linux-cve-announce - CVE-2025-21786: workqueue: Put the pwq after detaching the rescuer from the pool

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Message-ID: <2025022608-CVE-2025-21786-f31d@gregkh>
Date: Wed, 26 Feb 2025 18:17:42 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21786: workqueue: Put the pwq after detaching the rescuer from the pool

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2025-21786 to this issue.


Affected and fixed versions
===========================

	Fixed in 6.12.16 with commit e7c16028a424dd35be1064a68fa318be4359310f
	Fixed in 6.13.4 with commit 835b69c868f53f959d4986bbecd561ba6f38e492
	Fixed in 6.14-rc3 with commit e76946110137703c16423baf6ee177b751a34b7e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-21786
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/workqueue.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e7c16028a424dd35be1064a68fa318be4359310f
	https://git.kernel.org/stable/c/835b69c868f53f959d4986bbecd561ba6f38e492
	https://git.kernel.org/stable/c/e76946110137703c16423baf6ee177b751a34b7e