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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
46 #include <sys/types.h>
47 #include <sys/socket.h>
48 #include <arpa/inet.h>
49 #include <sys/select.h>
50 #include <netinet/ip.h>
51 #include <netinet/ip_icmp.h>
52 #include <netinet/in.h>
55 #include <sys/types.h>
65 typedef SOCKET Socket;
66 typedef unsigned short ushort;
72 * Must match IP given in the client.
74 #define DUMMY_IP "192.0.2.86"
79 * How often do we send our ICMP messages to receive replies?
81 #define ICMP_SEND_FREQUENCY_MS 500
89 uint16_t flags_frag_offset;
114 static Socket icmpsock;
116 static Socket rawsock;
118 static struct in_addr dummy;
121 calc_checksum(const uint16_t *data,
128 for (i=0;i<bytes/2;i++)
130 sum = (sum & 0xffff) + (sum >> 16);
131 sum = htons(0xffff - sum);
137 make_echo (const struct in_addr *src_ip,
138 struct icmp_packet *echo)
140 memset(echo, 0, sizeof(struct icmp_packet));
141 echo->type = ICMP_ECHO;
145 echo->checksum = htons(calc_checksum((uint16_t*)echo, sizeof (struct icmp_packet)));
150 * Send an ICMP message to the dummy IP.
152 * @param my_ip source address (our ip address)
155 send_icmp_echo (const struct in_addr *my_ip)
157 struct icmp_packet icmp_echo;
158 struct sockaddr_in dst;
161 struct ip_packet ip_pkt;
162 struct icmp_packet icmp_pkt;
163 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
166 memset(&ip_pkt, 0, sizeof(ip_pkt));
167 ip_pkt.vers_ihl = 0x45;
169 ip_pkt.pkt_len = sizeof (packet);
171 ip_pkt.flags_frag_offset = 0;
172 ip_pkt.ttl = IPDEFTTL;
173 ip_pkt.proto = IPPROTO_ICMP;
175 ip_pkt.src_ip = my_ip->s_addr;
176 ip_pkt.dst_ip = dummy.s_addr;
177 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
178 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
179 off += sizeof (ip_pkt);
180 make_echo (my_ip, &icmp_echo);
181 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
182 off += sizeof (icmp_echo);
184 memset (&dst, 0, sizeof (dst));
185 dst.sin_family = AF_INET;
186 dst.sin_addr = dummy;
187 err = sendto(rawsock,
189 (struct sockaddr*)&dst,
195 "sendto failed: %s\n", strerror(errno));
201 "Error: partial send of ICMP message\n");
207 process_icmp_response ()
212 struct ip_packet ip_pkt;
213 struct icmp_packet icmp_pkt;
214 struct udp_packet udp_pkt;
220 have = read (icmpsock, buf, sizeof (buf));
224 "Error reading raw socket: %s\n",
230 if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + sizeof(uint32_t))
234 else if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
238 "Received ICMP message of unexpected size: %u bytes\n",
239 (unsigned int) have);
244 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
245 off += sizeof (ip_pkt);
246 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
247 off += sizeof (icmp_pkt);
248 if ( ((ip_pkt.proto != IPPROTO_ICMP) && (ip_pkt.proto != IPPROTO_UDP)) ||
249 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
250 (icmp_pkt.code != 0) )
252 /* maybe we got an actual reply back... */
259 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
260 off += sizeof (ip_pkt);
263 if (ip_pkt.proto == IPPROTO_UDP)
270 memcpy(&port, &buf[sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2], sizeof(uint32_t));
277 sizeof (buf)), port);
281 memcpy(&udp_pkt, &buf[off], sizeof(udp_pkt));
287 sizeof (buf)), ntohl(udp_pkt.length));
307 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
311 "Error opening RAW socket: %s\n",
315 if (ret >= FD_SETSIZE)
318 "Socket number too large (%d > %u)\n",
320 (unsigned int) FD_SETSIZE);
338 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
342 "Error opening RAW socket: %s\n",
346 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
347 (char *)&one, sizeof(one)) == -1)
349 "setsockopt failed: %s\n",
351 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
352 (char *)&one, sizeof(one)) == -1)
354 "setsockopt failed: %s\n",
361 main (int argc, char *const *argv)
363 struct in_addr external;
371 if (WSAStartup (MAKEWORD (2, 1), &wsaData) != 0)
373 fprintf (stderr, "Failed to find Winsock 2.1 or better.\n");
378 if (-1 == (icmpsock = make_icmp_socket()))
380 if (-1 == (rawsock = make_raw_socket()))
386 if (0 != setresuid (uid, uid, uid))
388 "Failed to setresuid: %s\n",
393 "This program must be started with our (internal NAT) IP as the only argument.\n");
396 if (1 != inet_pton (AF_INET, argv[1], &external))
399 "Error parsing IPv4 address: %s\n",
403 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
407 FD_SET (icmpsock, &rs);
409 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
410 select (icmpsock + 1, &rs, NULL, NULL, &tv);
411 if (FD_ISSET (icmpsock, &rs))
412 process_icmp_response ();
413 send_icmp_echo (&external);
417 closesocket(icmpsock);
418 closesocket(rawsock);
425 /* end of gnunet-nat-server-windows.c */