oma: better format detection with small probe buffer

Signed-off-by: NDavid Goldwich <david.goldwich@gmail.com>
Signed-off-by: NAnton Khirnov <anton@khirnov.net>

libavformat/oma.c

@@ -394,14 +394,20 @@ static int oma_read_probe(AVProbeData *p)
     unsigned tag_len = 0;
 
     buf = p->buf;
-    /* version must be 3 and flags byte zero */
-    if (ff_id3v2_match(buf, ID3v2_EA3_MAGIC) && buf[3] == 3 && !buf[4])
-        tag_len = ff_id3v2_tag_len(buf);
 
-    // This check cannot overflow as tag_len has at most 28 bits
-    if (p->buf_size < tag_len + 5)
+    if (p->buf_size < ID3v2_HEADER_SIZE ||
+        !ff_id3v2_match(buf, ID3v2_EA3_MAGIC) ||
+        buf[3] != 3 || // version must be 3
+        buf[4]) // flags byte zero
         return 0;
 
+    tag_len = ff_id3v2_tag_len(buf);
+
+    /* This check cannot overflow as tag_len has at most 28 bits */
+    if (p->buf_size < tag_len + 5)
+        /* EA3 header comes late, might be outside of the probe buffer */
+        return AVPROBE_SCORE_MAX / 2;
+
     buf += tag_len;
 
     if (!memcmp(buf, "EA3", 3) && !buf[4] && buf[5] == EA3_HEADER_SIZE)