udf: New directory iteration code

[ Upstream commit d16076d9 ]

Add new support code for iterating directory entries. The code is also
more carefully verifying validity of on-disk directory entries to avoid
crashes on malicious media.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>