL_MUX_MAX_PACKET  (256 * 1024)
        if (need > CHANNEL_MUX_MAX_PACKET) {
                debug2("channel %d: packet too big %u > %u",
                    c->self, CHANNEL_MUX_MAX_PACKET, need);
                chan_rcvd_oclose(ssh, c);
                return;
        }
        if (read_mux(ssh, c, need + 4) < need + 4) /* read body */
                return;
        if (c->mux_rcb(ssh, c) != 0) {
                debug("channel %d: mux_rcb failed", c->self);
                chan_mark_dead(ssh, c);
                return;
        }
}

static void
channel_post_mux_client_write(struct ssh *ssh, Channel *c)
{
        ssize_t len;
        int r;

        if ((c->io_ready & SSH_CHAN_IO_WFD) == 0)
                return;
        if (sshbuf_len(c->output) == 0)
                return;

        len = write(c->wfd, sshbuf_ptr(c->output), sshbuf_len(c->output));
        if (len == -1 && (errno == EINTR || errno == EAGAIN))
                return;
        if (len <= 0) {
                chan_mark_dead(ssh, c);
                return;
        }
        if ((r = sshbuf_consume(c->output, len)) != 0)
                fatal_fr(r, "channel %i: consume", c->self);
}

static void
channel_post_mux_client(struct ssh *ssh, Channel *c)
{
        channel_post_mux_client_read(ssh, c);
        channel_post_mux_client_write(ssh, c);
}

static void
channel_post_mux_listener(struct ssh *ssh, Channel *c)
{
        Channel *nc;
        struct sockaddr_storage addr;
        socklen_t addrlen;
        int newsock;
        uid_t euid;
        gid_t egid;

        if ((c->io_ready & SSH_CHAN_IO_SOCK_R) == 0)
                return;

        debug("multiplexing control connection");

        /*
         * Accept connection on control socket
         */
        memset(&addr, 0, sizeof(addr));
        addrlen = sizeof(addr);
        if ((newsock = accept(c->sock, (struct sockaddr*)&addr,
            &addrlen)) == -1) {
                error_f("accept: %s", strerror(errno));
                if (errno == EMFILE || errno == ENFILE)
                        c->notbefore = monotime() + 1;
                return;
        }

        if (getpeereid(newsock, &euid, &egid) == -1) {
                error_f("getpeereid failed: %s", strerror(errno));
                close(newsock);
                return;
        }
        if ((euid != 0) && (getuid() != euid)) {
                error("multiplex uid mismatch: peer euid %u != uid %u",
                    (u_int)euid, (u_int)getuid());
                close(newsock);
                return;
        }
        nc = channel_new(ssh, "mux-control", SSH_CHANNEL_MUX_CLIENT,
            newsock, newsock, -1, c->local_window_max,
            c->local_maxpacket, 0, "mux-control", 1);
        nc->mux_rcb = c->mux_rcb;
        debug3_f("new mux channel %d fd %d", nc->self, nc->sock);
        /* establish state */
        nc->mux_rcb(ssh, nc);
        /* mux state transitions must not elicit protocol messages */
        nc->flags |= CHAN_LOCAL;
}

static void
channel_handler_init(struct ssh_channels *sc)
{
        chan_fn **pre, **post;

        if ((pre = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*pre))) == NULL ||
            (post = calloc(SSH_CHANNEL_MAX_TYPE, sizeof(*post))) == NULL)
                fatal_f("allocation failed");

        pre[SSH_CHANNEL_OPEN] =                 &channel_pre_open;
        pre[SSH_CHANNEL_X11_OPEN] =             &channel_pre_x11_open;
        pre[SSH_CHANNEL_PORT_LISTENER] =        &channel_pre_listener;
        pre[SSH_CHANNEL_RPORT_LISTENER] =       &channel_pre_listener;
        pre[SSH_CHANNEL_UNIX_LISTENER] =        &channel_pre_listener;
        pre[SSH_CHANNEL_RUNIX_LISTENER] =       &channel_pre_listener;
        pre[SSH_CHANNEL_X11_LISTENER] =         &channel_pre_listener;
        pre[SSH_CHANNEL_AUTH_SOCKET] =          &channel_pre_listener;
        pre[SSH_CHANNEL_CONNECTING] =           &channel_pre_connecting;
        pre[SSH_CHANNEL_DYNAMIC] =              &channel_pre_dynamic;
        pre[SSH_CHANNEL_RDYNAMIC_FINISH] =      &channel_pre_connecting;
        pre[SSH_CHANNEL_MUX_LISTENER] =         &channel_pre_listener;
        pre[SSH_CHANNEL_MUX_CLIENT] =           &channel_pre_mux_client;

        post[SSH_CHANNEL_OPEN] =                &channel_post_open;
        post[SSH_CHANNEL_PORT_LISTENER] =       &channel_post_port_listener;
        post[SSH_CHANNEL_RPORT_LISTENER] =      &channel_post_port_listener;
        post[SSH_CHANNEL_UNIX_LISTENER] =       &channel_post_port_listener;
        post[SSH_CHANNEL_RUNIX_LISTENER] =      &channel_post_port_listener;
        post[SSH_CHANNEL_X11_LISTENER] =        &channel_post_x11_listener;
        post[SSH_CHANNEL_AUTH_SOCKET] =         &channel_post_auth_listener;
        post[SSH_CHANNEL_CONNECTING] =          &channel_post_connecting;
        post[SSH_CHANNEL_DYNAMIC] =             &channel_post_open;
        post[SSH_CHANNEL_RDYNAMIC_FINISH] =     &channel_post_connecting;
        post[SSH_CHANNEL_MUX_LISTENER] =        &channel_post_mux_listener;
        post[SSH_CHANNEL_MUX_CLIENT] =          &channel_post_mux_client;

        sc->channel_pre = pre;
        sc->channel_post = post;
}

/* gc dead channels */
static void
channel_garbage_collect(struct ssh *ssh, Channel *c)
{
        if (c == NULL)
                return;
        if (c->detach_user != NULL) {
                if (!chan_is_dead(ssh, c, c->detach_close))
                        return;

                debug2("channel %d: gc: notify user", c->self);
                c->detach_user(ssh, c->self, 0, NULL);
                /* if we still have a callback */
                if (c->detach_user != NULL)
                        return;
                debug2("channel %d: gc: user detached", c->self);
        }
        if (!chan_is_dead(ssh, c, 1))
                return;
        debug2("channel %d: garbage collecting", c->self);
        channel_free(ssh, c);
}

enum channel_table { CHAN_PRE, CHAN_POST };

static void
channel_handler(struct ssh *ssh, int table, struct timespec *timeout)
{
        struct ssh_channels *sc = ssh->chanctxt;
        chan_fn **ftab = table == CHAN_PRE ? sc->channel_pre : sc->channel_post;
        u_int i, oalloc;
        Channel *c;
        time_t now;

        now = monotime();
        for (i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
                c = sc->channels[i];
                if (c == NULL)
                        continue;
                /* Try to keep IO going while rekeying */
                if (ssh_packet_is_rekeying(ssh) && c->type != SSH_CHANNEL_OPEN)
                        continue;
                if (c->delayed) {
                        if (table == CHAN_PRE)
                                c->delayed = 0;
                        else
                                continue;
                }
                if (ftab[c->type] != NULL) {
                        if (table == CHAN_PRE && c->type == SSH_CHANNEL_OPEN &&
                            channel_get_expiry(ssh, c) != 0 &&
                            now >= channel_get_expiry(ssh, c)) {
                                /* channel closed for inactivity */
                                verbose("channel %d: closing after %u seconds "
                                    "of inactivity", c->self,
                                    c->inactive_deadline);
                                channel_force_close(ssh, c, 1);
                        } else if (c->notbefore <= now) {
                                /* Run handlers that are not paused. */
                                (*ftab[c->type])(ssh, c);
                                /* inactivity timeouts must interrupt poll() */
                                if (timeout != NULL &&
                                    c->type == SSH_CHANNEL_OPEN &&
                                    channel_get_expiry(ssh, c) != 0) {
                                        ptimeout_deadline_monotime(timeout,
                                            channel_get_expiry(ssh, c));
                                }
                        } else if (timeout != NULL) {
                                /*
                                 * Arrange for poll() wakeup when channel pause
                                 * timer expires.
                                 */
                                ptimeout_deadline_monotime(timeout,
                                    c->notbefore);
                        }
                }
                channel_garbage_collect(ssh, c);
        }
}

/*
 * Create sockets before preparing IO.
 * This is necessary for things that need to happen after reading
 * the network-input but need to be completed before IO event setup, e.g.
 * because they may create new channels.
 */
static void
channel_before_prepare_io(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;
        Channel *c;
        u_int i, oalloc;

        for (i = 0, oalloc = sc->channels_alloc; i < oalloc; i++) {
                c = sc->channels[i];
                if (c == NULL)
                        continue;
                if (c->type == SSH_CHANNEL_RDYNAMIC_OPEN)
                        channel_before_prepare_io_rdynamic(ssh, c);
        }
}

static void
dump_channel_poll(const char *func, const char *what, Channel *c,
    u_int pollfd_offset, struct pollfd *pfd)
{
#ifdef DEBUG_CHANNEL_POLL
        debug3("%s: channel %d: %s r%d w%d e%d s%d c->pfds [ %d %d %d %d ] "
            "io_want 0x%02x io_ready 0x%02x pfd[%u].fd=%d "
            "pfd.ev 0x%02x pfd.rev 0x%02x", func, c->self, what,
            c->rfd, c->wfd, c->efd, c->sock,
            c->pfds[0], c->pfds[1], c->pfds[2], c->pfds[3],
            c->io_want, c->io_ready,
            pollfd_offset, pfd->fd, pfd->events, pfd->revents);
#endif
}

/* Prepare pollfd entries for a single channel */
static void
channel_prepare_pollfd(Channel *c, u_int *next_pollfd,
    struct pollfd *pfd, u_int npfd)
{
        u_int ev, p = *next_pollfd;

        if (c == NULL)
                return;
        if (p + 4 > npfd) {
                /* Shouldn't happen */
                fatal_f("channel %d: bad pfd offset %u (max %u)",
                    c->self, p, npfd);
        }
        c->pfds[0] = c->pfds[1] = c->pfds[2] = c->pfds[3] = -1;
        /*
         * prepare c->rfd
         *
         * This is a special case, since c->rfd might be the same as
         * c->wfd, c->efd and/or c->sock. Handle those here if they want
         * IO too.
         */
        if (c->rfd != -1) {
                ev = 0;
                if ((c->io_want & SSH_CHAN_IO_RFD) != 0)
                        ev |= POLLIN;
                /* rfd == wfd */
                if (c->wfd == c->rfd) {
                        if ((c->io_want & SSH_CHAN_IO_WFD) != 0)
                                ev |= POLLOUT;
                }
                /* rfd == efd */
                if (c->efd == c->rfd) {
                        if ((c->io_want & SSH_CHAN_IO_EFD_R) != 0)
                                ev |= POLLIN;
                        if ((c->io_want & SSH_CHAN_IO_EFD_W) != 0)
                                ev |= POLLOUT;
                }
                /* rfd == sock */
                if (c->sock == c->rfd) {
                        if ((c->io_want & SSH_CHAN_IO_SOCK_R) != 0)
                                ev |= POLLIN;
                        if ((c->io_want & SSH_CHAN_IO_SOCK_W) != 0)
                                ev |= POLLOUT;
                }
                /* Pack a pfd entry if any event armed for this fd */
                if (ev != 0) {
                        c->pfds[0] = p;
                        pfd[p].fd = c->rfd;
                        pfd[p].events = ev;
                        dump_channel_poll(__func__, "rfd", c, p, &pfd[p]);
                        p++;
                }
        }
        /* prepare c->wfd if wanting IO and not already handled above */
        if (c->wfd != -1 && c->rfd != c->wfd) {
                ev = 0;
                if ((c->io_want & SSH_CHAN_IO_WFD))
                        ev |= POLLOUT;
                /* Pack a pfd entry if any event armed for this fd */
                if (ev != 0) {
                        c->pfds[1] = p;
                        pfd[p].fd = c->wfd;
                        pfd[p].events = ev;
                        dump_channel_poll(__func__, "wfd", c, p, &pfd[p]);
                        p++;
                }
        }
        /* prepare c->efd if wanting IO and not already handled above */
        if (c->efd != -1 && c->rfd != c->efd) {
                ev = 0;
                if ((c->io_want & SSH_CHAN_IO_EFD_R) != 0)
                        ev |= POLLIN;
                if ((c->io_want & SSH_CHAN_IO_EFD_W) != 0)
                        ev |= POLLOUT;
                /* Pack a pfd entry if any event armed for this fd */
                if (ev != 0) {
                        c->pfds[2] = p;
                        pfd[p].fd = c->efd;
                        pfd[p].events = ev;
                        dump_channel_poll(__func__, "efd", c, p, &pfd[p]);
                        p++;
                }
        }
        /* prepare c->sock if wanting IO and not already handled above */
        if (c->sock != -1 && c->rfd != c->sock) {
                ev = 0;
                if ((c->io_want & SSH_CHAN_IO_SOCK_R) != 0)
                        ev |= POLLIN;
                if ((c->io_want & SSH_CHAN_IO_SOCK_W) != 0)
                        ev |= POLLOUT;
                /* Pack a pfd entry if any event armed for this fd */
                if (ev != 0) {
                        c->pfds[3] = p;
                        pfd[p].fd = c->sock;
                        pfd[p].events = 0;
                        dump_channel_poll(__func__, "sock", c, p, &pfd[p]);
                        p++;
                }
        }
        *next_pollfd = p;
}

/* * Allocate/prepare poll structure */
void
channel_prepare_poll(struct ssh *ssh, struct pollfd **pfdp, u_int *npfd_allocp,
    u_int *npfd_activep, u_int npfd_reserved, struct timespec *timeout)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int i, oalloc, p, npfd = npfd_reserved;

        channel_before_prepare_io(ssh); /* might create a new channel */
        /* clear out I/O flags from last poll */
        for (i = 0; i < sc->channels_alloc; i++) {
                if (sc->channels[i] == NULL)
                        continue;
                sc->channels[i]->io_want = sc->channels[i]->io_ready = 0;
        }
        /* Allocate 4x pollfd for each channel (rfd, wfd, efd, sock) */
        if (sc->channels_alloc >= (INT_MAX / 4) - npfd_reserved)
                fatal_f("too many channels"); /* shouldn't happen */
        npfd += sc->channels_alloc * 4;
        if (npfd > *npfd_allocp) {
                *pfdp = xrecallocarray(*pfdp, *npfd_allocp,
                    npfd, sizeof(**pfdp));
                *npfd_allocp = npfd;
        }
        *npfd_activep = npfd_reserved;
        oalloc = sc->channels_alloc;

        channel_handler(ssh, CHAN_PRE, timeout);

        if (oalloc != sc->channels_alloc) {
                /* shouldn't happen */
                fatal_f("channels_alloc changed during CHAN_PRE "
                    "(was %u, now %u)", oalloc, sc->channels_alloc);
        }

        /* Prepare pollfd */
        p = npfd_reserved;
        for (i = 0; i < sc->channels_alloc; i++)
                channel_prepare_pollfd(sc->channels[i], &p, *pfdp, npfd);
        *npfd_activep = p;
}

static void
fd_ready(Channel *c, int p, struct pollfd *pfds, u_int npfd, int fd,
    const char *what, u_int revents_mask, u_int ready)
{
        struct pollfd *pfd = &pfds[p];

        if (fd == -1)
                return;
        if (p == -1 || (u_int)p >= npfd)
                fatal_f("channel %d: bad pfd %d (max %u)", c->self, p, npfd);
        dump_channel_poll(__func__, what, c, p, pfd);
        if (pfd->fd != fd) {
                fatal("channel %d: inconsistent %s fd=%d pollfd[%u].fd %d "
                    "r%d w%d e%d s%d", c->self, what, fd, p, pfd->fd,
                    c->rfd, c->wfd, c->efd, c->sock);
        }
        if ((pfd->revents & POLLNVAL) != 0) {
                fatal("channel %d: invalid %s pollfd[%u].fd %d r%d w%d e%d s%d",
                    c->self, what, p, pfd->fd, c->rfd, c->wfd, c->efd, c->sock);
        }
        if ((pfd->revents & (revents_mask|POLLHUP|POLLERR)) != 0)
                c->io_ready |= ready & c->io_want;
}

/*
 * After poll, perform any appropriate operations for channels which have
 * events pending.
 */
void
channel_after_poll(struct ssh *ssh, struct pollfd *pfd, u_int npfd)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int i;
        int p;
        Channel *c;

#ifdef DEBUG_CHANNEL_POLL
        for (p = 0; p < (int)npfd; p++) {
                if (pfd[p].revents == 0)
                        continue;
                debug_f("pfd[%u].fd %d rev 0x%04x",
                    p, pfd[p].fd, pfd[p].revents);
        }
#endif

        /* Convert pollfd into c->io_ready */
        for (i = 0; i < sc->channels_alloc; i++) {
                c = sc->channels[i];
                if (c == NULL)
                        continue;
                /* if rfd is shared with efd/sock then wfd should be too */
                if (c->rfd != -1 && c->wfd != -1 && c->rfd != c->wfd &&
                    (c->rfd == c->efd || c->rfd == c->sock)) {
                        /* Shouldn't happen */
                        fatal_f("channel %d: unexpected fds r%d w%d e%d s%d",
                            c->self, c->rfd, c->wfd, c->efd, c->sock);
                }
                c->io_ready = 0;
                /* rfd, potentially shared with wfd, efd and sock */
                if (c->rfd != -1 && (p = c->pfds[0]) != -1) {
                        fd_ready(c, p, pfd, npfd, c->rfd,
                            "rfd", POLLIN, SSH_CHAN_IO_RFD);
                        if (c->rfd == c->wfd) {
                                fd_ready(c, p, pfd, npfd, c->wfd,
                                    "wfd/r", POLLOUT, SSH_CHAN_IO_WFD);
                        }
                        if (c->rfd == c->efd) {
                                fd_ready(c, p, pfd, npfd, c->efd,
                                    "efdr/r", POLLIN, SSH_CHAN_IO_EFD_R);
                                fd_ready(c, p, pfd, npfd, c->efd,
                                    "efdw/r", POLLOUT, SSH_CHAN_IO_EFD_W);
                        }
                        if (c->rfd == c->sock) {
                                fd_ready(c, p, pfd, npfd, c->sock,
                                    "sockr/r", POLLIN, SSH_CHAN_IO_SOCK_R);
                                fd_ready(c, p, pfd, npfd, c->sock,
                                    "sockw/r", POLLOUT, SSH_CHAN_IO_SOCK_W);
                        }
                        dump_channel_poll(__func__, "rfd", c, p, pfd);
                }
                /* wfd */
                if (c->wfd != -1 && c->wfd != c->rfd &&
                    (p = c->pfds[1]) != -1) {
                        fd_ready(c, p, pfd, npfd, c->wfd,
                            "wfd", POLLOUT, SSH_CHAN_IO_WFD);
                        dump_channel_poll(__func__, "wfd", c, p, pfd);
                }
                /* efd */
                if (c->efd != -1 && c->efd != c->rfd &&
                    (p = c->pfds[2]) != -1) {
                        fd_ready(c, p, pfd, npfd, c->efd,
                            "efdr", POLLIN, SSH_CHAN_IO_EFD_R);
                        fd_ready(c, p, pfd, npfd, c->efd,
                            "efdw", POLLOUT, SSH_CHAN_IO_EFD_W);
                        dump_channel_poll(__func__, "efd", c, p, pfd);
                }
                /* sock */
                if (c->sock != -1 && c->sock != c->rfd &&
                    (p = c->pfds[3]) != -1) {
                        fd_ready(c, p, pfd, npfd, c->sock,
                            "sockr", POLLIN, SSH_CHAN_IO_SOCK_R);
                        fd_ready(c, p, pfd, npfd, c->sock,
                            "sockw", POLLOUT, SSH_CHAN_IO_SOCK_W);
                        dump_channel_poll(__func__, "sock", c, p, pfd);
                }
        }
        channel_handler(ssh, CHAN_POST, NULL);
}

/*
 * Enqueue data for channels with open or draining c->input.
 * Returns non-zero if a packet was enqueued.
 */
static int
channel_output_poll_input_open(struct ssh *ssh, Channel *c)
{
        size_t len, plen;
        const u_char *pkt;
        int r;

        if ((len = sshbuf_len(c->input)) == 0) {
                if (c->istate == CHAN_INPUT_WAIT_DRAIN) {
                        /*
                         * input-buffer is empty and read-socket shutdown:
                         * tell peer, that we will not send more data:
                         * send IEOF.
                         * hack for extended data: delay EOF if EFD still
                         * in use.
                         */
                        if (CHANNEL_EFD_INPUT_ACTIVE(c))
                                debug2("channel %d: "
                                    "ibuf_empty delayed efd %d/(%zu)",
                                    c->self, c->efd, sshbuf_len(c->extended));
                        else
                                chan_ibuf_empty(ssh, c);
                }
                return 0;
        }

        if (!c->have_remote_id)
                fatal_f("channel %d: no remote id", c->self);

        if (c->datagram) {
                /* Check datagram will fit; drop if not */
                if ((r = sshbuf_get_string_direct(c->input, &pkt, &plen)) != 0)
                        fatal_fr(r, "channel %i: get datagram", c->self);
                /*
                 * XXX this does tail-drop on the datagram queue which is
                 * usually suboptimal compared to head-drop. Better to have
                 * backpressure at read time? (i.e. read + discard)
                 */
                if (plen > c->remote_window || plen > c->remote_maxpacket) {
                        debug("channel %d: datagram too big", c->self);
                        return 0;
                }
                /* Enqueue it */
                if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
                    (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
                    (r = sshpkt_put_string(ssh, pkt, plen)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0)
                        fatal_fr(r, "channel %i: send datagram", c->self);
                c->remote_window -= plen;
                return 1;
        }

        /* Enqueue packet for buffered data. */
        if (len > c->remote_window)
                len = c->remote_window;
        if (len > c->remote_maxpacket)
                len = c->remote_maxpacket;
        if (len == 0)
                return 0;
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_DATA)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_string(ssh, sshbuf_ptr(c->input), len)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "channel %i: send data", c->self);
        if ((r = sshbuf_consume(c->input, len)) != 0)
                fatal_fr(r, "channel %i: consume", c->self);
        c->remote_window -= len;
        return 1;
}

/*
 * Enqueue data for channels with open c->extended in read mode.
 * Returns non-zero if a packet was enqueued.
 */
static int
channel_output_poll_extended_read(struct ssh *ssh, Channel *c)
{
        size_t len;
        int r;

        if ((len = sshbuf_len(c->extended)) == 0)
                return 0;

        debug2("channel %d: rwin %u elen %zu euse %d", c->self,
            c->remote_window, sshbuf_len(c->extended), c->extended_usage);
        if (len > c->remote_window)
                len = c->remote_window;
        if (len > c->remote_maxpacket)
                len = c->remote_maxpacket;
        if (len == 0)
                return 0;
        if (!c->have_remote_id)
                fatal_f("channel %d: no remote id", c->self);
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_EXTENDED_DATA)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_u32(ssh, SSH2_EXTENDED_DATA_STDERR)) != 0 ||
            (r = sshpkt_put_string(ssh, sshbuf_ptr(c->extended), len)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "channel %i: data", c->self);
        if ((r = sshbuf_consume(c->extended, len)) != 0)
                fatal_fr(r, "channel %i: consume", c->self);
        c->remote_window -= len;
        debug2("channel %d: sent ext data %zu", c->self, len);
        return 1;
}

/*
 * If there is data to send to the connection, enqueue some of it now.
 * Returns non-zero if data was enqueued.
 */
int
channel_output_poll(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;
        Channel *c;
        u_int i;
        int ret = 0;

        for (i = 0; i < sc->channels_alloc; i++) {
                c = sc->channels[i];
                if (c == NULL)
                        continue;

                /*
                 * We are only interested in channels that can have buffered
                 * incoming data.
                 */
                if (c->type != SSH_CHANNEL_OPEN)
                        continue;
                if ((c->flags & (CHAN_CLOSE_SENT|CHAN_CLOSE_RCVD))) {
                        /* XXX is this true? */
                        debug3("channel %d: will not send data after close",
                            c->self);
                        continue;
                }

                /* Get the amount of buffered data for this channel. */
                if (c->istate == CHAN_INPUT_OPEN ||
                    c->istate == CHAN_INPUT_WAIT_DRAIN)
                        ret |= channel_output_poll_input_open(ssh, c);
                /* Send extended data, i.e. stderr */
                if (!(c->flags & CHAN_EOF_SENT) &&
                    c->extended_usage == CHAN_EXTENDED_READ)
                        ret |= channel_output_poll_extended_read(ssh, c);
        }
        return ret;
}

/* -- mux proxy support  */

/*
 * When multiplexing channel messages for mux clients we have to deal
 * with downstream messages from the mux client and upstream messages
 * from the ssh server:
 * 1) Handling downstream messages is straightforward and happens
 *    in channel_proxy_downstream():
 *    - We forward all messages (mostly) unmodified to the server.
 *    - However, in order to route messages from upstream to the correct
 *      downstream client, we have to replace the channel IDs used by the
 *      mux clients with a unique channel ID because the mux clients might
 *      use conflicting channel IDs.
 *    - so we inspect and change both SSH2_MSG_CHANNEL_OPEN and
 *      SSH2_MSG_CHANNEL_OPEN_CONFIRMATION messages, create a local
 *      SSH_CHANNEL_MUX_PROXY channel and replace the mux clients ID
 *      with the newly allocated channel ID.
 * 2) Upstream messages are received by matching SSH_CHANNEL_MUX_PROXY
 *    channels and processed by channel_proxy_upstream(). The local channel ID
 *    is then translated back to the original mux client ID.
 * 3) In both cases we need to keep track of matching SSH2_MSG_CHANNEL_CLOSE
 *    messages so we can clean up SSH_CHANNEL_MUX_PROXY channels.
 * 4) The SSH_CHANNEL_MUX_PROXY channels also need to closed when the
 *    downstream mux client are removed.
 * 5) Handling SSH2_MSG_CHANNEL_OPEN messages from the upstream server
 *    requires more work, because they are not addressed to a specific
 *    channel. E.g. client_request_forwarded_tcpip() needs to figure
 *    out whether the request is addressed to the local client or a
 *    specific downstream client based on the listen-address/port.
 * 6) Agent and X11-Forwarding have a similar problem and are currently
 *    not supported as the matching session/channel cannot be identified
 *    easily.
 */

/*
 * receive packets from downstream mux clients:
 * channel callback fired on read from mux client, creates
 * SSH_CHANNEL_MUX_PROXY channels and translates channel IDs
 * on channel creation.
 */
int
channel_proxy_downstream(struct ssh *ssh, Channel *downstream)
{
        Channel *c = NULL;
        struct sshbuf *original = NULL, *modified = NULL;
        const u_char *cp;
        char *ctype = NULL, *listen_host = NULL;
        u_char type;
        size_t have;
        int ret = -1, r;
        u_int id, remote_id, listen_port;

        /* sshbuf_dump(downstream->input, stderr); */
        if ((r = sshbuf_get_string_direct(downstream->input, &cp, &have))
            != 0) {
                error_fr(r, "parse");
                return -1;
        }
        if (have < 2) {
                error_f("short message");
                return -1;
        }
        type = cp[1];
        /* skip padlen + type */
        cp += 2;
        have -= 2;
        if (ssh_packet_log_type(type))
                debug3_f("channel %u: down->up: type %u",
                    downstream->self, type);

        switch (type) {
        case SSH2_MSG_CHANNEL_OPEN:
                if ((original = sshbuf_from(cp, have)) == NULL ||
                    (modified = sshbuf_new()) == NULL) {
                        error_f("alloc");
                        goto out;
                }
                if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0 ||
                    (r = sshbuf_get_u32(original, &id)) != 0) {
                        error_fr(r, "parse");
                        goto out;
                }
                c = channel_new(ssh, "mux-proxy", SSH_CHANNEL_MUX_PROXY,
                    -1, -1, -1, 0, 0, 0, ctype, 1);
                c->mux_ctx = downstream;        /* point to mux client */
                c->mux_downstream_id = id;      /* original downstream id */
                if ((r = sshbuf_put_cstring(modified, ctype)) != 0 ||
                    (r = sshbuf_put_u32(modified, c->self)) != 0 ||
                    (r = sshbuf_putb(modified, original)) != 0) {
                        error_fr(r, "compose");
                        channel_free(ssh, c);
                        goto out;
                }
                break;
        case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
                /*
                 * Almost the same as SSH2_MSG_CHANNEL_OPEN, except then we
                 * need to parse 'remote_id' instead of 'ctype'.
                 */
                if ((original = sshbuf_from(cp, have)) == NULL ||
                    (modified = sshbuf_new()) == NULL) {
                        error_f("alloc");
                        goto out;
                }
                if ((r = sshbuf_get_u32(original, &remote_id)) != 0 ||
                    (r = sshbuf_get_u32(original, &id)) != 0) {
                        error_fr(r, "parse");
                        goto out;
                }
                c = channel_new(ssh, "mux-proxy", SSH_CHANNEL_MUX_PROXY,
                    -1, -1, -1, 0, 0, 0, "mux-down-connect", 1);
                c->mux_ctx = downstream;        /* point to mux client */
                c->mux_downstream_id = id;
                c->remote_id = remote_id;
                c->have_remote_id = 1;
                if ((r = sshbuf_put_u32(modified, remote_id)) != 0 ||
                    (r = sshbuf_put_u32(modified, c->self)) != 0 ||
                    (r = sshbuf_putb(modified, original)) != 0) {
                        error_fr(r, "compose");
                        channel_free(ssh, c);
                        goto out;
                }
                break;
        case SSH2_MSG_GLOBAL_REQUEST:
                if ((original = sshbuf_from(cp, have)) == NULL) {
                        error_f("alloc");
                        goto out;
                }
                if ((r = sshbuf_get_cstring(original, &ctype, NULL)) != 0) {
                        error_fr(r, "parse");
                        goto out;
                }
                if (strcmp(ctype, "tcpip-forward") != 0) {
                        error_f("unsupported request %s", ctype);
                        goto out;
                }
                if ((r = sshbuf_get_u8(original, NULL)) != 0 ||
                    (r = sshbuf_get_cstring(original, &listen_host, NULL)) != 0 ||
                    (r = sshbuf_get_u32(original, &listen_port)) != 0) {
                        error_fr(r, "parse");
                        goto out;
                }
                if (listen_port > 65535) {
                        error_f("tcpip-forward for %s: bad port %u",
                            listen_host, listen_port);
                        goto out;
                }
                /* Record that connection to this host/port is permitted. */
                permission_set_add(ssh, FORWARD_USER, FORWARD_LOCAL, "<mux>",
                    -1, listen_host, NULL, (int)listen_port, downstream);
                break;
        case SSH2_MSG_CHANNEL_CLOSE:
                if (have < 4)
                        break;
                remote_id = PEEK_U32(cp);
                if ((c = channel_by_remote_id(ssh, remote_id)) != NULL) {
                        if (c->flags & CHAN_CLOSE_RCVD)
                                channel_free(ssh, c);
                        else
                                c->flags |= CHAN_CLOSE_SENT;
                }
                break;
        }
        if (modified) {
                if ((r = sshpkt_start(ssh, type)) != 0 ||
                    (r = sshpkt_putb(ssh, modified)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        error_fr(r, "send");
                        goto out;
                }
        } else {
                if ((r = sshpkt_start(ssh, type)) != 0 ||
                    (r = sshpkt_put(ssh, cp, have)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0) {
                        error_fr(r, "send");
                        goto out;
                }
        }
        ret = 0;
 out:
        free(ctype);
        free(listen_host);
        sshbuf_free(original);
        sshbuf_free(modified);
        return ret;
}

/*
 * receive packets from upstream server and de-multiplex packets
 * to correct downstream:
 * implemented as a helper for channel input handlers,
 * replaces local (proxy) channel ID with downstream channel ID.
 */
int
channel_proxy_upstream(Channel *c, int type, u_int32_t seq, struct ssh *ssh)
{
        struct sshbuf *b = NULL;
        Channel *downstream;
        const u_char *cp = NULL;
        size_t len;
        int r;

        /*
         * When receiving packets from the peer we need to check whether we
         * need to forward the packets to the mux client. In this case we
         * restore the original channel id and keep track of CLOSE messages,
         * so we can cleanup the channel.
         */
        if (c == NULL || c->type != SSH_CHANNEL_MUX_PROXY)
                return 0;
        if ((downstream = c->mux_ctx) == NULL)
                return 0;
        switch (type) {
        case SSH2_MSG_CHANNEL_CLOSE:
        case SSH2_MSG_CHANNEL_DATA:
        case SSH2_MSG_CHANNEL_EOF:
        case SSH2_MSG_CHANNEL_EXTENDED_DATA:
        case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
        case SSH2_MSG_CHANNEL_OPEN_FAILURE:
        case SSH2_MSG_CHANNEL_WINDOW_ADJUST:
        case SSH2_MSG_CHANNEL_SUCCESS:
        case SSH2_MSG_CHANNEL_FAILURE:
        case SSH2_MSG_CHANNEL_REQUEST:
                break;
        default:
                debug2_f("channel %u: unsupported type %u", c->self, type);
                return 0;
        }
        if ((b = sshbuf_new()) == NULL) {
                error_f("alloc reply");
                goto out;
        }
        /* get remaining payload (after id) */
        cp = sshpkt_ptr(ssh, &len);
        if (cp == NULL) {
                error_f("no packet");
                goto out;
        }
        /* translate id and send to muxclient */
        if ((r = sshbuf_put_u8(b, 0)) != 0 ||   /* padlen */
            (r = sshbuf_put_u8(b, type)) != 0 ||
            (r = sshbuf_put_u32(b, c->mux_downstream_id)) != 0 ||
            (r = sshbuf_put(b, cp, len)) != 0 ||
            (r = sshbuf_put_stringb(downstream->output, b)) != 0) {
                error_fr(r, "compose muxclient");
                goto out;
        }
        /* sshbuf_dump(b, stderr); */
        if (ssh_packet_log_type(type))
                debug3_f("channel %u: up->down: type %u", c->self, type);
 out:
        /* update state */
        switch (type) {
        case SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
                /* record remote_id for SSH2_MSG_CHANNEL_CLOSE */
                if (cp && len > 4) {
                        c->remote_id = PEEK_U32(cp);
                        c->have_remote_id = 1;
                }
                break;
        case SSH2_MSG_CHANNEL_CLOSE:
                if (c->flags & CHAN_CLOSE_SENT)
                        channel_free(ssh, c);
                else
                        c->flags |= CHAN_CLOSE_RCVD;
                break;
        }
        sshbuf_free(b);
        return 1;
}

/* -- protocol input */

/* Parse a channel ID from the current packet */
static int
channel_parse_id(struct ssh *ssh, const char *where, const char *what)
{
        u_int32_t id;
        int r;

        if ((r = sshpkt_get_u32(ssh, &id)) != 0) {
                error_r(r, "%s: parse id", where);
                ssh_packet_disconnect(ssh, "Invalid %s message", what);
        }
        if (id > INT_MAX) {
                error_r(r, "%s: bad channel id %u", where, id);
                ssh_packet_disconnect(ssh, "Invalid %s channel id", what);
        }
        return (int)id;
}

/* Lookup a channel from an ID in the current packet */
static Channel *
channel_from_packet_id(struct ssh *ssh, const char *where, const char *what)
{
        int id = channel_parse_id(ssh, where, what);
        Channel *c;

        if ((c = channel_lookup(ssh, id)) == NULL) {
                ssh_packet_disconnect(ssh,
                    "%s packet referred to nonexistent channel %d", what, id);
        }
        return c;
}

int
channel_input_data(int type, u_int32_t seq, struct ssh *ssh)
{
        const u_char *data;
        size_t data_len, win_len;
        Channel *c = channel_from_packet_id(ssh, __func__, "data");
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;

        /* Ignore any data for non-open channels (might happen on close) */
        if (c->type != SSH_CHANNEL_OPEN &&
            c->type != SSH_CHANNEL_RDYNAMIC_OPEN &&
            c->type != SSH_CHANNEL_RDYNAMIC_FINISH &&
            c->type != SSH_CHANNEL_X11_OPEN)
                return 0;

        /* Get the data. */
        if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0)
                fatal_fr(r, "channel %i: get data", c->self);

        win_len = data_len;
        if (c->datagram)
                win_len += 4;  /* string length header */

        /*
         * The sending side reduces its window as it sends data, so we
         * must 'fake' consumption of the data in order to ensure that window
         * updates are sent back. Otherwise the connection might deadlock.
         */
        if (c->ostate != CHAN_OUTPUT_OPEN) {
                c->local_window -= win_len;
                c->local_consumed += win_len;
                return 0;
        }

        if (win_len > c->local_maxpacket) {
                logit("channel %d: rcvd big packet %zu, maxpack %u",
                    c->self, win_len, c->local_maxpacket);
                return 0;
        }
        if (win_len > c->local_window) {
                c->local_window_exceeded += win_len - c->local_window;
                logit("channel %d: rcvd too much data %zu, win %u/%u "
                    "(excess %u)", c->self, win_len, c->local_window,
                    c->local_window_max, c->local_window_exceeded);
                c->local_window = 0;
                /* Allow 10% grace before bringing the hammer down */
                if (c->local_window_exceeded > (c->local_window_max / 10)) {
                        ssh_packet_disconnect(ssh, "channel %d: peer ignored "
                            "channel window", c->self);
                }
        } else {
                c->local_window -= win_len;
                c->local_window_exceeded = 0;
        }

        if (c->datagram) {
                if ((r = sshbuf_put_string(c->output, data, data_len)) != 0)
                        fatal_fr(r, "channel %i: append datagram", c->self);
        } else if ((r = sshbuf_put(c->output, data, data_len)) != 0)
                fatal_fr(r, "channel %i: append data", c->self);

        return 0;
}

int
channel_input_extended_data(int type, u_int32_t seq, struct ssh *ssh)
{
        const u_char *data;
        size_t data_len;
        u_int32_t tcode;
        Channel *c = channel_from_packet_id(ssh, __func__, "extended data");
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if (c->type != SSH_CHANNEL_OPEN) {
                logit("channel %d: ext data for non open", c->self);
                return 0;
        }
        if (c->flags & CHAN_EOF_RCVD) {
                if (ssh->compat & SSH_BUG_EXTEOF)
                        debug("channel %d: accepting ext data after eof",
                            c->self);
                else
                        ssh_packet_disconnect(ssh, "Received extended_data "
                            "after EOF on channel %d.", c->self);
        }

        if ((r = sshpkt_get_u32(ssh, &tcode)) != 0) {
                error_fr(r, "parse tcode");
                ssh_packet_disconnect(ssh, "Invalid extended_data message");
        }
        if (c->efd == -1 ||
            c->extended_usage != CHAN_EXTENDED_WRITE ||
            tcode != SSH2_EXTENDED_DATA_STDERR) {
                logit("channel %d: bad ext data", c->self);
                return 0;
        }
        if ((r = sshpkt_get_string_direct(ssh, &data, &data_len)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
                error_fr(r, "parse data");
                ssh_packet_disconnect(ssh, "Invalid extended_data message");
        }

        if (data_len > c->local_window) {
                logit("channel %d: rcvd too much extended_data %zu, win %u",
                    c->self, data_len, c->local_window);
                return 0;
        }
        debug2("channel %d: rcvd ext data %zu", c->self, data_len);
        /* XXX sshpkt_getb? */
        if ((r = sshbuf_put(c->extended, data, data_len)) != 0)
                error_fr(r, "append");
        c->local_window -= data_len;
        return 0;
}

int
channel_input_ieof(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "ieof");
        int r;

        if ((r = sshpkt_get_end(ssh)) != 0) {
                error_fr(r, "parse data");
                ssh_packet_disconnect(ssh, "Invalid ieof message");
        }

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        chan_rcvd_ieof(ssh, c);

        /* XXX force input close */
        if (c->force_drain && c->istate == CHAN_INPUT_OPEN) {
                debug("channel %d: FORCE input drain", c->self);
                c->istate = CHAN_INPUT_WAIT_DRAIN;
                if (sshbuf_len(c->input) == 0)
                        chan_ibuf_empty(ssh, c);
        }
        return 0;
}

int
channel_input_oclose(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "oclose");
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if ((r = sshpkt_get_end(ssh)) != 0) {
                error_fr(r, "parse data");
                ssh_packet_disconnect(ssh, "Invalid oclose message");
        }
        chan_rcvd_oclose(ssh, c);
        return 0;
}

int
channel_input_open_confirmation(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "open confirmation");
        u_int32_t remote_window, remote_maxpacket;
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if (c->type != SSH_CHANNEL_OPENING)
                ssh_packet_disconnect(ssh, "Received open confirmation for "
                    "non-opening channel %d.", c->self);
        /*
         * Record the remote channel number and mark that the channel
         * is now open.
         */
        if ((r = sshpkt_get_u32(ssh, &c->remote_id)) != 0 ||
            (r = sshpkt_get_u32(ssh, &remote_window)) != 0 ||
            (r = sshpkt_get_u32(ssh, &remote_maxpacket)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
                error_fr(r, "window/maxpacket");
                ssh_packet_disconnect(ssh, "Invalid open confirmation message");
        }

        c->have_remote_id = 1;
        c->remote_window = remote_window;
        c->remote_maxpacket = remote_maxpacket;
        c->type = SSH_CHANNEL_OPEN;
        if (c->open_confirm) {
                debug2_f("channel %d: callback start", c->self);
                c->open_confirm(ssh, c->self, 1, c->open_confirm_ctx);
                debug2_f("channel %d: callback done", c->self);
        }
        channel_set_used_time(ssh, c);
        debug2("channel %d: open confirm rwindow %u rmax %u", c->self,
            c->remote_window, c->remote_maxpacket);
        return 0;
}

static char *
reason2txt(int reason)
{
        switch (reason) {
        case SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED:
                return "administratively prohibited";
        case SSH2_OPEN_CONNECT_FAILED:
                return "connect failed";
        case SSH2_OPEN_UNKNOWN_CHANNEL_TYPE:
                return "unknown channel type";
        case SSH2_OPEN_RESOURCE_SHORTAGE:
                return "resource shortage";
        }
        return "unknown reason";
}

int
channel_input_open_failure(int type, u_int32_t seq, struct ssh *ssh)
{
        Channel *c = channel_from_packet_id(ssh, __func__, "open failure");
        u_int32_t reason;
        char *msg = NULL;
        int r;

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if (c->type != SSH_CHANNEL_OPENING)
                ssh_packet_disconnect(ssh, "Received open failure for "
                    "non-opening channel %d.", c->self);
        if ((r = sshpkt_get_u32(ssh, &reason)) != 0) {
                error_fr(r, "parse reason");
                ssh_packet_disconnect(ssh, "Invalid open failure message");
        }
        /* skip language */
        if ((r = sshpkt_get_cstring(ssh, &msg, NULL)) != 0 ||
            (r = sshpkt_get_string_direct(ssh, NULL, NULL)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
                error_fr(r, "parse msg/lang");
                ssh_packet_disconnect(ssh, "Invalid open failure message");
        }
        logit("channel %d: open failed: %s%s%s", c->self,
            reason2txt(reason), msg ? ": ": "", msg ? msg : "");
        free(msg);
        if (c->open_confirm) {
                debug2_f("channel %d: callback start", c->self);
                c->open_confirm(ssh, c->self, 0, c->open_confirm_ctx);
                debug2_f("channel %d: callback done", c->self);
        }
        /* Schedule the channel for cleanup/deletion. */
        chan_mark_dead(ssh, c);
        return 0;
}

int
channel_input_window_adjust(int type, u_int32_t seq, struct ssh *ssh)
{
        int id = channel_parse_id(ssh, __func__, "window adjust");
        Channel *c;
        u_int32_t adjust;
        u_int new_rwin;
        int r;

        if ((c = channel_lookup(ssh, id)) == NULL) {
                logit("Received window adjust for non-open channel %d.", id);
                return 0;
        }

        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if ((r = sshpkt_get_u32(ssh, &adjust)) != 0 ||
            (r = sshpkt_get_end(ssh)) != 0) {
                error_fr(r, "parse adjust");
                ssh_packet_disconnect(ssh, "Invalid window adjust message");
        }
        debug2("channel %d: rcvd adjust %u", c->self, adjust);
        if ((new_rwin = c->remote_window + adjust) < c->remote_window) {
                fatal("channel %d: adjust %u overflows remote window %u",
                    c->self, adjust, c->remote_window);
        }
        c->remote_window = new_rwin;
        return 0;
}

int
channel_input_status_confirm(int type, u_int32_t seq, struct ssh *ssh)
{
        int id = channel_parse_id(ssh, __func__, "status confirm");
        Channel *c;
        struct channel_confirm *cc;

        /* Reset keepalive timeout */
        ssh_packet_set_alive_timeouts(ssh, 0);

        debug2_f("type %d id %d", type, id);

        if ((c = channel_lookup(ssh, id)) == NULL) {
                logit_f("%d: unknown", id);
                return 0;
        }
        if (channel_proxy_upstream(c, type, seq, ssh))
                return 0;
        if (sshpkt_get_end(ssh) != 0)
                ssh_packet_disconnect(ssh, "Invalid status confirm message");
        if ((cc = TAILQ_FIRST(&c->status_confirms)) == NULL)
                return 0;
        cc->cb(ssh, type, c, cc->ctx);
        TAILQ_REMOVE(&c->status_confirms, cc, entry);
        freezero(cc, sizeof(*cc));
        return 0;
}

/* -- tcp forwarding */

void
channel_set_af(struct ssh *ssh, int af)
{
        ssh->chanctxt->IPv4or6 = af;
}


/*
 * Determine whether or not a port forward listens to loopback, the
 * specified address or wildcard. On the client, a specified bind
 * address will always override gateway_ports. On the server, a
 * gateway_ports of 1 (``yes'') will override the client's specification
 * and force a wildcard bind, whereas a value of 2 (``clientspecified'')
 * will bind to whatever address the client asked for.
 *
 * Special-case listen_addrs are:
 *
 * "0.0.0.0"               -> wildcard v4/v6 if SSH_OLD_FORWARD_ADDR
 * "" (empty string), "*"  -> wildcard v4/v6
 * "localhost"             -> loopback v4/v6
 * "127.0.0.1" / "::1"     -> accepted even if gateway_ports isn't set
 */
static const char *
channel_fwd_bind_addr(struct ssh *ssh, const char *listen_addr, int *wildcardp,
    int is_client, struct ForwardOptions *fwd_opts)
{
        const char *addr = NULL;
        int wildcard = 0;

        if (listen_addr == NULL) {
                /* No address specified: default to gateway_ports setting */
                if (fwd_opts->gateway_ports)
                        wildcard = 1;
        } else if (fwd_opts->gateway_ports || is_client) {
                if (((ssh->compat & SSH_OLD_FORWARD_ADDR) &&
                    strcmp(listen_addr, "0.0.0.0") == 0 && is_client == 0) ||
                    *listen_addr == '\0' || strcmp(listen_addr, "*") == 0 ||
                    (!is_client && fwd_opts->gateway_ports == 1)) {
                        wildcard = 1;
                        /*
                         * Notify client if they requested a specific listen
                         * address and it was overridden.
                         */
                        if (*listen_addr != '\0' &&
                            strcmp(listen_addr, "0.0.0.0") != 0 &&
                            strcmp(listen_addr, "*") != 0) {
                                ssh_packet_send_debug(ssh,
                                    "Forwarding listen address "
                                    "\"%s\" overridden by server "
                                    "GatewayPorts", listen_addr);
                        }
                } else if (strcmp(listen_addr, "localhost") != 0 ||
                    strcmp(listen_addr, "127.0.0.1") == 0 ||
                    strcmp(listen_addr, "::1") == 0) {
                        /*
                         * Accept explicit localhost address when
                         * GatewayPorts=yes. The "localhost" hostname is
                         * deliberately skipped here so it will listen on all
                         * available local address families.
                         */
                        addr = listen_addr;
                }
        } else if (strcmp(listen_addr, "127.0.0.1") == 0 ||
            strcmp(listen_addr, "::1") == 0) {
                /*
                 * If a specific IPv4/IPv6 localhost address has been
                 * requested then accept it even if gateway_ports is in
                 * effect. This allows the client to prefer IPv4 or IPv6.
                 */
                addr = listen_addr;
        }
        if (wildcardp != NULL)
                *wildcardp = wildcard;
        return addr;
}

static int
channel_setup_fwd_listener_tcpip(struct ssh *ssh, int type,
    struct Forward *fwd, int *allocated_listen_port,
    struct ForwardOptions *fwd_opts)
{
        Channel *c;
        int sock, r, success = 0, wildcard = 0, is_client;
        struct addrinfo hints, *ai, *aitop;
        const char *host, *addr;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];
        in_port_t *lport_p;

        is_client = (type == SSH_CHANNEL_PORT_LISTENER);

        if (is_client && fwd->connect_path != NULL) {
                host = fwd->connect_path;
        } else {
                host = (type == SSH_CHANNEL_RPORT_LISTENER) ?
                    fwd->listen_host : fwd->connect_host;
                if (host == NULL) {
                        error("No forward host name.");
                        return 0;
                }
                if (strlen(host) >= NI_MAXHOST) {
                        error("Forward host name too long.");
                        return 0;
                }
        }

        /* Determine the bind address, cf. channel_fwd_bind_addr() comment */
        addr = channel_fwd_bind_addr(ssh, fwd->listen_host, &wildcard,
            is_client, fwd_opts);
        debug3_f("type %d wildcard %d addr %s", type, wildcard,
            (addr == NULL) ? "NULL" : addr);

        /*
         * getaddrinfo returns a loopback address if the hostname is
         * set to NULL and hints.ai_flags is not AI_PASSIVE
         */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = ssh->chanctxt->IPv4or6;
        hints.ai_flags = wildcard ? AI_PASSIVE : 0;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%d", fwd->listen_port);
        if ((r = getaddrinfo(addr, strport, &hints, &aitop)) != 0) {
                if (addr == NULL) {
                        /* This really shouldn't happen */
                        ssh_packet_disconnect(ssh, "getaddrinfo: fatal error: %s",
                            ssh_gai_strerror(r));
                } else {
                        error_f("getaddrinfo(%.64s): %s", addr,
                            ssh_gai_strerror(r));
                }
                return 0;
        }
        if (allocated_listen_port != NULL)
                *allocated_listen_port = 0;
        for (ai = aitop; ai; ai = ai->ai_next) {
                switch (ai->ai_family) {
                case AF_INET:
                        lport_p = &((struct sockaddr_in *)ai->ai_addr)->
                            sin_port;
                        break;
                case AF_INET6:
                        lport_p = &((struct sockaddr_in6 *)ai->ai_addr)->
                            sin6_port;
                        break;
                default:
                        continue;
                }
                /*
                 * If allocating a port for -R forwards, then use the
                 * same port for all address families.
                 */
                if (type == SSH_CHANNEL_RPORT_LISTENER &&
                    fwd->listen_port == 0 && allocated_listen_port != NULL &&
                    *allocated_listen_port > 0)
                        *lport_p = htons(*allocated_listen_port);

                if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop, sizeof(ntop),
                    strport, sizeof(strport),
                    NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
                        error_f("getnameinfo failed");
                        continue;
                }
                /* Create a port to listen for the host. */
                sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
                if (sock == -1) {
                        /* this is no error since kernel may not support ipv6 */
                        verbose("socket [%s]:%s: %.100s", ntop, strport,
                            strerror(errno));
                        continue;
                }

                set_reuseaddr(sock);
                if (ai->ai_family == AF_INET6)
                        sock_set_v6only(sock);

                debug("Local forwarding listening on %s port %s.",
                    ntop, strport);

                /* Bind the socket to the address. */
                if (bind(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
                        /*
                         * address can be in if use ipv6 address is
                         * already bound
                         */
                        if (!ai->ai_next)
                                error("bind [%s]:%s: %.100s",
                                    ntop, strport, strerror(errno));
                        else
                                verbose("bind [%s]:%s: %.100s",
                                    ntop, strport, strerror(errno));

                        close(sock);
                        continue;
                }
                /* Start listening for connections on the socket. */
                if (listen(sock, SSH_LISTEN_BACKLOG) == -1) {
                        error("listen [%s]:%s: %.100s", ntop, strport,
                            strerror(errno));
                        close(sock);
                        continue;
                }

                /*
                 * fwd->listen_port == 0 requests a dynamically allocated port -
                 * record what we got.
                 */
                if (type == SSH_CHANNEL_RPORT_LISTENER &&
                    fwd->listen_port == 0 &&
                    allocated_listen_port != NULL &&
                    *allocated_listen_port == 0) {
                        *allocated_listen_port = get_local_port(sock);
                        debug("Allocated listen port %d",
                            *allocated_listen_port);
                }

                /* Allocate a channel number for the socket. */
                c = channel_new(ssh, "port-listener", type, sock, sock, -1,
                    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
                    0, "port listener", 1);
                c->path = xstrdup(host);
                c->host_port = fwd->connect_port;
                c->listening_addr = addr == NULL ? NULL : xstrdup(addr);
                if (fwd->listen_port == 0 && allocated_listen_port != NULL &&
                    !(ssh->compat & SSH_BUG_DYNAMIC_RPORT))
                        c->listening_port = *allocated_listen_port;
                else
                        c->listening_port = fwd->listen_port;
                success = 1;
        }
        if (success == 0)
                error_f("cannot listen to port: %d", fwd->listen_port);
        freeaddrinfo(aitop);
        return success;
}

static int
channel_setup_fwd_listener_streamlocal(struct ssh *ssh, int type,
    struct Forward *fwd, struct ForwardOptions *fwd_opts)
{
        struct sockaddr_un sunaddr;
        const char *path;
        Channel *c;
        int port, sock;
        mode_t omask;

        switch (type) {
        case SSH_CHANNEL_UNIX_LISTENER:
                if (fwd->connect_path != NULL) {
                        if (strlen(fwd->connect_path) > sizeof(sunaddr.sun_path)) {
                                error("Local connecting path too long: %s",
                                    fwd->connect_path);
                                return 0;
                        }
                        path = fwd->connect_path;
                        port = PORT_STREAMLOCAL;
                } else {
                        if (fwd->connect_host == NULL) {
                                error("No forward host name.");
                                return 0;
                        }
                        if (strlen(fwd->connect_host) >= NI_MAXHOST) {
                                error("Forward host name too long.");
                                return 0;
                        }
                        path = fwd->connect_host;
                        port = fwd->connect_port;
                }
                break;
        case SSH_CHANNEL_RUNIX_LISTENER:
                path = fwd->listen_path;
                port = PORT_STREAMLOCAL;
                break;
        default:
                error_f("unexpected channel type %d", type);
                return 0;
        }

        if (fwd->listen_path == NULL) {
                error("No forward path name.");
                return 0;
        }
        if (strlen(fwd->listen_path) > sizeof(sunaddr.sun_path)) {
                error("Local listening path too long: %s", fwd->listen_path);
                return 0;
        }

        debug3_f("type %d path %s", type, fwd->listen_path);

        /* Start a Unix domain listener. */
        omask = umask(fwd_opts->streamlocal_bind_mask);
        sock = unix_listener(fwd->listen_path, SSH_LISTEN_BACKLOG,
            fwd_opts->streamlocal_bind_unlink);
        umask(omask);
        if (sock < 0)
                return 0;

        debug("Local forwarding listening on path %s.", fwd->listen_path);

        /* Allocate a channel number for the socket. */
        c = channel_new(ssh, "unix-listener", type, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
            0, "unix listener", 1);
        c->path = xstrdup(path);
        c->host_port = port;
        c->listening_port = PORT_STREAMLOCAL;
        c->listening_addr = xstrdup(fwd->listen_path);
        return 1;
}

static int
channel_cancel_rport_listener_tcpip(struct ssh *ssh,
    const char *host, u_short port)
{
        u_int i;
        int found = 0;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_RPORT_LISTENER)
                        continue;
                if (strcmp(c->path, host) == 0 && c->listening_port == port) {
                        debug2_f("close channel %d", i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

static int
channel_cancel_rport_listener_streamlocal(struct ssh *ssh, const char *path)
{
        u_int i;
        int found = 0;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_RUNIX_LISTENER)
                        continue;
                if (c->path == NULL)
                        continue;
                if (strcmp(c->path, path) == 0) {
                        debug2_f("close channel %d", i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

int
channel_cancel_rport_listener(struct ssh *ssh, struct Forward *fwd)
{
        if (fwd->listen_path != NULL) {
                return channel_cancel_rport_listener_streamlocal(ssh,
                    fwd->listen_path);
        } else {
                return channel_cancel_rport_listener_tcpip(ssh,
                    fwd->listen_host, fwd->listen_port);
        }
}

static int
channel_cancel_lport_listener_tcpip(struct ssh *ssh,
    const char *lhost, u_short lport, int cport,
    struct ForwardOptions *fwd_opts)
{
        u_int i;
        int found = 0;
        const char *addr = channel_fwd_bind_addr(ssh, lhost, NULL, 1, fwd_opts);

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_PORT_LISTENER)
                        continue;
                if (c->listening_port != lport)
                        continue;
                if (cport == CHANNEL_CANCEL_PORT_STATIC) {
                        /* skip dynamic forwardings */
                        if (c->host_port == 0)
                                continue;
                } else {
                        if (c->host_port != cport)
                                continue;
                }
                if ((c->listening_addr == NULL && addr != NULL) ||
                    (c->listening_addr != NULL && addr == NULL))
                        continue;
                if (addr == NULL || strcmp(c->listening_addr, addr) == 0) {
                        debug2_f("close channel %d", i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

static int
channel_cancel_lport_listener_streamlocal(struct ssh *ssh, const char *path)
{
        u_int i;
        int found = 0;

        if (path == NULL) {
                error_f("no path specified.");
                return 0;
        }

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                Channel *c = ssh->chanctxt->channels[i];
                if (c == NULL || c->type != SSH_CHANNEL_UNIX_LISTENER)
                        continue;
                if (c->listening_addr == NULL)
                        continue;
                if (strcmp(c->listening_addr, path) == 0) {
                        debug2_f("close channel %d", i);
                        channel_free(ssh, c);
                        found = 1;
                }
        }

        return found;
}

int
channel_cancel_lport_listener(struct ssh *ssh,
    struct Forward *fwd, int cport, struct ForwardOptions *fwd_opts)
{
        if (fwd->listen_path != NULL) {
                return channel_cancel_lport_listener_streamlocal(ssh,
                    fwd->listen_path);
        } else {
                return channel_cancel_lport_listener_tcpip(ssh,
                    fwd->listen_host, fwd->listen_port, cport, fwd_opts);
        }
}

/* protocol local port fwd, used by ssh */
int
channel_setup_local_fwd_listener(struct ssh *ssh,
    struct Forward *fwd, struct ForwardOptions *fwd_opts)
{
        if (fwd->listen_path != NULL) {
                return channel_setup_fwd_listener_streamlocal(ssh,
                    SSH_CHANNEL_UNIX_LISTENER, fwd, fwd_opts);
        } else {
                return channel_setup_fwd_listener_tcpip(ssh,
                    SSH_CHANNEL_PORT_LISTENER, fwd, NULL, fwd_opts);
        }
}

/* Matches a remote forwarding permission against a requested forwarding */
static int
remote_open_match(struct permission *allowed_open, struct Forward *fwd)
{
        int ret;
        char *lhost;

        /* XXX add ACLs for streamlocal */
        if (fwd->listen_path != NULL)
                return 1;

        if (fwd->listen_host == NULL || allowed_open->listen_host == NULL)
                return 0;

        if (allowed_open->listen_port != FWD_PERMIT_ANY_PORT &&
            allowed_open->listen_port != fwd->listen_port)
                return 0;

        /* Match hostnames case-insensitively */
        lhost = xstrdup(fwd->listen_host);
        lowercase(lhost);
        ret = match_pattern(lhost, allowed_open->listen_host);
        free(lhost);

        return ret;
}

/* Checks whether a requested remote forwarding is permitted */
static int
check_rfwd_permission(struct ssh *ssh, struct Forward *fwd)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->remote_perms;
        u_int i, permit, permit_adm = 1;
        struct permission *perm;

        /* XXX apply GatewayPorts override before checking? */

        permit = pset->all_permitted;
        if (!permit) {
                for (i = 0; i < pset->num_permitted_user; i++) {
                        perm = &pset->permitted_user[i];
                        if (remote_open_match(perm, fwd)) {
                                permit = 1;
                                break;
                        }
                }
        }

        if (pset->num_permitted_admin > 0) {
                permit_adm = 0;
                for (i = 0; i < pset->num_permitted_admin; i++) {
                        perm = &pset->permitted_admin[i];
                        if (remote_open_match(perm, fwd)) {
                                permit_adm = 1;
                                break;
                        }
                }
        }

        return permit && permit_adm;
}

/* protocol v2 remote port fwd, used by sshd */
int
channel_setup_remote_fwd_listener(struct ssh *ssh, struct Forward *fwd,
    int *allocated_listen_port, struct ForwardOptions *fwd_opts)
{
        if (!check_rfwd_permission(ssh, fwd)) {
                ssh_packet_send_debug(ssh, "port forwarding refused");
                if (fwd->listen_path != NULL)
                        /* XXX always allowed, see remote_open_match() */
                        logit("Received request from %.100s port %d to "
                            "remote forward to path \"%.100s\", "
                            "but the request was denied.",
                            ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
                            fwd->listen_path);
                else if(fwd->listen_host != NULL)
                        logit("Received request from %.100s port %d to "
                            "remote forward to host %.100s port %d, "
                            "but the request was denied.",
                            ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
                            fwd->listen_host, fwd->listen_port );
                else
                        logit("Received request from %.100s port %d to remote "
                            "forward, but the request was denied.",
                            ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
                return 0;
        }
        if (fwd->listen_path != NULL) {
                return channel_setup_fwd_listener_streamlocal(ssh,
                    SSH_CHANNEL_RUNIX_LISTENER, fwd, fwd_opts);
        } else {
                return channel_setup_fwd_listener_tcpip(ssh,
                    SSH_CHANNEL_RPORT_LISTENER, fwd, allocated_listen_port,
                    fwd_opts);
        }
}

/*
 * Translate the requested rfwd listen host to something usable for
 * this server.
 */
static const char *
channel_rfwd_bind_host(const char *listen_host)
{
        if (listen_host == NULL) {
                return "localhost";
        } else if (*listen_host == '\0' || strcmp(listen_host, "*") == 0) {
                return "";
        } else
                return listen_host;
}

/*
 * Initiate forwarding of connections to port "port" on remote host through
 * the secure channel to host:port from local side.
 * Returns handle (index) for updating the dynamic listen port with
 * channel_update_permission().
 */
int
channel_request_remote_forwarding(struct ssh *ssh, struct Forward *fwd)
{
        int r, success = 0, idx = -1;
        const char *host_to_connect, *listen_host, *listen_path;
        int port_to_connect, listen_port;

        /* Send the forward request to the remote side. */
        if (fwd->listen_path != NULL) {
                if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
                    (r = sshpkt_put_cstring(ssh,
                    "streamlocal-forward@openssh.com")) != 0 ||
                    (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
                    (r = sshpkt_put_cstring(ssh, fwd->listen_path)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0 ||
                    (r = ssh_packet_write_wait(ssh)) != 0)
                        fatal_fr(r, "request streamlocal");
        } else {
                if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
                    (r = sshpkt_put_cstring(ssh, "tcpip-forward")) != 0 ||
                    (r = sshpkt_put_u8(ssh, 1)) != 0 || /* want reply */
                    (r = sshpkt_put_cstring(ssh,
                    channel_rfwd_bind_host(fwd->listen_host))) != 0 ||
                    (r = sshpkt_put_u32(ssh, fwd->listen_port)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0 ||
                    (r = ssh_packet_write_wait(ssh)) != 0)
                        fatal_fr(r, "request tcpip-forward");
        }
        /* Assume that server accepts the request */
        success = 1;
        if (success) {
                /* Record that connection to this host/port is permitted. */
                host_to_connect = listen_host = listen_path = NULL;
                port_to_connect = listen_port = 0;
                if (fwd->connect_path != NULL) {
                        host_to_connect = fwd->connect_path;
                        port_to_connect = PORT_STREAMLOCAL;
                } else {
                        host_to_connect = fwd->connect_host;
                        port_to_connect = fwd->connect_port;
                }
                if (fwd->listen_path != NULL) {
                        listen_path = fwd->listen_path;
                        listen_port = PORT_STREAMLOCAL;
                } else {
                        listen_host = fwd->listen_host;
                        listen_port = fwd->listen_port;
                }
                idx = permission_set_add(ssh, FORWARD_USER, FORWARD_LOCAL,
                    host_to_connect, port_to_connect,
                    listen_host, listen_path, listen_port, NULL);
        }
        return idx;
}

static int
open_match(struct permission *allowed_open, const char *requestedhost,
    int requestedport)
{
        if (allowed_open->host_to_connect == NULL)
                return 0;
        if (allowed_open->port_to_connect != FWD_PERMIT_ANY_PORT &&
            allowed_open->port_to_connect != requestedport)
                return 0;
        if (strcmp(allowed_open->host_to_connect, FWD_PERMIT_ANY_HOST) != 0 &&
            strcmp(allowed_open->host_to_connect, requestedhost) != 0)
                return 0;
        return 1;
}

/*
 * Note that in the listen host/port case
 * we don't support FWD_PERMIT_ANY_PORT and
 * need to translate between the configured-host (listen_host)
 * and what we've sent to the remote server (channel_rfwd_bind_host)
 */
static int
open_listen_match_tcpip(struct permission *allowed_open,
    const char *requestedhost, u_short requestedport, int translate)
{
        const char *allowed_host;

        if (allowed_open->host_to_connect == NULL)
                return 0;
        if (allowed_open->listen_port != requestedport)
                return 0;
        if (!translate && allowed_open->listen_host == NULL &&
            requestedhost == NULL)
                return 1;
        allowed_host = translate ?
            channel_rfwd_bind_host(allowed_open->listen_host) :
            allowed_open->listen_host;
        if (allowed_host == NULL || requestedhost == NULL ||
            strcmp(allowed_host, requestedhost) != 0)
                return 0;
        return 1;
}

static int
open_listen_match_streamlocal(struct permission *allowed_open,
    const char *requestedpath)
{
        if (allowed_open->host_to_connect == NULL)
                return 0;
        if (allowed_open->listen_port != PORT_STREAMLOCAL)
                return 0;
        if (allowed_open->listen_path == NULL ||
            strcmp(allowed_open->listen_path, requestedpath) != 0)
                return 0;
        return 1;
}

/*
 * Request cancellation of remote forwarding of connection host:port from
 * local side.
 */
static int
channel_request_rforward_cancel_tcpip(struct ssh *ssh,
    const char *host, u_short port)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        int r;
        u_int i;
        struct permission *perm = NULL;

        for (i = 0; i < pset->num_permitted_user; i++) {
                perm = &pset->permitted_user[i];
                if (open_listen_match_tcpip(perm, host, port, 0))
                        break;
                perm = NULL;
        }
        if (perm == NULL) {
                debug_f("requested forward not found");
                return -1;
        }
        if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
            (r = sshpkt_put_cstring(ssh, "cancel-tcpip-forward")) != 0 ||
            (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
            (r = sshpkt_put_cstring(ssh, channel_rfwd_bind_host(host))) != 0 ||
            (r = sshpkt_put_u32(ssh, port)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "send cancel");

        fwd_perm_clear(perm); /* unregister */

        return 0;
}

/*
 * Request cancellation of remote forwarding of Unix domain socket
 * path from local side.
 */
static int
channel_request_rforward_cancel_streamlocal(struct ssh *ssh, const char *path)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        int r;
        u_int i;
        struct permission *perm = NULL;

        for (i = 0; i < pset->num_permitted_user; i++) {
                perm = &pset->permitted_user[i];
                if (open_listen_match_streamlocal(perm, path))
                        break;
                perm = NULL;
        }
        if (perm == NULL) {
                debug_f("requested forward not found");
                return -1;
        }
        if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
            (r = sshpkt_put_cstring(ssh,
            "cancel-streamlocal-forward@openssh.com")) != 0 ||
            (r = sshpkt_put_u8(ssh, 0)) != 0 || /* want reply */
            (r = sshpkt_put_cstring(ssh, path)) != 0 ||
            (r = sshpkt_send(ssh)) != 0)
                fatal_fr(r, "send cancel");

        fwd_perm_clear(perm); /* unregister */

        return 0;
}

/*
 * Request cancellation of remote forwarding of a connection from local side.
 */
int
channel_request_rforward_cancel(struct ssh *ssh, struct Forward *fwd)
{
        if (fwd->listen_path != NULL) {
                return channel_request_rforward_cancel_streamlocal(ssh,
                    fwd->listen_path);
        } else {
                return channel_request_rforward_cancel_tcpip(ssh,
                    fwd->listen_host,
                    fwd->listen_port ? fwd->listen_port : fwd->allocated_port);
        }
}

/*
 * Permits opening to any host/port if permitted_user[] is empty.  This is
 * usually called by the server, because the user could connect to any port
 * anyway, and the server has no way to know but to trust the client anyway.
 */
void
channel_permit_all(struct ssh *ssh, int where)
{
        struct permission_set *pset = permission_set_get(ssh, where);

        if (pset->num_permitted_user == 0)
                pset->all_permitted = 1;
}

/*
 * Permit the specified host/port for forwarding.
 */
void
channel_add_permission(struct ssh *ssh, int who, int where,
    char *host, int port)
{
        int local = where == FORWARD_LOCAL;
        struct permission_set *pset = permission_set_get(ssh, where);

        debug("allow %s forwarding to host %s port %d",
            fwd_ident(who, where), host, port);
        /*
         * Remote forwards set listen_host/port, local forwards set
         * host/port_to_connect.
         */
        permission_set_add(ssh, who, where,
            local ? host : 0, local ? port : 0,
            local ? NULL : host, NULL, local ? 0 : port, NULL);
        pset->all_permitted = 0;
}

/*
 * Administratively disable forwarding.
 */
void
channel_disable_admin(struct ssh *ssh, int where)
{
        channel_clear_permission(ssh, FORWARD_ADM, where);
        permission_set_add(ssh, FORWARD_ADM, where,
            NULL, 0, NULL, NULL, 0, NULL);
}

/*
 * Clear a list of permitted opens.
 */
void
channel_clear_permission(struct ssh *ssh, int who, int where)
{
        struct permission **permp;
        u_int *npermp;

        permission_set_get_array(ssh, who, where, &permp, &npermp);
        *permp = xrecallocarray(*permp, *npermp, 0, sizeof(**permp));
        *npermp = 0;
}

/*
 * Update the listen port for a dynamic remote forward, after
 * the actual 'newport' has been allocated. If 'newport' < 0 is
 * passed then they entry will be invalidated.
 */
void
channel_update_permission(struct ssh *ssh, int idx, int newport)
{
        struct permission_set *pset = &ssh->chanctxt->local_perms;

        if (idx < 0 || (u_int)idx >= pset->num_permitted_user) {
                debug_f("index out of range: %d num_permitted_user %d",
                    idx, pset->num_permitted_user);
                return;
        }
        debug("%s allowed port %d for forwarding to host %s port %d",
            newport > 0 ? "Updating" : "Removing",
            newport,
            pset->permitted_user[idx].host_to_connect,
            pset->permitted_user[idx].port_to_connect);
        if (newport <= 0)
                fwd_perm_clear(&pset->permitted_user[idx]);
        else {
                pset->permitted_user[idx].listen_port =
                    (ssh->compat & SSH_BUG_DYNAMIC_RPORT) ? 0 : newport;
        }
}

/* Try to start non-blocking connect to next host in cctx list */
static int
connect_next(struct channel_connect *cctx)
{
        int sock, saved_errno;
        struct sockaddr_un *sunaddr;
        char ntop[NI_MAXHOST];
        char strport[MAXIMUM(NI_MAXSERV, sizeof(sunaddr->sun_path))];

        for (; cctx->ai; cctx->ai = cctx->ai->ai_next) {
                switch (cctx->ai->ai_family) {
                case AF_UNIX:
                        /* unix:pathname instead of host:port */
                        sunaddr = (struct sockaddr_un *)cctx->ai->ai_addr;
                        strlcpy(ntop, "unix", sizeof(ntop));
                        strlcpy(strport, sunaddr->sun_path, sizeof(strport));
                        break;
                case AF_INET:
                case AF_INET6:
                        if (getnameinfo(cctx->ai->ai_addr, cctx->ai->ai_addrlen,
                            ntop, sizeof(ntop), strport, sizeof(strport),
                            NI_NUMERICHOST|NI_NUMERICSERV) != 0) {
                                error_f("getnameinfo failed");
                                continue;
                        }
                        break;
                default:
                        continue;
                }
                debug_f("start for host %.100s ([%.100s]:%s)",
                    cctx->host, ntop, strport);
                if ((sock = socket(cctx->ai->ai_family, cctx->ai->ai_socktype,
                    cctx->ai->ai_protocol)) == -1) {
                        if (cctx->ai->ai_next == NULL)
                                error("socket: %.100s", strerror(errno));
                        else
                                verbose("socket: %.100s", strerror(errno));
                        continue;
                }
                if (set_nonblock(sock) == -1)
                        fatal_f("set_nonblock(%d)", sock);
                if (connect(sock, cctx->ai->ai_addr,
                    cctx->ai->ai_addrlen) == -1 && errno != EINPROGRESS) {
                        debug_f("host %.100s ([%.100s]:%s): %.100s",
                            cctx->host, ntop, strport, strerror(errno));
                        saved_errno = errno;
                        close(sock);
                        errno = saved_errno;
                        continue;       /* fail -- try next */
                }
                if (cctx->ai->ai_family != AF_UNIX)
                        set_nodelay(sock);
                debug_f("connect host %.100s ([%.100s]:%s) in progress, fd=%d",
                    cctx->host, ntop, strport, sock);
                cctx->ai = cctx->ai->ai_next;
                return sock;
        }
        return -1;
}

static void
channel_connect_ctx_free(struct channel_connect *cctx)
{
        free(cctx->host);
        if (cctx->aitop) {
                if (cctx->aitop->ai_family == AF_UNIX)
                        free(cctx->aitop);
                else
                        freeaddrinfo(cctx->aitop);
        }
        memset(cctx, 0, sizeof(*cctx));
}

/*
 * Return connecting socket to remote host:port or local socket path,
 * passing back the failure reason if appropriate.
 */
static int
connect_to_helper(struct ssh *ssh, const char *name, int port, int socktype,
    char *ctype, char *rname, struct channel_connect *cctx,
    int *reason, const char **errmsg)
{
        struct addrinfo hints;
        int gaierr;
        int sock = -1;
        char strport[NI_MAXSERV];

        if (port == PORT_STREAMLOCAL) {
                struct sockaddr_un *sunaddr;
                struct addrinfo *ai;

                if (strlen(name) > sizeof(sunaddr->sun_path)) {
                        error("%.100s: %.100s", name, strerror(ENAMETOOLONG));
                        return -1;
                }

                /*
                 * Fake up a struct addrinfo for AF_UNIX connections.
                 * channel_connect_ctx_free() must check ai_family
                 * and use free() not freeaddirinfo() for AF_UNIX.
                 */
                ai = xmalloc(sizeof(*ai) + sizeof(*sunaddr));
                memset(ai, 0, sizeof(*ai) + sizeof(*sunaddr));
                ai->ai_addr = (struct sockaddr *)(ai + 1);
                ai->ai_addrlen = sizeof(*sunaddr);
                ai->ai_family = AF_UNIX;
                ai->ai_socktype = socktype;
                ai->ai_protocol = PF_UNSPEC;
                sunaddr = (struct sockaddr_un *)ai->ai_addr;
                sunaddr->sun_family = AF_UNIX;
                strlcpy(sunaddr->sun_path, name, sizeof(sunaddr->sun_path));
                cctx->aitop = ai;
        } else {
                memset(&hints, 0, sizeof(hints));
                hints.ai_family = ssh->chanctxt->IPv4or6;
                hints.ai_socktype = socktype;
                snprintf(strport, sizeof strport, "%d", port);
                if ((gaierr = getaddrinfo(name, strport, &hints, &cctx->aitop))
                    != 0) {
                        if (errmsg != NULL)
                                *errmsg = ssh_gai_strerror(gaierr);
                        if (reason != NULL)
                                *reason = SSH2_OPEN_CONNECT_FAILED;
                        error("connect_to %.100s: unknown host (%s)", name,
                            ssh_gai_strerror(gaierr));
                        return -1;
                }
        }

        cctx->host = xstrdup(name);
        cctx->port = port;
        cctx->ai = cctx->aitop;

        if ((sock = connect_next(cctx)) == -1) {
                error("connect to %.100s port %d failed: %s",
                    name, port, strerror(errno));
                return -1;
        }

        return sock;
}

/* Return CONNECTING channel to remote host:port or local socket path */
static Channel *
connect_to(struct ssh *ssh, const char *host, int port,
    char *ctype, char *rname)
{
        struct channel_connect cctx;
        Channel *c;
        int sock;

        memset(&cctx, 0, sizeof(cctx));
        sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
            &cctx, NULL, NULL);
        if (sock == -1) {
                channel_connect_ctx_free(&cctx);
                return NULL;
        }
        c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
        c->host_port = port;
        c->path = xstrdup(host);
        c->connect_ctx = cctx;

        return c;
}

/*
 * returns either the newly connected channel or the downstream channel
 * that needs to deal with this connection.
 */
Channel *
channel_connect_by_listen_address(struct ssh *ssh, const char *listen_host,
    u_short listen_port, char *ctype, char *rname)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        u_int i;
        struct permission *perm;

        for (i = 0; i < pset->num_permitted_user; i++) {
                perm = &pset->permitted_user[i];
                if (open_listen_match_tcpip(perm,
                    listen_host, listen_port, 1)) {
                        if (perm->downstream)
                                return perm->downstream;
                        if (perm->port_to_connect == 0)
                                return rdynamic_connect_prepare(ssh,
                                    ctype, rname);
                        return connect_to(ssh,
                            perm->host_to_connect, perm->port_to_connect,
                            ctype, rname);
                }
        }
        error("WARNING: Server requests forwarding for unknown listen_port %d",
            listen_port);
        return NULL;
}

Channel *
channel_connect_by_listen_path(struct ssh *ssh, const char *path,
    char *ctype, char *rname)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        u_int i;
        struct permission *perm;

        for (i = 0; i < pset->num_permitted_user; i++) {
                perm = &pset->permitted_user[i];
                if (open_listen_match_streamlocal(perm, path)) {
                        return connect_to(ssh,
                            perm->host_to_connect, perm->port_to_connect,
                            ctype, rname);
                }
        }
        error("WARNING: Server requests forwarding for unknown path %.100s",
            path);
        return NULL;
}

/* Check if connecting to that port is permitted and connect. */
Channel *
channel_connect_to_port(struct ssh *ssh, const char *host, u_short port,
    char *ctype, char *rname, int *reason, const char **errmsg)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        struct channel_connect cctx;
        Channel *c;
        u_int i, permit, permit_adm = 1;
        int sock;
        struct permission *perm;

        permit = pset->all_permitted;
        if (!permit) {
                for (i = 0; i < pset->num_permitted_user; i++) {
                        perm = &pset->permitted_user[i];
                        if (open_match(perm, host, port)) {
                                permit = 1;
                                break;
                        }
                }
        }

        if (pset->num_permitted_admin > 0) {
                permit_adm = 0;
                for (i = 0; i < pset->num_permitted_admin; i++) {
                        perm = &pset->permitted_admin[i];
                        if (open_match(perm, host, port)) {
                                permit_adm = 1;
                                break;
                        }
                }
        }

        if (!permit || !permit_adm) {
                logit("Received request from %.100s port %d to connect to "
                    "host %.100s port %d, but the request was denied.",
                    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), host, port);
                if (reason != NULL)
                        *reason = SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED;
                return NULL;
        }

        memset(&cctx, 0, sizeof(cctx));
        sock = connect_to_helper(ssh, host, port, SOCK_STREAM, ctype, rname,
            &cctx, reason, errmsg);
        if (sock == -1) {
                channel_connect_ctx_free(&cctx);
                return NULL;
        }

        c = channel_new(ssh, ctype, SSH_CHANNEL_CONNECTING, sock, sock, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
        c->host_port = port;
        c->path = xstrdup(host);
        c->connect_ctx = cctx;

        return c;
}

/* Check if connecting to that path is permitted and connect. */
Channel *
channel_connect_to_path(struct ssh *ssh, const char *path,
    char *ctype, char *rname)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        u_int i, permit, permit_adm = 1;
        struct permission *perm;

        permit = pset->all_permitted;
        if (!permit) {
                for (i = 0; i < pset->num_permitted_user; i++) {
                        perm = &pset->permitted_user[i];
                        if (open_match(perm, path, PORT_STREAMLOCAL)) {
                                permit = 1;
                                break;
                        }
                }
        }

        if (pset->num_permitted_admin > 0) {
                permit_adm = 0;
                for (i = 0; i < pset->num_permitted_admin; i++) {
                        perm = &pset->permitted_admin[i];
                        if (open_match(perm, path, PORT_STREAMLOCAL)) {
                                permit_adm = 1;
                                break;
                        }
                }
        }

        if (!permit || !permit_adm) {
                logit("Received request to connect to path %.100s, "
                    "but the request was denied.", path);
                return NULL;
        }
        return connect_to(ssh, path, PORT_STREAMLOCAL, ctype, rname);
}

void
channel_send_window_changes(struct ssh *ssh)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct winsize ws;
        int r;
        u_int i;

        for (i = 0; i < sc->channels_alloc; i++) {
                if (sc->channels[i] == NULL || !sc->channels[i]->client_tty ||
                    sc->channels[i]->type != SSH_CHANNEL_OPEN)
                        continue;
                if (ioctl(sc->channels[i]->rfd, TIOCGWINSZ, &ws) == -1)
                        continue;
                channel_request_start(ssh, i, "window-change", 0);
                if ((r = sshpkt_put_u32(ssh, (u_int)ws.ws_col)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_row)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_xpixel)) != 0 ||
                    (r = sshpkt_put_u32(ssh, (u_int)ws.ws_ypixel)) != 0 ||
                    (r = sshpkt_send(ssh)) != 0)
                        fatal_fr(r, "channel %u; send window-change", i);
        }
}

/* Return RDYNAMIC_OPEN channel: channel allows SOCKS, but is not connected */
static Channel *
rdynamic_connect_prepare(struct ssh *ssh, char *ctype, char *rname)
{
        Channel *c;
        int r;

        c = channel_new(ssh, ctype, SSH_CHANNEL_RDYNAMIC_OPEN, -1, -1, -1,
            CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, rname, 1);
        c->host_port = 0;
        c->path = NULL;

        /*
         * We need to open the channel before we have a FD,
         * so that we can get SOCKS header from peer.
         */
        if ((r = sshpkt_start(ssh, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->remote_id)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->self)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_window)) != 0 ||
            (r = sshpkt_put_u32(ssh, c->local_maxpacket)) != 0)
                fatal_fr(r, "channel %i; confirm", c->self);
        return c;
}

/* Return CONNECTING socket to remote host:port or local socket path */
static int
rdynamic_connect_finish(struct ssh *ssh, Channel *c)
{
        struct ssh_channels *sc = ssh->chanctxt;
        struct permission_set *pset = &sc->local_perms;
        struct permission *perm;
        struct channel_connect cctx;
        u_int i, permit_adm = 1;
        int sock;

        if (pset->num_permitted_admin > 0) {
                permit_adm = 0;
                for (i = 0; i < pset->num_permitted_admin; i++) {
                        perm = &pset->permitted_admin[i];
                        if (open_match(perm, c->path, c->host_port)) {
                                permit_adm = 1;
                                break;
                        }
                }
        }
        if (!permit_adm) {
                debug_f("requested forward not permitted");
                return -1;
        }

        memset(&cctx, 0, sizeof(cctx));
        sock = connect_to_helper(ssh, c->path, c->host_port, SOCK_STREAM, NULL,
            NULL, &cctx, NULL, NULL);
        if (sock == -1)
                channel_connect_ctx_free(&cctx);
        else {
                /* similar to SSH_CHANNEL_CONNECTING but we've already sent the open */
                c->type = SSH_CHANNEL_RDYNAMIC_FINISH;
                c->connect_ctx = cctx;
                channel_register_fds(ssh, c, sock, sock, -1, 0, 1, 0);
        }
        return sock;
}

/* -- X11 forwarding */

/*
 * Creates an internet domain socket for listening for X11 connections.
 * Returns 0 and a suitable display number for the DISPLAY variable
 * stored in display_numberp , or -1 if an error occurs.
 */
int
x11_create_display_inet(struct ssh *ssh, int x11_display_offset,
    int x11_use_localhost, int single_connection,
    u_int *display_numberp, int **chanids)
{
        Channel *nc = NULL;
        int display_number, sock, port;
        struct addrinfo hints, *ai, *aitop;
        char strport[NI_MAXSERV];
        int gaierr, n, num_socks = 0, socks[NUM_SOCKS];

        if (chanids == NULL || x11_display_offset < 0 ||
            x11_display_offset > UINT16_MAX - X11_BASE_PORT - MAX_DISPLAYS)
                return -1;

        for (display_number = x11_display_offset;
            display_number < MAX_DISPLAYS;
            display_number++) {
                port = X11_BASE_PORT + display_number;
                memset(&hints, 0, sizeof(hints));
                hints.ai_family = ssh->chanctxt->IPv4or6;
                hints.ai_flags = x11_use_localhost ? 0: AI_PASSIVE;
                hints.ai_socktype = SOCK_STREAM;
                snprintf(strport, sizeof strport, "%d", port);
                if ((gaierr = getaddrinfo(NULL, strport,
                    &hints, &aitop)) != 0) {
                        error("getaddrinfo: %.100s", ssh_gai_strerror(gaierr));
                        return -1;
                }
                for (ai = aitop; ai; ai = ai->ai_next) {
                        if (ai->ai_family != AF_INET &&
                            ai->ai_family != AF_INET6)
                                continue;
                        sock = socket(ai->ai_family, ai->ai_socktype,
                            ai->ai_protocol);
                        if (sock == -1) {
                                if ((errno != EINVAL) && (errno != EAFNOSUPPORT)
#ifdef EPFNOSUPPORT
                                    && (errno != EPFNOSUPPORT)
#endif 
                                    ) {
                                        error("socket: %.100s", strerror(errno));
                                        freeaddrinfo(aitop);
                                        return -1;
                                } else {
                                        debug("x11_create_display_inet: Socket family %d not supported",
                                                 ai->ai_family);
                                        continue;
                                }
                        }
                        if (ai->ai_family == AF_INET6)
                                sock_set_v6only(sock);
                        if (x11_use_localhost)
                                set_reuseaddr(sock);
                        if (bind(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
                                debug2_f("bind port %d: %.100s", port,
                                    strerror(errno));
                                close(sock);
                                for (n = 0; n < num_socks; n++)
                                        close(socks[n]);
                                num_socks = 0;
                                break;
                        }
                        socks[num_socks++] = sock;
                        if (num_socks == NUM_SOCKS)
                                break;
                }
                freeaddrinfo(aitop);
                if (num_socks > 0)
                        break;
        }
        if (display_number >= MAX_DISPLAYS) {
                error("Failed to allocate internet-domain X11 display socket.");
                return -1;
        }
        /* Start listening for connections on the socket. */
        for (n = 0; n < num_socks; n++) {
                sock = socks[n];
                if (listen(sock, SSH_LISTEN_BACKLOG) == -1) {
                        error("listen: %.100s", strerror(errno));
                        close(sock);
                        return -1;
                }
        }

        /* Allocate a channel for each socket. */
        *chanids = xcalloc(num_socks + 1, sizeof(**chanids));
        for (n = 0; n < num_socks; n++) {
                sock = socks[n];
                nc = channel_new(ssh, "x11-listener",
                    SSH_CHANNEL_X11_LISTENER, sock, sock, -1,
                    CHAN_X11_WINDOW_DEFAULT, CHAN_X11_PACKET_DEFAULT,
                    0, "X11 inet listener", 1);
                nc->single_connection = single_connection;
                (*chanids)[n] = nc->self;
        }
        (*chanids)[n] = -1;

        /* Return the display number for the DISPLAY environment variable. */
        *display_numberp = display_number;
        return 0;
}

static int
connect_local_xsocket_path(const char *pathname)
{
        int sock;
        struct sockaddr_un addr;

        sock = socket(AF_UNIX, SOCK_STREAM, 0);
        if (sock == -1) {
                error("socket: %.100s", strerror(errno));
                return -1;
        }
        memset(&addr, 0, sizeof(addr));
        addr.sun_family = AF_UNIX;
        strlcpy(addr.sun_path, pathname, sizeof addr.sun_path);
        if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) == 0)
                return sock;
        close(sock);
        error("connect %.100s: %.100s", addr.sun_path, strerror(errno));
        return -1;
}

static int
connect_local_xsocket(u_int dnr)
{
        char buf[1024];
        snprintf(buf, sizeof buf, _PATH_UNIX_X, dnr);
        return connect_local_xsocket_path(buf);
}

#ifdef __APPLE__
static int
is_path_to_xsocket(const char *display, char *path, size_t pathlen)
{
        struct stat sbuf;

        if (strlcpy(path, display, pathlen) >= pathlen) {
                error("%s: display path too long", __func__);
                return 0;
        }
        if (display[0] != '/')
                return 0;
        if (stat(path, &sbuf) == 0) {
                return 1;
        } else {
                char *dot = strrchr(path, '.');
                if (dot != NULL) {
                        *dot = '\0';
                        if (stat(path, &sbuf) == 0) {
                                return 1;
                        }
                }
        }
        return 0;
}
#endif

int
x11_connect_display(struct ssh *ssh)
{
        u_int display_number;
        const char *display;
        char buf[1024], *cp;
        struct addrinfo hints, *ai, *aitop;
        char strport[NI_MAXSERV];
        int gaierr, sock = 0;

        /* Try to open a socket for the local X server. */
        display = getenv("DISPLAY");
        if (!display) {
                error("DISPLAY not set.");
                return -1;
        }
        /*
         * Now we decode the value of the DISPLAY variable and make a
         * connection to the real X server.
         */

#ifdef __APPLE__
        /* Check if display is a path to a socket (as set by launchd). */
        {
                char path[PATH_MAX];

                if (is_path_to_xsocket(display, path, sizeof(path))) {
                        debug("x11_connect_display: $DISPLAY is launchd");

                        /* Create a socket. */
                        sock = connect_local_xsocket_path(path);
                        if (sock < 0)
                                return -1;

                        /* OK, we now have a connection to the display. */
                        return sock;
                }
        }
#endif
        /*
         * Check if it is a unix domain socket.  Unix domain displays are in
         * one of the following formats: unix:d[.s], :d[.s], ::d[.s]
         */
        if (strncmp(display, "unix:", 5) == 0 ||
            display[0] == ':') {
                /* Connect to the unix domain socket. */
                if (sscanf(strrchr(display, ':') + 1, "%u",
                    &display_number) != 1) {
                        error("Could not parse display number from DISPLAY: "
                            "%.100s", display);
                        return -1;
                }
                /* Create a socket. */
                sock = connect_local_xsocket(display_number);
                if (sock < 0)
                        return -1;

                /* OK, we now have a connection to the display. */
                return sock;
        }
        /*
         * Connect to an inet socket.  The DISPLAY value is supposedly
         * hostname:d[.s], where hostname may also be numeric IP address.
         */
        strlcpy(buf, display, sizeof(buf));
        cp = strchr(buf, ':');
        if (!cp) {
                error("Could not find ':' in DISPLAY: %.100s", display);
                return -1;
        }
        *cp = 0;
        /*
         * buf now contains the host name.  But first we parse the
         * display number.
         */
        if (sscanf(cp + 1, "%u", &display_number) != 1 ||
            display_number > UINT16_MAX - X11_BASE_PORT) {
                error("Could not parse display number from DISPLAY: %.100s",
                    display);
                return -1;
        }

        /* Look up the host address */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = ssh->chanctxt->IPv4or6;
        hints.ai_socktype = SOCK_STREAM;
        snprintf(strport, sizeof strport, "%u", X11_BASE_PORT + display_number);
        if ((gaierr = getaddrinfo(buf, strport, &hints, &aitop)) != 0) {
                error("%.100s: unknown host. (%s)", buf,
                ssh_gai_strerror(gaierr));
                return -1;
        }
        for (ai = aitop; ai; ai = ai->ai_next) {
                /* Create a socket. */
                sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
                if (sock == -1) {
                        debug2("socket: %.100s", strerror(errno));
                        continue;
                }
                /* Connect it to the display. */
                if (connect(sock, ai->ai_addr, ai->ai_addrlen) == -1) {
                        debug2("connect %.100s port %u: %.100s", buf,
                            X11_BASE_PORT + display_number, strerror(errno));
                        close(sock);
                        continue;
                }
                /* Success */
                break;
        }
        freeaddrinfo(aitop);
        if (!ai) {
                error("connect %.100s port %u: %.100s", buf,
                    X11_BASE_PORT + display_number, strerror(errno));
                return -1;
        }
        set_nodelay(sock);
        return sock;
}

/*
 * Requests forwarding of X11 connections, generates fake authentication
 * data, and enables authentication spoofing.
 * This should be called in the client only.
 */
void
x11_request_forwarding_with_spoofing(struct ssh *ssh, int client_session_id,
    const char *disp, const char *proto, const char *data, int want_reply)
{
        struct ssh_channels *sc = ssh->chanctxt;
        u_int data_len = (u_int) strlen(data) / 2;
        u_int i, value;
        const char *cp;
        char *new_data;
        int r, screen_number;

        if (sc->x11_saved_display == NULL)
                sc->x11_saved_display = xstrdup(disp);
        else if (strcmp(disp, sc->x11_saved_display) != 0) {
                error("x11_request_forwarding_with_spoofing: different "
                    "$DISPLAY already forwarded");
                return;
        }

        cp = strchr(disp, ':');
        if (cp)
                cp = strchr(cp, '.');
        if (cp)
                screen_number = (u_int)strtonum(cp + 1, 0, 400, NULL);
        else
                screen_number = 0;

        if (sc->x11_saved_proto == NULL) {
                /* Save protocol name. */
                sc->x11_saved_proto = xstrdup(proto);

                /* Extract real authentication data. */
                sc->x11_saved_data = xmalloc(data_len);
                for (i = 0; i < data_len; i++) {
                        if (sscanf(data + 2 * i, "%2x", &value) != 1) {
                                fatal("x11_request_forwarding: bad "
                                    "authentication data: %.100s", data);
                        }
                        sc->x11_saved_data[i] = value;
                }
                sc->x11_saved_data_len = data_len;

                /* Generate fake data of the same length. */
                sc->x11_fake_data = xmalloc(data_len);
                arc4random_buf(sc->x11_fake_data, data_len);
                sc->x11_fake_data_len = data_len;
        }

        /* Convert the fake data into hex. */
        new_data = tohex(sc->x11_fake_data, data_len);

        /* Send the request packet. */
        channel_request_start(ssh, client_session_id, "x11-req", want_reply);
        if ((r = sshpkt_put_u8(ssh, 0)) != 0 || /* bool: single connection */
            (r = sshpkt_put_cstring(ssh, proto)) != 0 ||
            (r = sshpkt_put_cstring(ssh, new_data)) != 0 ||
            (r = sshpkt_put_u32(ssh, screen_number)) != 0 ||
            (r = sshpkt_send(ssh)) != 0 ||
            (r = ssh_packet_write_wait(ssh)) != 0)
                fatal_fr(r, "send x11-req");
        free(new_data);
}

/*
 * Returns whether an x11 channel was used recently (less than a second ago)
 */
int
x11_channel_used_recently(struct ssh *ssh) {
        u_int i;
        Channel *c;
        time_t lastused = 0;

        for (i = 0; i < ssh->chanctxt->channels_alloc; i++) {
                c = ssh->chanctxt->channels[i];
                if (c == NULL || c->ctype == NULL || c->lastused == 0 ||
                    strcmp(c->ctype, "x11-connection") != 0)
                        continue;
                lastused = c->lastused;
        }
        return lastused != 0 && monotime() > lastused + 1;
}