OpenBSD-4.6/libexec/tftp-proxy/tftp-proxy.c
/* $OpenBSD: tftp-proxy.c,v 1.6 2008/04/13 00:22:17 djm 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/empty"
#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
#define PKTSIZE SEGSIZE+4
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;
union {
struct cmsghdr hdr;
char buf[CMSG_SPACE(sizeof(struct sockaddr_storage))];
} cmsgbuf;
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);
}
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);
}
/* 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;
msg.msg_control = &cmsgbuf.buf;
msg.msg_controllen = sizeof(cmsgbuf.buf);
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_uniform(IPPORT_HILASTAUTO - IPPORT_HIFIRSTAUTO));
}
static void
usage(void)
{
syslog(LOG_ERR, "usage: %s [-v] [-w transwait]", __progname);
exit(1);
}