Note what the 3GPP spec is for this protocol.

Suggest a possible less-weak heuristic.

Note that we're not checking the T bit and handling RTP header
compression.

At least as I read TS 29.414, the length indicator isn't supposed to be
zero; however, a length indicator of 0 doesn't keep us from dissecting
further, so just don't bother dissecting the payload.  We should,
perhaps, add an expert info for this.

We should perhaps also catch exceptions thrown when dissecting the RTP
packet, so a malformed RTP packet will still let us continue dissecting
the rest of the Nb packet.

svn path=/trunk/; revision=29607

1 files changed, 23 insertions, 23 deletions

diff --git a/epan/dissectors/packet-nb_rtpmux.c b/epan/dissectors/packet-nb_rtpmux.c
index 637fd436fc..372bf663fe 100644
--- a/epan/dissectors/packet-nb_rtpmux.c
+++ b/epan/dissectors/packet-nb_rtpmux.c
@@ -1,5 +1,5 @@
 /* packet-nb_rtpmux.c
- * Routines for 3GPP RTP Multiplex dissection
+ * Routines for 3GPP RTP Multiplex dissection, 3GPP TS 29.414
  * Copyright 2009, ip.access ltd <amp@ipaccess.com>
  *
  * $Id$
@@ -69,6 +69,9 @@ dissect_nb_rtpmux(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
      * set the port on which to dissect it, or it needs to be a non-heuristic
      * dissector and *require* that a user use "Decode As..." to decode
      * traffic as Nb_RTPmux.
+     *
+     * Look for a payload that looks like an RTP packet, using the
+     * same (weakish) heuristics as RTP uses?
      */
 
     /* Check that there's enough data */
@@ -102,6 +105,7 @@ dissect_nb_rtpmux(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 	        length+5, FALSE);
             nb_rtpmux_tree = proto_item_add_subtree(ti, ett_nb_rtpmux);
 
+            /* XXX - what if the T bit is set? */
             proto_tree_add_item(nb_rtpmux_tree,
                 hf_nb_rtpmux_compressed, tvb, offset, 1, FALSE);
             dstport = (tvb_get_ntohs(tvb, offset) & 0x7fff) << 1;
@@ -111,28 +115,24 @@ dissect_nb_rtpmux(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
             srcport = (tvb_get_ntohs(tvb, offset+3) & 0x7fff) << 1;
             proto_tree_add_uint(nb_rtpmux_tree, hf_nb_rtpmux_srcport, tvb, offset+3, 2, srcport );
 
-            if (length == 0)
+            if (length != 0)
             {
-                /* XXX - is an item with a zero-length payload always
-                   an end marker? */
-                break;
-            }
-
-            /* We have an RTP payload. */
-            if (rtpdissector)
-            {
-                captured_length = tvb_length_remaining(tvb, offset + 5);
-                if (captured_length > (gint)length)
-                    captured_length = length;
-                next_tvb = tvb_new_subset(tvb, offset+5, captured_length,
-		    length);
-
-                call_dissector(rtpdissector, next_tvb, pinfo, nb_rtpmux_tree);
-            }
-            else
-            {
-                proto_tree_add_item(nb_rtpmux_tree,
-                    hf_nb_rtpmux_data, tvb, offset+5, length, FALSE);
+                /* We have an RTP payload. */
+                if (rtpdissector)
+                {
+                    captured_length = tvb_length_remaining(tvb, offset + 5);
+                    if (captured_length > (gint)length)
+                        captured_length = length;
+                    next_tvb = tvb_new_subset(tvb, offset+5, captured_length,
+                                              length);
+
+                    call_dissector(rtpdissector, next_tvb, pinfo, nb_rtpmux_tree);
+                }
+                else
+                {
+                    proto_tree_add_item(nb_rtpmux_tree,
+                        hf_nb_rtpmux_data, tvb, offset+5, length, FALSE);
+                }
             }
             offset += 5+length;
         }
@@ -163,7 +163,7 @@ proto_register_nb_rtpmux(void)
         },
         { &hf_nb_rtpmux_dstport,
             { "Dst port", "nb_rtpmux.dstport",
-             FT_UINT16, BASE_DEC, NULL, 0x00,
+             FT_UINT16, BASE_DEC, NULL, 0x0000,
             NULL, HFILL }
         },
         { &hf_nb_rtpmux_length,