linux-cve-announce - CVE-2025-39877: mm/damon/sysfs: fix use-after-free in state

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Message-ID: <2025092301-CVE-2025-39877-1244@gregkh>
Date: Tue, 23 Sep 2025 08:01:08 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39877: mm/damon/sysfs: fix use-after-free in state_show()

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

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

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

mm/damon/sysfs: fix use-after-free in state_show()

state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. 
This allows a use-after-free race:

CPU 0                         CPU 1
-----                         -----
state_show()                  damon_sysfs_turn_damon_on()
ctx = kdamond->damon_ctx;     mutex_lock(&damon_sysfs_lock);
                              damon_destroy_ctx(kdamond->damon_ctx);
                              kdamond->damon_ctx = NULL;
                              mutex_unlock(&damon_sysfs_lock);
damon_is_running(ctx);        /* ctx is freed */
mutex_lock(&ctx->kdamond_lock); /* UAF */

(The race can also occur with damon_sysfs_kdamonds_rm_dirs() and
damon_sysfs_kdamond_release(), which free or replace the context under
damon_sysfs_lock.)

Fix by taking damon_sysfs_lock before dereferencing the context, mirroring
the locking used in pid_show().

The bug has existed since state_show() first accessed kdamond->damon_ctx.

The Linux kernel CVE team has assigned CVE-2025-39877 to this issue.


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

	Issue introduced in 5.18 with commit a61ea561c87139992fe32afdee48a6f6b85d824a and fixed in 6.1.153 with commit 3858c44341ad49dc7544b19cc9f9ecffaa7cc50e
	Issue introduced in 5.18 with commit a61ea561c87139992fe32afdee48a6f6b85d824a and fixed in 6.6.107 with commit 60d7a3d2b985a395318faa1d88da6915fad11c19
	Issue introduced in 5.18 with commit a61ea561c87139992fe32afdee48a6f6b85d824a and fixed in 6.12.48 with commit 26d29b2ac87a2989071755f9828ebf839b560d4c
	Issue introduced in 5.18 with commit a61ea561c87139992fe32afdee48a6f6b85d824a and fixed in 6.16.8 with commit 4e87f461d61959647464a94d11ae15c011be58ce
	Issue introduced in 5.18 with commit a61ea561c87139992fe32afdee48a6f6b85d824a and fixed in 6.17-rc6 with commit 3260a3f0828e06f5f13fac69fb1999a6d60d9cff

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-2025-39877
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:
	mm/damon/sysfs.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/3858c44341ad49dc7544b19cc9f9ecffaa7cc50e
	https://git.kernel.org/stable/c/60d7a3d2b985a395318faa1d88da6915fad11c19
	https://git.kernel.org/stable/c/26d29b2ac87a2989071755f9828ebf839b560d4c
	https://git.kernel.org/stable/c/4e87f461d61959647464a94d11ae15c011be58ce
	https://git.kernel.org/stable/c/3260a3f0828e06f5f13fac69fb1999a6d60d9cff