CVE-2026-53064 is a null pointer dereference vulnerability in the Linux kernel's dm-cache subsystem when used in passthrough mode. When dm-cache invalidates a cache entry, concurrent writes to the same cached block can cause the bio prison cell lock to fail, leaving the cache cell pointer (mg->cell) null. The error handling code in invalidate_complete() then attempts to unlock and free this null pointer unconditionally, triggering a kernel null pointer dereference and crash. The issue was reproducible with specific dmsetup and fio commands that create a cache device, promote data blocks, switch to passthrough mode, and perform concurrent writes. The fix checks the validity of mg->cell before unlocking it to prevent the null dereference.

This vulnerability can cause a kernel null pointer dereference leading to a denial of service via system crash or kernel panic. There is no indication of confidentiality or integrity impact. The CVSS 3.1 base score is 5.5 (medium severity) reflecting local attack vector, low complexity, low privileges required, no user interaction, and impact limited to availability.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is applied, avoid using dm-cache in passthrough mode with concurrent writes to the same cached block to prevent triggering the null pointer dereference. Monitor vendor channels for updates and apply kernel updates that address this issue once available.