2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
5 GNUnet is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published
7 by the Free Software Foundation; either version 3, or (at your
8 option) any later version.
10 GNUnet is distributed in the hope that it will be useful, but
11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with GNUnet; see the file COPYING. If not, write to the
17 Free Software Foundation, Inc., 59 Temple Place - Suite 330,
18 Boston, MA 02111-1307, USA.
22 * @file src/transport/gnunet-nat-server.c
23 * @brief Tool to help bypass NATs using ICMP method; must run as root (SUID will do)
24 * This code will work under GNU/Linux only (or maybe BSDs, but never W32)
25 * @author Christian Grothoff
27 * This program will send ONE ICMP message every 500 ms RAW sockets
28 * to a DUMMY IP address and also listens for ICMP replies. Since
29 * it uses RAW sockets, it must be installed SUID or run as 'root'.
30 * In order to keep the security risk of the resulting SUID binary
31 * minimal, the program ONLY opens the two RAW sockets with root
32 * privileges, then drops them and only then starts to process
33 * command line arguments. The code also does not link against
34 * any shared libraries (except libc) and is strictly minimal
35 * (except for checking for errors). The following list of people
36 * have reviewed this code and considered it safe since the last
37 * modification (if you reviewed it, please have your name added
40 * - Christian Grothoff
43 #include <sys/types.h>
44 #include <sys/socket.h>
45 #include <arpa/inet.h>
46 #include <sys/select.h>
48 #include <sys/types.h>
56 #include <netinet/ip.h>
57 #include <netinet/ip_icmp.h>
58 #include <netinet/in.h>
61 * Must match IP given in the client.
63 #define DUMMY_IP "192.0.2.86"
68 * How often do we send our ICMP messages to receive replies?
70 #define ICMP_SEND_FREQUENCY_MS 500
78 uint16_t flags_frag_offset;
107 static struct in_addr dummy;
110 calc_checksum(const uint16_t *data,
117 for (i=0;i<bytes/2;i++)
119 sum = (sum & 0xffff) + (sum >> 16);
120 sum = htons(0xffff - sum);
126 make_echo (const struct in_addr *src_ip,
127 struct icmp_packet *echo)
129 memset(echo, 0, sizeof(struct icmp_packet));
130 echo->type = ICMP_ECHO;
134 echo->checksum = htons(calc_checksum((uint16_t*)echo, sizeof (struct icmp_packet)));
139 * Send an ICMP message to the dummy IP.
141 * @param my_ip source address (our ip address)
144 send_icmp_echo (const struct in_addr *my_ip)
146 struct icmp_packet icmp_echo;
147 struct sockaddr_in dst;
150 struct ip_packet ip_pkt;
151 struct icmp_packet icmp_pkt;
152 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
155 memset(&ip_pkt, 0, sizeof(ip_pkt));
156 ip_pkt.vers_ihl = 0x45;
158 ip_pkt.pkt_len = sizeof (packet);
160 ip_pkt.flags_frag_offset = 0;
161 ip_pkt.ttl = IPDEFTTL;
162 ip_pkt.proto = IPPROTO_ICMP;
164 ip_pkt.src_ip = my_ip->s_addr;
165 ip_pkt.dst_ip = dummy.s_addr;
166 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
167 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
168 off += sizeof (ip_pkt);
169 make_echo (my_ip, &icmp_echo);
170 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
171 off += sizeof (icmp_echo);
173 memset (&dst, 0, sizeof (dst));
174 dst.sin_family = AF_INET;
175 dst.sin_addr = dummy;
176 err = sendto(rawsock,
178 (struct sockaddr*)&dst,
184 "sendto failed: %s\n", strerror(errno));
190 "Error: partial send of ICMP message\n");
196 process_icmp_response ()
201 struct ip_packet ip_pkt;
202 struct icmp_packet icmp_pkt;
203 struct udp_packet udp_pkt;
209 have = read (icmpsock, buf, sizeof (buf));
213 "Error reading raw socket: %s\n",
219 if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + sizeof(uint32_t))
223 else if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
227 "Received ICMP message of unexpected size: %u bytes\n",
228 (unsigned int) have);
233 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
234 off += sizeof (ip_pkt);
235 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
236 off += sizeof (icmp_pkt);
237 if ( ((ip_pkt.proto != IPPROTO_ICMP) && (ip_pkt.proto != IPPROTO_UDP)) ||
238 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
239 (icmp_pkt.code != 0) )
241 /* maybe we got an actual reply back... */
248 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
249 off += sizeof (ip_pkt);
252 if (ip_pkt.proto == IPPROTO_UDP)
259 memcpy(&port, &buf[sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2], sizeof(uint32_t));
266 sizeof (buf)), port);
270 memcpy(&udp_pkt, &buf[off], sizeof(udp_pkt));
276 sizeof (buf)), ntohl(udp_pkt.length));
296 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
300 "Error opening RAW socket: %s\n",
304 if (ret >= FD_SETSIZE)
307 "Socket number too large (%d > %u)\n",
309 (unsigned int) FD_SETSIZE);
323 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
327 "Error opening RAW socket: %s\n",
331 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
332 (char *)&one, sizeof(one)) == -1)
334 "setsockopt failed: %s\n",
336 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
337 (char *)&one, sizeof(one)) == -1)
339 "setsockopt failed: %s\n",
346 main (int argc, char *const *argv)
348 struct in_addr external;
353 if (-1 == (icmpsock = make_icmp_socket()))
355 if (-1 == (rawsock = make_raw_socket()))
361 if (0 != setresuid (uid, uid, uid))
363 "Failed to setresuid: %s\n",
368 "This program must be started with our (internal NAT) IP as the only argument.\n");
371 if (1 != inet_pton (AF_INET, argv[1], &external))
374 "Error parsing IPv4 address: %s\n",
378 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
382 FD_SET (icmpsock, &rs);
384 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
385 select (icmpsock + 1, &rs, NULL, NULL, &tv);
386 if (FD_ISSET (icmpsock, &rs))
387 process_icmp_response ();
388 send_icmp_echo (&external);
394 /* end of gnunet-nat-server.c */