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3 (C) 2010 Christian Grothoff (and other contributing authors)
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22 * @file src/transport/gnunet-nat-server-windows.c
23 * @brief Windows tool to help bypass NATs using ICMP method
24 * This code will work under W32 only
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 run as an administrative user.
30 * In order to keep the security risk of the resulting binary
31 * minimal, the program ONLY opens the two RAW sockets with administrative
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
48 #include <sys/types.h>
58 * Should we print some debug output?
63 * TTL to use for our outgoing messages.
69 #define ICMP_TIME_EXCEEDED 11 /* Time Exceeded */
72 * Must match IP given in the client.
74 #define DUMMY_IP "192.0.2.86"
77 * How often do we send our ICMP messages to receive replies?
79 #define ICMP_SEND_FREQUENCY_MS 500
88 * Version (4 bits) + Internet header length (4 bits)
108 * Flags (3 bits) + Fragment offset (13 bits)
110 u_short flags_frag_offset;
133 * Destination address
139 * Format of ICMP packet.
150 * Beginning of UDP packet.
161 static SOCKET icmpsock;
163 static SOCKET rawsock;
165 static struct in_addr dummy;
168 * CRC-16 for IP/ICMP headers.
171 calc_checksum(const uint16_t *data,
178 for (i=0;i<bytes/2;i++)
180 sum = (sum & 0xffff) + (sum >> 16);
181 sum = htons(0xffff - sum);
186 * Convert IPv4 address from text to binary form.
188 * @param af address family
189 * @param cp the address to print
190 * @param buf where to write the address result
197 buf->s_addr = inet_addr(cp);
198 if (buf->s_addr == INADDR_NONE)
201 "Error %d handling address %s",
211 * Send an ICMP message to the dummy IP.
213 * @param my_ip source address (our ip address)
216 send_icmp_echo (const struct in_addr *my_ip)
218 struct icmp_packet icmp_echo;
219 struct sockaddr_in dst;
222 struct ip_packet ip_pkt;
223 struct icmp_packet icmp_pkt;
224 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
227 memset(&ip_pkt, 0, sizeof(ip_pkt));
228 ip_pkt.vers_ihl = 0x45;
230 ip_pkt.pkt_len = sizeof (packet);
231 ip_pkt.id = htons (256);
232 ip_pkt.flags_frag_offset = 0;
233 ip_pkt.ttl = IPDEFTTL;
234 ip_pkt.proto = IPPROTO_ICMP;
236 ip_pkt.src_ip = my_ip->s_addr;
237 ip_pkt.dst_ip = dummy.s_addr;
238 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
239 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
240 off += sizeof (ip_pkt);
242 icmp_echo.type = ICMP_ECHO;
244 icmp_echo.reserved = 0;
245 icmp_echo.checksum = 0;
246 icmp_echo.checksum = htons(calc_checksum((uint16_t*) &icmp_echo,
247 sizeof (struct icmp_packet)));
248 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
249 off += sizeof (icmp_echo);
251 memset (&dst, 0, sizeof (dst));
252 dst.sin_family = AF_INET;
253 dst.sin_addr = dummy;
254 err = sendto(rawsock,
256 (struct sockaddr*)&dst,
262 "sendto failed: %s\n", strerror(errno));
268 "Error: partial send of ICMP message\n");
274 process_icmp_response ()
279 struct ip_packet ip_pkt;
280 struct icmp_packet icmp_pkt;
281 struct udp_packet udp_pkt;
287 have = read (icmpsock, buf, sizeof (buf));
291 "Error reading raw socket: %s\n",
298 "Received message of %u bytes\n",
299 (unsigned int) have);
301 if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + sizeof(uint32_t))
305 else if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
309 "Received ICMP message of unexpected size: %u bytes\n",
310 (unsigned int) have);
315 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
316 off += sizeof (ip_pkt);
317 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
318 off += sizeof (icmp_pkt);
319 if ( ((ip_pkt.proto != IPPROTO_ICMP) && (ip_pkt.proto != IPPROTO_UDP)) ||
320 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
321 (icmp_pkt.code != 0) )
323 /* maybe we got an actual reply back... */
329 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
330 off += sizeof (ip_pkt);
331 have_udp = (ip_pkt.proto == IPPROTO_UDP);
336 &buf[sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2],
339 DWORD ssize = sizeof(buf);
340 WSAAddressToString((LPSOCKADDR)&sip,
355 DWORD ssize = sizeof(buf);
356 WSAAddressToString((LPSOCKADDR)&sip,
364 ntohs((int)udp_pkt.length));
368 DWORD ssize = sizeof(buf);
369 WSAAddressToString((LPSOCKADDR)&sip,
387 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
388 if (INVALID_SOCKET == ret)
391 "Error opening RAW socket: %s\n",
402 DWORD bOptVal = TRUE;
403 int bOptLen = sizeof(bOptVal);
405 rawsock = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
406 if (INVALID_SOCKET == rawsock)
409 "Error opening RAW socket: %s\n",
411 return INVALID_SOCKET;
414 if (setsockopt(rawsock,
417 (char*)&bOptVal, bOptLen) != 0)
420 "Error setting SO_BROADCAST to ON: %s\n",
422 closesocket(rawsock);
423 return INVALID_SOCKET;
425 if (setsockopt(rawsock,
428 (char*)&bOptVal, bOptLen) != 0)
431 "Error setting IP_HDRINCL to ON: %s\n",
433 closesocket(rawsock);
434 return INVALID_SOCKET;
444 struct in_addr external;
452 "This program must be started with our (internal NAT) IP as the only argument.\n");
455 if (1 != inet_pton (AF_INET, argv[1], &external))
458 "Error parsing IPv4 address: %s, error %s\n",
459 argv[1], strerror (errno));
462 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy))
465 "Internal error converting dummy IP to binary.\n");
468 if (WSAStartup (MAKEWORD (2, 1), &wsaData) != 0)
470 fprintf (stderr, "Failed to find Winsock 2.1 or better.\n");
473 if (-1 == (icmpsock = make_icmp_socket()))
477 if (-1 == (make_raw_socket()))
479 closesocket (icmpsock);
485 FD_SET (icmpsock, &rs);
487 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
488 if (0 != select (icmpsock + 1, &rs, NULL, NULL, &tv))
493 "select failed: %s\n",
497 if (FD_ISSET (icmpsock, &rs))
498 process_icmp_response ();
499 send_icmp_echo (&external);
501 closesocket(icmpsock);
502 closesocket(rawsock);
504 return 4; /* select failed! */
508 /* end of gnunet-nat-server-windows.c */