linux-cve-announce - CVE-2025-38522: sched/ext: Prevent update_locked

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Message-ID: <2025081652-CVE-2025-38522-641c@gregkh>
Date: Sat, 16 Aug 2025 13:13:53 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38522: sched/ext: Prevent update_locked_rq() calls with NULL rq

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

sched/ext: Prevent update_locked_rq() calls with NULL rq

Avoid invoking update_locked_rq() when the runqueue (rq) pointer is NULL
in the SCX_CALL_OP and SCX_CALL_OP_RET macros.

Previously, calling update_locked_rq(NULL) with preemption enabled could
trigger the following warning:

    BUG: using __this_cpu_write() in preemptible [00000000]

This happens because __this_cpu_write() is unsafe to use in preemptible
context.

rq is NULL when an ops invoked from an unlocked context. In such cases, we
don't need to store any rq, since the value should already be NULL
(unlocked). Ensure that update_locked_rq() is only called when rq is
non-NULL, preventing calling __this_cpu_write() on preemptible context.

The Linux kernel CVE team has assigned CVE-2025-38522 to this issue.

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

	Issue introduced in 6.15 with commit 18853ba782bef65fc81ef2b3370382e5b479c5eb and fixed in 6.15.8 with commit 237c43037b336e36a49eb9f2daac1c7719ec7f8b
	Issue introduced in 6.15 with commit 18853ba782bef65fc81ef2b3370382e5b479c5eb and fixed in 6.16 with commit e14fd98c6d66cb76694b12c05768e4f9e8c95664

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-2025-38522
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/sched/ext.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/237c43037b336e36a49eb9f2daac1c7719ec7f8b
	https://git.kernel.org/stable/c/e14fd98c6d66cb76694b12c05768e4f9e8c95664