CVE-2025-21786

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

workqueue: Put the pwq after detaching the rescuer from the pool

The commit 68f83057b913(workqueue: Reap workers via kthread_stop() and remove detach_completion) adds code to reap the normal workers but mistakenly does not handle the rescuer and also removes the code waiting for the rescuer in put_unbound_pool(), which caused a use-after-free bug reported by Cheung Wall.

To avoid the use-after-free bug, the pool’s reference must be held until the detachment is complete. Therefore, move the code that puts the pwq after detaching the rescuer from the pool.

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 Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.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/835b69c868f53f959d4986bbecd561ba6f38e492
• https://git.kernel.org/stable/c/e76946110137703c16423baf6ee177b751a34b7e
• https://git.kernel.org/stable/c/e7c16028a424dd35be1064a68fa318be4359310f