linux-cve-announce - CVE-2026-23195: cgroup/dmem: avoid pool UAF

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Message-ID: <2026021434-CVE-2026-23195-6042@gregkh>
Date: Sat, 14 Feb 2026 17:28:52 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2026-23195: cgroup/dmem: avoid pool UAF

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

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

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

cgroup/dmem: avoid pool UAF

An UAF issue was observed:

BUG: KASAN: slab-use-after-free in page_counter_uncharge+0x65/0x150
Write of size 8 at addr ffff888106715440 by task insmod/527

CPU: 4 UID: 0 PID: 527 Comm: insmod    6.19.0-rc7-next-20260129+ #11
Tainted: [O]=OOT_MODULE
Call Trace:
<TASK>
dump_stack_lvl+0x82/0xd0
kasan_report+0xca/0x100
kasan_check_range+0x39/0x1c0
page_counter_uncharge+0x65/0x150
dmem_cgroup_uncharge+0x1f/0x260

Allocated by task 527:

Freed by task 0:

The buggy address belongs to the object at ffff888106715400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 64 bytes inside of
freed 512-byte region [ffff888106715400, ffff888106715600)

The buggy address belongs to the physical page:

Memory state around the buggy address:
ffff888106715300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888106715380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888106715400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
				     ^
ffff888106715480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888106715500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

The issue occurs because a pool can still be held by a caller after its
associated memory region is unregistered. The current implementation frees
the pool even if users still hold references to it (e.g., before uncharge
operations complete).

This patch adds a reference counter to each pool, ensuring that a pool is
only freed when its reference count drops to zero.

The Linux kernel CVE team has assigned CVE-2026-23195 to this issue.


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

	Issue introduced in 6.14 with commit b168ed458ddecc176f3b9a1f4bcd83d7a4541c14 and fixed in 6.18.10 with commit d3081353acaa6a638dcf75726066ea556a2de8d5
	Issue introduced in 6.14 with commit b168ed458ddecc176f3b9a1f4bcd83d7a4541c14 and fixed in 6.19 with commit 99a2ef500906138ba58093b9893972a5c303c734

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-2026-23195
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/cgroup/dmem.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/d3081353acaa6a638dcf75726066ea556a2de8d5
	https://git.kernel.org/stable/c/99a2ef500906138ba58093b9893972a5c303c734