/* $OpenBSD: sftp-server.c,v 1.148 2024/04/30 06:23:51 djm Exp $ */
/*
 * Copyright (c) 2000-2004 Markus Friedl.  All rights reserved.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/resource.h>
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif
#ifdef HAVE_SYS_MOUNT_H
#include <sys/mount.h>
#endif
#ifdef HAVE_SYS_STATVFS_H
#include <sys/statvfs.h>
#endif

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#include <pwd.h>
#include <grp.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <stdarg.h>

#include "atomicio.h"
#include "xmalloc.h"
#include "sshbuf.h"
#include "ssherr.h"
#include "log.h"
#include "misc.h"
#include "match.h"
#include "uidswap.h"

#include "sftp.h"
#include "sftp-common.h"

char *sftp_realpath(const char *, char *); /* sftp-realpath.c */

/* Maximum data read that we are willing to accept */
#define SFTP_MAX_READ_LENGTH (SFTP_MAX_MSG_LENGTH - 1024)

/* Our verbosity */
static LogLevel log_level = SYSLOG_LEVEL_ERROR;

/* Our client */
static struct passwd *pw = NULL;
static char *client_addr = NULL;

/* input and output queue */
struct sshbuf *iqueue;
struct sshbuf *oqueue;

/* Version of client */
static u_int version;

/* SSH2_FXP_INIT received */
static int init_done;

/* Disable writes */
static int readonly;

/* Requests that are allowed/denied */
static char *request_allowlist, *request_denylist;

/* portable attributes, etc. */
typedef struct Stat Stat;

struct Stat {
        char *name;
        char *long_name;
        Attrib attrib;
};

/* Packet handlers */
static void process_open(u_int32_t id);
static void process_close(u_int32_t id);
static void process_read(u_int32_t id);
static void process_write(u_int32_t id);
static void process_stat(u_int32_t id);
static void process_lstat(u_int32_t id);
static void process_fstat(u_int32_t id);
static void process_setstat(u_int32_t id);
static void process_fsetstat(u_int32_t id);
static void process_opendir(u_int32_t id);
static void process_readdir(u_int32_t id);
static void process_remove(u_int32_t id);
static void process_mkdir(u_int32_t id);
static void process_rmdir(u_int32_t id);
static void process_realpath(u_int32_t id);
static void process_rename(u_int32_t id);
static void process_readlink(u_int32_t id);
static void process_symlink(u_int32_t id);
static void process_extended_posix_rename(u_int32_t id);
static void process_extended_statvfs(u_int32_t id);
static void process_extended_fstatvfs(u_int32_t id);
static void process_extended_hardlink(u_int32_t id);
static void process_extended_fsync(u_int32_t id);
static void process_extended_lsetstat(u_int32_t id);
static void process_extended_limits(u_int32_t id);
static void process_extended_expand(u_int32_t id);
static void process_extended_copy_data(u_int32_t id);
static void process_extended_home_directory(u_int32_t id);
static void process_extended_get_users_groups_by_id(u_int32_t id);
static void process_extended(u_int32_t id);

struct sftp_handler {
        const char *name;       /* user-visible name for fine-grained perms */
        const char *ext_name;   /* extended request name */
        u_int type;             /* packet type, for non extended packets */
        void (*handler)(u_int32_t);
        int does_write;         /* if nonzero, banned for readonly mode */
};

static const struct sftp_handler handlers[] = {
        /* NB. SSH2_FXP_OPEN does the readonly check in the handler itself */
        { "open", NULL, SSH2_FXP_OPEN, process_open, 0 },
        { "close", NULL, SSH2_FXP_CLOSE, process_close, 0 },
        { "read", NULL, SSH2_FXP_READ, process_read, 0 },
        { "write", NULL, SSH2_FXP_WRITE, process_write, 1 },
        { "lstat", NULL, SSH2_FXP_LSTAT, process_lstat, 0 },
        { "fstat", NULL, SSH2_FXP_FSTAT, process_fstat, 0 },
        { "setstat", NULL, SSH2_FXP_SETSTAT, process_setstat, 1 },
        { "fsetstat", NULL, SSH2_FXP_FSETSTAT, process_fsetstat, 1 },
        { "opendir", NULL, SSH2_FXP_OPENDIR, process_opendir, 0 },
        { "readdir", NULL, SSH2_FXP_READDIR, process_readdir, 0 },
        { "remove", NULL, SSH2_FXP_REMOVE, process_remove, 1 },
        { "mkdir", NULL, SSH2_FXP_MKDIR, process_mkdir, 1 },
        { "rmdir", NULL, SSH2_FXP_RMDIR, process_rmdir, 1 },
        { "realpath", NULL, SSH2_FXP_REALPATH, process_realpath, 0 },
        { "stat", NULL, SSH2_FXP_STAT, process_stat, 0 },
        { "rename", NULL, SSH2_FXP_RENAME, process_rename, 1 },
        { "readlink", NULL, SSH2_FXP_READLINK, process_readlink, 0 },
        { "symlink", NULL, SSH2_FXP_SYMLINK, process_symlink, 1 },
        { NULL, NULL, 0, NULL, 0 }
};

/* SSH2_FXP_EXTENDED submessages */
static const struct sftp_handler extended_handlers[] = {
        { "posix-rename", "posix-rename@openssh.com", 0,
            process_extended_posix_rename, 1 },
        { "statvfs", "statvfs@openssh.com", 0, process_extended_statvfs, 0 },
        { "fstatvfs", "fstatvfs@openssh.com", 0, process_extended_fstatvfs, 0 },
        { "hardlink", "hardlink@openssh.com", 0, process_extended_hardlink, 1 },
        { "fsync", "fsync@openssh.com", 0, process_extended_fsync, 1 },
        { "lsetstat", "lsetstat@openssh.com", 0, process_extended_lsetstat, 1 },
        { "limits", "limits@openssh.com", 0, process_extended_limits, 0 },
        { "expand-path", "expand-path@openssh.com", 0,
            process_extended_expand, 0 },
        { "copy-data", "copy-data", 0, process_extended_copy_data, 1 },
        { "home-directory", "home-directory", 0,
            process_extended_home_directory, 0 },
        { "users-groups-by-id", "users-groups-by-id@openssh.com", 0,
            process_extended_get_users_groups_by_id, 0 },
        { NULL, NULL, 0, NULL, 0 }
};

static const struct sftp_handler *
extended_handler_byname(const char *name)
{
        int i;

        for (i = 0; extended_handlers[i].handler != NULL; i++) {
                if (strcmp(name, extended_handlers[i].ext_name) == 0)
                        return &extended_handlers[i];
        }
        return NULL;
}

static int
request_permitted(const struct sftp_handler *h)
{
        char *result;

        if (readonly && h->does_write) {
                verbose("Refusing %s request in read-only mode", h->name);
                return 0;
        }
        if (request_denylist != NULL &&
            ((result = match_list(h->name, request_denylist, NULL))) != NULL) {
                free(result);
                verbose("Refusing denylisted %s request", h->name);
                return 0;
        }
        if (request_allowlist != NULL &&
            ((result = match_list(h->name, request_allowlist, NULL))) != NULL) {
                free(result);
                debug2("Permitting allowlisted %s request", h->name);
                return 1;
        }
        if (request_allowlist != NULL) {
                verbose("Refusing non-allowlisted %s request", h->name);
                return 0;
        }
        return 1;
}

static int
errno_to_portable(int unixerrno)
{
        int ret = 0;

        switch (unixerrno) {
        case 0:
                ret = SSH2_FX_OK;
                break;
        case ENOENT:
        case ENOTDIR:
        case EBADF:
        case ELOOP:
                ret = SSH2_FX_NO_SUCH_FILE;
                break;
        case EPERM:
        case EACCES:
        case EFAULT:
                ret = SSH2_FX_PERMISSION_DENIED;
                break;
        case ENAMETOOLONG:
        case EINVAL:
                ret = SSH2_FX_BAD_MESSAGE;
                break;
        case ENOSYS:
                ret = SSH2_FX_OP_UNSUPPORTED;
                break;
        default:
                ret = SSH2_FX_FAILURE;
                break;
        }
        return ret;
}

static int
flags_from_portable(int pflags)
{
        int flags = 0;

        if ((pflags & SSH2_FXF_READ) &&
            (pflags & SSH2_FXF_WRITE)) {
                flags = O_RDWR;
        } else if (pflags & SSH2_FXF_READ) {
                flags = O_RDONLY;
        } else if (pflags & SSH2_FXF_WRITE) {
                flags = O_WRONLY;
        }
        if (pflags & SSH2_FXF_APPEND)
                flags |= O_APPEND;
        if (pflags & SSH2_FXF_CREAT)
                flags |= O_CREAT;
        if (pflags & SSH2_FXF_TRUNC)
                flags |= O_TRUNC;
        if (pflags & SSH2_FXF_EXCL)
                flags |= O_EXCL;
        return flags;
}

static const char *
string_from_portable(int pflags)
{
        static char ret[128];

        *ret = '\0';

#define PAPPEND(str)    {                               \
                if (*ret != '\0')                       \
                        strlcat(ret, ",", sizeof(ret)); \
                strlcat(ret, str, sizeof(ret));         \
        }

        if (pflags & SSH2_FXF_READ)
                PAPPEND("READ")
        if (pflags & SSH2_FXF_WRITE)
                PAPPEND("WRITE")
        if (pflags & SSH2_FXF_APPEND)
                PAPPEND("APPEND")
        if (pflags & SSH2_FXF_CREAT)
                PAPPEND("CREATE")
        if (pflags & SSH2_FXF_TRUNC)
                PAPPEND("TRUNCATE")
        if (pflags & SSH2_FXF_EXCL)
                PAPPEND("EXCL")

        return ret;
}

/* handle handles */

typedef struct Handle Handle;
struct Handle {
        int use;
        DIR *dirp;
        int fd;
        int flags;
        char *name;
        u_int64_t bytes_read, bytes_write;
        int next_unused;
};

enum {
        HANDLE_UNUSED,
        HANDLE_DIR,
        HANDLE_FILE
};

static Handle *handles = NULL;
static u_int num_handles = 0;
static int first_unused_handle = -1;

static void handle_unused(int i)
{
        handles[i].use = HANDLE_UNUSED;
        handles[i].next_unused = first_unused_handle;
        first_unused_handle = i;
}

static int
handle_new(int use, const char *name, int fd, int flags, DIR *dirp)
{
        int i;

        if (first_unused_handle == -1) {
                if (num_handles + 1 <= num_handles)
                        return -1;
                num_handles++;
                handles = xreallocarray(handles, num_handles, sizeof(Handle));
                handle_unused(num_handles - 1);
        }

        i = first_unused_handle;
        first_unused_handle = handles[i].next_unused;

        handles[i].use = use;
        handles[i].dirp = dirp;
        handles[i].fd = fd;
        handles[i].flags = flags;
        handles[i].name = xstrdup(name);
        handles[i].bytes_read = handles[i].bytes_write = 0;

        return i;
}

static int
handle_is_ok(int i, int type)
{
        return i >= 0 && (u_int)i < num_handles && handles[i].use == type;
}

static int
handle_to_string(int handle, u_char **stringp, int *hlenp)
{
        if (stringp == NULL || hlenp == NULL)
                return -1;
        *stringp = xmalloc(sizeof(int32_t));
        put_u32(*stringp, handle);
        *hlenp = sizeof(int32_t);
        return 0;
}

static int
handle_from_string(const u_char *handle, u_int hlen)
{
        int val;

        if (hlen != sizeof(int32_t))
                return -1;
        val = get_u32(handle);
        if (handle_is_ok(val, HANDLE_FILE) ||
            handle_is_ok(val, HANDLE_DIR))
                return val;
        return -1;
}

static char *
handle_to_name(int handle)
{
        if (handle_is_ok(handle, HANDLE_DIR)||
            handle_is_ok(handle, HANDLE_FILE))
                return handles[handle].name;
        return NULL;
}

static DIR *
handle_to_dir(int handle)
{
        if (handle_is_ok(handle, HANDLE_DIR))
                return handles[handle].dirp;
        return NULL;
}

static int
handle_to_fd(int handle)
{
        if (handle_is_ok(handle, HANDLE_FILE))
                return handles[handle].fd;
        return -1;
}

static int
handle_to_flags(int handle)
{
        if (handle_is_ok(handle, HANDLE_FILE))
                return handles[handle].flags;
        return 0;
}

static void
handle_update_read(int handle, ssize_t bytes)
{
        if (handle_is_ok(handle, HANDLE_FILE) && bytes > 0)
                handles[handle].bytes_read += bytes;
}

static void
handle_update_write(int handle, ssize_t bytes)
{
        if (handle_is_ok(handle, HANDLE_FILE) && bytes > 0)
                handles[handle].bytes_write += bytes;
}

static u_int64_t
handle_bytes_read(int handle)
{
        if (handle_is_ok(handle, HANDLE_FILE))
                return (handles[handle].bytes_read);
        return 0;
}

static u_int64_t
handle_bytes_write(int handle)
{
        if (handle_is_ok(handle, HANDLE_FILE))
                return (handles[handle].bytes_write);
        return 0;
}

static int
handle_close(int handle)
{
        int ret = -1;

        if (handle_is_ok(handle, HANDLE_FILE)) {
                ret = close(handles[handle].fd);
                free(handles[handle].name);
                handle_unused(handle);
        } else if (handle_is_ok(handle, HANDLE_DIR)) {
                ret = closedir(handles[handle].dirp);
                free(handles[handle].name);
                handle_unused(handle);
        } else {
                errno = ENOENT;
        }
        return ret;
}

static void
handle_log_close(int handle, char *emsg)
{
        if (handle_is_ok(handle, HANDLE_FILE)) {
                logit("%s%sclose \"%s\" bytes read %llu written %llu",
                    emsg == NULL ? "" : emsg, emsg == NULL ? "" : " ",
                    handle_to_name(handle),
                    (unsigned long long)handle_bytes_read(handle),
                    (unsigned long long)handle_bytes_write(handle));
        } else {
                logit("%s%sclosedir \"%s\"",
                    emsg == NULL ? "" : emsg, emsg == NULL ? "" : " ",
                    handle_to_name(handle));
        }
}

static void
handle_log_exit(void)
{
        u_int i;

        for (i = 0; i < num_handles; i++)
                if (handles[i].use != HANDLE_UNUSED)
                        handle_log_close(i, "forced");
}

static int
get_handle(struct sshbuf *queue, int *hp)
{
        u_char *handle;
        int r;
        size_t hlen;

        *hp = -1;
        if ((r = sshbuf_get_string(queue, &handle, &hlen)) != 0)
                return r;
        if (hlen < 256)
                *hp = handle_from_string(handle, hlen);
        free(handle);
        return 0;
}

/* send replies */

static void
send_msg(struct sshbuf *m)
{
        int r;

        if ((r = sshbuf_put_stringb(oqueue, m)) != 0)
                fatal_fr(r, "enqueue");
        sshbuf_reset(m);
}

static const char *
status_to_message(u_int32_t status)
{
        static const char * const status_messages[] = {
                "Success",                      /* SSH_FX_OK */
                "End of file",                  /* SSH_FX_EOF */
                "No such file",                 /* SSH_FX_NO_SUCH_FILE */
                "Permission denied",            /* SSH_FX_PERMISSION_DENIED */
                "Failure",                      /* SSH_FX_FAILURE */
                "Bad message",                  /* SSH_FX_BAD_MESSAGE */
                "No connection",                /* SSH_FX_NO_CONNECTION */
                "Connection lost",              /* SSH_FX_CONNECTION_LOST */
                "Operation unsupported",        /* SSH_FX_OP_UNSUPPORTED */
                "Unknown error"                 /* Others */
        };
        return (status_messages[MINIMUM(status,SSH2_FX_MAX)]);
}

static void
send_status_errmsg(u_int32_t id, u_int32_t status, const char *errmsg)
{
        struct sshbuf *msg;
        int r;

        debug3("request %u: sent status %u", id, status);
        if (log_level > SYSLOG_LEVEL_VERBOSE ||
            (status != SSH2_FX_OK && status != SSH2_FX_EOF))
                logit("sent status %s", status_to_message(status));
        if ((msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_put_u8(msg, SSH2_FXP_STATUS)) != 0 ||
            (r = sshbuf_put_u32(msg, id)) != 0 ||
            (r = sshbuf_put_u32(msg, status)) != 0)
                fatal_fr(r, "compose");
        if (version >= 3) {
                if ((r = sshbuf_put_cstring(msg, errmsg == NULL ?
                    status_to_message(status) : errmsg)) != 0 ||
                    (r = sshbuf_put_cstring(msg, "")) != 0)
                        fatal_fr(r, "compose message");
        }
        send_msg(msg);
        sshbuf_free(msg);
}

static void
send_status(u_int32_t id, u_int32_t status)
{
        send_status_errmsg(id, status, NULL);
}

static void
send_data_or_handle(char type, u_int32_t id, const u_char *data, int dlen)
{
        struct sshbuf *msg;
        int r;

        if ((msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_put_u8(msg, type)) != 0 ||
            (r = sshbuf_put_u32(msg, id)) != 0 ||
            (r = sshbuf_put_string(msg, data, dlen)) != 0)
                fatal_fr(r, "compose");
        send_msg(msg);
        sshbuf_free(msg);
}

static void
send_data(u_int32_t id, const u_char *data, int dlen)
{
        debug("request %u: sent data len %d", id, dlen);
        send_data_or_handle(SSH2_FXP_DATA, id, data, dlen);
}

static void
send_handle(u_int32_t id, int handle)
{
        u_char *string;
        int hlen;

        handle_to_string(handle, &string, &hlen);
        debug("request %u: sent handle %d", id, handle);
        send_data_or_handle(SSH2_FXP_HANDLE, id, string, hlen);
        free(string);
}

static void
send_names(u_int32_t id, int count, const Stat *stats)
{
        struct sshbuf *msg;
        int i, r;

        if ((msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_put_u8(msg, SSH2_FXP_NAME)) != 0 ||
            (r = sshbuf_put_u32(msg, id)) != 0 ||
            (r = sshbuf_put_u32(msg, count)) != 0)
                fatal_fr(r, "compose");
        debug("request %u: sent names count %d", id, count);
        for (i = 0; i < count; i++) {
                if ((r = sshbuf_put_cstring(msg, stats[i].name)) != 0 ||
                    (r = sshbuf_put_cstring(msg, stats[i].long_name)) != 0 ||
                    (r = encode_attrib(msg, &stats[i].attrib)) != 0)
                        fatal_fr(r, "compose filenames/attrib");
        }
        send_msg(msg);
        sshbuf_free(msg);
}

static void
send_attrib(u_int32_t id, const Attrib *a)
{
        struct sshbuf *msg;
        int r;

        debug("request %u: sent attrib have 0x%x", id, a->flags);
        if ((msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_put_u8(msg, SSH2_FXP_ATTRS)) != 0 ||
            (r = sshbuf_put_u32(msg, id)) != 0 ||
            (r = encode_attrib(msg, a)) != 0)
                fatal_fr(r, "compose");
        send_msg(msg);
        sshbuf_free(msg);
}

static void
send_statvfs(u_int32_t id, struct statvfs *st)
{
        struct sshbuf *msg;
        u_int64_t flag;
        int r;

        flag = (st->f_flag & ST_RDONLY) ? SSH2_FXE_STATVFS_ST_RDONLY : 0;
        flag |= (st->f_flag & ST_NOSUID) ? SSH2_FXE_STATVFS_ST_NOSUID : 0;

        if ((msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_put_u8(msg, SSH2_FXP_EXTENDED_REPLY)) != 0 ||
            (r = sshbuf_put_u32(msg, id)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_bsize)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_frsize)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_blocks)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_bfree)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_bavail)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_files)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_ffree)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_favail)) != 0 ||
            (r = sshbuf_put_u64(msg, FSID_TO_ULONG(st->f_fsid))) != 0 ||
            (r = sshbuf_put_u64(msg, flag)) != 0 ||
            (r = sshbuf_put_u64(msg, st->f_namemax)) != 0)
                fatal_fr(r, "compose");
        send_msg(msg);
        sshbuf_free(msg);
}

/*
 * Prepare SSH2_FXP_VERSION extension advertisement for a single extension.
 * The extension is checked for permission prior to advertisement.
 */
static int
compose_extension(struct sshbuf *msg, const char *name, const char *ver)
{
        int r;
        const struct sftp_handler *exthnd;

        if ((exthnd = extended_handler_byname(name)) == NULL)
                fatal_f("internal error: no handler for %s", name);
        if (!request_permitted(exthnd)) {
                debug2_f("refusing to advertise disallowed extension %s", name);
                return 0;
        }
        if ((r = sshbuf_put_cstring(msg, name)) != 0 ||
            (r = sshbuf_put_cstring(msg, ver)) != 0)
                fatal_fr(r, "compose %s", name);
        return 0;
}

/* parse incoming */

static void
process_init(void)
{
        struct sshbuf *msg;
        int r;

        if ((r = sshbuf_get_u32(iqueue, &version)) != 0)
                fatal_fr(r, "parse");
        verbose("received client version %u", version);
        if ((msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_put_u8(msg, SSH2_FXP_VERSION)) != 0 ||
            (r = sshbuf_put_u32(msg, SSH2_FILEXFER_VERSION)) != 0)
                fatal_fr(r, "compose");

         /* extension advertisements */
        compose_extension(msg, "posix-rename@openssh.com", "1");
        compose_extension(msg, "statvfs@openssh.com", "2");
        compose_extension(msg, "fstatvfs@openssh.com", "2");
        compose_extension(msg, "hardlink@openssh.com", "1");
        compose_extension(msg, "fsync@openssh.com", "1");
        compose_extension(msg, "lsetstat@openssh.com", "1");
        compose_extension(msg, "limits@openssh.com", "1");
        compose_extension(msg, "expand-path@openssh.com", "1");
        compose_extension(msg, "copy-data", "1");
        compose_extension(msg, "home-directory", "1");
        compose_extension(msg, "users-groups-by-id@openssh.com", "1");

        send_msg(msg);
        sshbuf_free(msg);
}

static void
process_open(u_int32_t id)
{
        u_int32_t pflags;
        Attrib a;
        char *name;
        int r, handle, fd, flags, mode, status = SSH2_FX_FAILURE;

        if ((r = sshbuf_get_cstring(iqueue, &name, NULL)) != 0 ||
            (r = sshbuf_get_u32(iqueue, &pflags)) != 0 || /* portable flags */
            (r = decode_attrib(iqueue, &a)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: open flags %d", id, pflags);
        flags = flags_from_portable(pflags);
        mode = (a.flags & SSH2_FILEXFER_ATTR_PERMISSIONS) ? a.perm : 0666;
        logit("open \"%s\" flags %s mode 0%o",
            name, string_from_portable(pflags), mode);
        if (readonly &&
            ((flags & O_ACCMODE) != O_RDONLY ||
            (flags & (O_CREAT|O_TRUNC)) != 0)) {
                verbose("Refusing open request in read-only mode");
                status = SSH2_FX_PERMISSION_DENIED;
        } else {
                fd = open(name, flags, mode);
                if (fd == -1) {
                        status = errno_to_portable(errno);
                } else {
                        handle = handle_new(HANDLE_FILE, name, fd, flags, NULL);
                        if (handle < 0) {
                                close(fd);
                        } else {
                                send_handle(id, handle);
                                status = SSH2_FX_OK;
                        }
                }
        }
        if (status != SSH2_FX_OK)
                send_status(id, status);
        free(name);
}

static void
process_close(u_int32_t id)
{
        int r, handle, ret, status = SSH2_FX_FAILURE;

        if ((r = get_handle(iqueue, &handle)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: close handle %u", id, handle);
        handle_log_close(handle, NULL);
        ret = handle_close(handle);
        status = (ret == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        send_status(id, status);
}

static void
process_read(u_int32_t id)
{
        static u_char *buf;
        static size_t buflen;
        u_int32_t len;
        int r, handle, fd, ret, status = SSH2_FX_FAILURE;
        u_int64_t off;

        if ((r = get_handle(iqueue, &handle)) != 0 ||
            (r = sshbuf_get_u64(iqueue, &off)) != 0 ||
            (r = sshbuf_get_u32(iqueue, &len)) != 0)
                fatal_fr(r, "parse");

        debug("request %u: read \"%s\" (handle %d) off %llu len %u",
            id, handle_to_name(handle), handle, (unsigned long long)off, len);
        if ((fd = handle_to_fd(handle)) == -1)
                goto out;
        if (len > SFTP_MAX_READ_LENGTH) {
                debug2("read change len %u to %u", len, SFTP_MAX_READ_LENGTH);
                len = SFTP_MAX_READ_LENGTH;
        }
        if (len > buflen) {
                debug3_f("allocate %zu => %u", buflen, len);
                if ((buf = realloc(buf, len)) == NULL)
                        fatal_f("realloc failed");
                buflen = len;
        }
        if (lseek(fd, off, SEEK_SET) == -1) {
                status = errno_to_portable(errno);
                error_f("seek \"%.100s\": %s", handle_to_name(handle),
                    strerror(errno));
                goto out;
        }
        if (len == 0) {
                /* weird, but not strictly disallowed */
                ret = 0;
        } else if ((ret = read(fd, buf, len)) == -1) {
                status = errno_to_portable(errno);
                error_f("read \"%.100s\": %s", handle_to_name(handle),
                    strerror(errno));
                goto out;
        } else if (ret == 0) {
                status = SSH2_FX_EOF;
                goto out;
        }
        send_data(id, buf, ret);
        handle_update_read(handle, ret);
        /* success */
        status = SSH2_FX_OK;
 out:
        if (status != SSH2_FX_OK)
                send_status(id, status);
}

static void
process_write(u_int32_t id)
{
        u_int64_t off;
        size_t len;
        int r, handle, fd, ret, status;
        u_char *data;

        if ((r = get_handle(iqueue, &handle)) != 0 ||
            (r = sshbuf_get_u64(iqueue, &off)) != 0 ||
            (r = sshbuf_get_string(iqueue, &data, &len)) != 0)
                fatal_fr(r, "parse");

        debug("request %u: write \"%s\" (handle %d) off %llu len %zu",
            id, handle_to_name(handle), handle, (unsigned long long)off, len);
        fd = handle_to_fd(handle);

        if (fd < 0)
                status = SSH2_FX_FAILURE;
        else {
                if (!(handle_to_flags(handle) & O_APPEND) &&
                    lseek(fd, off, SEEK_SET) == -1) {
                        status = errno_to_portable(errno);
                        error_f("seek \"%.100s\": %s", handle_to_name(handle),
                            strerror(errno));
                } else {
/* XXX ATOMICIO ? */
                        ret = write(fd, data, len);
                        if (ret == -1) {
                                status = errno_to_portable(errno);
                                error_f("write \"%.100s\": %s",
                                    handle_to_name(handle), strerror(errno));
                        } else if ((size_t)ret == len) {
                                status = SSH2_FX_OK;
                                handle_update_write(handle, ret);
                        } else {
                                debug2_f("nothing at all written");
                                status = SSH2_FX_FAILURE;
                        }
                }
        }
        send_status(id, status);
        free(data);
}

static void
process_do_stat(u_int32_t id, int do_lstat)
{
        Attrib a;
        struct stat st;
        char *name;
        int r, status = SSH2_FX_FAILURE;

        if ((r = sshbuf_get_cstring(iqueue, &name, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: %sstat", id, do_lstat ? "l" : "");
        verbose("%sstat name \"%s\"", do_lstat ? "l" : "", name);
        r = do_lstat ? lstat(name, &st) : stat(name, &st);
        if (r == -1) {
                status = errno_to_portable(errno);
        } else {
                stat_to_attrib(&st, &a);
                send_attrib(id, &a);
                status = SSH2_FX_OK;
        }
        if (status != SSH2_FX_OK)
                send_status(id, status);
        free(name);
}

static void
process_stat(u_int32_t id)
{
        process_do_stat(id, 0);
}

static void
process_lstat(u_int32_t id)
{
        process_do_stat(id, 1);
}

static void
process_fstat(u_int32_t id)
{
        Attrib a;
        struct stat st;
        int fd, r, handle, status = SSH2_FX_FAILURE;

        if ((r = get_handle(iqueue, &handle)) != 0)
                fatal_fr(r, "parse");
        debug("request %u: fstat \"%s\" (handle %u)",
            id, handle_to_name(handle), handle);
        fd = handle_to_fd(handle);
        if (fd >= 0) {
                r = fstat(fd, &st);
                if (r == -1) {
                        status = errno_to_portable(errno);
                } else {
                        stat_to_attrib(&st, &a);
                        send_attrib(id, &a);
                        status = SSH2_FX_OK;
                }
        }
        if (status != SSH2_FX_OK)
                send_status(id, status);
}

static struct timeval *
attrib_to_tv(const Attrib *a)
{
        static struct timeval tv[2];

        tv[0].tv_sec = a->atime;
        tv[0].tv_usec = 0;
        tv[1].tv_sec = a->mtime;
        tv[1].tv_usec = 0;
        return tv;
}

static struct timespec *
attrib_to_ts(const Attrib *a)
{
        static struct timespec ts[2];

        ts[0].tv_sec = a->atime;
        ts[0].tv_nsec = 0;
        ts[1].tv_sec = a->mtime;
        ts[1].tv_nsec = 0;
        return ts;
}

static void
process_setstat(u_int32_t id)
{
        Attrib a;
        char *name;
        int r, status = SSH2_FX_OK;

        if ((r = sshbuf_get_cstring(iqueue, &name, NULL)) != 0 ||
            (r = decode_attrib(iqueue, &a)) != 0)
                fatal_fr(r, "parse");

        debug("request %u: setstat name \"%s\"", id, name);
        if (a.flags & SSH2_FILEXFER_ATTR_SIZE) {
                logit("set \"%s\" size %llu",
                    name, (unsigned long long)a.size);
                r = truncate(name, a.size);
                if (r == -1)
                        status = errno_to_portable(errno);
        }
        if (a.flags & SSH2_FILEXFER_ATTR_PERMISSIONS) {
                logit("set \"%s\" mode %04o", name, a.perm);
                r = chmod(name, a.perm & 07777);
                if (r == -1)
                        status = errno_to_portable(errno);
        }
        if (a.flags & SSH2_FILEXFER_ATTR_ACMODTIME) {
                char buf[64];
                time_t t = a.mtime;

                strftime(buf, sizeof(buf), "%Y%m%d-%H:%M:%S",
                    localtime(&t));
                logit("set \"%s\" modtime %s", name, buf);
                r = utimes(name, attrib_to_tv(&a));
                if (r == -1)
                        status = errno_to_portable(errno);
        }
        if (a.flags & SSH2_FILEXFER_ATTR_UIDGID) {
                logit("set \"%s\" owner %lu group %lu", name,
                    (u_long)a.uid, (u_long)a.gid);
                r = chown(name, a.uid, a.gid);
                if (r == -1)
                        status = errno_to_portable(errno);
        }
        send_status(id, status);
        free(name);
}

static void
process_fsetstat(u_int32_t id)
{
        Attrib a;
        int handle, fd, r;
        int status = SSH2_FX_OK;

        if ((r = get_handle(iqueue, &handle)) != 0 ||
            (r = decode_attrib(iqueue, &a)) != 0)
                fatal_fr(r, "parse");

        debug("request %u: fsetstat handle %d", id, handle);
        fd = handle_to_fd(handle);
        if (fd < 0)
                status = SSH2_FX_FAILURE;
        else {
                char *name = handle_to_name(handle);

                if (a.flags & SSH2_FILEXFER_ATTR_SIZE) {
                        logit("set \"%s\" size %llu",
                            name, (unsigned long long)a.size);
                        r = ftruncate(fd, a.size);
                        if (r == -1)
                                status = errno_to_portable(errno);
                }
                if (a.flags & SSH2_FILEXFER_ATTR_PERMISSIONS) {
                        logit("set \"%s\" mode %04o", name, a.perm);
#ifdef HAVE_FCHMOD
                        r = fchmod(fd, a.perm & 07777);
#else
                        r = chmod(name, a.perm & 07777);
#endif
                        if (r == -1)
                                status = errno_to_portable(errno);
                }
                if (a.flags & SSH2_FILEXFER_ATTR_ACMODTIME) {
                        char buf[64];
                        time_t t = a.mtime;

                        strftime(buf, sizeof(buf), "%Y%m%d-%H:%M:%S",
                            localtime(&t));
                        logit("set \"%s\" modtime %s", name, buf);
#ifdef HAVE_FUTIMES
                        r = futimes(fd, attrib_to_tv(&a));
#else
                        r = utimes(name, attrib_to_tv(&a));
#endif
                        if (r == -1)
                                status = errno_to_portable(errno);
                }
                if (a.flags & SSH2_FILEXFER_ATTR_UIDGID) {
                        logit("set \"%s\" owner %lu group %lu", name,
                            (u_long)a.uid, (u_long)a.gid);
#ifdef HAVE_FCHOWN
                        r = fchown(fd, a.uid, a.gid);
#else
                        r = chown(name, a.uid, a.gid);
#endif
                        if (r == -1)
                                status = errno_to_portable(errno);
                }
        }
        send_status(id, status);
}

static void
process_opendir(u_int32_t id)
{
        DIR *dirp = NULL;
        char *path;
        int r, handle, status = SSH2_FX_FAILURE;

        if ((r = sshbuf_get_cstring(iqueue, &path, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: opendir", id);
        logit("opendir \"%s\"", path);
        dirp = opendir(path);
        if (dirp == NULL) {
                status = errno_to_portable(errno);
        } else {
                handle = handle_new(HANDLE_DIR, path, 0, 0, dirp);
                if (handle < 0) {
                        closedir(dirp);
                } else {
                        send_handle(id, handle);
                        status = SSH2_FX_OK;
                }

        }
        if (status != SSH2_FX_OK)
                send_status(id, status);
        free(path);
}

static void
process_readdir(u_int32_t id)
{
        DIR *dirp;
        struct dirent *dp;
        char *path;
        int r, handle;

        if ((r = get_handle(iqueue, &handle)) != 0)
                fatal_fr(r, "parse");

        debug("request %u: readdir \"%s\" (handle %d)", id,
            handle_to_name(handle), handle);
        dirp = handle_to_dir(handle);
        path = handle_to_name(handle);
        if (dirp == NULL || path == NULL) {
                send_status(id, SSH2_FX_FAILURE);
        } else {
                struct stat st;
                char pathname[PATH_MAX];
                Stat *stats;
                int nstats = 10, count = 0, i;

                stats = xcalloc(nstats, sizeof(Stat));
                while ((dp = readdir(dirp)) != NULL) {
                        if (count >= nstats) {
                                nstats *= 2;
                                stats = xreallocarray(stats, nstats, sizeof(Stat));
                        }
/* XXX OVERFLOW ? */
                        snprintf(pathname, sizeof pathname, "%s%s%s", path,
                            strcmp(path, "/") ? "/" : "", dp->d_name);
                        if (lstat(pathname, &st) == -1)
                                continue;
                        stat_to_attrib(&st, &(stats[count].attrib));
                        stats[count].name = xstrdup(dp->d_name);
                        stats[count].long_name = ls_file(dp->d_name, &st,
                            0, 0, NULL, NULL);
                        count++;
                        /* send up to 100 entries in one message */
                        /* XXX check packet size instead */
                        if (count == 100)
                                break;
                }
                if (count > 0) {
                        send_names(id, count, stats);
                        for (i = 0; i < count; i++) {
                                free(stats[i].name);
                                free(stats[i].long_name);
                        }
                } else {
                        send_status(id, SSH2_FX_EOF);
                }
                free(stats);
        }
}

static void
process_remove(u_int32_t id)
{
        char *name;
        int r, status = SSH2_FX_FAILURE;

        if ((r = sshbuf_get_cstring(iqueue, &name, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: remove", id);
        logit("remove name \"%s\"", name);
        r = unlink(name);
        status = (r == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        send_status(id, status);
        free(name);
}

static void
process_mkdir(u_int32_t id)
{
        Attrib a;
        char *name;
        int r, mode, status = SSH2_FX_FAILURE;

        if ((r = sshbuf_get_cstring(iqueue, &name, NULL)) != 0 ||
            (r = decode_attrib(iqueue, &a)) != 0)
                fatal_fr(r, "parse");

        mode = (a.flags & SSH2_FILEXFER_ATTR_PERMISSIONS) ?
            a.perm & 07777 : 0777;
        debug3("request %u: mkdir", id);
        logit("mkdir name \"%s\" mode 0%o", name, mode);
        r = mkdir(name, mode);
        status = (r == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        send_status(id, status);
        free(name);
}

static void
process_rmdir(u_int32_t id)
{
        char *name;
        int r, status;

        if ((r = sshbuf_get_cstring(iqueue, &name, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: rmdir", id);
        logit("rmdir name \"%s\"", name);
        r = rmdir(name);
        status = (r == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        send_status(id, status);
        free(name);
}

static void
process_realpath(u_int32_t id)
{
        char resolvedname[PATH_MAX];
        char *path;
        int r;

        if ((r = sshbuf_get_cstring(iqueue, &path, NULL)) != 0)
                fatal_fr(r, "parse");

        if (path[0] == '\0') {
                free(path);
                path = xstrdup(".");
        }
        debug3("request %u: realpath", id);
        verbose("realpath \"%s\"", path);
        if (sftp_realpath(path, resolvedname) == NULL) {
                send_status(id, errno_to_portable(errno));
        } else {
                Stat s;
                attrib_clear(&s.attrib);
                s.name = s.long_name = resolvedname;
                send_names(id, 1, &s);
        }
        free(path);
}

static void
process_rename(u_int32_t id)
{
        char *oldpath, *newpath;
        int r, status;
        struct stat sb;

        if ((r = sshbuf_get_cstring(iqueue, &oldpath, NULL)) != 0 ||
            (r = sshbuf_get_cstring(iqueue, &newpath, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: rename", id);
        logit("rename old \"%s\" new \"%s\"", oldpath, newpath);
        status = SSH2_FX_FAILURE;
        if (lstat(oldpath, &sb) == -1)
                status = errno_to_portable(errno);
        else if (S_ISREG(sb.st_mode)) {
                /* Race-free rename of regular files */
                if (link(oldpath, newpath) == -1) {
                        if (errno == EOPNOTSUPP || errno == ENOSYS
#ifdef EXDEV
                            || errno == EXDEV
#endif
#ifdef LINK_OPNOTSUPP_ERRNO
                            || errno == LINK_OPNOTSUPP_ERRNO
#endif
                            ) {
                                struct stat st;

                                /*
                                 * fs doesn't support links, so fall back to
                                 * stat+rename.  This is racy.
                                 */
                                if (stat(newpath, &st) == -1) {
                                        if (rename(oldpath, newpath) == -1)
                                                status =
                                                    errno_to_portable(errno);
                                        else
                                                status = SSH2_FX_OK;
                                }
                        } else {
                                status = errno_to_portable(errno);
                        }
                } else if (unlink(oldpath) == -1) {
                        status = errno_to_portable(errno);
                        /* clean spare link */
                        unlink(newpath);
                } else
                        status = SSH2_FX_OK;
        } else if (stat(newpath, &sb) == -1) {
                if (rename(oldpath, newpath) == -1)
                        status = errno_to_portable(errno);
                else
                        status = SSH2_FX_OK;
        }
        send_status(id, status);
        free(oldpath);
        free(newpath);
}

static void
process_readlink(u_int32_t id)
{
        int r, len;
        char buf[PATH_MAX];
        char *path;

        if ((r = sshbuf_get_cstring(iqueue, &path, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: readlink", id);
        verbose("readlink \"%s\"", path);
        if ((len = readlink(path, buf, sizeof(buf) - 1)) == -1)
                send_status(id, errno_to_portable(errno));
        else {
                Stat s;

                buf[len] = '\0';
                attrib_clear(&s.attrib);
                s.name = s.long_name = buf;
                send_names(id, 1, &s);
        }
        free(path);
}

static void
process_symlink(u_int32_t id)
{
        char *oldpath, *newpath;
        int r, status;

        if ((r = sshbuf_get_cstring(iqueue, &oldpath, NULL)) != 0 ||
            (r = sshbuf_get_cstring(iqueue, &newpath, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: symlink", id);
        logit("symlink old \"%s\" new \"%s\"", oldpath, newpath);
        /* this will fail if 'newpath' exists */
        r = symlink(oldpath, newpath);
        status = (r == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        send_status(id, status);
        free(oldpath);
        free(newpath);
}

static void
process_extended_posix_rename(u_int32_t id)
{
        char *oldpath, *newpath;
        int r, status;

        if ((r = sshbuf_get_cstring(iqueue, &oldpath, NULL)) != 0 ||
            (r = sshbuf_get_cstring(iqueue, &newpath, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: posix-rename", id);
        logit("posix-rename old \"%s\" new \"%s\"", oldpath, newpath);
        r = rename(oldpath, newpath);
        status = (r == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        send_status(id, status);
        free(oldpath);
        free(newpath);
}

static void
process_extended_statvfs(u_int32_t id)
{
        char *path;
        struct statvfs st;
        int r;

        if ((r = sshbuf_get_cstring(iqueue, &path, NULL)) != 0)
                fatal_fr(r, "parse");
        debug3("request %u: statvfs", id);
        logit("statvfs \"%s\"", path);

        if (statvfs(path, &st) != 0)
                send_status(id, errno_to_portable(errno));
        else
                send_statvfs(id, &st);
        free(path);
}

static void
process_extended_fstatvfs(u_int32_t id)
{
        int r, handle, fd;
        struct statvfs st;

        if ((r = get_handle(iqueue, &handle)) != 0)
                fatal_fr(r, "parse");
        debug("request %u: fstatvfs \"%s\" (handle %u)",
            id, handle_to_name(handle), handle);
        if ((fd = handle_to_fd(handle)) < 0) {
                send_status(id, SSH2_FX_FAILURE);
                return;
        }
        if (fstatvfs(fd, &st) != 0)
                send_status(id, errno_to_portable(errno));
        else
                send_statvfs(id, &st);
}

static void
process_extended_hardlink(u_int32_t id)
{
        char *oldpath, *newpath;
        int r, status;

        if ((r = sshbuf_get_cstring(iqueue, &oldpath, NULL)) != 0 ||
            (r = sshbuf_get_cstring(iqueue, &newpath, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: hardlink", id);
        logit("hardlink old \"%s\" new \"%s\"", oldpath, newpath);
        r = link(oldpath, newpath);
        status = (r == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        send_status(id, status);
        free(oldpath);
        free(newpath);
}

static void
process_extended_fsync(u_int32_t id)
{
        int handle, fd, r, status = SSH2_FX_OP_UNSUPPORTED;

        if ((r = get_handle(iqueue, &handle)) != 0)
                fatal_fr(r, "parse");
        debug3("request %u: fsync (handle %u)", id, handle);
        verbose("fsync \"%s\"", handle_to_name(handle));
        if ((fd = handle_to_fd(handle)) < 0)
                status = SSH2_FX_NO_SUCH_FILE;
        else if (handle_is_ok(handle, HANDLE_FILE)) {
                r = fsync(fd);
                status = (r == -1) ? errno_to_portable(errno) : SSH2_FX_OK;
        }
        send_status(id, status);
}

static void
process_extended_lsetstat(u_int32_t id)
{
        Attrib a;
        char *name;
        int r, status = SSH2_FX_OK;

        if ((r = sshbuf_get_cstring(iqueue, &name, NULL)) != 0 ||
            (r = decode_attrib(iqueue, &a)) != 0)
                fatal_fr(r, "parse");

        debug("request %u: lsetstat name \"%s\"", id, name);
        if (a.flags & SSH2_FILEXFER_ATTR_SIZE) {
                /* nonsensical for links */
                status = SSH2_FX_BAD_MESSAGE;
                goto out;
        }
        if (a.flags & SSH2_FILEXFER_ATTR_PERMISSIONS) {
                logit("set \"%s\" mode %04o", name, a.perm);
                r = fchmodat(AT_FDCWD, name,
                    a.perm & 07777, AT_SYMLINK_NOFOLLOW);
                if (r == -1)
                        status = errno_to_portable(errno);
        }
        if (a.flags & SSH2_FILEXFER_ATTR_ACMODTIME) {
                char buf[64];
                time_t t = a.mtime;

                strftime(buf, sizeof(buf), "%Y%m%d-%H:%M:%S",
                    localtime(&t));
                logit("set \"%s\" modtime %s", name, buf);
                r = utimensat(AT_FDCWD, name,
                    attrib_to_ts(&a), AT_SYMLINK_NOFOLLOW);
                if (r == -1)
                        status = errno_to_portable(errno);
        }
        if (a.flags & SSH2_FILEXFER_ATTR_UIDGID) {
                logit("set \"%s\" owner %lu group %lu", name,
                    (u_long)a.uid, (u_long)a.gid);
                r = fchownat(AT_FDCWD, name, a.uid, a.gid,
                    AT_SYMLINK_NOFOLLOW);
                if (r == -1)
                        status = errno_to_portable(errno);
        }
 out:
        send_status(id, status);
        free(name);
}

static void
process_extended_limits(u_int32_t id)
{
        struct sshbuf *msg;
        int r;
        uint64_t nfiles = 0;
#if defined(HAVE_GETRLIMIT) && defined(RLIMIT_NOFILE)
        struct rlimit rlim;
#endif

        debug("request %u: limits", id);

#if defined(HAVE_GETRLIMIT) && defined(RLIMIT_NOFILE)
        if (getrlimit(RLIMIT_NOFILE, &rlim) != -1 && rlim.rlim_cur > 5)
                nfiles = rlim.rlim_cur - 5; /* stdio(3) + syslog + spare */
#endif

        if ((msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_put_u8(msg, SSH2_FXP_EXTENDED_REPLY)) != 0 ||
            (r = sshbuf_put_u32(msg, id)) != 0 ||
            /* max-packet-length */
            (r = sshbuf_put_u64(msg, SFTP_MAX_MSG_LENGTH)) != 0 ||
            /* max-read-length */
            (r = sshbuf_put_u64(msg, SFTP_MAX_READ_LENGTH)) != 0 ||
            /* max-write-length */
            (r = sshbuf_put_u64(msg, SFTP_MAX_MSG_LENGTH - 1024)) != 0 ||
            /* max-open-handles */
            (r = sshbuf_put_u64(msg, nfiles)) != 0)
                fatal_fr(r, "compose");
        send_msg(msg);
        sshbuf_free(msg);
}

static void
process_extended_expand(u_int32_t id)
{
        char cwd[PATH_MAX], resolvedname[PATH_MAX];
        char *path, *npath;
        int r;
        Stat s;

        if ((r = sshbuf_get_cstring(iqueue, &path, NULL)) != 0)
                fatal_fr(r, "parse");
        if (getcwd(cwd, sizeof(cwd)) == NULL) {
                send_status(id, errno_to_portable(errno));
                goto out;
        }

        debug3("request %u: expand, original \"%s\"", id, path);
        if (path[0] == '\0') {
                /* empty path */
                free(path);
                path = xstrdup(".");
        } else if (*path == '~') {
                /* ~ expand path */
                /* Special-case for "~" and "~/" to respect homedir flag */
                if (strcmp(path, "~") == 0) {
                        free(path);
                        path = xstrdup(cwd);
                } else if (strncmp(path, "~/", 2) == 0) {
                        npath = xstrdup(path + 2);
                        free(path);
                        xasprintf(&path, "%s/%s", cwd, npath);
                        free(npath);
                } else {
                        /* ~user expansions */
                        if (tilde_expand(path, pw->pw_uid, &npath) != 0) {
                                send_status_errmsg(id,
                                    errno_to_portable(ENOENT), "no such user");
                                goto out;
                        }
                        free(path);
                        path = npath;
                }
        } else if (*path != '/') {
                /* relative path */
                xasprintf(&npath, "%s/%s", cwd, path);
                free(path);
                path = npath;
        }
        verbose("expand \"%s\"", path);
        if (sftp_realpath(path, resolvedname) == NULL) {
                send_status(id, errno_to_portable(errno));
                goto out;
        }
        attrib_clear(&s.attrib);
        s.name = s.long_name = resolvedname;
        send_names(id, 1, &s);
 out:
        free(path);
}

static void
process_extended_copy_data(u_int32_t id)
{
        u_char buf[64*1024];
        int read_handle, read_fd, write_handle, write_fd;
        u_int64_t len, read_off, read_len, write_off;
        int r, copy_until_eof, status = SSH2_FX_OP_UNSUPPORTED;
        size_t ret;

        if ((r = get_handle(iqueue, &read_handle)) != 0 ||
            (r = sshbuf_get_u64(iqueue, &read_off)) != 0 ||
            (r = sshbuf_get_u64(iqueue, &read_len)) != 0 ||
            (r = get_handle(iqueue, &write_handle)) != 0 ||
            (r = sshbuf_get_u64(iqueue, &write_off)) != 0)
                fatal("%s: buffer error: %s", __func__, ssh_err(r));

        debug("request %u: copy-data from \"%s\" (handle %d) off %llu len %llu "
            "to \"%s\" (handle %d) off %llu",
            id, handle_to_name(read_handle), read_handle,
            (unsigned long long)read_off, (unsigned long long)read_len,
            handle_to_name(write_handle), write_handle,
            (unsigned long long)write_off);

        /* For read length of 0, we read until EOF. */
        if (read_len == 0) {
                read_len = (u_int64_t)-1 - read_off;
                copy_until_eof = 1;
        } else
                copy_until_eof = 0;

        read_fd = handle_to_fd(read_handle);
        write_fd = handle_to_fd(write_handle);

        /* Disallow reading & writing to the same handle or same path or dirs */
        if (read_handle == write_handle || read_fd < 0 || write_fd < 0 ||
            !strcmp(handle_to_name(read_handle), handle_to_name(write_handle))) {
                status = SSH2_FX_FAILURE;
                goto out;
        }

        if (lseek(read_fd, read_off, SEEK_SET) < 0) {
                status = errno_to_portable(errno);
                error("%s: read_seek failed", __func__);
                goto out;
        }

        if ((handle_to_flags(write_handle) & O_APPEND) == 0 &&
            lseek(write_fd, write_off, SEEK_SET) < 0) {
                status = errno_to_portable(errno);
                error("%s: write_seek failed", __func__);
                goto out;
        }

        /* Process the request in chunks. */
        while (read_len > 0 || copy_until_eof) {
                len = MINIMUM(sizeof(buf), read_len);
                read_len -= len;

                ret = atomicio(read, read_fd, buf, len);
                if (ret == 0 && errno == EPIPE) {
                        status = copy_until_eof ? SSH2_FX_OK : SSH2_FX_EOF;
                        break;
                } else if (ret == 0) {
                        status = errno_to_portable(errno);
                        error("%s: read failed: %s", __func__, strerror(errno));
                        break;
                }
                len = ret;
                handle_update_read(read_handle, len);

                ret = atomicio(vwrite, write_fd, buf, len);
                if (ret != len) {
                        status = errno_to_portable(errno);
                        error("%s: write failed: %llu != %llu: %s", __func__,
                            (unsigned long long)ret, (unsigned long long)len,
                            strerror(errno));
                        break;
                }
                handle_update_write(write_handle, len);
        }

        if (read_len == 0)
                status = SSH2_FX_OK;

 out:
        send_status(id, status);
}

static void
process_extended_home_directory(u_int32_t id)
{
        char *username;
        struct passwd *user_pw;
        int r;
        Stat s;

        if ((r = sshbuf_get_cstring(iqueue, &username, NULL)) != 0)
                fatal_fr(r, "parse");

        debug3("request %u: home-directory \"%s\"", id, username);
        if (username[0] == '\0') {
                user_pw = pw;
        } else if ((user_pw = getpwnam(username)) == NULL) {
                send_status(id, SSH2_FX_FAILURE);
                goto out;
        }

        verbose("home-directory \"%s\"", user_pw->pw_dir);
        attrib_clear(&s.attrib);
        s.name = s.long_name = user_pw->pw_dir;
        send_names(id, 1, &s);
 out:
        free(username);
}

static void
process_extended_get_users_groups_by_id(u_int32_t id)
{
        struct passwd *user_pw;
        struct group *gr;
        struct sshbuf *uids, *gids, *usernames, *groupnames, *msg;
        int r;
        u_int n, nusers = 0, ngroups = 0;
        const char *name;

        if ((usernames = sshbuf_new()) == NULL ||
            (groupnames = sshbuf_new()) == NULL ||
            (msg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((r = sshbuf_froms(iqueue, &uids)) != 0 ||
            (r = sshbuf_froms(iqueue, &gids)) != 0)
                fatal_fr(r, "parse");
        debug_f("uids len = %zu, gids len = %zu",
            sshbuf_len(uids), sshbuf_len(gids));
        while (sshbuf_len(uids) != 0) {
                if ((r = sshbuf_get_u32(uids, &n)) != 0)
                        fatal_fr(r, "parse inner uid");
                user_pw = getpwuid((uid_t)n);
                name = user_pw == NULL ? "" : user_pw->pw_name;
                debug3_f("uid %u => \"%s\"", n, name);
                if ((r = sshbuf_put_cstring(usernames, name)) != 0)
                        fatal_fr(r, "assemble uid reply");
                nusers++;
        }
        while (sshbuf_len(gids) != 0) {
                if ((r = sshbuf_get_u32(gids, &n)) != 0)
                        fatal_fr(r, "parse inner gid");
                gr = getgrgid((gid_t)n);
                name = gr == NULL ? "" : gr->gr_name;
                debug3_f("gid %u => \"%s\"", n, name);
                if ((r = sshbuf_put_cstring(groupnames, name)) != 0)
                        fatal_fr(r, "assemble gid reply");
                nusers++;
        }
        verbose("users-groups-by-id: %u users, %u groups", nusers, ngroups);

        if ((r = sshbuf_put_u8(msg, SSH2_FXP_EXTENDED_REPLY)) != 0 ||
            (r = sshbuf_put_u32(msg, id)) != 0 ||
            (r = sshbuf_put_stringb(msg, usernames)) != 0 ||
            (r = sshbuf_put_stringb(msg, groupnames)) != 0)
                fatal_fr(r, "compose");
        send_msg(msg);

        sshbuf_free(uids);
        sshbuf_free(gids);
        sshbuf_free(usernames);
        sshbuf_free(groupnames);
        sshbuf_free(msg);
}

static void
process_extended(u_int32_t id)
{
        char *request;
        int r;
        const struct sftp_handler *exthand;

        if ((r = sshbuf_get_cstring(iqueue, &request, NULL)) != 0)
                fatal_fr(r, "parse");
        if ((exthand = extended_handler_byname(request)) == NULL) {
                error("Unknown extended request \"%.100s\"", request);
                send_status(id, SSH2_FX_OP_UNSUPPORTED);        /* MUST */
        } else {
                if (!request_permitted(exthand))
                        send_status(id, SSH2_FX_PERMISSION_DENIED);
                else
                        exthand->handler(id);
        }
        free(request);
}

/* stolen from ssh-agent */

static void
process(void)
{
        u_int msg_len;
        u_int buf_len;
        u_int consumed;
        u_char type;
        const u_char *cp;
        int i, r;
        u_int32_t id;

        buf_len = sshbuf_len(iqueue);
        if (buf_len < 5)
                return;         /* Incomplete message. */
        cp = sshbuf_ptr(iqueue);
        msg_len = get_u32(cp);
        if (msg_len > SFTP_MAX_MSG_LENGTH) {
                error("bad message from %s local user %s",
                    client_addr, pw->pw_name);
                sftp_server_cleanup_exit(11);
        }
        if (buf_len < msg_len + 4)
                return;
        if ((r = sshbuf_consume(iqueue, 4)) != 0)
                fatal_fr(r, "consume");
        buf_len -= 4;
        if ((r = sshbuf_get_u8(iqueue, &type)) != 0)
                fatal_fr(r, "parse type");

        switch (type) {
        case SSH2_FXP_INIT:
                process_init();
                init_done = 1;
                break;
        case SSH2_FXP_EXTENDED:
                if (!init_done)
                        fatal("Received extended request before init");
                if ((r = sshbuf_get_u32(iqueue, &id)) != 0)
                        fatal_fr(r, "parse extended ID");
                process_extended(id);
                break;
        default:
                if (!init_done)
                        fatal("Received %u request before init", type);
                if ((r = sshbuf_get_u32(iqueue, &id)) != 0)
                        fatal_fr(r, "parse ID");
                for (i = 0; handlers[i].handler != NULL; i++) {
                        if (type == handlers[i].type) {
                                if (!request_permitted(&handlers[i])) {
                                        send_status(id,
                                            SSH2_FX_PERMISSION_DENIED);
                                } else {
                                        handlers[i].handler(id);
                                }
                                break;
                        }
                }
                if (handlers[i].handler == NULL)
                        error("Unknown message %u", type);
        }
        /* discard the remaining bytes from the current packet */
        if (buf_len < sshbuf_len(iqueue)) {
                error("iqueue grew unexpectedly");
                sftp_server_cleanup_exit(255);
        }
        consumed = buf_len - sshbuf_len(iqueue);
        if (msg_len < consumed) {
                error("msg_len %u < consumed %u", msg_len, consumed);
                sftp_server_cleanup_exit(255);
        }
        if (msg_len > consumed &&
            (r = sshbuf_consume(iqueue, msg_len - consumed)) != 0)
                fatal_fr(r, "consume");
}

/* Cleanup handler that logs active handles upon normal exit */
void
sftp_server_cleanup_exit(int i)
{
        if (pw != NULL && client_addr != NULL) {
                handle_log_exit();
                logit("session closed for local user %s from [%s]",
                    pw->pw_name, client_addr);
        }
        _exit(i);
}

static void
sftp_server_usage(void)
{
        extern char *__progname;

        fprintf(stderr,
            "usage: %s [-ehR] [-d start_directory] [-f log_facility] "
            "[-l log_level]\n\t[-P denied_requests] "
            "[-p allowed_requests] [-u umask]\n"
            "       %s -Q protocol_feature\n",
            __progname, __progname);
        exit(1);
}

int
sftp_server_main(int argc, char **argv, struct passwd *user_pw)
{
        int i, r, in, out, ch, skipargs = 0, log_stderr = 0;
        ssize_t len, olen;
        SyslogFacility log_facility = SYSLOG_FACILITY_AUTH;
        char *cp, *homedir = NULL, uidstr[32], buf[4*4096];
        long mask;

        extern char *optarg;
        extern char *__progname;

        __progname = ssh_get_progname(argv[0]);
        log_init(__progname, log_level, log_facility, log_stderr);

        pw = pwcopy(user_pw);

        while (!skipargs && (ch = getopt(argc, argv,
            "d:f:l:P:p:Q:u:cehR")) != -1) {
                switch (ch) {
                case 'Q':
                        if (strcasecmp(optarg, "requests") != 0) {
                                fprintf(stderr, "Invalid query type\n");
                                exit(1);
                        }
                        for (i = 0; handlers[i].handler != NULL; i++)
                                printf("%s\n", handlers[i].name);
                        for (i = 0; extended_handlers[i].handler != NULL; i++)
                                printf("%s\n", extended_handlers[i].name);
                        exit(0);
                        break;
                case 'R':
                        readonly = 1;
                        break;
                case 'c':
                        /*
                         * Ignore all arguments if we are invoked as a
                         * shell using "sftp-server -c command"
                         */
                        skipargs = 1;
                        break;
                case 'e':
                        log_stderr = 1;
                        break;
                case 'l':
                        log_level = log_level_number(optarg);
                        if (log_level == SYSLOG_LEVEL_NOT_SET)
                                error("Invalid log level \"%s\"", optarg);
                        break;
                case 'f':
                        log_facility = log_facility_number(optarg);
                        if (log_facility == SYSLOG_FACILITY_NOT_SET)
                                error("Invalid log facility \"%s\"", optarg);
                        break;
                case 'd':
                        cp = tilde_expand_filename(optarg, user_pw->pw_uid);
                        snprintf(uidstr, sizeof(uidstr), "%llu",
                            (unsigned long long)pw->pw_uid);
                        homedir = percent_expand(cp, "d", user_pw->pw_dir,
                            "u", user_pw->pw_name, "U", uidstr, (char *)NULL);
                        free(cp);
                        break;
                case 'p':
                        if (request_allowlist != NULL)
                                fatal("Permitted requests already set");
                        request_allowlist = xstrdup(optarg);
                        break;
                case 'P':
                        if (request_denylist != NULL)
                                fatal("Refused requests already set");
                        request_denylist = xstrdup(optarg);
                        break;
                case 'u':
                        errno = 0;
                        mask = strtol(optarg, &cp, 8);
                        if (mask < 0 || mask > 0777 || *cp != '\0' ||
                            cp == optarg || (mask == 0 && errno != 0))
                                fatal("Invalid umask \"%s\"", optarg);
                        (void)umask((mode_t)mask);
                        break;
                case 'h':
                default:
                        sftp_server_usage();
                }
        }

        log_init(__progname, log_level, log_facility, log_stderr);

        /*
         * On platforms where we can, avoid making /proc/self/{mem,maps}
         * available to the user so that sftp access doesn't automatically
         * imply arbitrary code execution access that will break
         * restricted configurations.
         */
        platform_disable_tracing(1);    /* strict */

        /* Drop any fine-grained privileges we don't need */
        platform_pledge_sftp_server();

        if ((cp = getenv("SSH_CONNECTION")) != NULL) {
                client_addr = xstrdup(cp);
                if ((cp = strchr(client_addr, ' ')) == NULL) {
                        error("Malformed SSH_CONNECTION variable: \"%s\"",
                            getenv("SSH_CONNECTION"));
                        sftp_server_cleanup_exit(255);
                }
                *cp = '\0';
        } else
                client_addr = xstrdup("UNKNOWN");

        logit("session opened for local user %s from [%s]",
            pw->pw_name, client_addr);

        in = STDIN_FILENO;
        out = STDOUT_FILENO;

#ifdef HAVE_CYGWIN
        setmode(in, O_BINARY);
        setmode(out, O_BINARY);
#endif

        if ((iqueue = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if ((oqueue = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");

        if (homedir != NULL) {
                if (chdir(homedir) != 0) {
                        error("chdir to \"%s\" failed: %s", homedir,
                            strerror(errno));
                }
        }

        for (;;) {
                struct pollfd pfd[2];

                memset(pfd, 0, sizeof pfd);
                pfd[0].fd = pfd[1].fd = -1;

                /*
                 * Ensure that we can read a full buffer and handle
                 * the worst-case length packet it can generate,
                 * otherwise apply backpressure by stopping reads.
                 */
                if ((r = sshbuf_check_reserve(iqueue, sizeof(buf))) == 0 &&
                    (r = sshbuf_check_reserve(oqueue,
                    SFTP_MAX_MSG_LENGTH)) == 0) {
                        pfd[0].fd = in;
                        pfd[0].events = POLLIN;
                }
                else if (r != SSH_ERR_NO_BUFFER_SPACE)
                        fatal_fr(r, "reserve");

                olen = sshbuf_len(oqueue);
                if (olen > 0) {
                        pfd[1].fd = out;
                        pfd[1].events = POLLOUT;
                }

                if (poll(pfd, 2, -1) == -1) {
                        if (errno == EINTR)
                                continue;
                        error("poll: %s", strerror(errno));
                        sftp_server_cleanup_exit(2);
                }

                /* copy stdin to iqueue */
                if (pfd[0].revents & (POLLIN|POLLHUP)) {
                        len = read(in, buf, sizeof buf);
                        if (len == 0) {
                                debug("read eof");
                                sftp_server_cleanup_exit(0);
                        } else if (len == -1) {
                                if (errno != EAGAIN && errno != EINTR) {
                                        error("read: %s", strerror(errno));
                                        sftp_server_cleanup_exit(1);
                                }
                        } else if ((r = sshbuf_put(iqueue, buf, len)) != 0)
                                fatal_fr(r, "sshbuf_put");
                }
                /* send oqueue to stdout */
                if (pfd[1].revents & (POLLOUT|POLLHUP)) {
                        len = write(out, sshbuf_ptr(oqueue), olen);
                        if (len == 0 || (len == -1 && errno == EPIPE)) {
                                debug("write eof");
                                sftp_server_cleanup_exit(0);
                        } else if (len == -1) {
                                sftp_server_cleanup_exit(1);
                                if (errno != EAGAIN && errno != EINTR) {
                                        error("write: %s", strerror(errno));
                                        sftp_server_cleanup_exit(1);
                                }
                        } else if ((r = sshbuf_consume(oqueue, len)) != 0)
                                fatal_fr(r, "consume");
                }

                /*
                 * Process requests from client if we can fit the results
                 * into the output buffer, otherwise stop processing input
                 * and let the output queue drain.
                 */
                r = sshbuf_check_reserve(oqueue, SFTP_MAX_MSG_LENGTH);
                if (r == 0)
                        process();
                else if (r != SSH_ERR_NO_BUFFER_SPACE)
                        fatal_fr(r, "reserve");
        }
}