keys: Fix UAF in key_put()

{
  "id": "aa39ef59f3912c860d930cca4b2a08b08060b1fb7085f87ffc6b634c9ae59a62",
  "url": "https://osv.dev/vulnerability/CVE-2025-21893",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "keys: Fix UAF in key_put()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: keys: Fix UAF in key_put() Once a key's reference count has been reduced to 0, the garbage collector thread may destroy it at any time and so key_put() is not allowed to touch the key after that point. The most key_put() is normally allowed to do is to touch key_gc_work as that's a static global variable. However, in an effort to speed up the reclamation of quota, this is now done in key_put() once the key's usage is reduced to 0 - but now the code is looking at the key after the deadline, which is forbidden. Fix this by using a flag to indicate that a key can be gc'd now rather than looking at the key's refcount in the garbage collector.",
    "evidence": "osv:CVE-2025-21893",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.21",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.13.9",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-21893",
      "aliases": [
        "CVE-2025-21893"
      ],
      "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": "9578e327b2b4935a25d49e3891b8fcca9b6c10c6"
                },
                {
                  "fixed": "6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3"
                },
                {
                  "fixed": "f6a3cf833188e897c97028cd7b926e3f2cb1a8c0"
                },
                {
                  "fixed": "75845c6c1a64483e9985302793dbf0dfa5f71e32"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21893.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.10.0"
                },
                {
                  "fixed": "6.12.21"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.13.9"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-21893.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:22.608173987Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3",
        "https://git.kernel.org/stable/c/75845c6c1a64483e9985302793dbf0dfa5f71e32",
        "https://git.kernel.org/stable/c/f6a3cf833188e897c97028cd7b926e3f2cb1a8c0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/21xxx/CVE-2025-21893.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-21893",
        "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/2025/21xxx/CVE-2025-21893.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-21893",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 488478,
  "published_at": "2025-03-31T19:41:46.137+00:00"
}