CVE-2025-39881

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Source
https://cve.org/CVERecord?id=CVE-2025-39881
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39881.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2025-39881
Downstream
Related
Published
2025-09-23T06:00:50Z
Modified
2026-08-12T03:51:34Z
Severity
  • 7.8 (High) CVSS_V3 - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H CVSS Calculator
Summary
kernfs: Fix UAF in polling when open file is released
Details

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

kernfs: Fix UAF in polling when open file is released

A use-after-free (UAF) vulnerability was identified in the PSI (Pressure Stall Information) monitoring mechanism:

BUG: KASAN: slab-use-after-free in psi_trigger_poll+0x3c/0x140 Read of size 8 at addr ffff3de3d50bd308 by task systemd/1

psi_trigger_poll+0x3c/0x140 cgroup_pressure_poll+0x70/0xa0 cgroup_file_poll+0x8c/0x100 kernfs_fop_poll+0x11c/0x1c0 ep_item_poll.isra.0+0x188/0x2c0

Allocated by task 1: cgroup_file_open+0x88/0x388 kernfs_fop_open+0x73c/0xaf0 do_dentry_open+0x5fc/0x1200 vfs_open+0xa0/0x3f0 do_open+0x7e8/0xd08 path_openat+0x2fc/0x6b0 do_filp_open+0x174/0x368

Freed by task 8462: cgroup_file_release+0x130/0x1f8 kernfs_drain_open_files+0x17c/0x440 kernfs_drain+0x2dc/0x360 kernfs_show+0x1b8/0x288 cgroup_file_show+0x150/0x268 cgroup_pressure_write+0x1dc/0x340 cgroup_file_write+0x274/0x548

Reproduction Steps:

  1. Open test/cpu.pressure and establish epoll monitoring
  2. Disable monitoring: echo 0 > test/cgroup.pressure
  3. Re-enable monitoring: echo 1 > test/cgroup.pressure

The race condition occurs because:

  1. When cgroup.pressure is disabled (echo 0 > cgroup.pressure), it:
    • Releases PSI triggers via cgroup_file_release()
    • Frees of->priv through kernfs_drain_open_files()
  2. While epoll still holds reference to the file and continues polling
  3. Re-enabling (echo 1 > cgroup.pressure) accesses freed of->priv

epolling disable/enable cgroup.pressure fd=open(cpu.pressure) while(1) ... epoll_wait kernfs_fop_poll kernfs_get_active = true echo 0 > cgroup.pressure ... cgroup_file_show kernfs_show // inactive kn kernfs_drain_open_files cft->release(of); kfree(ctx); ... kernfs_get_active = false echo 1 > cgroup.pressure kernfs_show kernfs_activate_one(kn); kernfs_fop_poll kernfs_get_active = true cgroup_file_poll psi_trigger_poll // UAF ... end: close(fd)

To address this issue, introduce kernfs_get_active_of() for kernfs open files to obtain active references. This function will fail if the open file has been released. Replace kernfs_get_active() with kernfs_get_active_of() to prevent further operations on released file descriptors.

Database specific 
{
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39881.json"
}
References

Affected packages

Git / git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git

Affected ranges

Type
GIT
Repo
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Events
Introduced
34f26a15611afb03c33df6819359d36f5b382589
Fixed
34d9cafd469c69ad85e6a36b4303c78382cf5c79
Fixed
854baafc00c433cccbe0ab4231b77aeb9b637b77
Fixed
7e64474aba78d240f7804f48f2d454dcca78b15f
Fixed
ac5cda4fae8818cf1963317bb699f7f2f85b60af
Fixed
3c9ba2777d6c86025e1ba4186dc5cd930e40ec5f

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39881.json"

Linux / Kernel

Package

Name
Kernel

Affected ranges

Type
ECOSYSTEM
Events
Introduced
6.1.0
Fixed
6.1.153
Type
ECOSYSTEM
Events
Introduced
6.2.0
Fixed
6.6.107
Type
ECOSYSTEM
Events
Introduced
6.7.0
Fixed
6.12.48
Type
ECOSYSTEM
Events
Introduced
6.13.0
Fixed
6.16.8

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39881.json"