CVE-2026-23169: mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()

CVE-2026-23169: mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()

[Greg Kroah-Hartman]

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

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

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

mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()

syzbot and Eulgyu Kim reported crashes in mptcp_pm_nl_get_local_id()
and/or mptcp_pm_nl_is_backup()

Root cause is list_splice_init() in mptcp_pm_nl_flush_addrs_doit()
which is not RCU ready.

list_splice_init_rcu() can not be called here while holding pernet->lock
spinlock.

Many thanks to Eulgyu Kim for providing a repro and testing our patches.

The Linux kernel CVE team has assigned CVE-2026-23169 to this issue.


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

	Issue introduced in 5.11 with commit 141694df6573b49aa4143c92556544b4b0bbda72 and fixed in 6.18.9 with commit 1f1b9523527df02685dde603f20ff6e603d8e4a1
	Issue introduced in 5.11 with commit 141694df6573b49aa4143c92556544b4b0bbda72 and fixed in 6.19 with commit e2a9eeb69f7d4ca4cf4c70463af77664fdb6ab1d

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-2026-23169
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:
	net/mptcp/pm_kernel.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/1f1b9523527df02685dde603f20ff6e603d8e4a1
	https://git.kernel.org/stable/c/e2a9eeb69f7d4ca4cf4c70463af77664fdb6ab1d