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3 (C) 2010 Christian Grothoff (and other contributing authors)
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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 (for now, later SUID will do)
24 * This code will work under GNU/Linux only (or maybe BSDs, but never W32)
25 * @author Christian Grothoff
28 #include <sys/types.h>
29 #include <sys/socket.h>
30 #include <arpa/inet.h>
31 #include <sys/select.h>
33 #include <sys/types.h>
41 #include <netinet/ip.h>
42 #include <netinet/ip_icmp.h>
43 #include <netinet/in.h>
48 * Number of UDP ports to keep open (typically >= 256)
50 #define NUM_UDP_PORTS 256
53 * Number of ICMP replies to send per message received (typically >= 1024)
55 #define NUM_ICMP_REPLIES 1024
58 * How often do we send our UDP messages to keep ports open? (typically < 100ms)
60 #define UDP_SEND_FREQUENCY_MS 50
63 * Port we use for the dummy target.
65 #define NAT_TRAV_PORT 2222
68 * How often do we retry to open and bind a UDP socket before giving up?
78 uint16_t flags_frag_offset;
90 uint16_t mlen_aka_reply_port_magic;
91 uint16_t checksum_aka_my_magic;
101 struct udp_packet udp;
105 static int udpsocks[NUM_UDP_PORTS];
107 static uint16_t udpports[NUM_UDP_PORTS];
113 static struct in_addr dummy;
115 static struct in_addr target;
119 * create a random port number that is not totally
120 * unlikely to be chosen by the nat box.
122 static uint16_t make_port ()
124 return 1024 + ( (unsigned int)rand ()) % (63 * 1024 - 2);
129 * create a fresh udp socket bound to a random local port.
132 make_udp_socket (uint16_t *port)
136 struct sockaddr_in src;
138 for (tries=0;tries<MAX_TRIES;tries++)
140 ret = socket (AF_INET, SOCK_DGRAM, 0);
144 "Error opening udp socket: %s\n",
148 if (ret >= FD_SETSIZE)
151 "Socket number too large (%d > %u)\n",
153 (unsigned int) FD_SETSIZE);
157 memset (&src, 0, sizeof (src));
158 src.sin_family = AF_INET;
159 src.sin_port = htons (make_port ());
160 if (0 != bind (ret, (struct sockaddr*) &src, sizeof (src)))
165 *port = ntohs (src.sin_port);
169 "Error binding udp socket: %s\n",
176 calc_checksum(const uint16_t *data,
183 for (i=0;i<bytes/2;i++)
185 sum = (sum & 0xffff) + (sum >> 16);
186 sum = htons(0xffff - sum);
192 * send an icmp message to the target.
194 * @param my_ip source address (our ip address)
195 * @param other target address
196 * @param target_port_number fake port number to put into icmp response
197 * as well as the icmpextradata as 'my_magic'
198 * @param source_port_number magic_number that enables the other peer to
199 * identify our port number ('reply in response to') to
200 * put in the data portion; 0 if we are initiating;
201 * goes into 'reply_port_magic' of the icmpextradata
204 send_icmp (const struct in_addr *my_ip,
205 const struct in_addr *other,
206 uint16_t target_port_number,
207 uint16_t source_port_number)
209 struct ip_packet ip_pkt;
210 struct icmp_packet icmp_pkt;
211 struct sockaddr_in dst;
212 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
216 /* ip header: send to (known) ip address */
218 memset(&ip_pkt, 0, sizeof(ip_pkt));
219 ip_pkt.vers_ihl = 0x45;//|(pkt_len>>2);//5;//(ipversion << 4) | (iphdr_size >> 2);
221 ip_pkt.pkt_len = sizeof (packet); /* huh? */
222 ip_pkt.id = 1; /* kernel will change anyway!? */
223 ip_pkt.flags_frag_offset = 0;
224 ip_pkt.ttl = IPDEFTTL;
225 ip_pkt.proto = IPPROTO_ICMP;
227 ip_pkt.src_ip = my_ip->s_addr;
228 ip_pkt.dst_ip = other->s_addr;
229 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
230 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
231 off += sizeof (ip_pkt);
233 /* icmp reply: time exceeded */
234 memset(&icmp_pkt, 0, sizeof(icmp_pkt));
235 icmp_pkt.type = ICMP_TIME_EXCEEDED;
236 icmp_pkt.code = ICMP_HOST_UNREACH;
237 icmp_pkt.reserved = 0;
238 icmp_pkt.checksum = 0;
240 /* ip header of the presumably 'lost' udp packet */
241 icmp_pkt.ip.vers_ihl = 0x45;
243 /* no idea why i need to shift the bits here, but not on ip_pkt->pkt_len... */
244 icmp_pkt.ip.pkt_len = (sizeof (ip_pkt) + sizeof (icmp_pkt)) << 8;
245 icmp_pkt.ip.id = 1; /* kernel sets proper value htons(ip_id_counter); */
246 icmp_pkt.ip.flags_frag_offset = 0;
247 icmp_pkt.ip.ttl = 1; /* real TTL would be 1 on a time exceeded packet */
248 icmp_pkt.ip.proto = IPPROTO_UDP;
249 icmp_pkt.ip.src_ip = other->s_addr;
250 icmp_pkt.ip.dst_ip = dummy.s_addr;
251 icmp_pkt.ip.checksum = 0;
252 icmp_pkt.ip.checksum = htons(calc_checksum((uint16_t*)&icmp_pkt.ip, sizeof (icmp_pkt.ip)));
253 icmp_pkt.udp.source_port = htons (target_port_number);
254 icmp_pkt.udp.dst_port = htons (NAT_TRAV_PORT);
255 icmp_pkt.udp.mlen_aka_reply_port_magic = htons (source_port_number);
256 icmp_pkt.udp.checksum_aka_my_magic = htons (target_port_number);
257 icmp_pkt.checksum = htons(calc_checksum((uint16_t*)&icmp_pkt, sizeof (icmp_pkt)));
258 memcpy (&packet[off], &icmp_pkt, sizeof (icmp_pkt));
259 off += sizeof (icmp_pkt);
261 memset (&dst, 0, sizeof (dst));
262 dst.sin_family = AF_INET;
263 dst.sin_addr = *other;
264 err = sendto(rawsock,
267 (struct sockaddr*)&dst,
268 sizeof(dst)); /* or sizeof 'struct sockaddr'? */
271 "sendto failed: %s\n", strerror(errno));
272 } else if (err != off)
274 "Error: partial send of ICMP message\n");
279 * We discovered the IP address of the other peer.
280 * Try to connect back to it.
283 try_connect (const struct in_addr *my_ip,
284 const struct in_addr *other,
288 char sbuf [INET_ADDRSTRLEN];
291 "Sending %u ICMPs to `%s' with reply magic %u\n",
298 for (i=0;i<NUM_ICMP_REPLIES;i++)
299 send_icmp (my_ip, other, make_port(), port_magic);
304 process_icmp_response (const struct in_addr *my_ip,
311 uint16_t reply_magic;
313 struct ip_packet ip_pkt;
314 struct icmp_packet icmp_pkt;
317 have = read (s, buf, sizeof (buf));
321 "Error reading raw socket: %s\n",
326 if (have != sizeof (struct ip_packet) + sizeof (struct icmp_packet))
329 "Received ICMP message of unexpected size: %u bytes\n",
330 (unsigned int) have);
334 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
335 off += sizeof (ip_pkt);
336 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
337 off += sizeof (icmp_pkt);
339 if ( (ip_pkt.proto == IPPROTO_ICMP) &&
340 (icmp_pkt.type == ICMP_DEST_UNREACH) &&
341 (icmp_pkt.code == ICMP_HOST_UNREACH) )
343 /* this is what is normal due to our UDP traffic */
346 if ( (ip_pkt.proto == IPPROTO_ICMP) &&
347 (icmp_pkt.type == ICMP_TIME_EXCEEDED) &&
348 (icmp_pkt.code == ICMP_HOST_UNREACH) )
350 /* this is what we might see on loopback: this is the format
351 we as the client send out (the host uses 'ICMP_NET_UNREACH');
355 if ( (ip_pkt.proto != IPPROTO_ICMP) ||
356 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
357 (icmp_pkt.code != ICMP_NET_UNREACH) )
359 /* Note the expected client response and not the normal network response */
362 "Received unexpected ICMP message contents (%u, %u, %u), ignoring\n",
369 memcpy(&sip, &ip_pkt.src_ip, sizeof (sip));
370 reply_magic = ntohs (icmp_pkt.udp.checksum_aka_my_magic);
371 my_magic = ntohs (icmp_pkt.udp.mlen_aka_reply_port_magic);
372 local_port = ntohs (icmp_pkt.udp.source_port);
376 /* we get these a lot during loopback testing... */
378 "Received ICMP without hint as to which port worked, dropping\n");
384 "Received ICMP from `%s' with outgoing port %u, listen port %u and incoming for other peer %u\n",
395 try_connect (my_ip, &sip, reply_magic);
399 send_icmp (my_ip, &target, my_magic, reply_magic);
400 printf ("%s:%u listen on %u\n",
407 /* technically, we're done here! */
418 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
422 "Error opening RAW socket: %s\n",
426 if (ret >= FD_SETSIZE)
429 "Socket number too large (%d > %u)\n",
431 (unsigned int) FD_SETSIZE);
445 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
449 "Error opening RAW socket: %s\n",
453 if (ret >= FD_SETSIZE)
456 "Socket number too large (%d > %u)\n",
458 (unsigned int) FD_SETSIZE);
462 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
463 (char *)&one, sizeof(one)) == -1)
465 "setsockopt failed: %s\n",
467 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
468 (char *)&one, sizeof(one)) == -1)
470 "setsockopt failed: %s\n",
477 main (int argc, char *const *argv)
479 struct in_addr external;
484 struct sockaddr_in dst;
490 "This program must be started with our IP, the targets external IP and the dummy IP address as arguments.\n");
493 if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
494 (1 != inet_pton (AF_INET, argv[2], &target)) ||
495 (1 != inet_pton (AF_INET, argv[3], &dummy)) )
498 "Error parsing IPv4 address: %s\n",
503 memset (&dst, 0, sizeof (dst));
504 dst.sin_family = AF_INET;
505 dst.sin_port = htons (NAT_TRAV_PORT);
506 dst.sin_addr = dummy;
508 if (-1 == (icmpsock = make_icmp_socket()))
510 if (-1 == (rawsock = make_raw_socket()))
515 for (i=0;i<NUM_UDP_PORTS;i++)
516 udpsocks[i] = make_udp_socket (&udpports[i]);
521 FD_SET (icmpsock, &rs);
523 tv.tv_usec = UDP_SEND_FREQUENCY_MS * 1000;
524 select (icmpsock + 1, &rs, NULL, NULL, &tv);
525 /* FIXME: do I need my external IP here? */
526 if (FD_ISSET (icmpsock, &rs))
528 process_icmp_response (&external, icmpsock);
533 "Sending UDP message to %s:%u\n",
537 if (-1 == sendto (udpsocks[pos],
539 (struct sockaddr*) &dst, sizeof (dst)))
542 "sendto failed: %s\n",
544 close (udpsocks[pos]);
545 udpsocks[pos] = make_udp_socket (&udpports[pos]);
550 "Sending fake ICMP message to %s:%u\n",
554 send_icmp (&external,
558 pos = (pos+1) % NUM_UDP_PORTS;
564 /* end of gnunet-nat-client.c */