/* $NetBSD: tftp-proxy.c,v 1.3 2009/06/16 02:18:07 minskim Exp $ */
/* $OpenBSD: tftp-proxy.c,v 1.2 2006/12/20 03:33:38 joel Exp $
 *
 * Copyright (c) 2005 DLS Internet Services
 * Copyright (c) 2004, 2005 Camiel Dobbelaar, <cd@sentia.nl>
 *
 * 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.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 * 
 * 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 <sys/types.h>
#include <sys/ioctl.h>
#include <sys/uio.h>
#include <unistd.h>

#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/tftp.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/pfvar.h>

#include <errno.h>
#include <pwd.h>
#include <stdio.h>
#include <syslog.h>
#include <string.h>
#include <stdlib.h>

#include "filter.h"

#define CHROOT_DIR      "/var/chroot/tftp-proxy"
#define NOPRIV_USER     "_proxy"

#define PF_NAT_PROXY_PORT_LOW   50001
#define PF_NAT_PROXY_PORT_HIGH  65535

#define DEFTRANSWAIT    2
#define NTOP_BUFS       4
#ifndef PKTSIZE
#define PKTSIZE         SEGSIZE+4
#endif /* !PKTSIZE */

#ifndef IPPORT_HIFIRSTAUTO
#define IPPORT_HIFIRSTAUTO      IPPORT_ANONMIN
#endif /* IPPORT_HIFIRSTAUTO */

#ifndef IPPORT_HILASTAUTO
#define IPPORT_HILASTAUTO       IPPORT_ANONMAX
#endif /* IPPORT_HILASTAUTO */

const char *opcode(int);
const char *sock_ntop(struct sockaddr *);
u_int16_t pick_proxy_port(void);
static void usage(void);

extern  char *__progname;
char    ntop_buf[NTOP_BUFS][INET6_ADDRSTRLEN];
int     verbose = 0;

int
main(int argc, char *argv[])
{
        int c, fd = 0, on = 1, out_fd = 0, peer, reqsize = 0;
        int transwait = DEFTRANSWAIT;
        char *p;
        struct tftphdr *tp;
        struct passwd *pw;
        size_t cbuflen;
        char *cbuf;
        char req[PKTSIZE];
        struct cmsghdr *cmsg;
        struct msghdr msg;
        struct iovec iov;

        struct sockaddr_storage from, proxy, server, proxy_to_server, s_in;
        struct sockaddr_in sock_out;
        socklen_t j;
        in_port_t bindport;

        openlog(__progname, LOG_PID | LOG_NDELAY, LOG_DAEMON);

        while ((c = getopt(argc, argv, "vw:")) != -1)
                switch (c) {
                case 'v':
                        verbose++;
                        break;
                case 'w':
                        transwait = strtoll(optarg, &p, 10);
                        if (transwait < 1) {
                                syslog(LOG_ERR, "invalid -w value");
                                exit(1);
                        }
                        break;
                default:
                        usage();
                        break;
                }

        /* open /dev/pf */
        init_filter(NULL, verbose);

        tzset();

        pw = getpwnam(NOPRIV_USER);
        if (!pw) {
                syslog(LOG_ERR, "no such user %s: %m", NOPRIV_USER);
                exit(1);
        }
        if (chroot(CHROOT_DIR) || chdir("/")) {
                syslog(LOG_ERR, "chroot %s: %m", CHROOT_DIR);
                exit(1);
        }
#ifdef __NetBSD__
        if (setgroups(1, &pw->pw_gid) ||
            setgid(pw->pw_gid) ||
            setuid(pw->pw_uid)) {
                syslog(LOG_ERR, "can't revoke privs: %m");
                exit(1);
        }
#else
        if (setgroups(1, &pw->pw_gid) ||
            setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) ||
            setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid)) {
                syslog(LOG_ERR, "can't revoke privs: %m");
                exit(1);
        }
#endif /* !__NetBSD__ */

        /* non-blocking io */
        if (ioctl(fd, FIONBIO, &on) < 0) {
                syslog(LOG_ERR, "ioctl(FIONBIO): %m");
                exit(1);
        }

        if (setsockopt(fd, IPPROTO_IP, IP_RECVDSTADDR, &on, sizeof(on)) == -1) {
                syslog(LOG_ERR, "setsockopt(IP_RECVDSTADDR): %m");
                exit(1);
        }

        j = sizeof(s_in);
        if (getsockname(fd, (struct sockaddr *)&s_in, &j) == -1) {
                syslog(LOG_ERR, "getsockname: %m");
                exit(1);
        }

        bindport = ((struct sockaddr_in *)&s_in)->sin_port;

        /* req will be pushed back out at the end, unchanged */
        j = sizeof(from);
        if ((reqsize = recvfrom(fd, req, sizeof(req), MSG_PEEK,
            (struct sockaddr *)&from, &j)) < 0) {
                syslog(LOG_ERR, "recvfrom: %m");
                exit(1);
        }

        bzero(&msg, sizeof(msg));
        iov.iov_base = req;
        iov.iov_len = sizeof(req);
        msg.msg_name = &from;
        msg.msg_namelen = sizeof(from);
        msg.msg_iov = &iov;
        msg.msg_iovlen = 1;

        cbuflen = CMSG_SPACE(sizeof(struct sockaddr_storage));
        if ((cbuf = malloc(cbuflen)) == NULL) {
                syslog(LOG_ERR, "malloc: %m");
                exit(1);
        }

        msg.msg_control = cbuf;
        msg.msg_controllen = cbuflen;

        if (recvmsg(fd, &msg, 0) < 0) {
                syslog(LOG_ERR, "recvmsg: %m");
                exit(1);
        }

        close(fd);
        close(1);

        peer = socket(from.ss_family, SOCK_DGRAM, 0);
        if (peer < 0) {
                syslog(LOG_ERR, "socket: %m");
                exit(1);
        }
        memset(&s_in, 0, sizeof(s_in));
        s_in.ss_family = from.ss_family;
        s_in.ss_len = from.ss_len;

        /* get local address if possible */
        for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL;
            cmsg = CMSG_NXTHDR(&msg, cmsg)) {
                if (cmsg->cmsg_level == IPPROTO_IP &&
                    cmsg->cmsg_type == IP_RECVDSTADDR) {
                        memcpy(&((struct sockaddr_in *)&s_in)->sin_addr,
                            CMSG_DATA(cmsg), sizeof(struct in_addr));
                        break;
                }
        }

        if (bind(peer, (struct sockaddr *)&s_in, s_in.ss_len) < 0) {
                syslog(LOG_ERR, "bind: %m");
                exit(1);
        }
        if (connect(peer, (struct sockaddr *)&from, from.ss_len) < 0) {
                syslog(LOG_ERR, "connect: %m");
                exit(1);
        }

        tp = (struct tftphdr *)req;
        if (!(ntohs(tp->th_opcode) == RRQ || ntohs(tp->th_opcode) == WRQ)) {
                /* not a tftp request, bail */
                if (verbose) {
                        syslog(LOG_WARNING, "not a valid tftp request");
                        exit(1);
                } else
                        /* exit 0 so inetd doesn't log anything */
                        exit(0);
        }

        j = sizeof(struct sockaddr_storage);
        if (getsockname(fd, (struct sockaddr *)&proxy, &j) == -1) {
                syslog(LOG_ERR, "getsockname: %m");
                exit(1);
        }

        ((struct sockaddr_in *)&proxy)->sin_port = bindport;

        /* find the un-rdr'd server and port the client wanted */
        if (server_lookup((struct sockaddr *)&from,
            (struct sockaddr *)&proxy, (struct sockaddr *)&server,
            IPPROTO_UDP) != 0) {
                syslog(LOG_ERR, "pf connection lookup failed (no rdr?)");
                exit(1);
        }

        /* establish a new outbound connection to the remote server */
        if ((out_fd = socket(((struct sockaddr *)&from)->sa_family,
            SOCK_DGRAM, IPPROTO_UDP)) < 0) {
                syslog(LOG_ERR, "couldn't create new socket");
                exit(1);
        }

        bzero((char *)&sock_out, sizeof(sock_out));
        sock_out.sin_family = from.ss_family;
        sock_out.sin_port = htons(pick_proxy_port());
        if (bind(out_fd, (struct sockaddr *)&sock_out, sizeof(sock_out)) < 0) {
                syslog(LOG_ERR, "couldn't bind to new socket: %m");
                exit(1);
        }

        if (connect(out_fd, (struct sockaddr *)&server,
            ((struct sockaddr *)&server)->sa_len) < 0 && errno != EINPROGRESS) {
                syslog(LOG_ERR, "couldn't connect to remote server: %m");
                exit(1);
        }

        j = sizeof(struct sockaddr_storage);
        if ((getsockname(out_fd, (struct sockaddr *)&proxy_to_server,
            &j)) < 0) {
                syslog(LOG_ERR, "getsockname: %m");
                exit(1);
        }

        if (verbose)
                syslog(LOG_INFO, "%s:%d -> %s:%d/%s:%d -> %s:%d \"%s %s\"",
                        sock_ntop((struct sockaddr *)&from),
                        ntohs(((struct sockaddr_in *)&from)->sin_port),
                        sock_ntop((struct sockaddr *)&proxy),
                        ntohs(((struct sockaddr_in *)&proxy)->sin_port),
                        sock_ntop((struct sockaddr *)&proxy_to_server),
                        ntohs(((struct sockaddr_in *)&proxy_to_server)->sin_port),
                        sock_ntop((struct sockaddr *)&server),
                        ntohs(((struct sockaddr_in *)&server)->sin_port),
                        opcode(ntohs(tp->th_opcode)),
                        tp->th_stuff);

        /* get ready to add rdr and pass rules */
        if (prepare_commit(1) == -1) {
                syslog(LOG_ERR, "couldn't prepare pf commit");
                exit(1);
        }

        /* rdr from server to us on our random port -> client on its port */
        if (add_rdr(1, (struct sockaddr *)&server,
            (struct sockaddr *)&proxy_to_server, ntohs(sock_out.sin_port),
            (struct sockaddr *)&from,
            ntohs(((struct sockaddr_in *)&from)->sin_port),
            IPPROTO_UDP) == -1) {
                syslog(LOG_ERR, "couldn't add rdr");
                exit(1);
        }

        /* explicitly allow the packets to return back to the client (which pf
         * will see post-rdr) */
        if (add_filter(1, PF_IN, (struct sockaddr *)&server,
            (struct sockaddr *)&from,
            ntohs(((struct sockaddr_in *)&from)->sin_port),
            IPPROTO_UDP) == -1) {
                syslog(LOG_ERR, "couldn't add pass in");
                exit(1);
        }
        if (add_filter(1, PF_OUT, (struct sockaddr *)&server,
            (struct sockaddr *)&from,
            ntohs(((struct sockaddr_in *)&from)->sin_port),
            IPPROTO_UDP) == -1) {
                syslog(LOG_ERR, "couldn't add pass out");
                exit(1);
        }

        /* and just in case, to pass out from us to the server */
        if (add_filter(1, PF_OUT, (struct sockaddr *)&proxy_to_server,
            (struct sockaddr *)&server,
            ntohs(((struct sockaddr_in *)&server)->sin_port),
            IPPROTO_UDP) == -1) {
                syslog(LOG_ERR, "couldn't add pass out");
                exit(1);
        }

        if (do_commit() == -1) {
                syslog(LOG_ERR, "couldn't commit pf rules");
                exit(1);
        }

        /* forward the initial tftp request and start the insanity */
        if (send(out_fd, tp, reqsize, 0) < 0) {
                syslog(LOG_ERR, "couldn't forward tftp packet: %m");
                exit(1);
        }

        /* allow the transfer to start to establish a state */
        sleep(transwait);

        /* delete our rdr rule and clean up */
        prepare_commit(1);
        do_commit();

        return(0);
}

const char *
opcode(int code)
{
        static char str[6];

        switch (code) {
        case 1:
                (void)snprintf(str, sizeof(str), "RRQ");
                break;
        case 2:
                (void)snprintf(str, sizeof(str), "WRQ");
                break;
        default:
                (void)snprintf(str, sizeof(str), "(%d)", code);
                break;
        }

        return (str);
}

const char *
sock_ntop(struct sockaddr *sa)
{
        static int n = 0;

        /* Cycle to next buffer. */
        n = (n + 1) % NTOP_BUFS;
        ntop_buf[n][0] = '\0';

        if (sa->sa_family == AF_INET) {
                struct sockaddr_in *sin = (struct sockaddr_in *)sa;

                return (inet_ntop(AF_INET, &sin->sin_addr, ntop_buf[n],
                    sizeof ntop_buf[0]));
        }

        if (sa->sa_family == AF_INET6) {
                struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)sa;

                return (inet_ntop(AF_INET6, &sin6->sin6_addr, ntop_buf[n],
                    sizeof ntop_buf[0]));
        }

        return (NULL);
}

u_int16_t
pick_proxy_port(void)
{
        return (IPPORT_HIFIRSTAUTO + (arc4random() %
            (IPPORT_HILASTAUTO - IPPORT_HIFIRSTAUTO)));
}

static void
usage(void)
{
        syslog(LOG_ERR, "usage: %s [-v] [-w transwait]", __progname);
        exit(1);
}