Summary
In the Linux kernel, the following vulnerability has been resolved: cgroup/cpuset: remove kernfs...
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'.
Impact
CVE-2025-21634 has a CVSS score of 5.5 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-21634? CVE-2025-21634 is a medium-severity security vulnerability. No fixed version is listed yet.
- How severe is CVE-2025-21634? CVE-2025-21634 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-21634? No fixed version is listed for CVE-2025-21634 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-21634 exploitable, and should I be worried? Whether CVE-2025-21634 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-21634 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.