Reject the descriptions that attempt to change the order of m= sections

webrtc/pc/webrtcsession.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 43 matching lines @@
 using cricket::PRFLX_PORT_TYPE;
 
 namespace webrtc {
 
 // Error messages
 const char kBundleWithoutRtcpMux[] = "RTCP-MUX must be enabled when BUNDLE "
                                      "is enabled.";
 const char kCreateChannelFailed[] = "Failed to create channels.";
 const char kInvalidCandidates[] = "Description contains invalid candidates.";
 const char kInvalidSdp[] = "Invalid session description.";
-const char kMlineMismatch[] =
-    "Offer and answer descriptions m-lines are not matching. Rejecting answer.";
+const char kMlineMismatchInAnswer[] =
+    "The order of m-lines in answer doesn't match order in offer. Rejecting "
+    "answer.";
+const char kMlineMismatchInSubsequentOffer[] =
+    "The order of m-lines in subsequent offer doesn't match order from "
+    "previous offer/answer.";
 const char kPushDownTDFailed[] =
     "Failed to push down transport description:";
 const char kSdpWithoutDtlsFingerprint[] =
     "Called with SDP without DTLS fingerprint.";
 const char kSdpWithoutSdesCrypto[] =
     "Called with SDP without SDES crypto.";
 const char kSdpWithoutIceUfragPwd[] =
     "Called with SDP without ice-ufrag and ice-pwd.";
 const char kSessionError[] = "Session error code: ";
 const char kSessionErrorDesc[] = "Session error description: ";
@@ skipping 53 matching lines @@
     return kIceCandidatePairRelayPrflx;
   if (l == prflx && r == host)
     return kIceCandidatePairPrflxHost;
   if (l == prflx && r == srflx)
     return kIceCandidatePairPrflxSrflx;
   if (l == prflx && r == relay)
     return kIceCandidatePairPrflxRelay;
   return kIceCandidatePairMax;
 }
 
-// Compares |answer| against |offer|. Comparision is done
-// for number of m-lines in answer against offer. If matches true will be
-// returned otherwise false.
-static bool VerifyMediaDescriptions(
-    const SessionDescription* answer, const SessionDescription* offer) {
-  if (offer->contents().size() != answer->contents().size())
+// Verify that the order of media sections in |desc1| matches |desc2|. The
+// number of m= sections could be different.
+static bool MediaSectionsInSameOrder(const SessionDescription* desc1,
+                                     const SessionDescription* desc2) {
+  if (!desc1 || !desc2) {
     return false;
-
-  for (size_t i = 0; i < offer->contents().size(); ++i) {
-    if ((offer->contents()[i].name) != answer->contents()[i].name) {
+  }
+  for (size_t i = 0;
+       i < desc1->contents().size() && i < desc2->contents().size(); ++i) {
+    if ((desc2->contents()[i].name) != desc1->contents()[i].name) {
       return false;
     }
-    const MediaContentDescription* offer_mdesc =
+    const MediaContentDescription* desc2_mdesc =
         static_cast<const MediaContentDescription*>(
-            offer->contents()[i].description);
-    const MediaContentDescription* answer_mdesc =
+            desc2->contents()[i].description);
+    const MediaContentDescription* desc1_mdesc =
         static_cast<const MediaContentDescription*>(
-            answer->contents()[i].description);
-    if (offer_mdesc->type() != answer_mdesc->type()) {
+            desc1->contents()[i].description);
+    if (desc2_mdesc->type() != desc1_mdesc->type()) {
       return false;
     }
   }
   return true;
 }
 
+static bool MediaSectionsHaveSameCount(const SessionDescription* desc1,
+                                       const SessionDescription* desc2) {
+  if (!desc1 || !desc2) {
+    return false;
+  }
+  return desc1->contents().size() == desc2->contents().size();
+}
+
 // Checks that each non-rejected content has SDES crypto keys or a DTLS
 // fingerprint, unless it's in a BUNDLE group, in which case only the
 // BUNDLE-tag section (first media section/description in the BUNDLE group)
 // needs a ufrag and pwd. Mismatches, such as replying with a DTLS fingerprint
 // to SDES keys, will be caught in JsepTransport negotiation, and backstopped
 // by Channel's |srtp_required| check.
 static bool VerifyCrypto(const SessionDescription* desc,
                          bool dtls_enabled,
                          std::string* error) {
   const cricket::ContentGroup* bundle =
@@ skipping 1972 matching lines @@
   }
 
   if (!ValidateBundleSettings(sdesc->description())) {
     return BadSdp(source, type, kBundleWithoutRtcpMux, err_desc);
   }
 
   // TODO(skvlad): When the local rtcp-mux policy is Require, reject any
   // m-lines that do not rtcp-mux enabled.
 
   // Verify m-lines in Answer when compared against Offer.
-  if (action == kAnswer) {
+  if (action == kAnswer || action == kPrAnswer) {
     const cricket::SessionDescription* offer_desc =
         (source == cricket::CS_LOCAL) ? remote_description()->description()
                                       : local_description()->description();
-    if (!VerifyMediaDescriptions(sdesc->description(), offer_desc)) {
-      return BadAnswerSdp(source, kMlineMismatch, err_desc);
+    if (!MediaSectionsHaveSameCount(sdesc->description(), offer_desc) ||
+        !MediaSectionsInSameOrder(sdesc->description(), offer_desc)) {
+      return BadAnswerSdp(source, kMlineMismatchInAnswer, err_desc);
+    }
+  } else {
+    // The re-offers should respect the order of m= sections in current local
+    // description. See RFC3264 Section 8 paragraph 4 for more details.
+    if (local_description() &&
+        !MediaSectionsInSameOrder(sdesc->description(),
+                                  local_description()->description())) {
+      return BadOfferSdp(source, kMlineMismatchInSubsequentOffer, err_desc);
     }
   }
 
   return true;
 }
 
 bool WebRtcSession::ExpectSetLocalDescription(Action action) {
   return ((action == kOffer && state() == STATE_INIT) ||
           // update local offer
           (action == kOffer && state() == STATE_SENTOFFER) ||
@@ skipping 311 matching lines @@
       (rtp_data_channel_->rtcp_dtls_transport() != nullptr);
   channel_manager_->DestroyRtpDataChannel(rtp_data_channel_.release());
   transport_controller_->DestroyDtlsTransport(
       transport_name, cricket::ICE_CANDIDATE_COMPONENT_RTP);
   if (need_to_delete_rtcp) {
     transport_controller_->DestroyDtlsTransport(
         transport_name, cricket::ICE_CANDIDATE_COMPONENT_RTCP);
   }
 }
 }  // namespace webrtc