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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/nat/gnunet-helper-nat-client-windows.c
23 * @brief Tool to help bypass NATs using ICMP method; must run as
24 * administrator on W32
25 * This code is forx W32.
26 * @author Nathan Evans
28 * This program will send ONE ICMP message using RAW sockets
29 * to the IP address specified as the second argument. Since
30 * it uses RAW sockets, it must be installed SUID or run as 'root'.
31 * In order to keep the security risk of the resulting SUID binary
32 * minimal, the program ONLY opens the RAW socket with root
33 * privileges, then drops them and only then starts to process
34 * command line arguments. The code also does not link against
35 * any shared libraries (except libc) and is strictly minimal
36 * (except for checking for errors). The following list of people
37 * have reviewed this code and considered it safe since the last
38 * modification (if you reviewed it, please have your name added
41 * - Christian Grothoff
46 #define FD_SETSIZE 1024
50 #include <sys/types.h>
62 #define ICMP_TIME_EXCEEDED 11
65 * Must match IP given in the server.
67 #define DUMMY_IP "192.0.2.86"
69 #define NAT_TRAV_PORT 22225
78 * Version (4 bits) + Internet header length (4 bits)
98 * Flags (3 bits) + Fragment offset (13 bits)
100 uint16_t flags_frag_offset;
123 * Destination address
130 * Format of ICMP packet.
132 struct icmp_ttl_exceeded_header
142 /* followed by original payload */
145 struct icmp_echo_header
157 * Beginning of UDP packet.
172 * Socket we use to send our ICMP packets.
174 static SOCKET rawsock;
177 * Target "dummy" address.
179 static struct in_addr dummy;
182 * Port we are listening on (communicated to the server).
184 static uint16_t port;
189 * Convert IPv4 address from text to binary form.
191 * @param af address family
192 * @param cp the address to print
193 * @param buf where to write the address result
194 * @return 1 on success
197 inet_pton (int af, const char *cp, struct in_addr *buf)
199 buf->s_addr = inet_addr (cp);
200 if (buf->s_addr == INADDR_NONE)
202 fprintf (stderr, "Error %d handling address %s", WSAGetLastError (), cp);
210 * CRC-16 for IP/ICMP headers.
212 * @param data what to calculate the CRC over
213 * @param bytes number of bytes in data (must be multiple of 2)
214 * @return the CRC 16.
217 calc_checksum (const uint16_t * data, unsigned int bytes)
223 for (i = 0; i < bytes / 2; i++)
225 sum = (sum & 0xffff) + (sum >> 16);
226 sum = htons (0xffff - sum);
232 * Send an ICMP message to the target.
234 * @param my_ip source address
235 * @param other target address
238 send_icmp_udp (const struct in_addr *my_ip, const struct in_addr *other)
240 char packet[sizeof (struct ip_header) * 2 +
241 sizeof (struct icmp_ttl_exceeded_header) +
242 sizeof (struct udp_header)];
243 struct ip_header ip_pkt;
244 struct icmp_ttl_exceeded_header icmp_pkt;
245 struct udp_header udp_pkt;
246 struct sockaddr_in dst;
250 /* ip header: send to (known) ip address */
252 ip_pkt.vers_ihl = 0x45;
254 ip_pkt.pkt_len = htons (sizeof (packet));
255 ip_pkt.id = htons (256);
256 ip_pkt.flags_frag_offset = 0;
258 ip_pkt.proto = IPPROTO_ICMP;
260 ip_pkt.src_ip = my_ip->s_addr;
261 ip_pkt.dst_ip = other->s_addr;
263 htons (calc_checksum ((uint16_t *) & ip_pkt, sizeof (struct ip_header)));
264 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_header));
265 off += sizeof (struct ip_header);
267 icmp_pkt.type = ICMP_TIME_EXCEEDED;
269 icmp_pkt.checksum = 0;
271 memcpy (&packet[off], &icmp_pkt, sizeof (struct icmp_ttl_exceeded_header));
272 off += sizeof (struct icmp_ttl_exceeded_header);
274 /* ip header of the presumably 'lost' udp packet */
275 ip_pkt.vers_ihl = 0x45;
278 htons (sizeof (struct ip_header) + sizeof (struct udp_header));
279 ip_pkt.id = htons (0);
280 ip_pkt.flags_frag_offset = 0;
282 ip_pkt.proto = IPPROTO_UDP;
284 ip_pkt.src_ip = other->s_addr;
285 ip_pkt.dst_ip = dummy.s_addr;
287 htons (calc_checksum ((uint16_t *) & ip_pkt, sizeof (struct ip_header)));
288 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_header));
289 off += sizeof (struct ip_header);
291 /* build UDP header */
292 udp_pkt.src_port = htons (NAT_TRAV_PORT);
293 udp_pkt.dst_port = htons (NAT_TRAV_PORT);
294 udp_pkt.length = htons (port);
296 memcpy (&packet[off], &udp_pkt, sizeof (struct udp_header));
297 off += sizeof (struct udp_header);
299 /* no go back to calculate ICMP packet checksum */
302 ((uint16_t *) & packet[off],
303 sizeof (struct icmp_ttl_exceeded_header) +
304 sizeof (struct ip_header) + sizeof (struct udp_header)));
305 memcpy (&packet[sizeof (struct ip_header)], &icmp_pkt,
306 sizeof (struct icmp_ttl_exceeded_header));
308 memset (&dst, 0, sizeof (dst));
309 dst.sin_family = AF_INET;
310 dst.sin_addr = *other;
312 sendto (rawsock, packet, sizeof (packet), 0, (struct sockaddr *) &dst,
316 fprintf (stderr, "sendto failed: %s\n", strerror (errno));
318 else if (sizeof (packet) != (size_t) err)
320 fprintf (stderr, "Error: partial send of ICMP message\n");
326 * Send an ICMP message to the target.
328 * @param my_ip source address
329 * @param other target address
332 send_icmp (const struct in_addr *my_ip, const struct in_addr *other)
334 struct ip_header ip_pkt;
335 struct icmp_ttl_exceeded_header icmp_ttl;
336 struct icmp_echo_header icmp_echo;
337 struct sockaddr_in dst;
338 char packet[sizeof (struct ip_header) * 2 +
339 sizeof (struct icmp_ttl_exceeded_header) +
340 sizeof (struct icmp_echo_header)];
344 /* ip header: send to (known) ip address */
346 ip_pkt.vers_ihl = 0x45;
348 ip_pkt.pkt_len = htons (sizeof (packet));
349 ip_pkt.id = htons (256);
350 ip_pkt.flags_frag_offset = 0;
351 ip_pkt.ttl = IPDEFTTL;
352 ip_pkt.proto = IPPROTO_ICMP;
354 ip_pkt.src_ip = my_ip->s_addr;
355 ip_pkt.dst_ip = other->s_addr;
357 htons (calc_checksum ((uint16_t *) & ip_pkt, sizeof (struct ip_header)));
358 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_header));
359 off += sizeof (ip_pkt);
361 /* icmp reply: time exceeded */
362 icmp_ttl.type = ICMP_TIME_EXCEEDED;
364 icmp_ttl.checksum = 0;
366 memcpy (&packet[off], &icmp_ttl, sizeof (struct icmp_ttl_exceeded_header));
367 off += sizeof (struct icmp_ttl_exceeded_header);
369 /* ip header of the presumably 'lost' udp packet */
370 ip_pkt.vers_ihl = 0x45;
373 htons (sizeof (struct ip_header) + sizeof (struct icmp_echo_header));
374 ip_pkt.id = htons (256);
375 ip_pkt.flags_frag_offset = 0;
376 ip_pkt.ttl = 1; /* real TTL would be 1 on a time exceeded packet */
377 ip_pkt.proto = IPPROTO_ICMP;
378 ip_pkt.src_ip = other->s_addr;
379 ip_pkt.dst_ip = dummy.s_addr;
382 htons (calc_checksum ((uint16_t *) & ip_pkt, sizeof (struct ip_header)));
383 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_header));
384 off += sizeof (struct ip_header);
386 icmp_echo.type = ICMP_ECHO;
388 icmp_echo.reserved = htonl (port);
389 icmp_echo.checksum = 0;
392 ((uint16_t *) & icmp_echo, sizeof (struct icmp_echo_header)));
393 memcpy (&packet[off], &icmp_echo, sizeof (struct icmp_echo_header));
395 /* no go back to calculate ICMP packet checksum */
396 off = sizeof (struct ip_header);
399 ((uint16_t *) & packet[off],
400 sizeof (struct icmp_ttl_exceeded_header) +
401 sizeof (struct ip_header) + sizeof (struct icmp_echo_header)));
402 memcpy (&packet[off], &icmp_ttl, sizeof (struct icmp_ttl_exceeded_header));
404 memset (&dst, 0, sizeof (dst));
405 dst.sin_family = AF_INET;
406 dst.sin_addr = *other;
409 sendto (rawsock, packet, sizeof (packet), 0, (struct sockaddr *) &dst,
414 fprintf (stderr, "sendto failed: %s\n", strerror (errno));
416 else if (sizeof (packet) != (size_t) err)
418 fprintf (stderr, "Error: partial send of ICMP message\n");
424 * Create an ICMP raw socket.
426 * @return INVALID_SOCKET on error
431 DWORD bOptVal = TRUE;
432 int bOptLen = sizeof (bOptVal);
435 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
436 if (INVALID_SOCKET == ret)
438 fprintf (stderr, "Error opening RAW socket: %s\n", strerror (errno));
439 return INVALID_SOCKET;
442 setsockopt (ret, SOL_SOCKET, SO_BROADCAST, (char *) &bOptVal, bOptLen))
444 fprintf (stderr, "Error setting SO_BROADCAST to ON: %s\n",
446 closesocket (rawsock);
447 return INVALID_SOCKET;
450 if (0 != setsockopt (ret, IPPROTO_IP, IP_HDRINCL, (char *) &bOptVal, bOptLen))
452 fprintf (stderr, "Error setting IP_HDRINCL to ON: %s\n", strerror (errno));
453 closesocket (rawsock);
454 return INVALID_SOCKET;
461 main (int argc, char *const *argv)
463 struct in_addr external;
464 struct in_addr target;
472 "This program must be started with our IP, the targets external IP, and our port as arguments.\n");
475 if ((1 != inet_pton (AF_INET, argv[1], &external)) ||
476 (1 != inet_pton (AF_INET, argv[2], &target)))
478 fprintf (stderr, "Error parsing IPv4 address: %s\n", strerror (errno));
481 if ((1 != sscanf (argv[3], "%u", &p)) || (0 == p) || (0xFFFF < p))
483 fprintf (stderr, "Error parsing port value `%s'\n", argv[3]);
488 if (0 != WSAStartup (MAKEWORD (2, 1), &wsaData))
490 fprintf (stderr, "Failed to find Winsock 2.1 or better.\n");
493 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy))
495 fprintf (stderr, "Internal error converting dummy IP to binary.\n");
498 if (-1 == (rawsock = make_raw_socket ()))
500 send_icmp (&external, &target);
501 send_icmp_udp (&external, &target);
502 closesocket (rawsock);
507 /* end of gnunet-helper-nat-client-windows.c */