sdp: reject duplicate ssrcs in ssrc-groups

while not really covered by
  https://www.rfc-editor.org/rfc/rfc5576.html#section-4.2
and using the same SSRC for RTX and primary payload may work
since payload type demuxing *could* be used is not a good idea.
This also applies to flexfec's FEC-FR.

For the nonstandard SIM ssrc-group duplicates make no sense.
This rejects duplicates for unknown ssrc-groups as well.

BUG=chromium:1454860

Change-Id: I3e86101dbd5d6c4099f2fdb7b4a52d5cd0809c5f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/308820
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#40292}

Author: fippo

pc/webrtc_sdp.cc

@@ -3545,6 +3545,11 @@ bool ParseSsrcGroupAttribute(absl::string_view line,
     if (!GetValueFromString(line, fields[i], &ssrc, error)) {
       return false;
     }
+    // Reject duplicates. While not forbidden by RFC 5576,
+    // they don't make sense.
+    if (absl::c_linear_search(ssrcs, ssrc)) {
+      return ParseFailed(line, "Duplicate SSRC in ssrc-group", error);
+    }
     ssrcs.push_back(ssrc);
   }
   ssrc_groups->push_back(SsrcGroup(semantics, ssrcs));

pc/webrtc_sdp_unittest.cc

@@ -5057,3 +5057,29 @@ TEST_F(WebRtcSdpTest, RejectSessionLevelMediaLevelExtmapMixedUsage) {
   JsepSessionDescription jdesc(kDummyType);
   EXPECT_FALSE(SdpDeserialize(sdp, &jdesc));
 }
+
+TEST_F(WebRtcSdpTest, RejectDuplicateSsrcInSsrcGroup) {
+  std::string sdp =
+      "v=0\r\n"
+      "o=- 0 3 IN IP4 127.0.0.1\r\n"
+      "s=-\r\n"
+      "t=0 0\r\n"
+      "a=group:BUNDLE 0\r\n"
+      "a=fingerprint:sha-1 "
+      "4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB\r\n"
+      "a=setup:actpass\r\n"
+      "a=ice-ufrag:ETEn\r\n"
+      "a=ice-pwd:OtSK0WpNtpUjkY4+86js7Z/l\r\n"
+      "m=video 9 UDP/TLS/RTP/SAVPF 96 97\r\n"
+      "c=IN IP4 0.0.0.0\r\n"
+      "a=rtcp-mux\r\n"
+      "a=sendonly\r\n"
+      "a=mid:0\r\n"
+      "a=rtpmap:96 VP8/90000\r\n"
+      "a=rtpmap:97 rtx/90000\r\n"
+      "a=fmtp:97 apt=96\r\n"
+      "a=ssrc-group:FID 1234 1234\r\n"
+      "a=ssrc:1234 cname:test\r\n";
+  JsepSessionDescription jdesc(kDummyType);
+  EXPECT_FALSE(SdpDeserialize(sdp, &jdesc));
+}