--- libavformat/oggparsevorbis.c.orig	2011-03-05 00:24:29.000000000 +0100
+++ libavformat/oggparsevorbis.c	2011-03-05 00:26:30.000000000 +0100
@@ -35,27 +35,28 @@ vorbis_comment(AVFormatContext * as, uin
 {
     const uint8_t *p = buf;
     const uint8_t *end = buf + size;
-    unsigned s, n, j;
+    unsigned n, j;
+    int s;
 
     if (size < 8) /* must have vendor_length and user_comment_list_length */
         return -1;
 
     s = bytestream_get_le32(&p);
 
-    if (end - p < s)
+    if (end - p - 4 < s || s < 0)
         return -1;
 
     p += s;
 
     n = bytestream_get_le32(&p);
 
-    while (p < end && n > 0) {
+    while (end - p >= 4 && n > 0) {
         const char *t, *v;
         int tl, vl;
 
         s = bytestream_get_le32(&p);
 
-        if (end - p < s)
+        if (end - p < s || s < 0)
             break;
 
         t = p;