[FFmpeg-cvslog] avformat/mov: compute absolute dts difference without overflow in mov_find_next_sample()

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Sat Sep 30 21:04:11 2023 +0200| [c53f2eaa2a40708582a600f4c7c5540bd146b58e] | committer: Michael Niedermayer

avformat/mov: compute absolute dts difference without overflow in mov_find_next_sample()

Fixes: signed integer overflow: -9223372036854775808 - 9222726413022000000 cannot be represented in type 'long'
Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-5959420033761280

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 3508b496e195440d0af0203e2822937b8c6f5598)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=c53f2eaa2a40708582a600f4c7c5540bd146b58e
---

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

diff --git a/libavformat/mov.c b/libavformat/mov.c
index ff0184400b..86f436642d 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -7676,12 +7676,13 @@ static AVIndexEntry *mov_find_next_sample(AVFormatContext *s, AVStream **st)
         if (msc->pb && msc->current_sample < avst->nb_index_entries) {
             AVIndexEntry *current_sample = &avst->index_entries[msc->current_sample];
             int64_t dts = av_rescale(current_sample->timestamp, AV_TIME_BASE, msc->time_scale);
+            uint64_t dtsdiff = best_dts > dts ? best_dts - (uint64_t)dts : ((uint64_t)dts - best_dts);
             av_log(s, AV_LOG_TRACE, "stream %d, sample %d, dts %"PRId64"\n", i, msc->current_sample, dts);
             if (!sample || (!(s->pb->seekable & AVIO_SEEKABLE_NORMAL) && current_sample->pos < sample->pos) ||
                 ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) &&
                  ((msc->pb != s->pb && dts < best_dts) || (msc->pb == s->pb && dts != AV_NOPTS_VALUE &&
-                 ((FFABS(best_dts - dts) <= AV_TIME_BASE && current_sample->pos < sample->pos) ||
-                  (FFABS(best_dts - dts) > AV_TIME_BASE && dts < best_dts)))))) {
+                 ((dtsdiff <= AV_TIME_BASE && current_sample->pos < sample->pos) ||
+                  (dtsdiff > AV_TIME_BASE && dts < best_dts)))))) {
                 sample = current_sample;
                 best_dts = dts;
                 *st = avst;