asm-generic: uaccess: add missing access_ok() check to strnlen_user()
The strnlen_user() function was missing a access_ok() check on the pointer
given. We've had cases on Blackfin systems where test programs caused
kernel crashes here because userspace passed up a NULL/-1 pointer and the
kernel gladly attempted to run strlen() on it.
Signed-off-by: Mike Frysinger <vapier@gentoo.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de>