Prevent SDP munging of duplicate SSRCs BUG=chromium:1459124 Change-Id: Ifa901955b79dc9ff40d198bc367e89a8a535c3e2 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/311802 Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org> Commit-Queue: Philipp Hancke <phancke@microsoft.com> Reviewed-by: Florent Castelli <orphis@webrtc.org> Cr-Commit-Position: refs/heads/main@{#40447}

diff --git a/pc/sdp_offer_answer.cc b/pc/sdp_offer_answer.cc
index a9e45d0..407cf9a 100644
--- a/pc/sdp_offer_answer.cc
+++ b/pc/sdp_offer_answer.cc

@@ -1721,7 +1721,7 @@
     if (type == SdpType::kOffer) {
       // TODO(bugs.webrtc.org/4676) - Handle CreateChannel failure, as new local
       // description is applied. Restore back to old description.
-      RTCError error = CreateChannels(*local_description()->description());
+      error = CreateChannels(*local_description()->description());
       if (!error.ok()) {
         RTC_LOG(LS_ERROR) << error.message() << " (" << SdpTypeToString(type)
                           << ")";
@@ -1753,6 +1753,23 @@
   // SCTP sids.
   AllocateSctpSids();
 
+  // Validate SSRCs, we do not allow duplicates.
+  if (ConfiguredForMedia()) {
+    std::set<uint32_t> used_ssrcs;
+    for (const auto& content : local_description()->description()->contents()) {
+      for (const auto& stream : content.media_description()->streams()) {
+        for (uint32_t ssrc : stream.ssrcs) {
+          auto result = used_ssrcs.insert(ssrc);
+          if (!result.second) {
+            LOG_AND_RETURN_ERROR(
+                RTCErrorType::INVALID_PARAMETER,
+                "Duplicate ssrc " + rtc::ToString(ssrc) + " is not allowed");
+          }
+        }
+      }
+    }
+  }
+
   if (IsUnifiedPlan()) {
     if (ConfiguredForMedia()) {
       // We must use List and not ListInternal here because