CVE-2024-42235

What it actually does

Missing NULL pointer validation in crst_table_free() and base_crst_free() after ptdesc conversion allows a NULL dereference during error handling in crst_table_upgrade() on s390, resulting in a kernel crash when allocations fail under artificial conditions such as FAIL_PAGE_ALLOC.

Why it matters to the business

Potential system instability and availability loss on s390 Linux systems; low overall risk given extremely low EPSS, no KEV listing, and no observed exploitation in the wild despite the issue being public for over two years.

How an attack unfolds

An attacker with local access enables failure injection (e.g., FAIL_PAGE_ALLOC) and forces an allocation failure inside crst_table_upgrade() so that the subsequent call to crst_table_free(NULL) triggers a kernel panic before the added guard was present.

How to fix it

Upgrade the Linux kernel to a version containing commit 794fa52b94637d6b2e8c9474fbe3983af5c9f046 or later; for AlmaLinux 8 fcoe-utils update to 1.0.33-4.git848bcc6.el8 or newer; apply the NULL checks to both crst_table_free() and base_crst_free().

How to confirm the fix worked

Confirm the presence of the explicit NULL pointer checks in crst_table_free() and base_crst_free(); verify the running kernel commit is at or beyond 794fa52b94637d6b2e8c9474fbe3983af5c9f046; test that allocation-failure error paths no longer panic.

Typical attack path

1. Obtain local user privileges on an s390 system running an unpatched kernel
2. Enable or trigger memory allocation failure injection
3. Invoke code paths that call crst_table_upgrade() and encounter the failure
4. Trigger the unguarded NULL dereference in crst_table_free() or base_crst_free()
5. Cause kernel panic and denial of service

How to detect it

Review kernel logs for unexpected crashes or oops messages referencing crst_table_free or base_crst_free during memory-upgrade error paths; no widespread exploitation indicators have been observed.

What your security team should do

• Prioritize kernel updates on all s390 systems within normal patching cycles
• Monitor for any future reports of exploitation given the memory-corruption family
• Ensure test environments do not rely on FAIL_PAGE_ALLOC in production workloads