2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
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7 by the Free Software Foundation; either version 3, or (at your
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
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22 * @file src/transport/gnunet-nat-server.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 (or maybe BSDs, but never W32)
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 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 two RAW sockets 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/select.h>
48 #include <sys/types.h>
56 #include <netinet/ip.h>
57 #include <netinet/ip_icmp.h>
58 #include <netinet/in.h>
61 * Must match IP given in the client.
63 #define DUMMY_IP "1.2.3.4"
68 * How often do we send our ICMP messages to receive replies?
70 #define ICMP_SEND_FREQUENCY_MS 500
78 uint16_t flags_frag_offset;
99 static struct in_addr dummy;
102 calc_checksum(const uint16_t *data,
109 for (i=0;i<bytes/2;i++)
111 sum = (sum & 0xffff) + (sum >> 16);
112 sum = htons(0xffff - sum);
118 make_echo (const struct in_addr *src_ip,
119 struct icmp_packet *echo)
121 memset(echo, 0, sizeof(struct icmp_packet));
122 echo->type = ICMP_ECHO;
126 echo->checksum = htons(calc_checksum((uint16_t*)echo, sizeof (struct icmp_packet)));
131 * Send an ICMP message to the dummy IP.
133 * @param my_ip source address (our ip address)
136 send_icmp_echo (const struct in_addr *my_ip)
138 struct icmp_packet icmp_echo;
139 struct sockaddr_in dst;
142 struct ip_packet ip_pkt;
143 struct icmp_packet icmp_pkt;
144 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
147 memset(&ip_pkt, 0, sizeof(ip_pkt));
148 ip_pkt.vers_ihl = 0x45;
150 ip_pkt.pkt_len = sizeof (packet);
152 ip_pkt.flags_frag_offset = 0;
153 ip_pkt.ttl = IPDEFTTL;
154 ip_pkt.proto = IPPROTO_ICMP;
156 ip_pkt.src_ip = my_ip->s_addr;
157 ip_pkt.dst_ip = dummy.s_addr;
158 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
159 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
160 off += sizeof (ip_pkt);
161 make_echo (my_ip, &icmp_echo);
162 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
163 off += sizeof (icmp_echo);
165 memset (&dst, 0, sizeof (dst));
166 dst.sin_family = AF_INET;
167 dst.sin_addr = dummy;
168 err = sendto(rawsock,
170 (struct sockaddr*)&dst,
176 "sendto failed: %s\n", strerror(errno));
182 "Error: partial send of ICMP message\n");
188 process_icmp_response ()
193 struct ip_packet ip_pkt;
194 struct icmp_packet icmp_pkt;
199 have = read (icmpsock, buf, sizeof (buf));
203 "Error reading raw socket: %s\n",
208 if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + sizeof(uint32_t))
212 else if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
216 "Received ICMP message of unexpected size: %u bytes\n",
217 (unsigned int) have);
222 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
223 off += sizeof (ip_pkt);
224 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
225 off += sizeof (icmp_pkt);
226 if ( (ip_pkt.proto != IPPROTO_ICMP) ||
227 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
228 (icmp_pkt.code != 0) )
230 /* maybe we got an actual reply back... */
238 memcpy(&port, &buf[sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2], sizeof(uint32_t));
245 sizeof (buf)), port);
265 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
269 "Error opening RAW socket: %s\n",
273 if (ret >= FD_SETSIZE)
276 "Socket number too large (%d > %u)\n",
278 (unsigned int) FD_SETSIZE);
292 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
296 "Error opening RAW socket: %s\n",
300 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
301 (char *)&one, sizeof(one)) == -1)
303 "setsockopt failed: %s\n",
305 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
306 (char *)&one, sizeof(one)) == -1)
308 "setsockopt failed: %s\n",
315 main (int argc, char *const *argv)
317 struct in_addr external;
322 if (-1 == (icmpsock = make_icmp_socket()))
324 if (-1 == (rawsock = make_raw_socket()))
330 if (0 != setresuid (uid, uid, uid))
332 "Failed to setresuid: %s\n",
337 "This program must be started with our (internal NAT) IP as the only argument.\n");
340 if (1 != inet_pton (AF_INET, argv[1], &external))
343 "Error parsing IPv4 address: %s\n",
347 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
351 FD_SET (icmpsock, &rs);
353 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
354 select (icmpsock + 1, &rs, NULL, NULL, &tv);
355 if (FD_ISSET (icmpsock, &rs))
356 process_icmp_response ();
357 send_icmp_echo (&external);
363 /* end of gnunet-nat-server.c */