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3 (C) 2010 Christian Grothoff (and other contributing authors)
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22 * @file src/transport/gnunet-nat-client.c
23 * @brief Tool to help bypass NATs using ICMP method; must run as root (SUID will do)
24 * This code will work under GNU/Linux only.
25 * @author Christian Grothoff
27 * This program will send ONE ICMP message using RAW sockets
28 * to the IP address specified as the second argument. Since
29 * it uses RAW sockets, it must be installed SUID or run as 'root'.
30 * In order to keep the security risk of the resulting SUID binary
31 * minimal, the program ONLY opens the RAW socket with root
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
40 * - Christian Grothoff
43 #include <sys/types.h>
44 #include <sys/socket.h>
45 #include <arpa/inet.h>
46 #include <sys/types.h>
53 #include <netinet/ip.h>
54 #include <netinet/ip_icmp.h>
55 #include <netinet/in.h>
58 * Must match IP given in the server.
60 #define DUMMY_IP "1.2.3.4"
62 #define NAT_TRAV_PORT 22225
70 uint16_t flags_frag_offset;
87 struct icmp_echo_packet
107 static struct in_addr dummy;
109 static struct in_addr target;
111 static uint32_t port;
114 calc_checksum(const uint16_t *data,
121 for (i=0;i<bytes/2;i++)
123 sum = (sum & 0xffff) + (sum >> 16);
124 sum = htons(0xffff - sum);
130 make_echo (const struct in_addr *src_ip,
131 struct icmp_echo_packet *echo, uint32_t num)
133 memset(echo, 0, sizeof(struct icmp_echo_packet));
134 echo->type = ICMP_ECHO;
138 echo->data = htons(num);
139 echo->checksum = htons(calc_checksum((uint16_t*)echo,
140 sizeof (struct icmp_echo_packet)));
145 * Send an ICMP message to the target.
147 * @param my_ip source address
148 * @param other target address
151 send_icmp_udp (const struct in_addr *my_ip,
152 const struct in_addr *other)
154 struct ip_packet ip_pkt;
155 struct icmp_packet icmp_pkt;
156 struct udp_packet udp_pkt;
158 struct sockaddr_in dst;
159 char packet[sizeof(ip_pkt) * 2 + sizeof(icmp_pkt) * 2 + sizeof(uint32_t)];
164 /* ip header: send to (known) ip address */
166 memset(&ip_pkt, 0, sizeof(ip_pkt));
167 ip_pkt.vers_ihl = 0x45;
169 ip_pkt.pkt_len = htons(sizeof (packet));
170 ip_pkt.id = htons(256);
171 ip_pkt.flags_frag_offset = 0;
173 ip_pkt.proto = IPPROTO_ICMP;
175 ip_pkt.src_ip = my_ip->s_addr;
176 ip_pkt.dst_ip = other->s_addr;
177 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
178 memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
179 off += sizeof(ip_pkt);
181 /* ip header of the presumably 'lost' udp packet */
182 ip_pkt.vers_ihl = 0x45;
184 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_echo_packet));
186 icmp_pkt.type = 11; /* TTL exceeded */
188 icmp_pkt.checksum = 0;
189 icmp_pkt.reserved = 0;
190 memcpy(&packet[off], &icmp_pkt, sizeof(icmp_pkt));
191 off += sizeof(icmp_pkt);
193 /* build inner IP header */
194 memset(&ip_pkt, 0, sizeof(ip_pkt));
195 ip_pkt.vers_ihl = 0x45;
197 ip_pkt.pkt_len = htons(sizeof (ip_pkt) + sizeof(udp_pkt));
198 ip_pkt.id = htons(0);
199 ip_pkt.flags_frag_offset = 0;
201 ip_pkt.proto = IPPROTO_UDP;
203 ip_pkt.src_ip = other->s_addr;
204 ip_pkt.dst_ip = dummy.s_addr;
205 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
206 memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
207 off += sizeof(ip_pkt);
209 /* build UDP header */
210 udp_pkt.src_port = htons(NAT_TRAV_PORT); /* FIXME: does this port matter? */
211 udp_pkt.dst_port = htons(NAT_TRAV_PORT);
213 memset(&udp_pkt.length, 0, sizeof(uint32_t));
214 udp_pkt.length = htonl(port);
215 memcpy(&packet[off], &udp_pkt, sizeof(udp_pkt));
216 off += sizeof(udp_pkt);
218 /* set ICMP checksum */
219 icmp_pkt.checksum = htons(calc_checksum((uint16_t*)&packet[sizeof(ip_pkt)],
220 sizeof (icmp_pkt) + sizeof(ip_pkt) + sizeof(udp_pkt)));
221 memcpy (&packet[sizeof(ip_pkt)], &icmp_pkt, sizeof (icmp_pkt));
224 memset (&dst, 0, sizeof (dst));
225 dst.sin_family = AF_INET;
226 dst.sin_addr = *other;
227 err = sendto(rawsock,
230 (struct sockaddr*)&dst,
236 "sendto failed: %s\n", strerror(errno));
241 "Error: partial send of ICMP message\n");
247 * Send an ICMP message to the target.
249 * @param my_ip source address
250 * @param other target address
253 send_icmp (const struct in_addr *my_ip,
254 const struct in_addr *other)
256 struct ip_packet ip_pkt;
257 struct icmp_packet *icmp_pkt;
258 struct icmp_echo_packet icmp_echo;
259 struct sockaddr_in dst;
260 char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet) + sizeof(struct icmp_echo_packet)];
265 /* ip header: send to (known) ip address */
267 memset(&ip_pkt, 0, sizeof(ip_pkt));
268 ip_pkt.vers_ihl = 0x45;
270 ip_pkt.pkt_len = sizeof (packet); /* huh? */
272 ip_pkt.flags_frag_offset = 0;
273 ip_pkt.ttl = IPDEFTTL;
274 ip_pkt.proto = IPPROTO_ICMP;
276 ip_pkt.src_ip = my_ip->s_addr;
277 ip_pkt.dst_ip = other->s_addr;
278 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
279 memcpy (packet, &ip_pkt, sizeof (struct ip_packet));
280 off += sizeof (ip_pkt);
281 /* icmp reply: time exceeded */
282 icmp_pkt = (struct icmp_packet*) &packet[off];
283 memset(icmp_pkt, 0, sizeof(struct icmp_packet));
284 icmp_pkt->type = ICMP_TIME_EXCEEDED;
286 icmp_pkt->reserved = 0;
287 icmp_pkt->checksum = 0;
289 off += sizeof (struct icmp_packet);
291 /* ip header of the presumably 'lost' udp packet */
292 ip_pkt.vers_ihl = 0x45;
294 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_echo_packet));
297 ip_pkt.flags_frag_offset = 0;
298 ip_pkt.ttl = 1; /* real TTL would be 1 on a time exceeded packet */
299 ip_pkt.proto = IPPROTO_ICMP;
300 ip_pkt.src_ip = other->s_addr;
301 ip_pkt.dst_ip = dummy.s_addr;
303 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
304 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_packet));
305 off += sizeof (struct ip_packet);
307 make_echo (other, &icmp_echo, port);
308 memcpy (&packet[off], &icmp_echo, sizeof(struct icmp_echo_packet));
309 off += sizeof (struct icmp_echo_packet);
311 icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt,
312 sizeof (struct icmp_packet) + sizeof(struct ip_packet) + sizeof(struct icmp_echo_packet)));
314 memset (&dst, 0, sizeof (dst));
315 dst.sin_family = AF_INET;
316 dst.sin_addr = *other;
317 err = sendto(rawsock,
320 (struct sockaddr*)&dst,
321 sizeof(dst)); /* or sizeof 'struct sockaddr'? */
325 "sendto failed: %s\n", strerror(errno));
330 "Error: partial send of ICMP message\n");
341 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
345 "Error opening RAW socket: %s\n",
349 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
350 (char *)&one, sizeof(one)) == -1)
352 "setsockopt failed: %s\n",
354 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
355 (char *)&one, sizeof(one)) == -1)
357 "setsockopt failed: %s\n",
364 main (int argc, char *const *argv)
366 struct in_addr external;
369 if (-1 == (rawsock = make_raw_socket()))
372 if (0 != setresuid (uid, uid, uid))
374 "Failed to setresuid: %s\n",
380 "This program must be started with our IP, the targets external IP, and our port as arguments.\n");
383 port = atoi(argv[3]);
385 if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
386 (1 != inet_pton (AF_INET, argv[2], &target)) )
389 "Error parsing IPv4 address: %s\n",
393 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
394 send_icmp (&external,
396 send_icmp_udp (&external,
402 /* end of gnunet-nat-client.c */