mpc8: Check the seek table size parsed from the bitstream

Limit the size to INT_MAX/2 (for simplicity) to be sure that
size + FF_INPUT_BUFFER_PADDING_SIZE won't overflow.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/mpc8.c

@@ -145,6 +145,10 @@ static void mpc8_parse_seektable(AVFormatContext *s, int64_t off)
         av_log(s, AV_LOG_ERROR, "No seek table at given position\n");
         return;
     }
+    if (size < 0 || size >= INT_MAX / 2) {
+        av_log(s, AV_LOG_ERROR, "Bad seek table size\n");
+        return;
+    }
     if(!(buf = av_malloc(size + FF_INPUT_BUFFER_PADDING_SIZE)))
         return;
     avio_read(s->pb, buf, size);