gnunet-helper-nat-client.c

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/*
     This file is part of GNUnet.
     Copyright (C) 2010 GNUnet e.V.
 
     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     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
     Affero General Public License for more details.
 
     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
     SPDX-License-Identifier: AGPL3.0-or-later
 */
 
#if HAVE_CONFIG_H
/* Just needed for HAVE_SOCKADDR_IN_SIN_LEN test macro! */
#include "platform.h"
#include "gnunet_private_config.h"
#else
#define _GNU_SOURCE
#endif
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.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>
 
/* The following constant is missing from FreeBSD 9.2 */
#ifndef ICMP_TIME_EXCEEDED
#define ICMP_TIME_EXCEEDED 11
#endif
 
#define GNUNET_memcpy(dst, src, n) do { if (0 != n) { (void) memcpy (dst, src, \
                                                                     n); \
                                        } } while (0)
 
#define DUMMY_IP "192.0.2.86"
 
#define NAT_TRAV_PORT 22225
 
#define PACKET_ID 256
 
struct ip_header
{
  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_ttl_exceeded_header
{
  uint8_t type;
 
  uint8_t code;
 
  uint16_t checksum;
 
  uint32_t unused;
 
  /* followed by original payload */
};
 
struct icmp_echo_header
{
  uint8_t type;
 
  uint8_t code;
 
  uint16_t checksum;
 
  uint32_t reserved;
};
 
struct udp_header
{
  uint16_t src_port;
 
  uint16_t dst_port;
 
  uint16_t length;
 
  uint16_t crc;
};
 
static int rawsock;
 
static struct in_addr dummy;
 
static uint16_t port;
 
 
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;
}
 
 
static void
send_icmp_udp (const struct in_addr *my_ip, const struct in_addr *other)
{
  char packet[sizeof(struct ip_header) * 2
              + sizeof(struct icmp_ttl_exceeded_header)
              + sizeof(struct udp_header)];
  struct ip_header ip_pkt;
  struct icmp_ttl_exceeded_header icmp_pkt;
  struct udp_header udp_pkt;
  struct sockaddr_in dst;
  size_t off;
  int err;
 
  /* ip header: send to (known) ip address */
  off = 0;
  ip_pkt.vers_ihl = 0x45;
  ip_pkt.tos = 0;
  /* should this be BSD only? */
#if defined(BSD) && defined(__FreeBSD__) && defined(__FreeBSD_kernel__)
  ip_pkt.pkt_len = sizeof(packet);  /* Workaround PR kern/21737 */
#else
  ip_pkt.pkt_len = htons (sizeof(packet));
#endif
  ip_pkt.id = htons (PACKET_ID);
  ip_pkt.flags_frag_offset = 0;
  ip_pkt.ttl = 128;
  ip_pkt.proto = IPPROTO_ICMP;
  ip_pkt.checksum = 0;
  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(struct ip_header)));
  GNUNET_memcpy (&packet[off],
                 &ip_pkt,
                 sizeof(struct ip_header));
  off += sizeof(struct ip_header);
 
  icmp_pkt.type = ICMP_TIME_EXCEEDED;
  icmp_pkt.code = 0;
  icmp_pkt.checksum = 0;
  icmp_pkt.unused = 0;
  GNUNET_memcpy (&packet[off],
                 &icmp_pkt,
                 sizeof(struct icmp_ttl_exceeded_header));
  off += sizeof(struct icmp_ttl_exceeded_header);
 
  /* ip header of the presumably 'lost' udp packet */
  ip_pkt.vers_ihl = 0x45;
  ip_pkt.tos = 0;
  ip_pkt.pkt_len =
    htons (sizeof(struct ip_header) + sizeof(struct udp_header));
  ip_pkt.id = htons (0);
  ip_pkt.flags_frag_offset = 0;
  ip_pkt.ttl = 128;
  ip_pkt.proto = IPPROTO_UDP;
  ip_pkt.checksum = 0;
  ip_pkt.src_ip = other->s_addr;
  ip_pkt.dst_ip = dummy.s_addr;
  ip_pkt.checksum =
    htons (calc_checksum ((uint16_t *) &ip_pkt, sizeof(struct ip_header)));
  GNUNET_memcpy (&packet[off],
                 &ip_pkt,
                 sizeof(struct ip_header));
  off += sizeof(struct ip_header);
 
  /* build UDP header */
  udp_pkt.src_port = htons (NAT_TRAV_PORT);
  udp_pkt.dst_port = htons (NAT_TRAV_PORT);
  udp_pkt.length = htons (port);
  udp_pkt.crc = 0;
  GNUNET_memcpy (&packet[off],
                 &udp_pkt,
                 sizeof(struct udp_header));
  off += sizeof(struct udp_header);
 
  /* set ICMP checksum */
  icmp_pkt.checksum =
    htons (calc_checksum
             ((uint16_t *) &packet[sizeof(struct ip_header)],
             sizeof(struct icmp_ttl_exceeded_header)
             + sizeof(struct ip_header) + sizeof(struct udp_header)));
  GNUNET_memcpy (&packet[sizeof(struct ip_header)],
                 &icmp_pkt,
                 sizeof(struct icmp_ttl_exceeded_header));
 
  memset (&dst, 0, sizeof(dst));
  dst.sin_family = AF_INET;
#if HAVE_SOCKADDR_IN_SIN_LEN
  dst.sin_len = sizeof(struct sockaddr_in);
#endif
  dst.sin_addr = *other;
  err =
    sendto (rawsock, packet, sizeof(packet), 0, (struct sockaddr *) &dst,
            sizeof(dst));
  if (err < 0)
  {
    fprintf (stderr, "sendto failed: %s\n", strerror (errno));
  }
  else if (sizeof(packet) != (size_t) err)
  {
    fprintf (stderr, "Error: partial send of ICMP message with size %lu\n",
             (unsigned long) off);
  }
}
 
 
static void
send_icmp (const struct in_addr *my_ip, const struct in_addr *other)
{
  struct ip_header ip_pkt;
  struct icmp_ttl_exceeded_header icmp_ttl;
  struct icmp_echo_header icmp_echo;
  struct sockaddr_in dst;
  char packet[sizeof(struct ip_header) * 2
              + sizeof(struct icmp_ttl_exceeded_header)
              + sizeof(struct icmp_echo_header)];
  size_t off;
  int err;
 
  /* ip header: send to (known) ip address */
  off = 0;
  ip_pkt.vers_ihl = 0x45;
  ip_pkt.tos = 0;
#if defined(BSD) && defined(__FreeBSD__) && defined(__FreeBSD_kernel__)
  ip_pkt.pkt_len = sizeof(packet);  /* Workaround PR kern/21737 */
#else
  ip_pkt.pkt_len = htons (sizeof(packet));
#endif
  ip_pkt.id = htons (PACKET_ID);
  ip_pkt.flags_frag_offset = 0;
  ip_pkt.ttl = IPDEFTTL;
  ip_pkt.proto = IPPROTO_ICMP;
  ip_pkt.checksum = 0;
  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(struct ip_header)));
  GNUNET_memcpy (&packet[off],
                 &ip_pkt,
                 sizeof(struct ip_header));
  off = sizeof(ip_pkt);
 
  /* icmp reply: time exceeded */
  icmp_ttl.type = ICMP_TIME_EXCEEDED;
  icmp_ttl.code = 0;
  icmp_ttl.checksum = 0;
  icmp_ttl.unused = 0;
  GNUNET_memcpy (&packet[off],
                 &icmp_ttl,
                 sizeof(struct icmp_ttl_exceeded_header));
  off += sizeof(struct icmp_ttl_exceeded_header);
 
  /* ip header of the presumably 'lost' udp packet */
  ip_pkt.vers_ihl = 0x45;
  ip_pkt.tos = 0;
  ip_pkt.pkt_len =
    htons (sizeof(struct ip_header) + sizeof(struct icmp_echo_header));
  ip_pkt.id = htons (PACKET_ID);
  ip_pkt.flags_frag_offset = 0;
  ip_pkt.ttl = 1;               /* real TTL would be 1 on a time exceeded packet */
  ip_pkt.proto = IPPROTO_ICMP;
  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(struct ip_header)));
  GNUNET_memcpy (&packet[off],
                 &ip_pkt,
                 sizeof(struct ip_header));
  off += sizeof(struct ip_header);
 
  icmp_echo.type = ICMP_ECHO;
  icmp_echo.code = 0;
  icmp_echo.reserved = htonl (port);
  icmp_echo.checksum = 0;
  icmp_echo.checksum =
    htons (calc_checksum
             ((uint16_t *) &icmp_echo, sizeof(struct icmp_echo_header)));
  GNUNET_memcpy (&packet[off],
                 &icmp_echo,
                 sizeof(struct icmp_echo_header));
 
  /* no go back to calculate ICMP packet checksum */
  off = sizeof(struct ip_header);
  icmp_ttl.checksum =
    htons (calc_checksum
             ((uint16_t *) &packet[off],
             sizeof(struct icmp_ttl_exceeded_header)
             + sizeof(struct ip_header) + sizeof(struct icmp_echo_header)));
  GNUNET_memcpy (&packet[off],
                 &icmp_ttl,
                 sizeof(struct icmp_ttl_exceeded_header));
 
  /* prepare for transmission */
  memset (&dst, 0, sizeof(dst));
  dst.sin_family = AF_INET;
#if HAVE_SOCKADDR_IN_SIN_LEN
  dst.sin_len = sizeof(struct sockaddr_in);
#endif
  dst.sin_addr = *other;
  err =
    sendto (rawsock, packet, sizeof(packet), 0, (struct sockaddr *) &dst,
            sizeof(dst));
  if (err < 0)
  {
    fprintf (stderr, "sendto failed: %s\n", strerror (errno));
  }
  else if (sizeof(packet) != (size_t) err)
  {
    fprintf (stderr, "Error: partial send of ICMP message\n");
  }
}
 
 
int
main (int argc, char *const *argv)
{
  const int one = 1;
  struct in_addr external;
  struct in_addr target;
  uid_t uid;
  unsigned int p;
  int raw_eno;
  int global_ret;
 
  /* Create an ICMP raw socket for writing (only operation that requires root) */
  rawsock = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
  raw_eno = errno; /* for later error checking */
 
  /* now drop root privileges */
  uid = getuid ();
#ifdef HAVE_SETRESUID
  if (0 != setresuid (uid, uid, uid))
  {
    fprintf (stderr, "Failed to setresuid: %s\n", strerror (errno));
    global_ret = 1;
    goto cleanup;
  }
#else
  if (0 != (setuid (uid) | seteuid (uid)))
  {
    fprintf (stderr, "Failed to setuid: %s\n", strerror (errno));
    global_ret = 2;
    goto cleanup;
  }
#endif
  if (-1 == rawsock)
  {
    fprintf (stderr, "Error opening RAW socket: %s\n", strerror (raw_eno));
    global_ret = 3;
    goto cleanup;
  }
  if (0 !=
      setsockopt (rawsock, SOL_SOCKET, SO_BROADCAST, (char *) &one,
                  sizeof(one)))
  {
    fprintf (stderr, "setsockopt failed: %s\n", strerror (errno));
    global_ret = 4;
    goto cleanup;
  }
  if (0 !=
      setsockopt (rawsock, IPPROTO_IP, IP_HDRINCL, (char *) &one, sizeof(one)))
  {
    fprintf (stderr, "setsockopt failed: %s\n", strerror (errno));
    global_ret = 5;
    goto cleanup;
  }
 
  if (4 != argc)
  {
    fprintf (stderr,
             "This program must be started with our IP, the targets external IP, and our port as arguments.\n");
    global_ret = 6;
    goto cleanup;
  }
  if ((1 != inet_pton (AF_INET, argv[1], &external)) ||
      (1 != inet_pton (AF_INET, argv[2], &target)))
  {
    fprintf (stderr, "Error parsing IPv4 address: %s\n", strerror (errno));
    global_ret = 7;
    goto cleanup;
  }
  if ((1 != sscanf (argv[3], "%u", &p)) || (0 == p) || (0xFFFF < p))
  {
    fprintf (stderr, "Error parsing port value `%s'\n", argv[3]);
    global_ret = 8;
    goto cleanup;
  }
  port = (uint16_t) p;
  if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy))
  {
    fprintf (stderr, "Internal error converting dummy IP to binary.\n");
    global_ret = 9;
    goto cleanup;
  }
  send_icmp (&external, &target);
  send_icmp_udp (&external, &target);
  global_ret = 0;
cleanup:
  if (-1 != rawsock)
    (void) close (rawsock);
  return global_ret;
}
 
 
/* end of gnunet-helper-nat-client.c */