CVE-2026-53116

In the Linux kernel, the following vulnerability has been resolved:

s390/ap: use generic driver_override infrastructure

When the AP masks are updated via apmask_store() or aqmask_store(), ap_bus_revise_bindings() is called after ap_attr_mutex has been released.

This calls __ap_revise_reserved(), which accesses the driver_override field without holding any lock, racing against a concurrent driver_override_store() that may free the old string, resulting in a potential UAF.

Fix this by using the driver-core driver_override infrastructure, which protects all accesses with an internal spinlock.

Note that unlike most other buses, the AP bus does not check driver_override in its match() callback; the override is checked in ap_device_probe() and __ap_revise_reserved() instead.

Also note that we do not enable the driver_override feature of struct bus_type, as AP - in contrast to most other buses - passes to sysfs_emit() when the driver_override pointer is NULL. Thus, printing n instead of (null)n.

Additionally, AP has a custom counter that is modified in the corresponding custom driver_override_store().

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/81d6f7c3a70b10ff757ee8b5f8114a190871cf1e
• https://git.kernel.org/stable/c/8f2eca0570438b94602da1297353eb7b10dcb6cb