--- /dev/null
+/*
+ This file is part of GNUnet.
+ (C) 2010 Christian Grothoff (and other contributing authors)
+
+ GNUnet is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published
+ by the Free Software Foundation; either version 3, or (at your
+ option) any later version.
+
+ GNUnet is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with GNUnet; see the file COPYING. If not, write to the
+ Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ Boston, MA 02111-1307, USA.
+*/
+
+/**
+ * @file src/transport/gnunet-nat-server.c
+ * @brief Tool to help bypass NATs using ICMP method; must run as root (for now, later SUID will do)
+ * This code will work under GNU/Linux only (or maybe BSDs, but never W32)
+ * @author Christian Grothoff
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <arpa/inet.h>
+#include <sys/select.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <netinet/ip.h>
+#include <netinet/ip_icmp.h>
+#include <netinet/in.h>
+
+/**
+ * Number of UDP ports to keep open.
+ */
+#define NUM_UDP_PORTS 512
+
+/**
+ * How often do we send our UDP messages to keep ports open?
+ */
+#define UDP_SEND_FREQUENCY_MS 50
+
+/**
+ * Port we use for the dummy target.
+ */
+#define NAT_TRAV_PORT 2222
+
+/**
+ * How often do we retry to open and bind a UDP socket before giving up?
+ */
+#define MAX_TRIES 10
+
+
+struct ip_packet
+{
+
+ uint8_t vers_ihl;
+ uint8_t tos;
+ uint16_t pkt_len;
+ uint16_t id;
+ uint16_t flags_frag_offset;
+ uint8_t ttl;
+ uint8_t proto;
+ uint16_t checksum;
+ uint32_t src_ip;
+ uint32_t dst_ip;
+};
+
+struct icmp_packet
+{
+ uint8_t type;
+ uint8_t code;
+ uint16_t checksum;
+ uint32_t reserved;
+};
+
+struct udp_packet
+{
+ uint16_t source_port;
+ uint16_t dst_port;
+ uint16_t mlen_aka_reply_port_magic;
+ uint16_t checksum_aka_my_magic;
+};
+
+
+/**
+ * Structure of the data we tack on to the fake ICMP reply
+ * (last 4 bytes of the 64 bytes).
+ */
+struct extra_packet
+{
+ /**
+ * if this is a reply to an icmp, what was the 'my_magic'
+ * value from the original icmp?
+ */
+ uint16_t reply_port_magic;
+
+ /**
+ * magic value of the sender of this icmp message.
+ */
+ uint16_t my_magic;
+};
+
+static int udpsocks[NUM_UDP_PORTS];
+
+static uint16_t udpports[NUM_UDP_PORTS];
+
+static int icmpsock;
+
+static struct in_addr dummy;
+
+
+/**
+ * create a random port number that is not totally
+ * unlikely to be chosen by the nat box.
+ */
+static uint16_t make_port ()
+{
+ return 1024 + ( (unsigned int)rand ()) % (63 * 1024 - 2);
+}
+
+
+/**
+ * create a fresh udp socket bound to a random local port.
+ */
+static int
+make_udp_socket (uint16_t *port)
+{
+ int ret;
+ int tries;
+ struct sockaddr_in src;
+
+ for (tries=0;tries<MAX_TRIES;tries++)
+ {
+ ret = socket (AF_INET, SOCK_DGRAM, 0);
+ if (-1 == ret)
+ {
+ fprintf (stderr,
+ "Error opening udp socket: %s\n",
+ strerror (errno));
+ return -1;
+ }
+ if (ret >= FD_SETSIZE)
+ {
+ fprintf (stderr,
+ "Socket number too large (%d > %u)\n",
+ ret,
+ (unsigned int) FD_SETSIZE);
+ close (ret);
+ return -1;
+ }
+ memset (&src, 0, sizeof (src));
+ src.sin_family = AF_INET;
+ src.sin_port = htons (make_port ());
+ if (0 != bind (ret, (struct sockaddr*) &src, sizeof (src)))
+ {
+ close (ret);
+ continue;
+ }
+ *port = ntohs (src.sin_port);
+ return ret;
+ }
+ fprintf (stderr,
+ "Error binding udp socket: %s\n",
+ strerror (errno));
+ return -1;
+}
+
+
+static uint16_t
+calc_checksum(const uint16_t *data,
+ unsigned int bytes)
+{
+ uint32_t sum;
+ unsigned int i;
+
+ sum = 0;
+ for (i=0;i<bytes/2;i++)
+ sum += data[i];
+ sum = (sum & 0xffff) + (sum >> 16);
+ sum = htons(0xffff - sum);
+ return sum;
+}
+
+
+/**
+ * send an icmp message to the target.
+ *
+ * @param my_ip source address (our ip address)
+ * @param other target address
+ * @param target_port_number fake port number to put into icmp response
+ * as well as the icmpextradata as 'my_magic'
+ * @param source_port_number magic_number that enables the other peer to
+ * identify our port number ('reply in response to') to
+ * put in the data portion; 0 if we are initiating;
+ * goes into 'reply_port_magic' of the icmpextradata
+ */
+static void
+send_icmp (const struct in_addr *my_ip,
+ const struct in_addr *other,
+ uint16_t target_port_number,
+ uint16_t source_port_number)
+{
+ struct ip_packet ip_pkt;
+ struct icmp_packet icmp_pkt;
+ struct udp_packet udp_pkt;
+ struct sockaddr_in dst;
+ char packet[sizeof (ip_pkt) + sizeof (icmp_pkt) + sizeof (udp_pkt)];
+ char sbuf [INET_ADDRSTRLEN];
+ size_t off;
+ int err;
+
+ fprintf (stderr,
+ "Sending ICMP to `%s' at %u with reply magic %u\n",
+ inet_ntop (AF_INET,
+ other,
+ sbuf,
+ sizeof (sbuf)),
+ target_port_number,
+ source_port_number);
+ /* ip header: send to (known) ip address */
+ off = 0;
+ memset(&ip_pkt, 0, sizeof(ip_pkt));
+ ip_pkt.vers_ihl = 0x45;//|(pkt_len>>2);//5;//(ipversion << 4) | (iphdr_size >> 2);
+ ip_pkt.tos = 0;
+ ip_pkt.pkt_len = sizeof (packet); /* huh? */
+ ip_pkt.id = 1; /* kernel will change anyway!? */
+ ip_pkt.flags_frag_offset = 0;
+ ip_pkt.ttl = IPDEFTTL;
+ ip_pkt.proto = IPPROTO_ICMP;
+ ip_pkt.checksum = 0; /* maybe the kernel helps us out..? */
+ ip_pkt.src_ip = my_ip->s_addr;
+ ip_pkt.dst_ip = other->s_addr;
+ ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
+ memcpy (packet, &ip_pkt, sizeof (ip_pkt));
+ off += sizeof (ip_pkt);
+
+ /* icmp reply: time exceeded */
+ memset(&icmp_pkt, 0, sizeof(icmp_pkt));
+ icmp_pkt.type = ICMP_TIME_EXCEEDED;
+ icmp_pkt.code = ICMP_NET_UNREACH;
+ icmp_pkt.reserved = 0;
+ icmp_pkt.checksum = 0;
+ icmp_pkt.checksum = htons(calc_checksum((uint16_t*)&icmp_pkt, sizeof (icmp_pkt)));
+ memcpy (&packet[off], &icmp_pkt, sizeof (icmp_pkt));
+ off += sizeof (icmp_pkt);
+
+ /* ip header of the presumably 'lost' udp packet */
+ memset(&ip_pkt, 0, sizeof (ip_pkt));
+ ip_pkt.vers_ihl = 0x45;
+ ip_pkt.tos = 0;
+ /* no idea why i need to shift the bits here, but not on ip_pkt->pkt_len... */
+ ip_pkt.pkt_len = (sizeof (ip_pkt) + sizeof (icmp_pkt)) << 8;
+ ip_pkt.id = 1; /* kernel sets proper value htons(ip_id_counter); */
+ ip_pkt.flags_frag_offset = 0;
+ ip_pkt.ttl = 1; /* real TTL would be 1 on a time exceeded packet */
+ ip_pkt.proto = IPPROTO_UDP;
+ ip_pkt.src_ip = other->s_addr;
+ ip_pkt.dst_ip = dummy.s_addr;
+ ip_pkt.checksum = 0;
+ ip_pkt.checksum = htons(calc_checksum((uint16_t*)&ip_pkt, sizeof (ip_pkt)));
+ memcpy (&packet[off], &ip_pkt, sizeof (ip_pkt));
+ off += sizeof (ip_pkt);
+
+ memset(&udp_pkt, 0, sizeof (udp_pkt));
+ udp_pkt.source_port = htons (target_port_number);
+ udp_pkt.dst_port = htons (NAT_TRAV_PORT);
+ udp_pkt.mlen_aka_reply_port_magic = htons (source_port_number);
+ udp_pkt.checksum_aka_my_magic = htons (target_port_number);
+ memcpy (&packet[off], &udp_pkt, sizeof (udp_pkt));
+ off += sizeof (udp_pkt);
+
+ memset (&dst, 0, sizeof (dst));
+ dst.sin_family = AF_INET;
+ dst.sin_addr = *other;
+ err = sendto(icmpsock,
+ packet,
+ off, 0,
+ (struct sockaddr*)&dst,
+ sizeof(dst)); /* or sizeof 'struct sockaddr'? */
+ if (err < 0) {
+ fprintf(stderr,
+ "sendto failed: %s\n", strerror(errno));
+ } else if (err != off)
+ fprintf(stderr,
+ "Error: partial send of ICMP message\n");
+}
+
+
+/**
+ * We discovered the IP address of the other peer.
+ * Try to connect back to it.
+ */
+static void
+try_connect (const struct in_addr *my_ip,
+ const struct in_addr *other,
+ uint16_t port_magic)
+{
+ unsigned int i;
+
+ for (i=0;i<NUM_UDP_PORTS;i++)
+ send_icmp (my_ip, other, make_port(), port_magic);
+}
+
+
+static void
+process_icmp_response (const struct in_addr *my_ip,
+ int s)
+{
+ char buf[65536];
+ ssize_t have;
+ struct in_addr sip;
+ uint16_t my_magic;
+ uint16_t reply_magic;
+ struct ip_packet ip_pkt;
+ struct icmp_packet icmp_pkt;
+ struct udp_packet udp_pkt;
+ size_t off;
+
+ have = read (s, buf, sizeof (buf));
+ if (have == -1)
+ {
+ fprintf (stderr,
+ "Error reading raw socket: %s\n",
+ strerror (errno));
+ /* What now? */
+ return;
+ }
+ if (have < sizeof (struct ip_packet) + sizeof (struct icmp_packet) +
+ sizeof (struct udp_packet))
+ {
+ fprintf (stderr,
+ "Received invalid ICMP message: only %u bytes\n",
+ (unsigned int) have);
+ return;
+ }
+ off = 0;
+ memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
+ off += sizeof (ip_pkt);
+ memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
+ off += sizeof (icmp_pkt);
+ memcpy (&udp_pkt, &buf[off], sizeof (udp_pkt));
+ off += sizeof (struct udp_packet);
+
+ /* If not ICMP and not TTL exceeded */
+ if ( (ip_pkt.proto != IPPROTO_ICMP) ||
+ (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
+ (icmp_pkt.code != ICMP_NET_UNREACH) )
+ {
+ fprintf (stderr,
+ "Received unexpected ICMP message contents, ignoring\n");
+ return;
+ }
+ memcpy(&sip, &ip_pkt.src_ip, sizeof (sip));
+ my_magic = ntohs (udp_pkt.checksum_aka_my_magic);
+ reply_magic = ntohs (udp_pkt.mlen_aka_reply_port_magic);
+ fprintf (stderr,
+ "Received ICMP from `%s' with hints %u and %u\n",
+ inet_ntop (AF_INET,
+ &sip,
+ buf,
+ sizeof (buf)),
+ my_magic,
+ reply_magic);
+ if (my_magic == 0)
+ {
+ try_connect (my_ip, &sip, reply_magic);
+ }
+ else
+ {
+ printf ("%s:%u\n",
+ inet_ntop (AF_INET,
+ &sip,
+ buf,
+ sizeof(buf)),
+ my_magic);
+ }
+}
+
+
+static int
+make_icmp_socket ()
+{
+ const int one = 1;
+ int ret;
+
+ ret = socket (AF_INET, SOCK_RAW, 0);
+ if (-1 == ret)
+ {
+ fprintf (stderr,
+ "Error opening RAW socket: %s\n",
+ strerror (errno));
+ return -1;
+ }
+ if (ret >= FD_SETSIZE)
+ {
+ fprintf (stderr,
+ "Socket number too large (%d > %u)\n",
+ ret,
+ (unsigned int) FD_SETSIZE);
+ close (ret);
+ return -1;
+ }
+ if (setsockopt(ret, SOL_SOCKET, SO_BROADCAST,
+ (char *)&one, sizeof(one)) == -1)
+ fprintf(stderr,
+ "setsockopt failed: %s\n",
+ strerror (errno));
+ if (setsockopt(ret, IPPROTO_IP, IP_HDRINCL,
+ (char *)&one, sizeof(one)) == -1)
+ fprintf(stderr,
+ "setsockopt failed: %s\n",
+ strerror (errno));
+ return ret;
+}
+
+
+int
+main (int argc, char *const *argv)
+{
+ struct in_addr external;
+ unsigned int i;
+ unsigned int pos;
+ fd_set rs;
+ struct timeval tv;
+ struct sockaddr_in dst;
+
+ if (argc != 3)
+ {
+ fprintf (stderr,
+ "This program must be started with our external IP and the dummy IP address as arguments.\n");
+ return 1;
+ }
+ if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
+ (1 != inet_pton (AF_INET, argv[2], &dummy)) )
+ {
+ fprintf (stderr,
+ "Error parsing IPv4 address: %s\n",
+ strerror (errno));
+ return 1;
+ }
+ memset (&dst, 0, sizeof (dst));
+ dst.sin_family = AF_INET;
+ dst.sin_port = htons (NAT_TRAV_PORT);
+ dst.sin_addr = dummy;
+ if (-1 == (icmpsock = make_icmp_socket()))
+ return 1;
+ for (i=0;i<NUM_UDP_PORTS;i++)
+ udpsocks[i] = make_udp_socket (&udpports[i]);
+ pos = 0;
+ while (1)
+ {
+ FD_ZERO (&rs);
+ FD_SET (icmpsock, &rs);
+ tv.tv_sec = 0;
+ tv.tv_usec = UDP_SEND_FREQUENCY_MS * 1000 * 1000;
+ select (icmpsock + 1, &rs, NULL, NULL, &tv);
+ /* FIXME: do I need my external IP here? */
+ if (FD_ISSET (icmpsock, &rs))
+ process_icmp_response (&external, icmpsock);
+ if (-1 == sendto (udpsocks[pos],
+ NULL, 0, 0,
+ (struct sockaddr*) &dst, sizeof (dst)))
+ {
+ fprintf (stderr,
+ "sendto failed: %s\n",
+ strerror (errno));
+ close (udpsocks[pos]);
+ udpsocks[pos] = make_udp_socket (&udpports[pos]);
+ }
+ pos = (pos+1) % NUM_UDP_PORTS;
+ }
+ return 0;
+}
+
+
+/* end of gnunet-nat-server.c */
projects / oweals / gnunet.git / commitdiff