2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
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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
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
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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
44 /* Just needed for HAVE_SOCKADDR_IN_SIN_LEN test macro! */
45 #include "gnunet_config.h"
49 #include <sys/types.h>
50 #include <sys/socket.h>
51 #include <arpa/inet.h>
52 #include <sys/select.h>
54 #include <sys/types.h>
62 #include <netinet/ip.h>
63 #include <netinet/ip_icmp.h>
64 #include <netinet/in.h>
67 * Should we print some debug output?
72 * Must match IP given in the client.
74 #define DUMMY_IP "192.0.2.86"
79 #define NAT_TRAV_PORT 22225
82 * How often do we send our ICMP messages to receive replies?
84 #define ICMP_SEND_FREQUENCY_MS 500
93 * Version (4 bits) + Internet header length (4 bits)
113 * Flags (3 bits) + Fragment offset (13 bits)
115 uint16_t flags_frag_offset;
138 * Destination address
144 * Format of ICMP packet.
158 * Beginning of UDP packet.
170 * Socket we use to receive "fake" ICMP replies.
175 * Socket we use to send our ICMP requests.
180 * Socket we use to send our UDP requests.
185 * Target "dummy" address.
187 static struct in_addr dummy;
191 * CRC-16 for IP/ICMP headers.
193 * @param data what to calculate the CRC over
194 * @param bytes number of bytes in data (must be multiple of 2)
195 * @return the CRC 16.
198 calc_checksum(const uint16_t *data,
205 for (i=0;i<bytes/2;i++)
207 sum = (sum & 0xffff) + (sum >> 16);
208 sum = htons(0xffff - sum);
214 * Send an ICMP message to the dummy IP.
216 * @param my_ip source address (our ip address)
219 send_icmp_echo (const struct in_addr *my_ip)
221 struct icmp_packet icmp_echo;
222 struct sockaddr_in dst;
225 struct ip_packet ip_pkt;
226 struct icmp_packet icmp_pkt;
227 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
230 memset(&ip_pkt, 0, sizeof(ip_pkt));
231 ip_pkt.vers_ihl = 0x45;
233 ip_pkt.pkt_len = sizeof (packet);
235 ip_pkt.flags_frag_offset = 0;
236 ip_pkt.ttl = IPDEFTTL;
237 ip_pkt.proto = IPPROTO_ICMP;
239 ip_pkt.src_ip = my_ip->s_addr;
240 ip_pkt.dst_ip = dummy.s_addr;
241 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
242 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
243 off += sizeof (ip_pkt);
245 icmp_echo.type = ICMP_ECHO;
247 icmp_echo.reserved = 0;
248 icmp_echo.checksum = 0;
249 icmp_echo.checksum = htons(calc_checksum((uint16_t*)&icmp_echo,
250 sizeof (struct icmp_packet)));
251 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
252 off += sizeof (icmp_echo);
254 memset (&dst, 0, sizeof (dst));
255 dst.sin_family = AF_INET;
256 #if HAVE_SOCKADDR_IN_SIN_LEN
257 dst.sin_len = sizeof (struct sockaddr_in);
259 dst.sin_addr = dummy;
260 err = sendto(rawsock,
262 (struct sockaddr*)&dst,
268 "sendto failed: %s\n", strerror(errno));
271 else if (err != sizeof (packet))
274 "Error: partial send of ICMP message\n");
280 * Send a UDP message to the dummy IP.
282 * @param my_ip source address (our ip address)
285 send_udp (const struct in_addr *my_ip)
287 struct sockaddr_in dst;
290 memset (&dst, 0, sizeof (dst));
291 dst.sin_family = AF_INET;
292 #if HAVE_SOCKADDR_IN_SIN_LEN
293 dst.sin_len = sizeof (struct sockaddr_in);
295 dst.sin_addr = dummy;
296 dst.sin_port = htons (NAT_TRAV_PORT);
297 err = sendto(udpsock,
299 (struct sockaddr*)&dst,
305 "sendto failed: %s\n", strerror(errno));
311 "Error: partial send of ICMP message\n");
318 * We've received an ICMP response. Process it.
321 process_icmp_response ()
326 struct ip_packet ip_pkt;
327 struct icmp_packet icmp_pkt;
328 struct udp_packet udp_pkt;
333 have = read (icmpsock, buf, sizeof (buf));
337 "Error reading raw socket: %s\n",
344 "Received message of %u bytes\n",
345 (unsigned int) have);
347 if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + sizeof(uint32_t))
351 else if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
355 "Received ICMP message of unexpected size: %u bytes\n",
356 (unsigned int) have);
361 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
362 off += sizeof (ip_pkt);
363 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
364 off += sizeof (icmp_pkt);
365 if ( ((ip_pkt.proto != IPPROTO_ICMP) && (ip_pkt.proto != IPPROTO_UDP)) ||
366 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
367 (icmp_pkt.code != 0) )
369 /* maybe we got an actual reply back... */
375 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
376 off += sizeof (ip_pkt);
381 &buf[sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2],
392 else if (ip_pkt.proto == IPPROTO_UDP)
403 ntohs((uint16_t) udp_pkt.length));
419 * Create an ICMP raw socket for reading.
421 * @return -1 on error
428 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
432 "Error opening RAW socket: %s\n",
436 if (ret >= FD_SETSIZE)
439 "Socket number too large (%d > %u)\n",
441 (unsigned int) FD_SETSIZE);
450 * Create an ICMP raw socket for writing.
452 * @return -1 on error
460 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
464 "Error opening RAW socket: %s\n",
475 "setsockopt failed: %s\n",
483 (char *)&one, sizeof(one)) == -1)
486 "setsockopt failed: %s\n",
496 * Create a UDP socket for writinging.
498 * @return -1 on error
504 struct sockaddr_in addr;
506 ret = socket (AF_INET, SOCK_DGRAM, 0);
510 "Error opening UDP socket: %s\n",
514 memset (&addr, 0, sizeof (addr));
515 addr.sin_family = AF_INET;
516 #if HAVE_SOCKADDR_IN_SIN_LEN
517 addr.sin_len = sizeof (struct sockaddr_in);
519 /* addr.sin_addr zero == ours (hopefully...) */
520 addr.sin_port = htons (NAT_TRAV_PORT);
527 "Error binding UDP socket to port %u: %s\n",
530 /* likely problematic, but not certain, try to continue */
540 struct in_addr external;
549 "This program must be started with our (internal NAT) IP as the only argument.\n");
552 if (1 != inet_pton (AF_INET, argv[1], &external))
555 "Error parsing IPv4 address: %s\n",
559 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy))
562 "Internal error converting dummy IP to binary.\n");
565 if (-1 == (icmpsock = make_icmp_socket()))
569 if (-1 == (rawsock = make_raw_socket()))
575 if (0 != setresuid (uid, uid, uid))
578 "Failed to setresuid: %s\n",
580 /* not critical, continue anyway */
582 if (-1 == (udpsock = make_udp_socket()))
592 FD_SET (icmpsock, &rs);
594 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
595 if (-1 == select (icmpsock + 1, &rs, NULL, NULL, &tv))
600 "select failed: %s\n",
604 if (FD_ISSET (icmpsock, &rs))
605 process_icmp_response ();
606 if (0 == (++alt % 2))
607 send_icmp_echo (&external);
609 send_udp (&external);
611 /* select failed (internal error or OS out of resources) */
619 /* end of gnunet-nat-server.c */