-document ICMP MESH messages better, discard ICMP payload on exit->mesh->vpn path for certain ICMP types

git-svn-id: https://gnunet.org/svn/gnunet@19301 140774ce-b5e7-0310-ab8b-a85725594a96

2 files changed, 27 insertions, 12 deletions

diff --git a/src/exit/exit.h b/src/exit/exit.h
index 92918b92a8..f7366df202 100644
--- a/src/exit/exit.h
+++ b/src/exit/exit.h
@@ -218,7 +218,10 @@ struct GNUNET_EXIT_IcmpServiceMessage
   struct GNUNET_MessageHeader header;
 
   /**
-   * Address family, AF_INET or AF_INET6, in network byte order.
+   * Address family, AF_INET or AF_INET6, in network byte order.  This
+   * AF value determines if the 'icmp_header' is ICMPv4 or ICMPv6.
+   * The receiver (exit) may still have to translate (PT) to the services'
+   * ICMP version (if possible).
    */
   int32_t af;
 
@@ -232,7 +235,10 @@ struct GNUNET_EXIT_IcmpServiceMessage
    */
   struct GNUNET_TUN_IcmpHeader icmp_header;
 
-  /* followed by ICMP payload */
+  /* followed by ICMP payload; however, for certain ICMP message
+     types where the payload is the original IP packet, the payload
+     is omitted as it is useless for the receiver (who will need
+     to create some fake payload manually)  */
 };
 
 
@@ -249,18 +255,25 @@ struct GNUNET_EXIT_IcmpInternetMessage
 
   /**
    * Address family, AF_INET or AF_INET6, in network byte order.
+   * Determines both the ICMP version used in the 'icmp_header' and
+   * the IP address format that is used for the target IP.  If
+   * PT is necessary, the sender has already done it.
    */
   int32_t af;
 
   /**
-   * ICMP header to use.
+   * ICMP header to use.  Must match the target 'af' given
+   * above.
    */
   struct GNUNET_TUN_IcmpHeader icmp_header;
 
   /* followed by IP address of the destination; either
      'struct in_addr' or 'struct in6_addr', depending on af */
 
-  /* followed by ICMP payload */
+  /* followed by ICMP payload; however, for certain ICMP message
+     types where the payload is the original IP packet, the payload
+     is omitted as it is useless for the receiver (who will need
+     to create some fake payload manually)   */
 };
 
 
@@ -277,15 +290,19 @@ struct GNUNET_EXIT_IcmpToVPNMessage
 
   /**
    * Address family, AF_INET or AF_INET6, in network byte order.
+   * Useful to determine if this is an ICMPv4 or ICMPv6 header.
    */
   int32_t af;
 
   /**
-   * ICMP header to use.
+   * ICMP header to use.  ICMPv4 or ICMPv6, depending on 'af'.
    */
   struct GNUNET_TUN_IcmpHeader icmp_header;
 
-  /* followed by ICMP payload */
+  /* followed by ICMP payload; however, for certain ICMP message
+     types where the payload is the original IP packet, the payload
+     is omitted as it is useless for the receiver (who will need
+     to create some fake payload manually) */
 };
 
 
diff --git a/src/exit/gnunet-daemon-exit.c b/src/exit/gnunet-daemon-exit.c
index dec263b53c..4179e88a7b 100644
--- a/src/exit/gnunet-daemon-exit.c
+++ b/src/exit/gnunet-daemon-exit.c
@@ -644,6 +644,8 @@ icmp_from_helper (const struct GNUNET_TUN_IcmpHeader *icmp,
 	udp = (const struct GNUNET_TUN_UdpHeader *) &ipv4[1];
 	spt = ntohs (udp->spt);
 	dpt = ntohs (udp->dpt);
+	/* throw away ICMP payload, won't be useful for the other side anyway */
+	pktlen = sizeof (struct GNUNET_TUN_IcmpHeader);
 	break;
       default:
 	GNUNET_STATISTICS_update (stats,
@@ -674,6 +676,8 @@ icmp_from_helper (const struct GNUNET_TUN_IcmpHeader *icmp,
 	udp = (const struct GNUNET_TUN_UdpHeader *) &ipv6[1];
 	spt = ntohs (udp->spt);
 	dpt = ntohs (udp->dpt);
+	/* throw away ICMP payload, won't be useful for the other side anyway */
+	pktlen = sizeof (struct GNUNET_TUN_IcmpHeader);
 	break;
       case GNUNET_TUN_ICMPTYPE6_ECHO_REQUEST:
       case GNUNET_TUN_ICMPTYPE6_ECHO_REPLY:
@@ -735,12 +739,6 @@ icmp_from_helper (const struct GNUNET_TUN_IcmpHeader *icmp,
   memcpy (&i2v->icmp_header,
 	  icmp,
 	  pktlen);
-  /* FIXME: should we sanitize the host-specific payload here?  On the
-     one hand, quite a bit of what we send is meaningless on the other
-     side (our IPs, ports, etc.); on the other hand, trying to compact
-     the packet would be very messy, and blanking fields out is also
-     hardly productive as they seem to contain nothing remotely
-     sensitive. */  
   send_packet_to_mesh_tunnel (state->tunnel,
 			      tnq);
 }