2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
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6 it under the terms of the GNU General Public License as published
7 by the Free Software Foundation; either version 3, or (at your
8 option) any later version.
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11 WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 General Public License for more details.
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17 Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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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 * priviledges, 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"
66 * How often do we send our ICMP messages to receive replies?
68 #define ICMP_SEND_FREQUENCY_MS 500
76 uint16_t flags_frag_offset;
97 static struct in_addr dummy;
100 calc_checksum(const uint16_t *data,
107 for (i=0;i<bytes/2;i++)
109 sum = (sum & 0xffff) + (sum >> 16);
110 sum = htons(0xffff - sum);
116 make_echo (const struct in_addr *src_ip,
117 struct icmp_packet *echo)
119 memset(echo, 0, sizeof(struct icmp_packet));
120 echo->type = ICMP_ECHO;
124 echo->checksum = htons(calc_checksum((uint16_t*)echo, sizeof (struct icmp_packet)));
129 * Send an ICMP message to the dummy IP.
131 * @param my_ip source address (our ip address)
134 send_icmp_echo (const struct in_addr *my_ip)
136 struct icmp_packet icmp_echo;
137 struct sockaddr_in dst;
140 struct ip_packet ip_pkt;
141 struct icmp_packet icmp_pkt;
142 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
145 memset(&ip_pkt, 0, sizeof(ip_pkt));
146 ip_pkt.vers_ihl = 0x45;
148 ip_pkt.pkt_len = sizeof (packet);
150 ip_pkt.flags_frag_offset = 0;
151 ip_pkt.ttl = IPDEFTTL;
152 ip_pkt.proto = IPPROTO_ICMP;
154 ip_pkt.src_ip = my_ip->s_addr;
155 ip_pkt.dst_ip = dummy.s_addr;
156 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
157 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
158 off += sizeof (ip_pkt);
159 make_echo (my_ip, &icmp_echo);
160 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
161 off += sizeof (icmp_echo);
163 memset (&dst, 0, sizeof (dst));
164 dst.sin_family = AF_INET;
165 dst.sin_addr = dummy;
166 err = sendto(rawsock,
168 (struct sockaddr*)&dst,
173 "sendto failed: %s\n", strerror(errno));
178 "Error: partial send of ICMP message\n");
184 process_icmp_response ()
189 struct ip_packet ip_pkt;
190 struct icmp_packet icmp_pkt;
193 have = read (icmpsock, buf, sizeof (buf));
197 "Error reading raw socket: %s\n",
201 if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
204 "Received ICMP message of unexpected size: %u bytes\n",
205 (unsigned int) have);
209 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
210 off += sizeof (ip_pkt);
211 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
212 off += sizeof (icmp_pkt);
213 if ( (ip_pkt.proto != IPPROTO_ICMP) ||
214 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
215 (icmp_pkt.code != 0) )
217 /* maybe we got an actual reply back... */
238 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
242 "Error opening RAW socket: %s\n",
246 if (ret >= FD_SETSIZE)
249 "Socket number too large (%d > %u)\n",
251 (unsigned int) FD_SETSIZE);
265 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
269 "Error opening RAW socket: %s\n",
273 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
274 (char *)&one, sizeof(one)) == -1)
276 "setsockopt failed: %s\n",
278 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
279 (char *)&one, sizeof(one)) == -1)
281 "setsockopt failed: %s\n",
288 main (int argc, char *const *argv)
290 struct in_addr external;
295 if (-1 == (icmpsock = make_icmp_socket()))
297 if (-1 == (rawsock = make_raw_socket()))
303 if (0 != setresuid (uid, uid, uid))
305 "Failed to setresuid: %s\n",
310 "This program must be started with our external IP as the only argument.\n");
313 if (1 != inet_pton (AF_INET, argv[1], &external))
316 "Error parsing IPv4 address: %s\n",
320 if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
324 FD_SET (icmpsock, &rs);
326 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
327 select (icmpsock + 1, &rs, NULL, NULL, &tv);
328 if (FD_ISSET (icmpsock, &rs))
329 process_icmp_response ();
330 send_icmp_echo (&external);
336 /* end of gnunet-nat-server.c */