/*
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-server-windows.c
* @brief Windows tool to help bypass NATs using ICMP method
* This code will work under W32 only
* @author Christian Grothoff
*
* This program will send ONE ICMP message every 500 ms RAW sockets
* to a DUMMY IP address and also listens for ICMP replies. Since
* it uses RAW sockets, it must be run as an administrative user.
* In order to keep the security risk of the resulting binary
* minimal, the program ONLY opens the two RAW sockets with administrative
* 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):
*
* - Nathan Evans
* - Christian Grothoff
*/
#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
/**
* Should we print some debug output?
*/
#define VERBOSE 0
/**
* Must match IP given in the client.
*/
#define DUMMY_IP "192.0.2.86"
/**
* Default Port
*/
#define NAT_TRAV_PORT 22225
/**
* Must match packet ID used by gnunet-helper-nat-client.c
*/
#define PACKET_ID 256
/**
* TTL to use for our outgoing messages.
*/
#define IPDEFTTL 64
#define ICMP_ECHO 8
#define ICMP_TIME_EXCEEDED 11
/**
* How often do we send our ICMP messages to receive replies?
*/
#define ICMP_SEND_FREQUENCY_MS 500
/**
* 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 receive "fake" ICMP replies.
*/
static _win_socket icmpsock;
/**
* Socket we use to send our ICMP requests.
*/
static _win_socket rawsock;
/**
* Socket we use to send our UDP requests.
*/
static _win_socket udpsock;
/**
* Target "dummy" address.
*/
static struct in_addr dummy;
/**
* 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;
}
/**
* 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;
}
/**
* Send an ICMP message to the dummy IP.
*
* @param my_ip source address (our ip address)
*/
static void
send_icmp_echo(const struct in_addr *my_ip)
{
char packet[sizeof(struct ip_header) + sizeof(struct icmp_echo_header)];
struct icmp_echo_header icmp_echo;
struct ip_header ip_pkt;
struct sockaddr_in dst;
size_t off;
int err;
off = 0;
ip_pkt.vers_ihl = 0x45;
ip_pkt.tos = 0;
ip_pkt.pkt_len = htons(sizeof(packet));
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 = 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);
icmp_echo.type = ICMP_ECHO;
icmp_echo.code = 0;
icmp_echo.reserved = 0;
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));
off += sizeof(struct icmp_echo_header);
memset(&dst, 0, sizeof(dst));
dst.sin_family = AF_INET;
dst.sin_addr = dummy;
err =
sendto(rawsock, packet, off, 0, (struct sockaddr *)&dst, sizeof(dst));
if (err < 0)
{
#if VERBOSE
fprintf(stderr, "sendto failed: %s\n", strerror(errno));
#endif
}
else if (err != off)
{
fprintf(stderr, "Error: partial send of ICMP message\n");
}
}
/**
* Send a UDP message to the dummy IP.
*/
static void
send_udp()
{
struct sockaddr_in dst;
ssize_t err;
memset(&dst, 0, sizeof(dst));
dst.sin_family = AF_INET;
dst.sin_addr = dummy;
dst.sin_port = htons(NAT_TRAV_PORT);
err = sendto(udpsock, NULL, 0, 0, (struct sockaddr *)&dst, sizeof(dst));
if (err < 0)
{
#if VERBOSE
fprintf(stderr, "sendto failed: %s\n", strerror(errno));
#endif
}
else if (0 != err)
{
fprintf(stderr, "Error: partial send of ICMP message\n");
}
}
/**
* We've received an ICMP response. Process it.
*/
static void
process_icmp_response()
{
char buf[65536];
ssize_t have;
struct in_addr source_ip;
struct ip_header ip_pkt;
struct icmp_ttl_exceeded_header icmp_ttl;
struct icmp_echo_header icmp_echo;
struct udp_header udp_pkt;
size_t off;
uint16_t port;
DWORD ssize;
have = read(icmpsock, buf, sizeof(buf));
if (have == -1)
{
fprintf(stderr, "Error reading raw socket: %s\n", strerror(errno));
return;
}
#if VERBOSE
fprintf(stderr, "Received message of %u bytes\n", (unsigned int)have);
#endif
if (have <
(ssize_t)(sizeof(struct ip_header) +
sizeof(struct icmp_ttl_exceeded_header) +
sizeof(struct ip_header)))
{
/* malformed */
return;
}
off = 0;
GNUNET_memcpy(&ip_pkt, &buf[off], sizeof(struct ip_header));
off += sizeof(struct ip_header);
GNUNET_memcpy(&source_ip, &ip_pkt.src_ip, sizeof(source_ip));
GNUNET_memcpy(&icmp_ttl, &buf[off], sizeof(struct icmp_ttl_exceeded_header));
off += sizeof(struct icmp_ttl_exceeded_header);
if ((ICMP_TIME_EXCEEDED != icmp_ttl.type) || (0 != icmp_ttl.code))
{
/* different type than what we want */
return;
}
/* skip 2nd IP header */
GNUNET_memcpy(&ip_pkt, &buf[off], sizeof(struct ip_header));
off += sizeof(struct ip_header);
switch (ip_pkt.proto)
{
case IPPROTO_ICMP:
if (have !=
(sizeof(struct ip_header) * 2 +
sizeof(struct icmp_ttl_exceeded_header) +
sizeof(struct icmp_echo_header)))
{
/* malformed */
return;
}
/* grab ICMP ECHO content */
GNUNET_memcpy(&icmp_echo, &buf[off], sizeof(struct icmp_echo_header));
port = (uint16_t)ntohl(icmp_echo.reserved);
break;
case IPPROTO_UDP:
if (have !=
(sizeof(struct ip_header) * 2 +
sizeof(struct icmp_ttl_exceeded_header) + sizeof(struct udp_header)))
{
/* malformed */
return;
}
/* grab UDP content */
GNUNET_memcpy(&udp_pkt, &buf[off], sizeof(struct udp_header));
port = ntohs(udp_pkt.length);
break;
default:
/* different type than what we want */
return;
}
ssize = sizeof(buf);
WSAAddressToString((LPSOCKADDR)&source_ip, sizeof(source_ip), NULL, buf,
&ssize);
if (port == 0)
fprintf(stdout, "%s\n", buf);
else
fprintf(stdout, "%s:%u\n", buf, (unsigned int)port);
fflush(stdout);
}
/**
* Create an ICMP raw socket for reading.
*
* @return INVALID_SOCKET on error
*/
static _win_socket
make_icmp_socket()
{
_win_socket ret;
ret = _win_socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
if (INVALID_SOCKET == ret)
{
fprintf(stderr, "Error opening RAW socket: %s\n", strerror(errno));
return INVALID_SOCKET;
}
return ret;
}
/**
* Create an ICMP raw socket for writing.
*
* @return INVALID_SOCKET on error
*/
static _win_socket
make_raw_socket()
{
DWORD bOptVal = TRUE;
int bOptLen = sizeof(bOptVal);
rawsock = _win_socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
if (INVALID_SOCKET == rawsock)
{
fprintf(stderr, "Error opening RAW socket: %s\n", strerror(errno));
return INVALID_SOCKET;
}
if (0 !=
_win_setsockopt(rawsock, 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 !=
_win_setsockopt(rawsock, 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 rawsock;
}
/**
* Create a UDP socket for writing.
*
* @param my_ip source address (our ip address)
* @return INVALID_SOCKET on error
*/
static _win_socket
make_udp_socket(const struct in_addr *my_ip)
{
_win_socket ret;
struct sockaddr_in addr;
ret = _win_socket(AF_INET, SOCK_DGRAM, 0);
if (INVALID_SOCKET == ret)
{
fprintf(stderr, "Error opening UDP socket: %s\n", strerror(errno));
return INVALID_SOCKET;
}
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr = *my_ip;
addr.sin_port = htons(NAT_TRAV_PORT);
if (0 != bind(ret, (struct sockaddr *)&addr, sizeof(addr)))
{
fprintf(stderr, "Error binding UDP socket to port %u: %s\n", NAT_TRAV_PORT,
strerror(errno));
/* likely problematic, but not certain, try to continue */
}
return ret;
}
int
main(int argc, char *const *argv)
{
struct in_addr external;
fd_set rs;
struct timeval tv;
WSADATA wsaData;
unsigned int alt = 0;
if ((argc > 1) && (0 != strcmp(argv[1], "-d")))
{
privilege_testing = TRUE;
fprintf(stderr,
"%s",
"DEBUG: Running binary in privilege testing mode.");
argv++;
argc--;
}
if (2 != argc)
{
fprintf(stderr,
"This program must be started with our (internal NAT) IP as the only argument.\n");
return 1;
}
if (1 != inet_pton(AF_INET, argv[1], &external))
{
fprintf(stderr, "Error parsing IPv4 address: %s, error %s\n", argv[1],
strerror(errno));
return 1;
}
if (1 != inet_pton(AF_INET, DUMMY_IP, &dummy))
{
fprintf(stderr, "Internal error converting dummy IP to binary.\n");
return 2;
}
if (WSAStartup(MAKEWORD(2, 1), &wsaData) != 0)
{
fprintf(stderr, "Failed to find Winsock 2.1 or better.\n");
return 2;
}
if (INVALID_SOCKET == (icmpsock = make_icmp_socket()))
{
return 3;
}
if (INVALID_SOCKET == (make_raw_socket()))
{
closesocket(icmpsock);
return 3;
}
if (INVALID_SOCKET == (udpsock = make_udp_socket(&external)))
{
closesocket(icmpsock);
closesocket(rawsock);
return 3;
}
while (!privilege_testing)
{
FD_ZERO(&rs);
FD_SET(icmpsock, &rs);
tv.tv_sec = 0;
tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 1000;
if (-1 == select(icmpsock + 1, &rs, NULL, NULL, &tv))
{
if (errno == EINTR)
continue;
fprintf(stderr, "select failed: %s\n", strerror(errno));
break;
}
if (FD_ISSET(icmpsock, &rs))
process_icmp_response();
if (0 == (++alt % 2))
send_icmp_echo(&external);
else
send_udp();
}
/* select failed (internal error or OS out of resources) */
closesocket(icmpsock);
closesocket(rawsock);
closesocket(udpsock);
WSACleanup();
if (privilege_testing)
return 0;
return 4;
}
/* end of gnunet-helper-nat-server-windows.c */