2 This file is part of GNUnet.
3 (C) 2010 Christian Grothoff (and other contributing authors)
5 GNUnet is free software; you can redistribute it and/or modify
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.
15 You should have received a copy of the GNU General Public License
16 along with GNUnet; see the file COPYING. If not, write to the
17 Free Software Foundation, Inc., 59 Temple Place - Suite 330,
18 Boston, MA 02111-1307, USA.
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
28 #include <sys/types.h>
29 #include <sys/socket.h>
30 #include <arpa/inet.h>
31 #include <sys/select.h>
33 #include <sys/types.h>
41 #include <netinet/ip.h>
42 #include <netinet/ip_icmp.h>
43 #include <netinet/in.h>
46 * Must match IP given in the client.
48 #define DUMMY_IP "1.2.3.4"
51 * How often do we send our ICMP messages to receive replies?
53 #define ICMP_SEND_FREQUENCY_MS 500
61 uint16_t flags_frag_offset;
82 static struct in_addr dummy;
85 calc_checksum(const uint16_t *data,
92 for (i=0;i<bytes/2;i++)
94 sum = (sum & 0xffff) + (sum >> 16);
95 sum = htons(0xffff - sum);
101 make_echo (const struct in_addr *src_ip,
102 struct icmp_packet *echo)
104 memset(echo, 0, sizeof(struct icmp_packet));
105 echo->type = ICMP_ECHO;
109 echo->checksum = htons(calc_checksum((uint16_t*)echo, sizeof (struct icmp_packet)));
114 * Send an ICMP message to the dummy IP.
116 * @param my_ip source address (our ip address)
119 send_icmp_echo (const struct in_addr *my_ip)
121 struct icmp_packet icmp_echo;
122 struct sockaddr_in dst;
125 struct ip_packet ip_pkt;
126 struct icmp_packet icmp_pkt;
127 char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
130 memset(&ip_pkt, 0, sizeof(ip_pkt));
131 ip_pkt.vers_ihl = 0x45;
133 ip_pkt.pkt_len = sizeof (packet);
135 ip_pkt.flags_frag_offset = 0;
136 ip_pkt.ttl = IPDEFTTL;
137 ip_pkt.proto = IPPROTO_ICMP;
139 ip_pkt.src_ip = my_ip->s_addr;
140 ip_pkt.dst_ip = dummy.s_addr;
141 ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
142 memcpy (packet, &ip_pkt, sizeof (ip_pkt));
143 off += sizeof (ip_pkt);
144 make_echo (my_ip, &icmp_echo);
145 memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
146 off += sizeof (icmp_echo);
148 memset (&dst, 0, sizeof (dst));
149 dst.sin_family = AF_INET;
150 dst.sin_addr = dummy;
151 err = sendto(rawsock,
153 (struct sockaddr*)&dst,
158 "sendto failed: %s\n", strerror(errno));
163 "Error: partial send of ICMP message\n");
169 process_icmp_response ()
174 struct ip_packet ip_pkt;
175 struct icmp_packet icmp_pkt;
178 have = read (icmpsock, buf, sizeof (buf));
182 "Error reading raw socket: %s\n",
186 if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
189 "Received ICMP message of unexpected size: %u bytes\n",
190 (unsigned int) have);
194 memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
195 off += sizeof (ip_pkt);
196 memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
197 off += sizeof (icmp_pkt);
198 if ( (ip_pkt.proto != IPPROTO_ICMP) ||
199 (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
200 (icmp_pkt.code != 0) )
202 /* maybe we got an actual reply back... */
222 ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
226 "Error opening RAW socket: %s\n",
230 if (ret >= FD_SETSIZE)
233 "Socket number too large (%d > %u)\n",
235 (unsigned int) FD_SETSIZE);
249 ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
253 "Error opening RAW socket: %s\n",
257 if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
258 (char *)&one, sizeof(one)) == -1)
260 "setsockopt failed: %s\n",
262 if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
263 (char *)&one, sizeof(one)) == -1)
265 "setsockopt failed: %s\n",
272 main (int argc, char *const *argv)
274 struct in_addr external;
279 if (-1 == (icmpsock = make_icmp_socket()))
281 if (-1 == (rawsock = make_raw_socket()))
287 if (0 != setresuid (uid, uid, uid))
289 "Failed to setresuid: %s\n",
294 "This program must be started with our external IP as the only argument.\n");
297 if (1 != inet_pton (AF_INET, argv[1], &external))
300 "Error parsing IPv4 address: %s\n",
304 inet_pton (AF_INET, DUMMY_IP, &dummy);
308 FD_SET (icmpsock, &rs);
310 tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
311 select (icmpsock + 1, &rs, NULL, NULL, &tv);
312 if (FD_ISSET (icmpsock, &rs))
313 process_icmp_response ();
314 send_icmp_echo (&external);
320 /* end of gnunet-nat-server.c */