[FFmpeg-cvslog] avformat/mov: Fix last mfra check

[Michael Niedermayer]

ffmpeg | branch: release/4.4 | Michael Niedermayer <michael at niedermayer.cc> | Wed Sep 15 21:52:00 2021 +0200| [71d776740c2e11ae48295f1d34941ce8871d62b3] | committer: Michael Niedermayer

avformat/mov: Fix last mfra check

Fixes: signed integer overflow: 9223372036854775360 + 536870912 cannot be represented in type 'long'
Fixes: 37940/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-6095637855207424

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 451ceb5131fa67b0b380d4823981e421909c16db)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=71d776740c2e11ae48295f1d34941ce8871d62b3
---

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

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 04dda63212..4af796ee31 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -5148,7 +5148,7 @@ static int mov_read_sidx(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     // See if the remaining bytes are just an mfra which we can ignore.
     is_complete = offset == stream_size;
-    if (!is_complete && (pb->seekable & AVIO_SEEKABLE_NORMAL)) {
+    if (!is_complete && (pb->seekable & AVIO_SEEKABLE_NORMAL) && stream_size > 0 ) {
         int64_t ret;
         int64_t original_pos = avio_tell(pb);
         if (!c->have_read_mfra_size) {
@@ -5159,7 +5159,7 @@ static int mov_read_sidx(MOVContext *c, AVIOContext *pb, MOVAtom atom)
             if ((ret = avio_seek(pb, original_pos, SEEK_SET)) < 0)
                 return ret;
         }
-        if (offset + c->mfra_size == stream_size)
+        if (offset == stream_size - c->mfra_size)
             is_complete = 1;
     }