Infinite loop bug in TagLib

[Philip Van Baren]

On some mpeg video files (particularly on incomplete or corrupt files)
TagLib gets stuck using 100% CPU.

The problem is an infinite loop in Filters/TagLib/Mpeg/File.cs
ReadVideoPacket function.  If the FindMarker doesn't find the right packet
type, it doesn't increment offset, and just calls FindMarker again with the
same offset, and repeats...

Here is a version of that function which prevents the infinite loop:

void ReadVideoPacket (ref long position)
{
    Seek (position + 4);
    int length = ReadBlock (2).ToUShort ();
    long offset = position + 6;
    // Put a sanity limit on how long we search
    int sanity_limit = 1000;
    int i=0;

    while (!video_found && (i < sanity_limit) && offset < position + length)
{
        if (FindMarker (ref offset) ==
            Marker.VideoSyncPacket) {
            video_header = new VideoHeader (this,
                offset + 4);
            video_found = true;
        } else {
            // Make sure we keep moving forward, because this one didn't
match
            offset += 4;
        }
        i++;
    }

    position += length;
}
http://bugzilla.gnome.org/show_bug.cgi?id=542582

Philip Van Baren