/**
* @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)
+ * @brief Tool to help bypass NATs using ICMP method; must run as root (SUID will do)
* This code will work under GNU/Linux only (or maybe BSDs, but never W32)
* @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 installed SUID or run as 'root'.
+ * In order to keep the security risk of the resulting SUID binary
+ * minimal, the program ONLY opens the two RAW sockets 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
*/
-
+#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <errno.h>
#include <stdlib.h>
#include <stdint.h>
+#include <time.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?
+ * Must match IP given in the client.
*/
-#define UDP_SEND_FREQUENCY_MS 500
+#define DUMMY_IP "192.0.2.86"
-/**
- * Port we use for the dummy target.
- */
-#define NAT_TRAV_PORT 2222
+#define VERBOSE 0
/**
- * How often do we retry to open and bind a UDP socket before giving up?
+ * How often do we send our ICMP messages to receive replies?
*/
-#define MAX_TRIES 10
-
+#define ICMP_SEND_FREQUENCY_MS 500
struct ip_packet
{
-
uint8_t vers_ihl;
uint8_t tos;
uint16_t pkt_len;
struct udp_packet
{
- uint16_t source_port;
- uint16_t dst_port;
- uint16_t mlen_aka_reply_port_magic;
- uint16_t checksum_aka_my_magic;
-};
+ uint16_t src_port;
+ uint16_t dst_port;
-/**
- * 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;
+ uint32_t length;
};
-static int udpsocks[NUM_UDP_PORTS];
-
-static uint16_t udpports[NUM_UDP_PORTS];
-
static int icmpsock;
static int rawsock;
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,
}
+static void
+make_echo (const struct in_addr *src_ip,
+ struct icmp_packet *echo)
+{
+ memset(echo, 0, sizeof(struct icmp_packet));
+ echo->type = ICMP_ECHO;
+ echo->code = 0;
+ echo->reserved = 0;
+ echo->checksum = 0;
+ echo->checksum = htons(calc_checksum((uint16_t*)echo, sizeof (struct icmp_packet)));
+}
+
+
/**
- * send an icmp message to the target.
+ * Send an ICMP message to the dummy IP.
*
* @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)
+send_icmp_echo (const struct in_addr *my_ip)
{
- struct ip_packet ip_pkt;
- struct icmp_packet icmp_pkt;
- struct udp_packet udp_pkt;
+ struct icmp_packet icmp_echo;
struct sockaddr_in dst;
- char packet[sizeof (ip_pkt) + sizeof (icmp_pkt) + sizeof (udp_pkt)];
size_t off;
int err;
+ struct ip_packet ip_pkt;
+ struct icmp_packet icmp_pkt;
+ char packet[sizeof (ip_pkt) + sizeof (icmp_pkt)];
- /* 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.vers_ihl = 0x45;
ip_pkt.tos = 0;
- ip_pkt.pkt_len = sizeof (packet); /* huh? */
- ip_pkt.id = 1; /* kernel will change anyway!? */
+ ip_pkt.pkt_len = sizeof (packet);
+ ip_pkt.id = 1;
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.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 (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));
+ memcpy (packet, &ip_pkt, sizeof (ip_pkt));
off += sizeof (ip_pkt);
-
- memset(&udp_pkt, 0, sizeof (udp_pkt));
- udp_pkt.source_port = htons (target_port_number); /* this one will be re-written by NAT */
- 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); /* this one should be bounced back to me as 'reply_port_magic' */
- memcpy (&packet[off], &udp_pkt, sizeof (udp_pkt));
- off += sizeof (udp_pkt);
-
+ make_echo (my_ip, &icmp_echo);
+ memcpy (&packet[off], &icmp_echo, sizeof (icmp_echo));
+ off += sizeof (icmp_echo);
+
memset (&dst, 0, sizeof (dst));
dst.sin_family = AF_INET;
- dst.sin_addr = *other;
+ dst.sin_addr = dummy;
err = sendto(rawsock,
- packet,
- off, 0,
+ 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;
- char sbuf [INET_ADDRSTRLEN];
-
- fprintf (stderr,
- "Sending %u ICMPs to `%s' with reply magic %u\n",
- NUM_UDP_PORTS,
- inet_ntop (AF_INET,
- other,
- sbuf,
- sizeof (sbuf)),
- port_magic);
- for (i=0;i<NUM_UDP_PORTS;i++)
- send_icmp (my_ip, other, make_port(), port_magic);
+ 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");
+ }
}
static void
-process_icmp_response (const struct in_addr *my_ip,
- int s)
+process_icmp_response ()
{
char buf[65536];
ssize_t have;
struct in_addr sip;
- uint16_t my_magic;
- uint16_t reply_magic;
- uint16_t local_port;
struct ip_packet ip_pkt;
struct icmp_packet icmp_pkt;
- struct udp_packet udp_pkt;
+ struct udp_packet udp_pkt;
size_t off;
+ int have_port;
+ int have_udp;
+ uint32_t port;
- have = read (s, buf, sizeof (buf));
+ have = read (icmpsock, buf, sizeof (buf));
if (have == -1)
{
fprintf (stderr,
"Error reading raw socket: %s\n",
strerror (errno));
- /* What now? */
return;
}
- if (have != 2 * sizeof (struct ip_packet) + sizeof (struct icmp_packet) +
- sizeof (struct udp_packet))
+ have_port = 0;
+
+ if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + sizeof(uint32_t))
+ {
+ have_port = 1;
+ }
+ else if (have != sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2)
{
+#if VERBOSE
fprintf (stderr,
"Received ICMP message of unexpected size: %u bytes\n",
(unsigned int) have);
+#endif
return;
}
off = 0;
off += sizeof (ip_pkt);
memcpy (&icmp_pkt, &buf[off], sizeof (icmp_pkt));
off += sizeof (icmp_pkt);
+ if ( ((ip_pkt.proto != IPPROTO_ICMP) && (ip_pkt.proto != IPPROTO_UDP)) ||
+ (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
+ (icmp_pkt.code != 0) )
+ {
+ /* maybe we got an actual reply back... */
+ return;
+ }
+ memcpy(&sip,
+ &ip_pkt.src_ip,
+ sizeof (sip));
+
+ memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
off += sizeof (ip_pkt);
- memcpy (&udp_pkt, &buf[off], sizeof (udp_pkt));
- off += sizeof (struct udp_packet);
- if ( (ip_pkt.proto == IPPROTO_ICMP) &&
- (icmp_pkt.type == ICMP_DEST_UNREACH) &&
- (icmp_pkt.code == ICMP_HOST_UNREACH) )
+ have_udp = 0;
+ if (ip_pkt.proto == IPPROTO_UDP)
{
- /* this is what is normal due to our UDP traffic */
- return;
+ have_udp = 1;
}
- if ( (ip_pkt.proto != IPPROTO_ICMP) ||
- (icmp_pkt.type != ICMP_TIME_EXCEEDED) ||
- (icmp_pkt.code != ICMP_NET_UNREACH) )
+
+ if (have_port)
{
- /* Note the expected client response and not the normal network response */
- fprintf (stderr,
- "Received unexpected ICMP message contents (%u, %u, %u), ignoring\n",
- ip_pkt.proto,
- icmp_pkt.type,
- icmp_pkt.code);
- return;
+ memcpy(&port, &buf[sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2], sizeof(uint32_t));
+ port = ntohs(port);
+ fprintf (stdout,
+ "%s:%d\n",
+ inet_ntop (AF_INET,
+ &sip,
+ buf,
+ sizeof (buf)), port);
}
- memcpy(&sip, &ip_pkt.src_ip, sizeof (sip));
- reply_magic = ntohs (udp_pkt.checksum_aka_my_magic);
- my_magic = ntohs (udp_pkt.mlen_aka_reply_port_magic);
- local_port = ntohs (udp_pkt.source_port);
- 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)
+ else if (have_udp)
{
- try_connect (my_ip, &sip, reply_magic);
+ memcpy(&udp_pkt, &buf[off], sizeof(udp_pkt));
+ fprintf (stdout,
+ "%s:%d\n",
+ inet_ntop (AF_INET,
+ &sip,
+ buf,
+ sizeof (buf)), ntohl(udp_pkt.length));
}
else
{
- /* FIXME: should close 'local_port' */
- printf ("%s:%u listen on %u\n",
- inet_ntop (AF_INET,
- &sip,
- buf,
- sizeof(buf)),
- my_magic,
- local_port);
+ fprintf (stdout,
+ "%s\n",
+ inet_ntop (AF_INET,
+ &sip,
+ buf,
+ sizeof (buf)));
}
+ fflush (stdout);
}
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,
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)
+ uid_t uid;
+
+ if (-1 == (icmpsock = make_icmp_socket()))
+ return 1;
+ if (-1 == (rawsock = make_raw_socket()))
+ {
+ close (icmpsock);
+ return 1;
+ }
+ uid = getuid ();
+ if (0 != setresuid (uid, uid, uid))
+ fprintf (stderr,
+ "Failed to setresuid: %s\n",
+ strerror (errno));
+ if (argc != 2)
{
fprintf (stderr,
- "This program must be started with our external IP and the dummy IP address as arguments.\n");
+ "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)) ||
- (1 != inet_pton (AF_INET, argv[2], &dummy)) )
+ if (1 != inet_pton (AF_INET, argv[1], &external))
{
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;
- if (-1 == (rawsock = make_raw_socket()))
- {
- close (icmpsock);
- return 1;
- }
- for (i=0;i<NUM_UDP_PORTS;i++)
- udpsocks[i] = make_udp_socket (&udpports[i]);
- pos = 0;
+ if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
while (1)
{
FD_ZERO (&rs);
FD_SET (icmpsock, &rs);
tv.tv_sec = 0;
- tv.tv_usec = UDP_SEND_FREQUENCY_MS * 1000;
+ tv.tv_usec = ICMP_SEND_FREQUENCY_MS * 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);
- continue;
- }
- fprintf (stderr,
- "Sending UDP message to %s:%u\n",
- argv[2],
- NAT_TRAV_PORT);
-
- 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;
+ process_icmp_response ();
+ send_icmp_echo (&external);
}
return 0;
}
projects / oweals / gnunet.git / blobdiff