omadec: Properly check lengths before incrementing the position

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

libavformat/omadec.c

@@ -172,7 +172,11 @@ static int nprobe(AVFormatContext *s, uint8_t *enc_header, unsigned size,
     taglen  = AV_RB32(&enc_header[pos + 32]);
     datalen = AV_RB32(&enc_header[pos + 36]) >> 4;
 
-    pos += 44 + taglen;
+    pos += 44;
+    if (size - pos < taglen)
+        return -1;
+
+    pos += taglen;
 
     if (datalen << 4 > size - pos)
         return -1;