[GNUnet-SVN] r11636 - gnunet/src/transport

[gnunet]

Author: nevans
Date: 2010-06-08 15:27:11 +0200 (Tue, 08 Jun 2010)
New Revision: 11636

Modified:
   gnunet/src/transport/Makefile.am
   gnunet/src/transport/gnunet-nat-client-udp.c
   gnunet/src/transport/gnunet-nat-client.c
   gnunet/src/transport/gnunet-nat-server-udp.c
   gnunet/src/transport/gnunet-nat-server.c
Log:
add UDP inside ICMP for NAT punch

Modified: gnunet/src/transport/Makefile.am
===================================================================
--- gnunet/src/transport/Makefile.am    2010-06-08 11:41:15 UTC (rev 11635)
+++ gnunet/src/transport/Makefile.am    2010-06-08 13:27:11 UTC (rev 11636)
@@ -53,7 +53,6 @@
 gnunet_nat_client_SOURCES = \
  gnunet-nat-client.c         
 
-
 gnunet_transport_SOURCES = \
  gnunet-transport.c         
 gnunet_transport_LDADD = \

Modified: gnunet/src/transport/gnunet-nat-client-udp.c
===================================================================
--- gnunet/src/transport/gnunet-nat-client-udp.c        2010-06-08 11:41:15 UTC 
(rev 11635)
+++ gnunet/src/transport/gnunet-nat-client-udp.c        2010-06-08 13:27:11 UTC 
(rev 11636)
@@ -20,9 +20,27 @@
 
 /**
  * @file src/transport/gnunet-nat-client-udp.c
- * @brief Test for NAT traversal using ICMP method.
+ * @brief Tool to help bypass NATs using ICMP method; must run as root (SUID 
will do)
+ *        This code will work under GNU/Linux only.  
  * @author Christian Grothoff
+ *
+ * This program will send ONE ICMP message using RAW sockets
+ * to the IP address specified as the second argument.  The ICMP
+ * message will have as it's payload a UDP packet.  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
  */
+#define _GNU_SOURCE
 #include <sys/types.h> 
 #include <sys/socket.h>
 #include <arpa/inet.h>
@@ -33,143 +51,312 @@
 #include <errno.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include <netinet/ip.h>
+#include <netinet/ip_icmp.h>
 #include <netinet/in.h> 
-#include <time.h>
 
 /**
- * How often do we send our UDP messages to keep ports open (and to
- * try to connect, of course).  Use small value since we are the
- * initiator and should hence be rather aggressive.
+ * Must match IP given in the server.
  */
-#define UDP_SEND_FREQUENCY_MS 5
+#define DUMMY_IP "1.2.3.4"
+#define HAVE_PORT 1
 
 /**
  * Port we always try to use.
  */
-#define NAT_TRAV_PORT 22223
+#define NAT_TRAV_PORT 22225
 
-/**
- * Number of UDP ports to keep open at the same time (typically >= 256).
- * Should be less than FD_SETSIZE.
- */
-#define NUM_UDP_PORTS 1000
+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;
+};
 
-/**
- * How often do we retry to open and bind a UDP socket before giving up?
- */
-#define MAX_BIND_TRIES 10
+struct icmp_packet 
+{
+  uint8_t type;
+  uint8_t code;
+  uint16_t checksum;
+  uint32_t reserved;
 
-/**
- * How often do we try at most?  We expect to need (for the worst kind
- * of NAT) on average 64512 / 512 = 126 attempts to have the right
- * destination port and we then need to also (in the worst case) have
- * the right source port (so 126 * 64512 = 8128512 packets on
- * average!).  That's obviously a bit much, so we give up earlier.  The
- * given value corresponds to about 1 minute of runtime (for a send
- * frequency of one packet per ms).
- *
- * NOW: if the *server* would listen for Linux-generated ICMP 
- * "Destination unreachables" we *might* increase our chances since
- * maybe the firewall has some older/other UDP rules (this was
- * the case during testing for me), but obviously that would mean
- * more SUID'ed code. Yuck.
- */
-#define MAX_TRIES 62500
+};
 
-#define LOW_PORT 32768
+struct icmp_echo_packet
+{
+  uint8_t type;
+  uint8_t code;
+  uint16_t checksum;
+  uint32_t reserved;
+  uint32_t data;
+};
 
-/**
- * create a random port number that is not totally
- * unlikely to be chosen by the nat box.
- */
+struct udp_packet
+{
+  uint16_t src_port;
+
+  uint16_t dst_port;
+
+  uint32_t length;
+};
+
+ 
+static int rawsock;
+
+static struct in_addr dummy;
+ 
+static struct in_addr target;
+
+#if HAVE_PORT
+  static uint32_t port;
+#endif
+
 static uint16_t 
-make_port ()
+calc_checksum(const uint16_t *data, 
+             unsigned int bytes)
 {
-  return LOW_PORT + ( (unsigned int)rand ()) % (64 * 1024 - LOW_PORT);
+  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;
 }
 
-
 /**
- * create a fresh udp socket bound to a random local port,
- * or, if the argument is zero, to the NAT_TRAV_PORT.
+ * Send an ICMP message to the target.
  *
- * @param i counter
- * @return -1 on error
+ * @param my_ip source address
+ * @param other target address
  */
-static int
-make_udp_socket (int i)
+static void
+send_icmp (const struct in_addr *my_ip,
+          const struct in_addr *other)
 {
-  int ret;
-  int tries;
-  struct sockaddr_in src;
+  struct ip_packet ip_pkt;
+  struct icmp_packet icmp_pkt;
+  struct udp_packet udp_pkt;
 
-  for (tries=0;tries<MAX_BIND_TRIES;tries++)
+  struct sockaddr_in dst;
+  char packet[sizeof(ip_pkt) * 2 + sizeof(icmp_pkt) * 2 + sizeof(char)];
+
+#if ORIGINAL
+#if HAVE_PORT
+  char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet) + 
sizeof(struct icmp_echo_packet)];
+#else
+  char packet[sizeof (struct ip_packet)*2 + sizeof (struct icmp_packet)*2];
+#endif
+#endif
+  size_t off;
+  int err;
+
+  /* ip header: send to (known) ip address */
+#if ORIGINAL
+  off = 0;
+  memset(&ip_pkt, 0, sizeof(ip_pkt));
+  ip_pkt.vers_ihl = 0x45;
+  ip_pkt.tos = 0;
+  ip_pkt.pkt_len = sizeof (packet); /* huh? */
+  ip_pkt.id = 1; 
+  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_packet)));
+  memcpy (packet, &ip_pkt, sizeof (struct ip_packet));
+  off += sizeof (ip_pkt);
+  /* icmp reply: time exceeded */
+  icmp_pkt = (struct icmp_packet*) &packet[off];
+  memset(icmp_pkt, 0, sizeof(struct icmp_packet));
+  icmp_pkt->type = ICMP_TIME_EXCEEDED;
+  icmp_pkt->code = 0; 
+  icmp_pkt->reserved = 0;
+  icmp_pkt->checksum = 0;
+
+  off += sizeof (struct icmp_packet);
+#endif
+
+  off = 0;
+  memset(&ip_pkt, 0, sizeof(ip_pkt));
+  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 (ip_pkt)));
+  memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
+  off += sizeof(ip_pkt);
+
+  /* ip header of the presumably 'lost' udp packet */
+  ip_pkt.vers_ihl = 0x45;
+  ip_pkt.tos = 0;
+#if HAVE_PORT
+  ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct 
icmp_echo_packet));
+#else
+  ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct icmp_packet));
+#endif
+
+  icmp_pkt.type = 11; // TTL exceeded
+  icmp_pkt.code = 0;
+  icmp_pkt.checksum = 0;
+  icmp_pkt.reserved = 0;
+  memcpy(&packet[off], &icmp_pkt, sizeof(icmp_pkt));
+  off += sizeof(icmp_pkt);
+
+
+  // build inner IP header
+  memset(&ip_pkt, 0, sizeof(ip_pkt));
+  ip_pkt.vers_ihl = 0x45;
+  ip_pkt.tos = 0;
+  ip_pkt.pkt_len = htons(sizeof (ip_pkt) + sizeof(udp_pkt));
+  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 (ip_pkt)));
+  memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
+  off += sizeof(ip_pkt);
+
+  // build UDP header
+  udp_pkt.src_port = htons(NAT_TRAV_PORT); /* FIXME: does this port matter? */
+  udp_pkt.dst_port = htons(NAT_TRAV_PORT);
+  uint32_t newval = inet_addr("1.2.3.4");
+  memcpy(&udp_pkt.length, &newval, sizeof(uint32_t));
+  memcpy(&packet[off], &udp_pkt, sizeof(udp_pkt));
+  off += sizeof(udp_pkt);
+
+
+
+  // set ICMP checksum
+  icmp_pkt.checksum = htons(calc_checksum((uint16_t*)&packet[sizeof(ip_pkt)],
+                            sizeof (icmp_pkt) + sizeof(ip_pkt) + 
sizeof(udp_pkt)));
+  memcpy (&packet[sizeof(ip_pkt)], &icmp_pkt, sizeof (icmp_pkt));
+
+  /* End of new code */
+#if ORIGINAL
+  ip_pkt.id = 1; 
+  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_packet)));  
+  memcpy (&packet[off], &ip_pkt, sizeof (struct ip_packet));
+  off += sizeof (struct ip_packet);
+
+
+#if HAVE_PORT
+  icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt,
+                                             sizeof (struct icmp_packet) + 
sizeof(struct ip_packet) + sizeof(struct icmp_echo_packet)));
+
+#else
+  icmp_pkt->checksum = htons(calc_checksum((uint16_t*)icmp_pkt, 
+                                             sizeof (struct icmp_packet)*2 + 
sizeof(struct ip_packet)));
+
+#endif
+
+
+#endif
+
+  memset (&dst, 0, sizeof (dst));
+  dst.sin_family = AF_INET;
+  dst.sin_addr = *other;
+  err = sendto(rawsock, 
+              packet, 
+              off, 0, 
+              (struct sockaddr*)&dst, 
+              sizeof(dst)); /* or sizeof 'struct sockaddr'? */
+  if (err < 0) 
     {
-      ret = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);
-      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;
-      if (i == 0)
-       src.sin_port = htons (NAT_TRAV_PORT);
-      else
-       src.sin_port = htons (make_port ());
-      if (0 != bind (ret, (struct sockaddr*) &src, sizeof (src)))
-        {
-          close (ret);
-          continue;
-        }
-      return ret;
+      fprintf(stderr,
+             "sendto failed: %s\n", strerror(errno));
     }
-  fprintf (stderr,
-           "Error binding udp socket: %s\n",
-           strerror (errno));
-  return -1;
+  else if (err != off) 
+    {
+      fprintf(stderr,
+             "Error: partial send of ICMP message\n");
+    }
 }
 
 
+static int
+make_raw_socket ()
+{
+  const int one = 1;
+  int ret;
 
+  ret = socket (AF_INET, SOCK_RAW, IPPROTO_RAW);
+  if (-1 == ret)
+    {
+      fprintf (stderr,
+              "Error opening RAW socket: %s\n",
+              strerror (errno));
+      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)
 {
-  int udpsocks[NUM_UDP_PORTS];
-  char command[512];
   struct in_addr external;
-  struct in_addr target;
-  int ret;
-  unsigned int pos;
-  int i;
-  int max;
-  struct sockaddr_in dst;
-  struct sockaddr_in src;
-  int first_round = 1;
-  char dummybuf[65536];
-  unsigned int tries;
-  struct timeval tv;
-  socklen_t slen;
-  fd_set rs;
- 
+  uid_t uid;
+
+  if (-1 == (rawsock = make_raw_socket()))
+    return 1;     
+  uid = getuid ();
+  if (0 != setresuid (uid, uid, uid))
+    fprintf (stderr,
+            "Failed to setresuid: %s\n",
+            strerror (errno));
+#if HAVE_PORT
+  if (argc != 4)
+    {
+      fprintf (stderr,
+              "This program must be started with our IP, the targets external 
IP, and our port as arguments.\n");
+      return 1;
+    }
+  port = atoi(argv[3]);
+#else
   if (argc != 3)
     {
       fprintf (stderr,
-              "This program must be started with our IP and the targets 
external IP as arguments.\n");
+               "This program must be started with our IP and the targets 
external IP as arguments.\n");
       return 1;
     }
+#endif
   if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
        (1 != inet_pton (AF_INET, argv[2], &target)) )
     {
@@ -178,121 +365,11 @@
               strerror (errno));
       return 1;
     }
-  snprintf (command, 
-           sizeof (command),
-           "gnunet-nat-client %s %s",
-           argv[1],
-           argv[2]);
-  if (0 != (ret = system (command)))
-    {
-      if (ret == -1)
-       fprintf (stderr,
-                "Error running `%s': %s\n",
-                command,
-                strerror (errno));
-      return 1;
-    }
-  fprintf (stderr,
-          "Trying to connect to `%s'\n",
-          argv[2]);
-  srand (time(NULL));
-  for (i=0;i<NUM_UDP_PORTS;i++)
-    udpsocks[i] = make_udp_socket (i); 
-  memset (&dst, 0, sizeof (dst));
-  dst.sin_family = AF_INET;
-  dst.sin_addr = target;
-  pos = 0;
-  tries = 0;
-  while (MAX_TRIES > tries++)
-    {
-      FD_ZERO (&rs);
-      for (i=0;i<NUM_UDP_PORTS;i++)
-       {
-         if (udpsocks[i] != -1)
-           FD_SET (udpsocks[i], &rs);
-         if (udpsocks[i] > max)
-           max = udpsocks[i];
-       }
-      tv.tv_sec = 0;
-      tv.tv_usec = UDP_SEND_FREQUENCY_MS * 1000;
-      select (max + 1, &rs, NULL, NULL, &tv);
-      for (i=0;i<NUM_UDP_PORTS;i++)
-       {
-         if (udpsocks[i] == -1)
-           continue;
-         if (! FD_ISSET (udpsocks[i], &rs))
-           continue;
-         slen = sizeof (src);
-         recvfrom (udpsocks[i], 
-                   dummybuf, sizeof (dummybuf), 0,
-                   (struct sockaddr*) &src,
-                   &slen);
-         if (slen != sizeof (src))
-           {
-             fprintf (stderr,
-                      "Unexpected size of address.\n");
-             continue;
-           }
-         if (0 != memcmp (&src.sin_addr,
-                          &target,
-                          sizeof (external)))
-           {
-             fprintf (stderr,
-                      "Unexpected sender IP\n");
-             continue;
-           }
-         /* discovered port! */
-         fprintf (stdout,
-                  "%s:%u\n",
-                  argv[2],
-                  ntohs (src.sin_port));
-         dst.sin_port = src.sin_port;
-         if (-1 == sendto (udpsocks[i],
-                           NULL, 0, 0,
-                           (struct sockaddr*) &dst, sizeof (dst)))
-           {
-             fprintf (stderr,
-                      "sendto failed: %s\n",
-                      strerror (errno));             
-             return 2; /* oops */
-           }     
-         /* success! */
-         fprintf (stderr,
-                  "Succeeded after %u packets.\n",
-                  tries);
-         return 0;
-        }
-      if (udpsocks[pos] == -1)
-       {
-          udpsocks[pos] = make_udp_socket (pos);
-         continue;
-       }
-      if ( (0 == ((unsigned int)rand() % NUM_UDP_PORTS)) ||
-          (1 == first_round) )
-       dst.sin_port = htons (NAT_TRAV_PORT);
-      else
-       dst.sin_port = htons (make_port ());
-      fprintf (stderr,
-              "Sending UDP packet to `%s:%u'\n",
-              argv[2],
-              ntohs (dst.sin_port));
-      first_round = 0;
-      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 (pos);
-        }
-      pos = (pos+1) % NUM_UDP_PORTS;
-    }
-  fprintf (stderr,
-          "Giving up after %u tries.\n",
-          tries);
-  return 3;
+  if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
+  send_icmp (&external,
+            &target);
+  close (rawsock);
+  return 0;
 }
 
-/* end of client-test.c */
+/* end of gnunet-nat-client-udp.c */

Modified: gnunet/src/transport/gnunet-nat-client.c
===================================================================
--- gnunet/src/transport/gnunet-nat-client.c    2010-06-08 11:41:15 UTC (rev 
11635)
+++ gnunet/src/transport/gnunet-nat-client.c    2010-06-08 13:27:11 UTC (rev 
11636)
@@ -60,6 +60,8 @@
 #define DUMMY_IP "1.2.3.4"
 #define HAVE_PORT 1
 
+#define NAT_TRAV_PORT 22225
+
 struct ip_packet 
 {
   uint8_t vers_ihl;
@@ -92,7 +94,15 @@
   uint32_t data;
 };
 
- 
+struct udp_packet
+{
+  uint16_t src_port;
+
+  uint16_t dst_port;
+
+  uint32_t length;
+};
+
 static int rawsock;
 
 static struct in_addr dummy;
@@ -150,7 +160,110 @@
 }
 #endif
 
+/**
+ * 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)
+{
+  struct ip_packet ip_pkt;
+  struct icmp_packet icmp_pkt;
+  struct udp_packet udp_pkt;
 
+  struct sockaddr_in dst;
+  char packet[sizeof(ip_pkt) * 2 + sizeof(icmp_pkt) * 2 + sizeof(uint32_t)];
+
+  size_t off;
+  int err;
+
+  /* ip header: send to (known) ip address */
+  off = 0;
+  memset(&ip_pkt, 0, sizeof(ip_pkt));
+  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 (ip_pkt)));
+  memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
+  off += sizeof(ip_pkt);
+
+  /* ip header of the presumably 'lost' udp packet */
+  ip_pkt.vers_ihl = 0x45;
+  ip_pkt.tos = 0;
+  ip_pkt.pkt_len = (sizeof (struct ip_packet) + sizeof (struct 
icmp_echo_packet));
+
+  icmp_pkt.type = 11; /* TTL exceeded */
+  icmp_pkt.code = 0;
+  icmp_pkt.checksum = 0;
+  icmp_pkt.reserved = 0;
+  memcpy(&packet[off], &icmp_pkt, sizeof(icmp_pkt));
+  off += sizeof(icmp_pkt);
+
+  /* build inner IP header */
+  memset(&ip_pkt, 0, sizeof(ip_pkt));
+  ip_pkt.vers_ihl = 0x45;
+  ip_pkt.tos = 0;
+  ip_pkt.pkt_len = htons(sizeof (ip_pkt) + sizeof(udp_pkt));
+  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 (ip_pkt)));
+  memcpy(&packet[off], &ip_pkt, sizeof(ip_pkt));
+  off += sizeof(ip_pkt);
+
+  /* build UDP header */
+  udp_pkt.src_port = htons(NAT_TRAV_PORT); /* FIXME: does this port matter? */
+  udp_pkt.dst_port = htons(NAT_TRAV_PORT);
+
+  memset(&udp_pkt.length, 0, sizeof(uint32_t));
+#if HAVE_PORT
+  udp_pkt.length = htonl(port);
+#endif
+  memcpy(&packet[off], &udp_pkt, sizeof(udp_pkt));
+  off += sizeof(udp_pkt);
+
+  /* set ICMP checksum */
+  icmp_pkt.checksum = htons(calc_checksum((uint16_t*)&packet[sizeof(ip_pkt)],
+                            sizeof (icmp_pkt) + sizeof(ip_pkt) + 
sizeof(udp_pkt)));
+  memcpy (&packet[sizeof(ip_pkt)], &icmp_pkt, sizeof (icmp_pkt));
+
+
+  memset (&dst, 0, sizeof (dst));
+  dst.sin_family = AF_INET;
+  dst.sin_addr = *other;
+  err = sendto(rawsock,
+               packet,
+               off, 0,
+               (struct sockaddr*)&dst,
+               sizeof(dst));
+
+  if (err < 0)
+    {
+      fprintf(stderr,
+              "sendto failed: %s\n", strerror(errno));
+    }
+  else if (err != off)
+    {
+      fprintf(stderr,
+              "Error: partial send of ICMP message\n");
+    }
+}
+
+
 /**
  * Send an ICMP message to the target.
  *
@@ -334,6 +447,8 @@
   if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
   send_icmp (&external,
             &target);
+  send_icmp_udp (&external,
+             &target);
   close (rawsock);
   return 0;
 }

Modified: gnunet/src/transport/gnunet-nat-server-udp.c
===================================================================
--- gnunet/src/transport/gnunet-nat-server-udp.c        2010-06-08 11:41:15 UTC 
(rev 11635)
+++ gnunet/src/transport/gnunet-nat-server-udp.c        2010-06-08 13:27:11 UTC 
(rev 11636)
@@ -20,7 +20,9 @@
 
 /**
  * @file src/transport/gnunet-nat-server-udp.c
- * @brief Test for NAT traversal using ICMP method.
+ * @brief  This program will send ONE UDP message every 500 ms
+ *         to a DUMMY IP address and also listens for ICMP replies.
+ *
  * @author Christian Grothoff
  */
 #include <sys/types.h> 
@@ -37,16 +39,13 @@
 #include <time.h>
 
 
+#define DUMMY_IP "1.2.3.4"
 
 /**
- * How often do we send our UDP messages to keep ports open (and to
- * try to connect, of course).  Assuming the NAT closes UDP ports
- * after 60s, we need at least about 100ms here for 512 ports;
- * however, we should open the ports quickly (and we don't yet
- * differentiate between the first round and later rounds), so we pick
- * a much lower value here for now.
+ * How often do we send our UDP message to keep ports open (and to
+ * try to connect, of course).
  */
-#define UDP_SEND_FREQUENCY_MS 50
+#define UDP_SEND_FREQUENCY_MS 500
 
 /**
  * Port we always try to use.
@@ -54,50 +53,83 @@
 #define NAT_TRAV_PORT 22225
 
 /**
- * Number of UDP ports to keep open at the same time (typically >= 256).
- * Should be less than FD_SETSIZE.
+ * Number of UDP ports to send to
  */
-#define NUM_UDP_PORTS 1000
+#define NUM_UDP_PORTS 1
 
 /**
  * How often do we retry to open and bind a UDP socket before giving up?
  */
 #define MAX_BIND_TRIES 10
 
-/**
- * How long do we try at most?  We expect the other side to give
- * up after about one minute for now.
- */
-#define MAX_DURATION 60000
-
 #define LOW_PORT 32768
 
-/**
- * create a random port number that is not totally
- * unlikely to be chosen by the nat box.
- */
-static uint16_t 
-make_port ()
+static struct in_addr dummy;
+
+static int icmpsock;
+
+struct icmp_packet
 {
-  return LOW_PORT + ( (unsigned int)rand ()) % (64 * 1024 - LOW_PORT - 2);
+  uint8_t type;
+  uint8_t code;
+  uint16_t checksum;
+  uint32_t reserved;
+
+};
+
+struct udp_packet
+{
+  uint16_t src_port;
+
+  uint16_t dst_port;
+
+  uint32_t length;
+};
+
+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;
+};
+
+#if DUMMY
+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;
 }
+#endif
 
-
 /**
- * create a fresh udp socket bound to a random local port,
- * or, if the argument is zero, to the NAT_TRAV_PORT.
+ * create a fresh udp socket bound to the NAT_TRAV_PORT.
  *
- * @param i counter
  * @return -1 on error
  */
 static int
-make_udp_socket (int i)
+make_udp_socket ()
 {
   int ret;
   int tries;
   struct sockaddr_in src;
 
-  for (tries=0;tries<MAX_BIND_TRIES;tries++)
+  for (tries=0; tries<MAX_BIND_TRIES; tries++)
     {
       ret = socket (AF_INET, SOCK_DGRAM, IPPROTO_UDP);
       if (-1 == ret)
@@ -118,10 +150,8 @@
         }
       memset (&src, 0, sizeof (src));
       src.sin_family = AF_INET;
-      if (i == 0)
-       src.sin_port = htons (NAT_TRAV_PORT);
-      else
-       src.sin_port = htons (make_port ());
+      src.sin_port = htons (NAT_TRAV_PORT);
+
       if (0 != bind (ret, (struct sockaddr*) &src, sizeof (src)))
         {
           close (ret);
@@ -135,113 +165,224 @@
   return -1;
 }
 
+#define LOW_PORT 32768
 
+/**
+ * create a random port number that is not totally
+ * unlikely to be chosen by the nat box.
+ */
+static uint16_t
+make_port ()
+{
+  return LOW_PORT + ( (unsigned int)rand ()) % (64 * 1024 - LOW_PORT - 2);
+}
+
+static int
+make_icmp_socket ()
+{
+  int ret;
+
+  ret = socket (AF_INET, SOCK_RAW, IPPROTO_ICMP);
+  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;
+    }
+  return ret;
+}
+
+#if DUMMY
+/**
+ * Send a UDP message to the dummy IP.
+ *
+ * @param my_ip source address (our ip address)
+ */
+static void
+send_dummy_udp (const struct in_addr *my_ip)
+{
+  struct sockaddr_in dst;
+  size_t off;
+  int err;
+  struct ip_packet ip_pkt;
+  struct ip_packet udp_pkt;
+  char packet[sizeof (ip_pkt) + sizeof (udp_pkt)];
+
+
+  // build inner IP header
+  memset(&ip_pkt, 0, sizeof(ip_pkt));
+  ip_pkt.vers_ihl = 0x45;
+  ip_pkt.tos = 0;
+  ip_pkt.pkt_len = htons(sizeof (ip_pkt) + sizeof(udp_pkt));
+  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 = my_ip->s_addr;
+  ip_pkt.dst_ip = inet_addr(dummy.s_addr);
+  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);
+
+  // build UDP header
+  udp_pkt.src_port = NAT_TRAV_PORT;
+  udp_pkt.dst_port = htons(NAT_TRAV_PORT);
+
+  uint32_t newval = inet_addr("1.2.3.4");
+  memcpy(&udp_pkt.length, &newval, sizeof(uint32_t));
+
+  off += sizeof(udp_pkt);
+
+  err = sendto(rawsock,
+               ip_pkt, 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 UDP message\n");
+    }
+}
+#endif
+
+static void
+process_icmp_response()
+{
+  char buf[65536];
+  ssize_t have;
+  struct in_addr sip;
+  struct ip_packet ip_pkt;
+  struct icmp_packet icmp_pkt;
+  size_t off;
+  int have_port;
+  //uint32_t port;
+
+  have = read (icmpsock, buf, sizeof (buf));
+  if (have == -1)
+    {
+      fprintf (stderr,
+               "Error reading raw socket: %s\n",
+               strerror (errno));
+      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);
+  if ( (ip_pkt.proto != IPPROTO_ICMP) ||
+       (icmp_pkt.type != 11) ||
+       (icmp_pkt.code != 0) )
+    {
+      /* maybe we got an actual reply back... */
+      return;
+    }
+
+  memcpy(&sip,
+         &ip_pkt.src_ip,
+         sizeof (sip));
+
+  fprintf (stderr,
+           "Received ICMP message of size: %u bytes from %s\n",
+           (unsigned int) have,
+           inet_ntop (AF_INET,
+                      &sip,
+                      buf,
+                      sizeof (buf)));
+
+  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;
+    }
+}
+
 int
 main (int argc, char *const *argv)
 {
   int udpsocks[NUM_UDP_PORTS];
-  char command[512];
   struct in_addr external;
-  struct in_addr target;
-  int ret;
   unsigned int pos;
   int i;
-  int max;
   struct sockaddr_in dst;
-  struct sockaddr_in src;
   int first_round = 1;
-  char dummybuf[65536];
   unsigned int tries;
   struct timeval tv;
-  socklen_t slen;
   fd_set rs;
   time_t stime;
  
-  if (argc != 3)
+  if (argc != 2)
     {
       fprintf (stderr,
-              "This program must be started with our IP and the targets 
external IP as arguments.\n");
+              "This program must be started with our (internal) IP as the 
single argument.\n");
       return 1;
     }
-  if ( (1 != inet_pton (AF_INET, argv[1], &external)) ||
-       (1 != inet_pton (AF_INET, argv[2], &target)) )
+  if ( (1 != inet_pton (AF_INET, argv[1], &external)))
     {
       fprintf (stderr,
               "Error parsing IPv4 address: %s\n",
               strerror (errno));
       return 1;
     }
+
+  if (1 != inet_pton (AF_INET, DUMMY_IP, &dummy)) abort ();
+
   fprintf (stderr,
           "Trying to connect to %s\n",
-          argv[2]);
+          DUMMY_IP);
   srand (stime = time(NULL));
   for (i=0;i<NUM_UDP_PORTS;i++)
     udpsocks[i] = make_udp_socket (i); 
+
+  if (-1 == (icmpsock = make_icmp_socket()))
+    return 1;
+
   memset (&dst, 0, sizeof (dst));
   dst.sin_family = AF_INET;
-  dst.sin_addr = target;
+  dst.sin_addr = dummy;
   pos = 0;
   tries = 0;
-  while (stime + MAX_DURATION >= time (NULL))
+
+  while (1)
     {
       tries++;
+
       FD_ZERO (&rs);
-      for (i=0;i<NUM_UDP_PORTS;i++)
-       {
-         if (udpsocks[i] != -1)
-           FD_SET (udpsocks[i], &rs);
-         if (udpsocks[i] > max)
-           max = udpsocks[i];
-       }
+      FD_SET (icmpsock, &rs);
       tv.tv_sec = 0;
       tv.tv_usec = UDP_SEND_FREQUENCY_MS * 1000;
-      select (max + 1, &rs, NULL, NULL, &tv);
-      for (i=0;i<NUM_UDP_PORTS;i++)
-       {
-         if (udpsocks[i] == -1)
-           continue;
-         if (! FD_ISSET (udpsocks[i], &rs))
-           continue;
-         slen = sizeof (src);
-         recvfrom (udpsocks[i], 
-                   dummybuf, sizeof (dummybuf), 0,
-                   (struct sockaddr*) &src,
-                   &slen);
-         if (slen != sizeof (src))
-           {
-             fprintf (stderr,
-                      "Unexpected size of address.\n");
-             continue;
-           }
-         if (0 != memcmp (&src.sin_addr,
-                          &target,
-                          sizeof (external)))
-           {
-             fprintf (stderr,
-                      "Unexpected sender IP\n");
-             continue;
-           }
-         /* discovered port! */
-         fprintf (stdout,
-                  "%s:%u\n",
-                  argv[2],
-                  ntohs (src.sin_port));
-         dst.sin_port = src.sin_port;
-         if (-1 == sendto (udpsocks[i],
-                           NULL, 0, 0,
-                           (struct sockaddr*) &dst, sizeof (dst)))
-           {
-             fprintf (stderr,
-                      "sendto failed: %s\n",
-                      strerror (errno));             
-             return 2; /* oops */
-           }     
-         /* success! */
-         fprintf (stderr,
-                  "Succeeded after %u packets.\n",
-                  tries);
-         return 0;
-        }
+      select (icmpsock + 1, &rs, NULL, NULL, &tv);
+      if (FD_ISSET (icmpsock, &rs))
+        process_icmp_response ();
+
       if (udpsocks[pos] == -1)
        {
           udpsocks[pos] = make_udp_socket (pos);
@@ -252,10 +393,13 @@
        dst.sin_port = htons (NAT_TRAV_PORT);
       else
        dst.sin_port = htons (make_port ());
+#if VERBOSE
       fprintf (stderr,
               "Sending UDP packet to `%s:%u'\n",
-              argv[2],
+              DUMMY_IP,
               ntohs (dst.sin_port));
+
+#endif
       first_round = 0;
       if (-1 == sendto (udpsocks[pos],
                         NULL, 0, 0,
@@ -275,4 +419,4 @@
   return 3;
 }
 
-/* end of server-test.c */
+/* end of gnunet-nat-server-udp.c */

Modified: gnunet/src/transport/gnunet-nat-server.c
===================================================================
--- gnunet/src/transport/gnunet-nat-server.c    2010-06-08 11:41:15 UTC (rev 
11635)
+++ gnunet/src/transport/gnunet-nat-server.c    2010-06-08 13:27:11 UTC (rev 
11636)
@@ -91,7 +91,15 @@
   uint32_t reserved;
 };
 
+struct udp_packet
+{
+  uint16_t src_port;
 
+  uint16_t dst_port;
+
+  uint32_t length;
+};
+
 static int icmpsock;
 
 static int rawsock;
@@ -192,8 +200,10 @@
   struct in_addr sip;
   struct ip_packet ip_pkt;
   struct icmp_packet icmp_pkt;
+  struct udp_packet udp_pkt;
   size_t off;
   int have_port;
+  int have_udp;
   uint32_t port;
   
   have = read (icmpsock, buf, sizeof (buf));
@@ -205,6 +215,7 @@
       return; 
     }
   have_port = 0;
+
   if (have == sizeof (struct ip_packet) *2 + sizeof (struct icmp_packet) * 2 + 
sizeof(uint32_t))
     {
       have_port = 1;
@@ -233,6 +244,15 @@
   memcpy(&sip, 
         &ip_pkt.src_ip, 
         sizeof (sip));
+
+  memcpy (&ip_pkt, &buf[off], sizeof (ip_pkt));
+  off += sizeof (ip_pkt);
+
+  if (ip_pkt.proto == IPPROTO_UDP)
+    {
+      have_udp = 1;
+    }
+
   if (have_port)
     {
       memcpy(&port, &buf[sizeof (struct ip_packet) *2 + sizeof (struct 
icmp_packet) * 2], sizeof(uint32_t));
@@ -244,6 +264,16 @@
                          buf,
                          sizeof (buf)), port);
     }
+  else if (have_udp)
+    {
+      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
     {
       fprintf (stdout,