[FFmpeg-cvslog] avformat/jacosubdec: Use 64bit intermediate for start/end timestamp shift

[Michael Niedermayer]

ffmpeg | branch: release/4.4 | Michael Niedermayer <michael at niedermayer.cc> | Thu Feb 11 22:44:36 2021 +0100| [79ff380da7a68fc48a52bd823148f233f10df960] | committer: Michael Niedermayer

avformat/jacosubdec: Use 64bit intermediate for start/end timestamp shift

Fixes: signed integer overflow: -1957694447 + -1620425806 cannot be represented in type 'int'
Fixes: 30207/clusterfuzz-testcase-minimized-ffmpeg_dem_JACOSUB_fuzzer-5050791771635712

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 2c477be08a64a78ab0a358ae00e2f2dc746f2b47)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=79ff380da7a68fc48a52bd823148f233f10df960
---

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

diff --git a/libavformat/jacosubdec.c b/libavformat/jacosubdec.c
index b44e3b7783..0576784da4 100644
--- a/libavformat/jacosubdec.c
+++ b/libavformat/jacosubdec.c
@@ -125,8 +125,8 @@ static const char *read_ts(JACOsubContext *jacosub, const char *buf,
     return NULL;
 
 shift_and_ret:
-    ts_start64  = (ts_start + jacosub->shift) * 100LL / jacosub->timeres;
-    ts_end64    = (ts_end   + jacosub->shift) * 100LL / jacosub->timeres;
+    ts_start64  = (ts_start + (int64_t)jacosub->shift) * 100LL / jacosub->timeres;
+    ts_end64    = (ts_end   + (int64_t)jacosub->shift) * 100LL / jacosub->timeres;
     *start    = ts_start64;
     *duration = ts_end64 - ts_start64;
     return buf + len;