[FFmpeg-cvslog] avformat/matroskadec: Check pre_ns for overflow

[Michael Niedermayer]

ffmpeg | branch: release/2.8 | Michael Niedermayer <michael at niedermayer.cc> | Wed Dec 11 21:36:11 2024 +0100| [cf7670f4604b1913eb628393b68c5e92129a3b52] | committer: Michael Niedermayer

avformat/matroskadec: Check pre_ns for overflow

Fixes: signed integer overflow: -3483479120376300096 - 7442323944145700864 cannot be represented in type 'long'
Fixes: 383187489/clusterfuzz-testcase-minimized-ffmpeg_dem_WEBM_DASH_MANIFEST_fuzzer-4561470580391936

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 361d24e6d920e4f7e4e5fa1fd6fbb6922bff35f2)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=cf7670f4604b1913eb628393b68c5e92129a3b52
---

 libavformat/matroskadec.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 32956d4509..74e6f1049b 100644
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -3375,9 +3375,10 @@ static int64_t webm_dash_manifest_compute_bandwidth(AVFormatContext *s, int64_t
             // The prebuffer ends in the last Cue. Estimate how much data was
             // 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)
+            if (desc_end.end_time_ns <= desc_end.start_time_ns ||
+                desc_end.end_time_ns - (uint64_t)desc_end.start_time_ns > INT64_MAX)
                 return -1;
+            pre_ns = desc_end.end_time_ns - desc_end.start_time_ns;
             pre_sec = pre_ns / nano_seconds_per_second;
             prebuffer_bytes +=
                 pre_bytes * ((temp_prebuffer_ns / nano_seconds_per_second) / pre_sec);