s390/pkey: Prevent overflow in size calculation for memdup_user()

s390/pkey: Prevent overflow in size calculation for memdup_user()

Number of apqn target list entries contained in 'nr_apqns' variable is
determined by userspace via an ioctl call so the result of the product in
calculation of size passed to memdup_user() may overflow.

In this case the actual size of the allocated area and the value
describing it won't be in sync leading to various types of unpredictable
behaviour later.

Use a proper memdup_array_user() helper which returns an error if an
overflow is detected. Note that it is different from when nr_apqns is
initially zero - that case is considered valid and should be handled in
subsequent pkey_handler implementations.

Found by Linux Verification Center (linuxtesting.org).

Fixes: f2bbc96e7cfa ("s390/pkey: add CCA AES cipher key support")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20250611192011.206057-1-pchelkin@ispras.ru
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>