[FFmpeg-cvslog] avformat/mpsubdec: Use av_sat_add/sub64() in fracval handling

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Sat Jan 16 21:48:57 2021 +0100| [463e024363d0ba0254c1f08b348bef02f148bb6a] | committer: Michael Niedermayer

avformat/mpsubdec: Use av_sat_add/sub64() in fracval handling

Fixes: signed integer overflow: 9223372036850000000 + 9000000 cannot be represented in type 'long long'
Fixes: 26910/clusterfuzz-testcase-minimized-ffmpeg_dem_MPSUB_fuzzer-665448017480908

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=463e024363d0ba0254c1f08b348bef02f148bb6a
---

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

diff --git a/libavformat/mpsubdec.c b/libavformat/mpsubdec.c
index e7b83a1d85..2e6dc883eb 100644
--- a/libavformat/mpsubdec.c
+++ b/libavformat/mpsubdec.c
@@ -72,8 +72,8 @@ static int parse_line(const char *line, int64_t *value, int64_t *value2)
                 fracval *= 10;
             for (;p2 - p1 > 7 + 1; p1++)
                 fracval /= 10;
-            if (intval > 0) intval += fracval;
-            else            intval -= fracval;
+            if (intval > 0) intval = av_sat_add64(intval, fracval);
+            else            intval = av_sat_sub64(intval, fracval);
             line += p2;
         } else
             line += p1;