nfsd: fix nfsd_file reference leak in nfsd4_add_rdaccess_to_wrdeleg()

{
  "id": "db2a2fb08242739f3a53418c70c099b6c9738d84a7772340a944ec5961ed56a7",
  "url": "https://osv.dev/vulnerability/CVE-2025-71090",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "nfsd: fix nfsd_file reference leak in nfsd4_add_rdaccess_to_wrdeleg()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: nfsd: fix nfsd_file reference leak in nfsd4_add_rdaccess_to_wrdeleg() nfsd4_add_rdaccess_to_wrdeleg() unconditionally overwrites fp->fi_fds[O_RDONLY] with a newly acquired nfsd_file. However, if the client already has a SHARE_ACCESS_READ open from a previous OPEN operation, this action overwrites the existing pointer without releasing its reference, orphaning the previous reference. Additionally, the function originally stored the same nfsd_file pointer in both fp->fi_fds[O_RDONLY] and fp->fi_rdeleg_file with only a single reference. When put_deleg_file() runs, it clears fi_rdeleg_file and calls nfs4_file_put_access() to release the file. However, nfs4_file_put_access() only releases fi_fds[O_RDONLY] when the fi_access[O_RDONLY] counter drops to zero. If another READ open exists on the file, the counter remains elevated and the nfsd_file reference from the delegation is never released. This potentially causes open conflicts on that file. Then, on server shutdown, these leaks cause __nfsd_file_cache_purge() to encounter files with an elevated reference count that cannot be cleaned up, ultimately triggering a BUG() in kmem_cache_destroy() because there are still nfsd_file objects allocated in that cache.",
    "evidence": "osv:CVE-2025-71090",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-71090",
      "aliases": [
        "CVE-2025-71090"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e7a8ebc305f26cab608e59a916a4ae89d6656c5f"
                },
                {
                  "fixed": "c07dc84ed67c5a182273171639bacbbb87c12175"
                },
                {
                  "fixed": "8072e34e1387d03102b788677d491e2bcceef6f5"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-71090.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.17.0"
                },
                {
                  "fixed": "6.18.4"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-71090.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:29.818300704Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/8072e34e1387d03102b788677d491e2bcceef6f5",
        "https://git.kernel.org/stable/c/c07dc84ed67c5a182273171639bacbbb87c12175",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/71xxx/CVE-2025-71090.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-71090",
        "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/2025/71xxx/CVE-2025-71090.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-71090",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 496579,
  "published_at": "2026-01-13T15:34:51.777+00:00"
}