kernfs: Fix UAF in polling when open file is released

{
  "id": "a21709601297f082afe37993414df18b9c8a25f7c2bd04d17eee28c0aa7034df",
  "url": "https://osv.dev/vulnerability/CVE-2025-39881",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "kernfs: Fix UAF in polling when open file is released",
    "summary": "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=ope",
    "evidence": "osv:CVE-2025-39881",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.153",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.107",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.48",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.16.8",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-39881",
      "aliases": [
        "CVE-2025-39881"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "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"
          }
        },
        {
          "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"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39881.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:35.531396954Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/34d9cafd469c69ad85e6a36b4303c78382cf5c79",
        "https://git.kernel.org/stable/c/3c9ba2777d6c86025e1ba4186dc5cd930e40ec5f",
        "https://git.kernel.org/stable/c/7e64474aba78d240f7804f48f2d454dcca78b15f",
        "https://git.kernel.org/stable/c/854baafc00c433cccbe0ab4231b77aeb9b637b77",
        "https://git.kernel.org/stable/c/ac5cda4fae8818cf1963317bb699f7f2f85b60af",
        "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39881.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-39881",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39881.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-39881",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 502978,
  "published_at": "2025-09-23T06:00:50.496+00:00"
}