Medium [CVE-2026-80545] Improve EP11 CPRB length and overflow checks

In the Linux kernel, the following vulnerability has been resolved: s390/zcrypt: Improve EP11 CPRB length and overflow checks The xcrb_msg_to_type6_ep11cprb_msgx() function lacks proper input validation, creating security vulnerabilities: 1.

Missing minimum size validation: The ep11_cprb structure and subsequent payload fields (pld_tag, pld_lenfmt) are copied from userspace without verifying sufficient buffer length. 2.

Arithmetic overflow in length calculations: CEIL4 alignment could overflow, bypassing size checks and enabling buffer overflows. 3.

The payload is asn1 encoded but the function just uses a simple c struct overlay to access some fields of the payload. Fix by using size_t for length calculations, adding U32_MAX boundary checks after alignment, and validating minimum request size and minimum reply size before copying from userspace.

Do a very simple asn1 parsing of the payload up to the function value field. This vulnerability stems from insufficient input validation in the `xcrb_msg_to_type6_ep11cprb_msgx()` function when handling EP11 Cryptographic Coprocessor Request Block (CPRB) messages.

A local attacker could exploit this by crafting a malicious message, leading to arithmetic overflows in length calculations and subsequent buffer overflows. This could result in a denial of service or potentially allow for privilege escalation.