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3 (C) 2010 Christian Grothoff (and other contributing authors)
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13 General Public License for more details.
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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"
69 uint16_t flags_frag_offset;
86 struct icmp_echo_packet
98 static struct in_addr dummy;
100 static struct in_addr target;
103 static uint32_t port;
107 calc_checksum(const uint16_t *data,
114 for (i=0;i<bytes/2;i++)
116 sum = (sum & 0xffff) + (sum >> 16);
117 sum = htons(0xffff - sum);
126 make_echo (const struct in_addr *src_ip,
127 struct icmp_echo_packet *echo, uint32_t num)
129 memset(echo, 0, sizeof(struct icmp_echo_packet));
130 echo->type = ICMP_ECHO;
134 echo->data = htons(num);
135 echo->checksum = htons(calc_checksum((uint16_t*)echo,
136 sizeof (struct icmp_echo_packet)));
140 make_echo (const struct in_addr *src_ip,
141 struct icmp_packet *echo)
143 memset(echo, 0, sizeof(struct icmp_packet));
144 echo->type = ICMP_ECHO;
148 echo->checksum = htons(calc_checksum((uint16_t*)echo,
149 sizeof (struct icmp_packet)));
155 * Send an ICMP message to the target.
157 * @param my_ip source address
158 * @param other target address
161 send_icmp (const struct in_addr *my_ip,
162 const struct in_addr *other)
164 struct ip_packet ip_pkt;
165 struct icmp_packet *icmp_pkt;
167 struct icmp_echo_packet icmp_echo;
169 struct icmp_packet icmp_echo;
171 struct sockaddr_in dst;
173 char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet) + sizeof(struct icmp_echo_packet)];
175 char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet)*2];
180 /* ip header: send to (known) ip address */
182 memset(&ip_pkt, 0, sizeof(ip_pkt));
183 ip_pkt.vers_ihl = 0x45;
185 ip_pkt.pkt_len = sizeof (packet); /* huh? */
187 ip_pkt.flags_frag_offset = 0;
188 ip_pkt.ttl = IPDEFTTL;
189 ip_pkt.proto = IPPROTO_ICMP;
191 ip_pkt.src_ip = my_ip->s_addr;
192 ip_pkt.dst_ip = other->s_addr;
193 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
194 memcpy (packet, &ip_pkt, sizeof (struct ip_packet));
195 off += sizeof (ip_pkt);
196 /* icmp reply: time exceeded */
197 icmp_pkt = (struct icmp_packet*) &packet[off];
198 memset(icmp_pkt, 0, sizeof(struct icmp_packet));
199 icmp_pkt->type = ICMP_TIME_EXCEEDED;
201 icmp_pkt->reserved = 0;
202 icmp_pkt->checksum = 0;
204 off += sizeof (struct icmp_packet);
206 /* ip header of the presumably 'lost' udp packet */
207 ip_pkt.vers_ihl = 0x45;
210 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_echo_packet));
212 ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_packet));
216 ip_pkt.flags_frag_offset = 0;
217 ip_pkt.ttl = 1; /* real TTL would be 1 on a time exceeded packet */
218 ip_pkt.proto = IPPROTO_ICMP;
219 ip_pkt.src_ip = other->s_addr;
220 ip_pkt.dst_ip = dummy.s_addr;
222 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (struct ip_packet)));
223 memcpy (&packet[off], &ip_pkt, sizeof (struct ip_packet));
224 off += sizeof (struct ip_packet);
227 make_echo (other, &icmp_echo, port);
228 memcpy (&packet[off], &icmp_echo, sizeof(struct icmp_echo_packet));
229 off += sizeof (struct icmp_echo_packet);
231 make_echo (other, &icmp_echo);
232 memcpy (&packet[off], &icmp_echo, sizeof(struct icmp_packet));
233 off += sizeof (struct icmp_packet);
237 icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt,
238 sizeof (struct icmp_packet) + sizeof(struct ip_packet) + sizeof(struct icmp_echo_packet)));
241 icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt,
242 sizeof (struct icmp_packet)*2 + sizeof(struct ip_packet)));
248 memset (&dst, 0, sizeof (dst));
249 dst.sin_family = AF_INET;
250 dst.sin_addr = *other;
251 err = sendto(rawsock,
254 (struct sockaddr*)&dst,
255 sizeof(dst)); /* or sizeof 'struct sockaddr'? */
259 "sendto failed: %s\n", strerror(errno));
264 "Error: partial send of ICMP message\n");
275 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
279 "Error opening RAW socket: %s\n",
283 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
284 (char *)&one, sizeof(one)) == -1)
286 "setsockopt failed: %s\n",
288 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
289 (char *)&one, sizeof(one)) == -1)
291 "setsockopt failed: %s\n",
298 main (int argc, char *const *argv)
300 struct in_addr external;
303 if (-1 == (rawsock = make_raw_socket()))
306 if (0 != setresuid (uid, uid, uid))
308 "Failed to setresuid: %s\n",
314 "This program must be started with our IP, the targets external IP, and our port as arguments.\n");
317 port = atoi(argv[3]);
322 "This program must be started with our IP and the targets external IP as arguments.\n");
326 if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
327 (1 != inet_pton (AF_INET, argv[2], &target)) )
330 "Error parsing IPv4 address: %s\n",
334 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
335 send_icmp (&external,
341 /* end of gnunet-nat-client.c */