BugLink: http://bugs.launchpad.net/bugs/1572722

commit a0ad220c upstream.

A malicious device missing interface can make the driver oops.
Add sanity checking.
Signed-off-by: Oliver Neukum <ONeukum@suse.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>