s390/zcrypt: Improve CCA CPRB length and overflow checks

s390/zcrypt: Improve CCA CPRB length and overflow checks

The xcrb_msg_to_type6cprb_msgx() function lacks proper input
validation, creating security vulnerabilities:
1. Integer overflow after CEIL4 alignment: Signed int variables could
   overflow during 4-byte boundary alignment, causing undersized
   buffer allocations or incorrect bounds checking.
2. Missing minimum size validation: The CPRBX structure is copied from
   userspace without verifying sufficient buffer length. Undersized
   buffers cause uninitialized memory access when reading structure
   fields like cprbx.cprb_len and cprbx.domain.
3. Arithmetic overflow in sum calculations: Adding control block and
   data block sizes could overflow, bypassing size checks and enabling
   buffer overflows.

Fix by using size_t for length calculations, adding U32_MAX boundary
checks after alignment, validating minimum control block size before
copying from userspace, and detecting sum calculation overflows.

Fixes: e2c6d91eb8b1 ("s390/zcrypt: Rework domain processing within zcrypt device driver")
Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
Reviewed-by: Holger Dengler <dengler@linux.ibm.com>
Cc: stable@vger.kernel.org # 7.1+
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>