linux-cve-announce - CVE-2025-38704: rcu/nocb: Fix possible invalid rdp's->nocb_cb

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Message-ID: <2025090454-CVE-2025-38704-4353@gregkh>
Date: Thu,  4 Sep 2025 17:33:09 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38704: rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access

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

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

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

rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access

In the preparation stage of CPU online, if the corresponding
the rdp's->nocb_cb_kthread does not exist, will be created,
there is a situation where the rdp's rcuop kthreads creation fails,
and then de-offload this CPU's rdp, does not assign this CPU's
rdp->nocb_cb_kthread pointer, but this rdp's->nocb_gp_rdp and
rdp's->rdp_gp->nocb_gp_kthread is still valid.

This will cause the subsequent re-offload operation of this offline
CPU, which will pass the conditional check and the kthread_unpark()
will access invalid rdp's->nocb_cb_kthread pointer.

This commit therefore use rdp's->nocb_gp_kthread instead of
rdp_gp's->nocb_gp_kthread for safety check.

The Linux kernel CVE team has assigned CVE-2025-38704 to this issue.

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

	Fixed in 6.12.43 with commit cce3d027227c69e85896af9fbc6fa9af5c68f067
	Fixed in 6.15.11 with commit 1c951683a720b17c9ecaad1932bc95b29044611f
	Fixed in 6.16.2 with commit 9b5ec8e6b31755288a07b3abeeab8cd38e9d3c9d
	Fixed in 6.17-rc1 with commit 1bba3900ca18bdae28d1b9fa10f16a8f8cb2ada1

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-2025-38704
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/rcu/tree_nocb.h

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/cce3d027227c69e85896af9fbc6fa9af5c68f067
	https://git.kernel.org/stable/c/1c951683a720b17c9ecaad1932bc95b29044611f
	https://git.kernel.org/stable/c/9b5ec8e6b31755288a07b3abeeab8cd38e9d3c9d
	https://git.kernel.org/stable/c/1bba3900ca18bdae28d1b9fa10f16a8f8cb2ada1