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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
47 #include <sys/types.h>
48 #include <sys/socket.h>
49 #include <arpa/inet.h>
50 #include <sys/select.h>
51 #include <netinet/ip.h>
55 #include <sys/types.h>
63 #include <netinet/ip_icmp.h>
64 #include <netinet/in.h>
67 typedef SOCKET Socket;
68 typedef unsigned short ushort;
74 * Must match IP given in the client.
76 #define DUMMY_IP "192.0.2.86"
81 * How often do we send our ICMP messages to receive replies?
83 #define ICMP_SEND_FREQUENCY_MS 500
91 uint16_t flags_frag_offset;
116 static Socket icmpsock;
118 static Socket rawsock;
120 static struct in_addr dummy;
123 calc_checksum(const uint16_t *data,
130 for (i=0;i<bytes/2;i++)
132 sum = (sum & 0xffff) + (sum >> 16);
133 sum = htons(0xffff - sum);
139 make_echo (const struct in_addr *src_ip,
140 struct icmp_packet *echo)
142 memset(echo, 0, sizeof(struct icmp_packet));
143 echo->type = ICMP_ECHO;
147 echo->checksum = htons(calc_checksum((uint16_t*)echo, sizeof (struct icmp_packet)));
152 * Send an ICMP message to the dummy IP.
154 * @param my_ip source address (our ip address)
157 send_icmp_echo (const struct in_addr *my_ip)
159 struct icmp_packet icmp_echo;
160 struct sockaddr_in dst;
163 struct ip_packet ip_pkt;
164 struct icmp_packet icmp_pkt;
165 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
168 memset(&ip_pkt, 0, sizeof(ip_pkt));
169 ip_pkt.vers_ihl = 0x45;
171 ip_pkt.pkt_len = sizeof (packet);
173 ip_pkt.flags_frag_offset = 0;
174 ip_pkt.ttl = IPDEFTTL;
175 ip_pkt.proto = IPPROTO_ICMP;
177 ip_pkt.src_ip = my_ip->s_addr;
178 ip_pkt.dst_ip = dummy.s_addr;
179 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
180 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
181 off += sizeof (ip_pkt);
182 make_echo (my_ip, &icmp_echo);
183 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
184 off += sizeof (icmp_echo);
186 memset (&dst, 0, sizeof (dst));
187 dst.sin_family = AF_INET;
188 dst.sin_addr = dummy;
189 err = sendto(rawsock,
191 (struct sockaddr*)&dst,
197 "sendto failed: %s\n", strerror(errno));
203 "Error: partial send of ICMP message\n");
209 process_icmp_response ()
214 struct ip_packet ip_pkt;
215 struct icmp_packet icmp_pkt;
216 struct udp_packet udp_pkt;
222 have = read (icmpsock, buf, sizeof (buf));
226 "Error reading raw socket: %s\n",
232 if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + sizeof(uint32_t))
236 else if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
240 "Received ICMP message of unexpected size: %u bytes\n",
241 (unsigned int) have);
246 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
247 off += sizeof (ip_pkt);
248 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
249 off += sizeof (icmp_pkt);
250 if ( ((ip_pkt.proto != IPPROTO_ICMP) && (ip_pkt.proto != IPPROTO_UDP)) ||
251 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
252 (icmp_pkt.code != 0) )
254 /* maybe we got an actual reply back... */
261 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
262 off += sizeof (ip_pkt);
265 if (ip_pkt.proto == IPPROTO_UDP)
272 memcpy(&port, &buf[sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2], sizeof(uint32_t));
279 sizeof (buf)), port);
283 memcpy(&udp_pkt, &buf[off], sizeof(udp_pkt));
289 sizeof (buf)), ntohl(udp_pkt.length));
309 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
313 "Error opening RAW socket: %s\n",
317 if (ret >= FD_SETSIZE)
320 "Socket number too large (%d > %u)\n",
322 (unsigned int) FD_SETSIZE);
340 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
344 "Error opening RAW socket: %s\n",
348 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
349 (char *)&one, sizeof(one)) == -1)
351 "setsockopt failed: %s\n",
353 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
354 (char *)&one, sizeof(one)) == -1)
356 "setsockopt failed: %s\n",
363 main (int argc, char *const *argv)
365 struct in_addr external;
373 if (WSAStartup (MAKEWORD (2, 1), &wsaData) != 0)
375 fprintf (stderr, "Failed to find Winsock 2.1 or better.\n");
380 if (-1 == (icmpsock = make_icmp_socket()))
382 if (-1 == (rawsock = make_raw_socket()))
388 if (0 != setresuid (uid, uid, uid))
390 "Failed to setresuid: %s\n",
395 "This program must be started with our (internal NAT) IP as the only argument.\n");
398 if (1 != inet_pton (AF_INET, argv[1], &external))
401 "Error parsing IPv4 address: %s\n",
405 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
409 FD_SET (icmpsock, &rs);
411 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
412 select (icmpsock + 1, &rs, NULL, NULL, &tv);
413 if (FD_ISSET (icmpsock, &rs))
414 process_icmp_response ();
415 send_icmp_echo (&external);
419 closesocket(icmpsock);
420 closesocket(rawsock);
427 /* end of gnunet-nat-server-windows.c */