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: f2bbc96 ("s390/pkey: add CCA AES cipher key support")
Cc: [email protected]
Signed-off-by: Fedor Pchelkin <[email protected]>
Reviewed-by: Holger Dengler <[email protected]>
Reviewed-by: Heiko Carstens <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexander Gordeev <[email protected]>

Author: pchelkin91

drivers/s390/crypto/pkey_api.c

@@ -86,7 +86,7 @@ static void *_copy_apqns_from_user(void __user *uapqns, size_t nr_apqns)
 	if (!uapqns || nr_apqns == 0)
 		return NULL;
 
-	return memdup_user(uapqns, nr_apqns * sizeof(struct pkey_apqn));
+	return memdup_array_user(uapqns, nr_apqns, sizeof(struct pkey_apqn));
 }
 
 static int pkey_ioctl_genseck(struct pkey_genseck __user *ugs)