commit fa8b18ed upstream.

This prevents in-memory corruption and possible panics if the on-disk
ACL is badly corrupted.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>