From 2ca4cea5385d8fc63768dcf607cee460c7d0f79d Mon Sep 17 00:00:00 2001
From: =?utf8?q?Olivier=20Cr=C3=AAte?= <olivier.crete@collabora.com>
Date: Fri, 26 Mar 2021 20:02:13 -0400
Subject: [PATCH] webrtcbin: Validate locked m-lines in set*Description

Verify that the remote description match the locked m-lines, otherwise
just reject the SDP.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2104>
---
 ext/webrtc/gstwebrtcbin.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/ext/webrtc/gstwebrtcbin.c b/ext/webrtc/gstwebrtcbin.c
index 9913185..d439657 100644
--- a/ext/webrtc/gstwebrtcbin.c
+++ b/ext/webrtc/gstwebrtcbin.c
@@ -4716,6 +4716,61 @@ check_transceivers_not_removed (GstWebRTCBin * webrtc,
   return TRUE;
 }
 
+static gboolean
+check_locked_mlines (GstWebRTCBin * webrtc, GstWebRTCSessionDescription * sdp,
+    GError ** error)
+{
+  guint i;
+
+  for (i = 0; i < gst_sdp_message_medias_len (sdp->sdp); i++) {
+    const GstSDPMedia *media = gst_sdp_message_get_media (sdp->sdp, i);
+    GstWebRTCRTPTransceiver *rtp_trans;
+    WebRTCTransceiver *trans;
+
+    rtp_trans = _find_transceiver_for_sdp_media (webrtc, sdp->sdp, i);
+    /* only look for matching mid */
+    if (rtp_trans == NULL)
+      continue;
+
+    trans = WEBRTC_TRANSCEIVER (rtp_trans);
+
+    /* We only validate the locked mlines for now */
+    if (!trans->mline_locked)
+      continue;
+
+    if (rtp_trans->mline != i) {
+      g_set_error (error, GST_WEBRTC_BIN_ERROR,
+          GST_WEBRTC_BIN_ERROR_IMPOSSIBLE_MLINE_RESTRICTION,
+          "m-line with mid %s is at position %d, but was locked to %d, "
+          "rejecting", rtp_trans->mid, i, rtp_trans->mline);
+      return FALSE;
+    }
+
+    if (rtp_trans->kind != GST_WEBRTC_KIND_UNKNOWN) {
+      if (!g_strcmp0 (gst_sdp_media_get_media (media), "audio") &&
+          rtp_trans->kind != GST_WEBRTC_KIND_AUDIO) {
+        g_set_error (error, GST_WEBRTC_BIN_ERROR,
+            GST_WEBRTC_BIN_ERROR_IMPOSSIBLE_MLINE_RESTRICTION,
+            "m-line %d was locked to audio, but SDP has %s media", i,
+            gst_sdp_media_get_media (media));
+        return FALSE;
+      }
+
+      if (!g_strcmp0 (gst_sdp_media_get_media (media), "video") &&
+          rtp_trans->kind != GST_WEBRTC_KIND_VIDEO) {
+        g_set_error (error, GST_WEBRTC_BIN_ERROR,
+            GST_WEBRTC_BIN_ERROR_IMPOSSIBLE_MLINE_RESTRICTION,
+            "m-line %d was locked to video, but SDP has %s media", i,
+            gst_sdp_media_get_media (media));
+        return FALSE;
+      }
+    }
+  }
+
+  return TRUE;
+}
+
+
 struct set_description
 {
   GstPromise *promise;
@@ -4797,6 +4852,9 @@ _set_description_task (GstWebRTCBin * webrtc, struct set_description *sd)
     goto out;
   }
 
+  if (!check_locked_mlines (webrtc, sd->sdp, &error))
+    goto out;
+
   switch (sd->sdp->type) {
     case GST_WEBRTC_SDP_TYPE_OFFER:{
       if (sd->source == SDP_LOCAL) {
-- 
2.7.4