[FFmpeg-cvslog] avformat/matroskadec: Check pre_ns

[Michael Niedermayer]

ffmpeg | branch: release/3.4 | Michael Niedermayer <michael at niedermayer.cc> | Sun Feb 13 15:20:02 2022 +0100| [92521686ce4b0c607d5d8a57a2f7dadfc08f40f5] | committer: Michael Niedermayer

avformat/matroskadec: Check pre_ns

Fixes: division by 0
Fixes: 44615/clusterfuzz-testcase-minimized-ffmpeg_dem_WEBM_DASH_MANIFEST_fuzzer-6681108677263360

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 710e51677a6f3a5c2b37dc31a597957a22a5e531)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=92521686ce4b0c607d5d8a57a2f7dadfc08f40f5
---

 libavformat/matroskadec.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 37f6d55e75..5def4e311a 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -3811,6 +3811,8 @@ static int64_t webm_dash_manifest_compute_bandwidth(AVFormatContext *s, int64_t
             // prebuffered.
             pre_bytes = desc_end.end_offset - desc_end.start_offset;
             pre_ns = desc_end.end_time_ns - desc_end.start_time_ns;
+            if (pre_ns <= 0)
+                return -1;
             pre_sec = pre_ns / nano_seconds_per_second;
             prebuffer_bytes +=
                 pre_bytes * ((temp_prebuffer_ns / nano_seconds_per_second) / pre_sec);