commit d9bcd462 upstream.

So far we completely rely on the caller to provide valid arguments.
To be on the safe side perform an own sanity check.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>