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@niedermayer.cc>

diff --git a/libavformat/mpc8.c b/libavformat/mpc8.c
index ff7da2ef55397d969276ef7073a73834d3a911e6..b12a417f63239db9cbed402a04c77987a6da4179 100644 (file)
--- 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)