Fix bug 9021: 'RTP not decoded inside the conversation in v.1.10.1'

The behavior for SIP/SDP handling of RTP conversation tracking
changed in v1.10, with some unintended consequences.  The bugs did not
show up at the time because wireshark makes 2 passes of the packet list,
and so the problems auto-corrected themselves in most cases.  Unfortunately,
a change in r53641 modified how UDP behaves, making it always create
conversations for UDP packets, and that exposed the bugs inherent in the
SIP/SDP code changes.

This commit reverts the behavior of SIP/SDP to its pre-1.10 model, but
creates a new preference setting for "Delay SDP changes for tracking media",
which if enabled, will turn on the new (but buggy) model introduced in 1.10.
This preference is *disabled* by default, since for a majority of cases the
new behavior is worse than the previous behavior.

The preference, and this commit's fix, is not intended to last long. I intend
to re-write the SIP/SDP/RTP interaction model for release 1.11 - I think it's
too big a change for 1.10, however, which is why I submitted this commit.

Change-Id: Ic5601749d6c2344e952ced8206dd9296bfdc4b90
Reviewed-on: https://code.wireshark.org/review/543
Reviewed-by: Evan Huus <eapache@gmail.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/epan/dissectors/packet-sip.c b/epan/dissectors/packet-sip.c
index 7072d76d40..09bec53be8 100644
--- a/epan/dissectors/packet-sip.c
+++ b/epan/dissectors/packet-sip.c
@@ -57,7 +57,6 @@
 
 #include "packet-sdp.h"  /* SDP needs a transport layer to determine request/response */
 
-
 #define TCP_PORT_SIP 5060
 #define UDP_PORT_SIP 5060
 #define TLS_PORT_SIP 5061
@@ -811,6 +810,9 @@ static gboolean sip_desegment_body = TRUE;
  */
 static gboolean sip_retrans_the_same_sport = TRUE;
 
+/* whether we hold off tracking RTP conversations until an SDP answer is received */
+static gboolean sip_delay_sdp_changes = FALSE;
+
 /* Extension header subdissectors */
 static dissector_table_t ext_hdr_subdissector_table;
 
@@ -3506,15 +3508,15 @@ dissect_sip_common(tvbuff_t *tvb, int offset, packet_info *pinfo, proto_tree *tr
                 /* Resends don't count */
                 if (resend_for_packet == 0) {
                     if (line_type == REQUEST_LINE) {
-                        setup_sdp_transport(next_tvb, pinfo, SDP_EXCHANGE_OFFER, pinfo->fd->num);
+                        setup_sdp_transport(next_tvb, pinfo, SDP_EXCHANGE_OFFER, pinfo->fd->num, sip_delay_sdp_changes);
                     } else if (line_type == STATUS_LINE) {
                         if (stat_info->response_code >= 400) {
                             /* SIP client request failed, so SDP offer should fail */
-                            setup_sdp_transport(next_tvb, pinfo, SDP_EXCHANGE_ANSWER_REJECT, request_for_response);
+                            setup_sdp_transport(next_tvb, pinfo, SDP_EXCHANGE_ANSWER_REJECT, request_for_response, sip_delay_sdp_changes);
                         }
                         else if ((stat_info->response_code >= 200) && (stat_info->response_code <= 299)) {
                             /* SIP success request, so SDP offer should be accepted */
-                            setup_sdp_transport(next_tvb, pinfo, SDP_EXCHANGE_ANSWER_ACCEPT, request_for_response);
+                            setup_sdp_transport(next_tvb, pinfo, SDP_EXCHANGE_ANSWER_ACCEPT, request_for_response, sip_delay_sdp_changes);
                         }
                     }
                 } else {
@@ -5576,6 +5578,13 @@ void proto_register_sip(void)
         "Retransmissions always use the same source port",
         "Whether retransmissions are detected coming from the same source port only.",
         &sip_retrans_the_same_sport);
+    prefs_register_bool_preference(sip_module, "delay_sdp_changes",
+        "Delay SDP changes for tracking media",
+        "Whether SIP should delay tracking the media (e.g., RTP/RTCP) until an SDP offer "
+        "is answered. If enabled, mid-dialog changes to SDP and media state only take "
+        "effect if and when an SDP offer is successfully answered; however enabling this "
+        "prevents tracking media in early-media call scenarios",
+        &sip_delay_sdp_changes);
 
     prefs_register_obsolete_preference(sip_module, "tcp.port");