/*
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 .
SPDX-License-Identifier: AGPL3.0-or-later
*/
/**
* @file src/nat/gnunet-helper-nat-client-windows.c
* @brief Tool to help bypass NATs using ICMP method; must run as
* administrator on W32
* This code is forx W32.
* @author Nathan Evans
*
* This program will send ONE ICMP message using RAW sockets
* to the IP address specified as the second argument. Since
* it uses RAW sockets, it must be installed SUID or run as 'root'.
* In order to keep the security risk of the resulting SUID binary
* minimal, the program ONLY opens the RAW socket with root
* privileges, then drops them and only then starts to process
* command line arguments. The code also does not link against
* any shared libraries (except libc) and is strictly minimal
* (except for checking for errors). The following list of people
* have reviewed this code and considered it safe since the last
* modification (if you reviewed it, please have your name added
* to the list):
*
* - Christian Grothoff
* - Nathan Evans
*/
#define _GNU_SOURCE
/* Instead of including gnunet_common.h */
#define GNUNET_memcpy(dst,src,n) do { if (0 != n) { (void) memcpy (dst,src,n); } } while (0)
#define FD_SETSIZE 1024
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define ICMP_ECHO 8
#define IPDEFTTL 64
#define ICMP_TIME_EXCEEDED 11
/**
* Must match IP given in the server.
*/
#define DUMMY_IP "192.0.2.86"
#define NAT_TRAV_PORT 22225
/**
* IPv4 header.
*/
struct ip_header
{
/**
* Version (4 bits) + Internet header length (4 bits)
*/
uint8_t vers_ihl;
/**
* Type of service
*/
uint8_t tos;
/**
* Total length
*/
uint16_t pkt_len;
/**
* Identification
*/
uint16_t id;
/**
* Flags (3 bits) + Fragment offset (13 bits)
*/
uint16_t flags_frag_offset;
/**
* Time to live
*/
uint8_t ttl;
/**
* Protocol
*/
uint8_t proto;
/**
* Header checksum
*/
uint16_t checksum;
/**
* Source address
*/
uint32_t src_ip;
/**
* Destination address
*/
uint32_t dst_ip;
};
/**
* Format of ICMP packet.
*/
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;
};
/**
* Beginning of UDP packet.
*/
struct udp_header
{
uint16_t src_port;
uint16_t dst_port;
uint16_t length;
uint16_t crc;
};
/**
* Will this binary be run in permissions testing mode?
*/
static boolean privilege_testing = FALSE;
/**
* Socket we use to send our ICMP packets.
*/
static SOCKET rawsock;
/**
* Target "dummy" address.
*/
static struct in_addr dummy;
/**
* Port we are listening on (communicated to the server).
*/
static uint16_t port;
/**
* Convert IPv4 address from text to binary form.
*
* @param af address family
* @param cp the address to print
* @param buf where to write the address result
* @return 1 on success
*/
static int
inet_pton (int af, const char *cp, struct in_addr *buf)
{
buf->s_addr = inet_addr (cp);
if (buf->s_addr == INADDR_NONE)
{
fprintf (stderr, "Error %d handling address %s", WSAGetLastError (), cp);
return 0;
}
return 1;
}
/**
* CRC-16 for IP/ICMP headers.
*
* @param data what to calculate the CRC over
* @param bytes number of bytes in data (must be multiple of 2)
* @return the CRC 16.
*/
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
* @param other target address
*/
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;
ip_pkt.pkt_len = htons (sizeof (packet));
ip_pkt.id = htons (256);
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);
/* no go back to calculate ICMP packet checksum */
icmp_pkt.checksum =
htons (calc_checksum
((uint16_t *) & packet[off],
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;
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");
}
}
/**
* Send an ICMP message to the target.
*
* @param my_ip source address
* @param other target address
*/
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;
ip_pkt.pkt_len = htons (sizeof (packet));
ip_pkt.id = htons (256);
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 (256);
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));
memset (&dst, 0, sizeof (dst));
dst.sin_family = AF_INET;
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");
}
}
/**
* Create an ICMP raw socket.
*
* @return INVALID_SOCKET on error
*/
static SOCKET
make_raw_socket ()
{
DWORD bOptVal = TRUE;
int bOptLen = sizeof (bOptVal);
SOCKET ret;
ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
if (INVALID_SOCKET == ret)
{
fprintf (stderr, "Error opening RAW socket: %s\n", strerror (errno));
return INVALID_SOCKET;
}
if (0 !=
setsockopt (ret, SOL_SOCKET, SO_BROADCAST, (char *) &bOptVal, bOptLen))
{
fprintf (stderr, "Error setting SO_BROADCAST to ON: %s\n",
strerror (errno));
closesocket (rawsock);
return INVALID_SOCKET;
}
if (0 != setsockopt (ret, IPPROTO_IP, IP_HDRINCL, (char *) &bOptVal, bOptLen))
{
fprintf (stderr, "Error setting IP_HDRINCL to ON: %s\n", strerror (errno));
closesocket (rawsock);
return INVALID_SOCKET;
}
return ret;
}
int
main (int argc, char *const *argv)
{
struct in_addr external;
struct in_addr target;
WSADATA wsaData;
unsigned int p;
if (argc > 1 && 0 != strcmp (argv[1], "-d")){
privilege_testing = TRUE;
fprintf (stderr,
"%s",
"DEBUG: Running binary in privilege testing mode.");
argv++;
argc--;
}
if (argc != 4)
{
fprintf (stderr,
"%s",
"This program must be started with our IP, the targets external IP, and our port as arguments.\n");
return 1;
}
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));
return 1;
}
if ((1 != sscanf (argv[3], "%u", &p)) || (0 == p) || (0xFFFF < p))
{
fprintf (stderr,
"Error parsing port value `%s'\n",
argv[3]);
return 1;
}
port = (uint16_t) p;
if (0 != WSAStartup (MAKEWORD (2, 1), &wsaData))
{
fprintf (stderr,
"%s",
"Failed to find Winsock 2.1 or better.\n");
return 2;
}
if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy))
{
fprintf (stderr,
"%s",
"Internal error converting dummy IP to binary.\n");
return 2;
}
if (-1 == (rawsock = make_raw_socket ()))
return 3;
if (!privilege_testing){
send_icmp (&external, &target);
send_icmp_udp (&external, &target);
}
closesocket (rawsock);
WSACleanup ();
return 0;
}
/* end of gnunet-helper-nat-client-windows.c */