[FFmpeg-cvslog] avformat/mpc8: check for size overflow in mpc8_get_chunk_header()

[Michael Niedermayer]

ffmpeg | branch: release/4.4 | Michael Niedermayer <michael at niedermayer.cc> | Wed Mar 17 21:58:53 2021 +0100| [807b703a48a7859098709916a0e438e3eec3bd7c] | committer: Michael Niedermayer

avformat/mpc8: check for size overflow in mpc8_get_chunk_header()

Fixes: signed integer overflow: -9223372036854775760 - 50 cannot be represented in type 'long'
Fixes: 31673/clusterfuzz-testcase-minimized-ffmpeg_dem_MPC8_fuzzer-580134751869337

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 6cc65d3d6760cfb08c5a9e57d4306d88428e18d0)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=807b703a48a7859098709916a0e438e3eec3bd7c
---

 libavformat/mpc8.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavformat/mpc8.c b/libavformat/mpc8.c
index f33323a599..88c55e3d22 100644
--- a/libavformat/mpc8.c
+++ b/libavformat/mpc8.c
@@ -127,7 +127,11 @@ static void mpc8_get_chunk_header(AVIOContext *pb, int *tag, int64_t *size)
     pos = avio_tell(pb);
     *tag = avio_rl16(pb);
     *size = ffio_read_varlen(pb);
-    *size -= avio_tell(pb) - pos;
+    pos -= avio_tell(pb);
+    if (av_sat_add64(*size, pos) != (uint64_t)*size + pos) {
+        *size = -1;
+    } else
+        *size += pos;
 }
 
 static void mpc8_parse_seektable(AVFormatContext *s, int64_t off)