[FFmpeg-cvslog] avformat/mpegts: use actually read packet size in mpegts_resync special case

[Michael Niedermayer]

ffmpeg | branch: release/3.4 | Michael Niedermayer <michael at niedermayer.cc> | Thu Sep 16 23:12:42 2021 +0200| [67b9b10b70ada6c8df513958c180eb7bd2f9c2d7] | committer: Michael Niedermayer

avformat/mpegts: use actually read packet size in mpegts_resync special case

Fixes: infinite loop
Fixes: 37986/clusterfuzz-testcase-minimized-ffmpeg_dem_MPEGTSRAW_fuzzer-5292311517462528 -

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Marton Balint <cus at passwd.hu>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 83b2e4c8f15a00f037040131e26e20de83f0d842)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=67b9b10b70ada6c8df513958c180eb7bd2f9c2d7
---

 libavformat/mpegts.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavformat/mpegts.c b/libavformat/mpegts.c
index e4976d76d2..3342193868 100644
--- a/libavformat/mpegts.c
+++ b/libavformat/mpegts.c
@@ -2419,8 +2419,8 @@ static int mpegts_resync(AVFormatContext *s, int seekback, const uint8_t *curren
     int64_t back = FFMIN(seekback, pos);
 
     //Special case for files like 01c56b0dc1.ts
-    if (current_packet[0] == 0x80 && current_packet[12] == 0x47) {
-        avio_seek(pb, 12 - back, SEEK_CUR);
+    if (current_packet[0] == 0x80 && current_packet[12] == 0x47 && pos >= TS_PACKET_SIZE) {
+        avio_seek(pb, 12 - TS_PACKET_SIZE, SEEK_CUR);
         return 0;
     }