cve/published/2025/CVE-2025-21823.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2025-21823: batman-adv: Drop unmanaged ELP metric worker

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

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

batman-adv: Drop unmanaged ELP metric worker

The ELP worker needs to calculate new metric values for all neighbors
"reachable" over an interface. Some of the used metric sources require
locks which might need to sleep. This sleep is incompatible with the RCU
list iterator used for the recorded neighbors. The initial approach to work
around of this problem was to queue another work item per neighbor and then
run this in a new context.

Even when this solved the RCU vs might_sleep() conflict, it has a major
problems: Nothing was stopping the work item in case it is not needed
anymore - for example because one of the related interfaces was removed or
the batman-adv module was unloaded - resulting in potential invalid memory
accesses.

Directly canceling the metric worker also has various problems:

* cancel_work_sync for a to-be-deactivated interface is called with
  rtnl_lock held. But the code in the ELP metric worker also tries to use
  rtnl_lock() - which will never return in this case. This also means that
  cancel_work_sync would never return because it is waiting for the worker
  to finish.
* iterating over the neighbor list for the to-be-deactivated interface is
  currently done using the RCU specific methods. Which means that it is
  possible to miss items when iterating over it without the associated
  spinlock - a behaviour which is acceptable for a periodic metric check
  but not for a cleanup routine (which must "stop" all still running
  workers)

The better approch is to get rid of the per interface neighbor metric
worker and handle everything in the interface worker. The original problems
are solved by:

* creating a list of neighbors which require new metric information inside
  the RCU protected context, gathering the metric according to the new list
  outside the RCU protected context
* only use rcu_trylock inside metric gathering code to avoid a deadlock
  when the cancel_delayed_work_sync is called in the interface removal code
  (which is called with the rtnl_lock held)

The Linux kernel CVE team has assigned CVE-2025-21823 to this issue.


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

	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 5.4.291 with commit 1c334629176c2d644befc31a20d4bf75542f7631
	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 5.10.235 with commit a0019971f340ae02ba54cf1861f72da7e03e6b66
	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 5.15.179 with commit 3c0e0aecb78cb2a2ca1dc701982d08fedb088dc6
	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.1.129 with commit 781a06fd265a8151f7601122d9c2e985663828ff
	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.6.79 with commit a7aa2317285806640c844acd4cd2cd768e395264
	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.12.16 with commit 0fdc3c166ac17b26014313fa2b93696354511b24
	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.13.4 with commit af264c2a9adc37f4bdf88ca7f3affa15d8c7de9e
	Issue introduced in 4.6 with commit c833484e5f3872a38fe232c663586069d5ad9645 and fixed in 6.14 with commit 8c8ecc98f5c65947b0070a24bac11e12e47cc65d

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-2025-21823
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/batman-adv/bat_v.c
	net/batman-adv/bat_v_elp.c
	net/batman-adv/bat_v_elp.h
	net/batman-adv/types.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/1c334629176c2d644befc31a20d4bf75542f7631
	https://git.kernel.org/stable/c/a0019971f340ae02ba54cf1861f72da7e03e6b66
	https://git.kernel.org/stable/c/3c0e0aecb78cb2a2ca1dc701982d08fedb088dc6
	https://git.kernel.org/stable/c/781a06fd265a8151f7601122d9c2e985663828ff
	https://git.kernel.org/stable/c/a7aa2317285806640c844acd4cd2cd768e395264
	https://git.kernel.org/stable/c/0fdc3c166ac17b26014313fa2b93696354511b24
	https://git.kernel.org/stable/c/af264c2a9adc37f4bdf88ca7f3affa15d8c7de9e
	https://git.kernel.org/stable/c/8c8ecc98f5c65947b0070a24bac11e12e47cc65d