2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
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13 General Public License for more details.
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22 * @file src/transport/gnunet-nat-client.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.
25 * @author Christian Grothoff
27 * This program will send ONE ICMP message using RAW sockets
28 * to the IP address specified as the second argument. 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 RAW socket 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/types.h>
53 #include <netinet/ip.h>
54 #include <netinet/ip_icmp.h>
55 #include <netinet/in.h>
58 * Must match IP given in the server.
60 #define DUMMY_IP "1.2.3.4"
63 #define NAT_TRAV_PORT 22225
71 uint16_t flags_frag_offset;
88 struct icmp_echo_packet
108 static struct in_addr dummy;
110 static struct in_addr target;
113 static uint32_t port;
117 calc_checksum(const uint16_t *data,
124 for (i=0;i<bytes/2;i++)
126 sum = (sum & 0xffff) + (sum >> 16);
127 sum = htons(0xffff - sum);
136 make_echo (const struct in_addr *src_ip,
137 struct icmp_echo_packet *echo, uint32_t num)
139 memset(echo, 0, sizeof(struct icmp_echo_packet));
140 echo->type = ICMP_ECHO;
144 echo->data = htons(num);
145 echo->checksum = htons(calc_checksum((uint16_t*)echo,
146 sizeof (struct icmp_echo_packet)));
150 make_echo (const struct in_addr *src_ip,
151 struct icmp_packet *echo)
153 memset(echo, 0, sizeof(struct icmp_packet));
154 echo->type = ICMP_ECHO;
158 echo->checksum = htons(calc_checksum((uint16_t*)echo,
159 sizeof (struct icmp_packet)));
164 * Send an ICMP message to the target.
166 * @param my_ip source address
167 * @param other target address
170 send_icmp_udp (const struct in_addr *my_ip,
171 const struct in_addr *other)
173 struct ip_packet ip_pkt;
174 struct icmp_packet icmp_pkt;
175 struct udp_packet udp_pkt;
177 struct sockaddr_in dst;
178 char packet[sizeof(ip_pkt) * 2 + sizeof(icmp_pkt) * 2 + sizeof(uint32_t)];
183 /* ip header: send to (known) ip address */
185 memset(&ip_pkt, 0, sizeof(ip_pkt));
186 ip_pkt.vers_ihl = 0x45;
188 ip_pkt.pkt_len = htons(sizeof (packet));
189 ip_pkt.id = htons(256);
190 ip_pkt.flags_frag_offset = 0;
192 ip_pkt.proto = IPPROTO_ICMP;
194 ip_pkt.src_ip = my_ip->s_addr;
195 ip_pkt.dst_ip = other->s_addr;
196 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
197 memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
198 off += sizeof(ip_pkt);
200 /* ip header of the presumably 'lost' udp packet */
201 ip_pkt.vers_ihl = 0x45;
203 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_echo_packet));
205 icmp_pkt.type = 11; /* TTL exceeded */
207 icmp_pkt.checksum = 0;
208 icmp_pkt.reserved = 0;
209 memcpy(&packet[off], &icmp_pkt, sizeof(icmp_pkt));
210 off += sizeof(icmp_pkt);
212 /* build inner IP header */
213 memset(&ip_pkt, 0, sizeof(ip_pkt));
214 ip_pkt.vers_ihl = 0x45;
216 ip_pkt.pkt_len = htons(sizeof (ip_pkt) + sizeof(udp_pkt));
217 ip_pkt.id = htons(0);
218 ip_pkt.flags_frag_offset = 0;
220 ip_pkt.proto = IPPROTO_UDP;
222 ip_pkt.src_ip = other->s_addr;
223 ip_pkt.dst_ip = dummy.s_addr;
224 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
225 memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
226 off += sizeof(ip_pkt);
228 /* build UDP header */
229 udp_pkt.src_port = htons(NAT_TRAV_PORT); /* FIXME: does this port matter? */
230 udp_pkt.dst_port = htons(NAT_TRAV_PORT);
232 memset(&udp_pkt.length, 0, sizeof(uint32_t));
234 udp_pkt.length = htonl(port);
236 memcpy(&packet[off], &udp_pkt, sizeof(udp_pkt));
237 off += sizeof(udp_pkt);
239 /* set ICMP checksum */
240 icmp_pkt.checksum = htons(calc_checksum((uint16_t*)&packet[sizeof(ip_pkt)],
241 sizeof (icmp_pkt) + sizeof(ip_pkt) + sizeof(udp_pkt)));
242 memcpy (&packet[sizeof(ip_pkt)], &icmp_pkt, sizeof (icmp_pkt));
245 memset (&dst, 0, sizeof (dst));
246 dst.sin_family = AF_INET;
247 dst.sin_addr = *other;
248 err = sendto(rawsock,
251 (struct sockaddr*)&dst,
257 "sendto failed: %s\n", strerror(errno));
262 "Error: partial send of ICMP message\n");
268 * Send an ICMP message to the target.
270 * @param my_ip source address
271 * @param other target address
274 send_icmp (const struct in_addr *my_ip,
275 const struct in_addr *other)
277 struct ip_packet ip_pkt;
278 struct icmp_packet *icmp_pkt;
280 struct icmp_echo_packet icmp_echo;
282 struct icmp_packet icmp_echo;
284 struct sockaddr_in dst;
286 char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet) + sizeof(struct icmp_echo_packet)];
288 char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet)*2];
293 /* ip header: send to (known) ip address */
295 memset(&ip_pkt, 0, sizeof(ip_pkt));
296 ip_pkt.vers_ihl = 0x45;
298 ip_pkt.pkt_len = sizeof (packet); /* huh? */
300 ip_pkt.flags_frag_offset = 0;
301 ip_pkt.ttl = IPDEFTTL;
302 ip_pkt.proto = IPPROTO_ICMP;
304 ip_pkt.src_ip = my_ip->s_addr;
305 ip_pkt.dst_ip = other->s_addr;
306 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
307 memcpy (packet, &ip_pkt, sizeof (struct ip_packet));
308 off += sizeof (ip_pkt);
309 /* icmp reply: time exceeded */
310 icmp_pkt = (struct icmp_packet*) &packet[off];
311 memset(icmp_pkt, 0, sizeof(struct icmp_packet));
312 icmp_pkt->type = ICMP_TIME_EXCEEDED;
314 icmp_pkt->reserved = 0;
315 icmp_pkt->checksum = 0;
317 off += sizeof (struct icmp_packet);
319 /* ip header of the presumably 'lost' udp packet */
320 ip_pkt.vers_ihl = 0x45;
323 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_echo_packet));
325 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_packet));
329 ip_pkt.flags_frag_offset = 0;
330 ip_pkt.ttl = 1; /* real TTL would be 1 on a time exceeded packet */
331 ip_pkt.proto = IPPROTO_ICMP;
332 ip_pkt.src_ip = other->s_addr;
333 ip_pkt.dst_ip = dummy.s_addr;
335 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
336 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_packet));
337 off += sizeof (struct ip_packet);
340 make_echo (other, &icmp_echo, port);
341 memcpy (&packet[off], &icmp_echo, sizeof(struct icmp_echo_packet));
342 off += sizeof (struct icmp_echo_packet);
344 make_echo (other, &icmp_echo);
345 memcpy (&packet[off], &icmp_echo, sizeof(struct icmp_packet));
346 off += sizeof (struct icmp_packet);
350 icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt,
351 sizeof (struct icmp_packet) + sizeof(struct ip_packet) + sizeof(struct icmp_echo_packet)));
354 icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt,
355 sizeof (struct icmp_packet)*2 + sizeof(struct ip_packet)));
361 memset (&dst, 0, sizeof (dst));
362 dst.sin_family = AF_INET;
363 dst.sin_addr = *other;
364 err = sendto(rawsock,
367 (struct sockaddr*)&dst,
368 sizeof(dst)); /* or sizeof 'struct sockaddr'? */
372 "sendto failed: %s\n", strerror(errno));
377 "Error: partial send of ICMP message\n");
388 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
392 "Error opening RAW socket: %s\n",
396 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
397 (char *)&one, sizeof(one)) == -1)
399 "setsockopt failed: %s\n",
401 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
402 (char *)&one, sizeof(one)) == -1)
404 "setsockopt failed: %s\n",
411 main (int argc, char *const *argv)
413 struct in_addr external;
416 if (-1 == (rawsock = make_raw_socket()))
419 if (0 != setresuid (uid, uid, uid))
421 "Failed to setresuid: %s\n",
427 "This program must be started with our IP, the targets external IP, and our port as arguments.\n");
430 port = atoi(argv[3]);
435 "This program must be started with our IP and the targets external IP as arguments.\n");
439 if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
440 (1 != inet_pton (AF_INET, argv[2], &target)) )
443 "Error parsing IPv4 address: %s\n",
447 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
448 send_icmp (&external,
450 send_icmp_udp (&external,
456 /* end of gnunet-nat-client.c */