linux-cve-announce - CVE-2025-21634: cgroup/cpuset: remove kernfs active break

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <2025011942-CVE-2025-21634-011f@gregkh>
Date: Sun, 19 Jan 2025 11:17:43 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21634: cgroup/cpuset: remove kernfs active break

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

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

cgroup/cpuset: remove kernfs active break

A warning was found:

WARNING: CPU: 10 PID: 3486953 at fs/kernfs/file.c:828
CPU: 10 PID: 3486953 Comm: rmdir Kdump: loaded Tainted: G
RIP: 0010:kernfs_should_drain_open_files+0x1a1/0x1b0
RSP: 0018:ffff8881107ef9e0 EFLAGS: 00010202
RAX: 0000000080000002 RBX: ffff888154738c00 RCX: dffffc0000000000
RDX: 0000000000000007 RSI: 0000000000000004 RDI: ffff888154738c04
RBP: ffff888154738c04 R08: ffffffffaf27fa15 R09: ffffed102a8e7180
R10: ffff888154738c07 R11: 0000000000000000 R12: ffff888154738c08
R13: ffff888750f8c000 R14: ffff888750f8c0e8 R15: ffff888154738ca0
FS:  00007f84cd0be740(0000) GS:ffff8887ddc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555f9fbe00c8 CR3: 0000000153eec001 CR4: 0000000000370ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 kernfs_drain+0x15e/0x2f0
 __kernfs_remove+0x165/0x300
 kernfs_remove_by_name_ns+0x7b/0xc0
 cgroup_rm_file+0x154/0x1c0
 cgroup_addrm_files+0x1c2/0x1f0
 css_clear_dir+0x77/0x110
 kill_css+0x4c/0x1b0
 cgroup_destroy_locked+0x194/0x380
 cgroup_rmdir+0x2a/0x140

It can be explained by:
rmdir 				echo 1 > cpuset.cpus
				kernfs_fop_write_iter // active=0
cgroup_rm_file
kernfs_remove_by_name_ns	kernfs_get_active // active=1
__kernfs_remove					  // active=0x80000002
kernfs_drain			cpuset_write_resmask
wait_event
//waiting (active == 0x80000001)
				kernfs_break_active_protection
				// active = 0x80000001
// continue
				kernfs_unbreak_active_protection
				// active = 0x80000002
...
kernfs_should_drain_open_files
// warning occurs
				kernfs_put_active

This warning is caused by 'kernfs_break_active_protection' when it is
writing to cpuset.cpus, and the cgroup is removed concurrently.

The commit 3a5a6d0c2b03 ("cpuset: don't nest cgroup_mutex inside
get_online_cpus()") made cpuset_hotplug_workfn asynchronous, This change
involves calling flush_work(), which can create a multiple processes
circular locking dependency that involve cgroup_mutex, potentially leading
to a deadlock. To avoid deadlock. the commit 76bb5ab8f6e3 ("cpuset: break
kernfs active protection in cpuset_write_resmask()") added
'kernfs_break_active_protection' in the cpuset_write_resmask. This could
lead to this warning.

After the commit 2125c0034c5d ("cgroup/cpuset: Make cpuset hotplug
processing synchronous"), the cpuset_write_resmask no longer needs to
wait the hotplug to finish, which means that concurrent hotplug and cpuset
operations are no longer possible. Therefore, the deadlock doesn't exist
anymore and it does not have to 'break active protection' now. To fix this
warning, just remove kernfs_break_active_protection operation in the
'cpuset_write_resmask'.

The Linux kernel CVE team has assigned CVE-2025-21634 to this issue.


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

	Issue introduced in 3.16 with commit 76bb5ab8f6e3e7bebdcefec4146ff305e7d0b465 and fixed in 6.12.10 with commit 11cb1d643a74665a4e14749414f48f82cbc15c64
	Issue introduced in 3.16 with commit 76bb5ab8f6e3e7bebdcefec4146ff305e7d0b465 and fixed in 6.13-rc7 with commit 3cb97a927fffe443e1e7e8eddbfebfdb062e86ed

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-2025-21634
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/cpuset.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/11cb1d643a74665a4e14749414f48f82cbc15c64
	https://git.kernel.org/stable/c/3cb97a927fffe443e1e7e8eddbfebfdb062e86ed