From 1f5e9a9335e5604316fab4ac1f060ef95a3d533d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Mon, 23 Oct 2023 21:46:45 +0300
Subject: [PATCH] rtpav1depay: Skip unexpected leading fragments

If a packet is starting with a leading fragment but we do not expect to
receive one, then skip over it to the next OBU.

Not doing so would cause parsing of the middle of an OBU, which would
most likely fail and cause unnecessary warning messages about a
corrupted stream.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1367>
---
 net/rtp/src/av1/depay/imp.rs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/net/rtp/src/av1/depay/imp.rs b/net/rtp/src/av1/depay/imp.rs
index f9fe838f..b7c8b0f1 100644
--- a/net/rtp/src/av1/depay/imp.rs
+++ b/net/rtp/src/av1/depay/imp.rs
@@ -33,6 +33,8 @@ struct State {
     marked_packet: bool,
     /// if the next output buffer needs the DISCONT flag set
     needs_discont: bool,
+    /// if we saw a valid OBU since the last reset
+    found_valid_obu: bool,
     /// holds data for a fragment
     obu_fragment: Option<(UnsizedObu, Vec<u8>)>,
 }
@@ -43,6 +45,7 @@ impl Default for State {
             last_timestamp: None,
             marked_packet: false,
             needs_discont: true,
+            found_valid_obu: false,
             obu_fragment: None,
         }
     }
@@ -291,6 +294,21 @@ impl RTPAv1Depay {
             let (element_size, is_last_obu) =
                 self.find_element_info(rtp, &mut reader, &aggr_header, idx)?;
 
+            if idx == 0 && aggr_header.leading_fragment {
+                if state.found_valid_obu {
+                    gst::error!(
+                        CAT,
+                        imp: self,
+                        "invalid packet: unexpected leading OBU fragment"
+                    );
+                }
+                reader
+                    .seek(SeekFrom::Current(element_size as i64))
+                    .map_err(err_flow!(self, buf_read))?;
+                idx += 1;
+                continue;
+            }
+
             let header_pos = reader.position();
             let mut bitreader = BitReader::endian(&mut reader, ENDIANNESS);
             let obu = UnsizedObu::parse(&mut bitreader).map_err(err_flow!(self, obu_read))?;
@@ -299,6 +317,8 @@ impl RTPAv1Depay {
                 .seek(SeekFrom::Start(header_pos))
                 .map_err(err_flow!(self, buf_read))?;
 
+            state.found_valid_obu = true;
+
             // ignore these OBU types
             if matches!(obu.obu_type, ObuType::TemporalDelimiter | ObuType::TileList) {
                 reader