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3 (C) 2010 Christian Grothoff (and other contributing authors)
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22 * @file src/transport/gnunet-nat-client-windows.c
23 * @brief Tool to help bypass NATs using ICMP method; must run as
24 * root (SUID will do) or administrator on W32
25 * This code will work under GNU/Linux or 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
49 #include <sys/types.h>
61 #define ICMP_TIME_EXCEEDED 11
64 * Must match IP given in the server.
66 #define DUMMY_IP "192.0.2.86"
68 #define NAT_TRAV_PORT 22225
77 * Version (4 bits) + Internet header length (4 bits)
97 * Flags (3 bits) + Fragment offset (13 bits)
99 uint16_t flags_frag_offset;
122 * Destination address
129 * Format of ICMP packet.
142 struct icmp_echo_packet
152 * Beginning of UDP packet.
165 * Socket we use to send our ICMP packets.
167 static SOCKET rawsock;
170 * Target "dummy" address.
172 static struct in_addr dummy;
175 * Port we are listening on (communicated to the server).
177 static uint16_t port;
182 * Convert IPv4 address from text to binary form.
184 * @param af address family
185 * @param cp the address to print
186 * @param buf where to write the address result
187 * @return 1 on success
194 buf->s_addr = inet_addr(cp);
195 if (buf->s_addr == INADDR_NONE)
198 "Error %d handling address %s",
208 * CRC-16 for IP/ICMP headers.
210 * @param data what to calculate the CRC over
211 * @param bytes number of bytes in data (must be multiple of 2)
212 * @return the CRC 16.
215 calc_checksum(const uint16_t *data,
222 for (i=0;i<bytes/2;i++)
224 sum = (sum & 0xffff) + (sum >> 16);
225 sum = htons(0xffff - sum);
231 * Send an ICMP message to the target.
233 * @param my_ip source address
234 * @param other target address
237 send_icmp_udp (const struct in_addr *my_ip,
238 const struct in_addr *other)
240 struct ip_packet ip_pkt;
241 struct icmp_packet icmp_pkt;
242 struct udp_packet udp_pkt;
244 struct sockaddr_in dst;
245 char packet[sizeof(ip_pkt) * 2 + sizeof(icmp_pkt) * 2 + sizeof(uint32_t)];
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;
262 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
263 memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
264 off += sizeof(ip_pkt);
266 /* ip header of the presumably 'lost' udp packet */
267 ip_pkt.vers_ihl = 0x45;
269 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_echo_packet));
271 icmp_pkt.type = 11; /* TTL exceeded */
273 icmp_pkt.checksum = 0;
274 icmp_pkt.reserved = 0;
275 memcpy(&packet[off], &icmp_pkt, sizeof(icmp_pkt));
276 off += sizeof(icmp_pkt);
278 /* build inner IP header */
279 memset(&ip_pkt, 0, sizeof(ip_pkt));
280 ip_pkt.vers_ihl = 0x45;
282 ip_pkt.pkt_len = htons(sizeof (ip_pkt) + sizeof(udp_pkt));
283 ip_pkt.id = htons(0);
284 ip_pkt.flags_frag_offset = 0;
286 ip_pkt.proto = IPPROTO_UDP;
288 ip_pkt.src_ip = other->s_addr;
289 ip_pkt.dst_ip = dummy.s_addr;
290 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
291 memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
292 off += sizeof(ip_pkt);
294 /* build UDP header */
295 udp_pkt.src_port = htons(NAT_TRAV_PORT);
296 udp_pkt.dst_port = htons(NAT_TRAV_PORT);
298 memset(&udp_pkt.length, 0, sizeof(uint32_t));
299 udp_pkt.length = htons (port);
300 memcpy(&packet[off], &udp_pkt, sizeof(udp_pkt));
301 off += sizeof(udp_pkt);
303 /* set ICMP checksum */
304 icmp_pkt.checksum = htons(calc_checksum((uint16_t*)&packet[sizeof(ip_pkt)],
305 sizeof (icmp_pkt) + sizeof(ip_pkt) + sizeof(udp_pkt)));
306 memcpy (&packet[sizeof(ip_pkt)], &icmp_pkt, sizeof (icmp_pkt));
309 memset (&dst, 0, sizeof (dst));
310 dst.sin_family = AF_INET;
311 dst.sin_addr = *other;
312 err = sendto(rawsock,
315 (struct sockaddr*)&dst,
321 "sendto failed: %s\n", strerror(errno));
326 "Error: partial send of ICMP message\n");
332 * Send an ICMP message to the target.
334 * @param my_ip source address
335 * @param other target address
338 send_icmp (const struct in_addr *my_ip,
339 const struct in_addr *other)
341 struct ip_packet ip_pkt;
342 struct icmp_packet *icmp_pkt;
343 struct icmp_echo_packet icmp_echo;
344 struct sockaddr_in dst;
345 char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet) + sizeof(struct icmp_echo_packet)];
350 memset(packet, 0, sizeof(packet));
351 /* ip header: send to (known) ip address */
353 memset(&ip_pkt, 0, sizeof(ip_pkt));
354 ip_pkt.vers_ihl = 0x45;
356 ip_pkt.pkt_len = sizeof (packet); /* huh? */
358 ip_pkt.flags_frag_offset = 0;
359 ip_pkt.ttl = IPDEFTTL;
360 ip_pkt.proto = IPPROTO_ICMP;
362 ip_pkt.src_ip = my_ip->s_addr;
363 ip_pkt.dst_ip = other->s_addr;
364 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
366 memcpy (packet, &ip_pkt, sizeof (struct ip_packet));
367 off += sizeof (ip_pkt);
368 memset (&dst, 0, sizeof (dst));
369 dst.sin_family = AF_INET;
370 dst.sin_addr = *other;
372 /* icmp reply: time exceeded */
373 icmp_pkt = (struct icmp_packet*) &packet[off];
374 memset(icmp_pkt, 0, sizeof(struct icmp_packet));
375 icmp_pkt->type = ICMP_TIME_EXCEEDED;
377 icmp_pkt->reserved = 0;
378 icmp_pkt->checksum = 0;
380 off += sizeof (struct icmp_packet);
382 /* ip header of the presumably 'lost' udp packet */
383 ip_pkt.vers_ihl = 0x45;
385 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_echo_packet));
387 ip_pkt.flags_frag_offset = 0;
388 ip_pkt.ttl = 1; /* real TTL would be 1 on a time exceeded packet */
389 ip_pkt.proto = IPPROTO_ICMP;
390 ip_pkt.src_ip = other->s_addr;
391 ip_pkt.dst_ip = dummy.s_addr;
393 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
394 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_packet));
395 off += sizeof (struct ip_packet);
397 icmp_echo.type = ICMP_ECHO;
399 icmp_echo.reserved = 0;
400 icmp_echo.checksum = 0;
401 icmp_echo.data = htons(port);
402 icmp_echo.checksum = htons(calc_checksum((uint16_t*) &icmp_echo,
403 sizeof (struct icmp_echo_packet)));
405 memcpy (&packet[off], &icmp_echo, sizeof(struct icmp_echo_packet));
406 off += sizeof (struct icmp_echo_packet);
408 icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt,
409 sizeof (struct icmp_packet) + sizeof(struct ip_packet) + sizeof(struct icmp_echo_packet)));
411 err = sendto(rawsock,
414 (struct sockaddr*)&dst,
415 sizeof(dst)); /* or sizeof 'struct sockaddr'? */
420 "sendto failed: %s\n", strerror(errno));
425 "Error: partial send of ICMP message\n");
431 * Create an ICMP raw socket.
433 * @return INVALID_SOCKET on error
438 DWORD bOptVal = TRUE;
439 int bOptLen = sizeof(bOptVal);
442 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
443 if (INVALID_SOCKET == ret)
446 "Error opening RAW socket: %s\n",
448 return INVALID_SOCKET;
450 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST, (char*)&bOptVal, bOptLen) != 0)
453 "Error setting SO_BROADCAST to ON: %s\n",
455 closesocket(rawsock);
456 return INVALID_SOCKET;
459 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL, (char*)&bOptVal, bOptLen) != 0)
462 "Error setting IP_HDRINCL to ON: %s\n",
464 closesocket(rawsock);
465 return INVALID_SOCKET;
472 main (int argc, char *const *argv)
474 struct in_addr external;
475 struct in_addr target;
483 "This program must be started with our IP, the targets external IP, and our port as arguments.\n");
486 if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
487 (1 != inet_pton (AF_INET, argv[2], &target)) )
490 "Error parsing IPv4 address: %s\n",
494 if ( (1 != sscanf (argv[3], "%u", &p) ) ||
499 "Error parsing port value `%s'\n",
505 if (WSAStartup (MAKEWORD (2, 1), &wsaData) != 0)
507 fprintf (stderr, "Failed to find Winsock 2.1 or better.\n");
510 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy))
513 "Internal error converting dummy IP to binary.\n");
516 if (-1 == (rawsock = make_raw_socket()))
518 send_icmp (&external,
520 send_icmp_udp (&external,
522 closesocket (rawsock);
527 /* end of gnunet-nat-client-windows.c */