nfsd: fix UAF in async copy cancel and shutdown

{
  "id": "88c528ad8e641c98a13f79e6961896c6ee1b487c7ee8beeb49b008ece30b2e4d",
  "url": "https://osv.dev/vulnerability/CVE-2026-89675",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "nfsd: fix UAF in async copy cancel and shutdown",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: nfsd: fix UAF in async copy cancel and shutdown An async copy could be freed or used after free while a teardown caller (OFFLOAD_CANCEL, nfsd4_shutdown_copy, nfsd4_cancel_copy_by_sb) raced the copy kthread: - find_async_copy() bumped copy->refcount but left the copy on clp->async_copies, so the reaper's cleanup_async_copy() could run release_copy_files() concurrently with a cancel/shutdown caller. Both put and NULL nf_src/nf_dst without a common lock, double-putting the nfsd_file and freeing it early. - nfsd4_do_async_copy() set NFSD4_COPY_F_STOPPED before its final uses of the copy (nfsd_update_cmtime_attr() on copy->nf_dst, nfsd4_send_cb_offload()). nfsd4_stop_copy() treats a set STOPPED bit as \"kthread done, skip kthread_stop()\", so a teardown caller ran release_copy_files() -- which puts and NULLs nf_dst -- while the kthread still dereferenced it (NULL/UAF). - copy->copy_task was never pinned. The one-shot kthread self-reaps on return, so kthread_stop()'s get_task_struct() could touch a freed task_struct. - co_cb is embedded in the copy, but nfsd4_send_cb_offload() held a reference only on the client, so a concurrent teardown could free the copy while the CB_OFFLOAD callback was in flight. Fix the teardown lifetime as a whole: - find_async_copy() unlinks the copy (clear cp_clp, list_del_init) under async_lock; the cancel, shutdown, and sb-cancel paths drop the list-membership reference via nfs4_put_copy()",
    "evidence": "osv:CVE-2026-89675",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.51",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.2.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-89675",
      "aliases": [
        "CVE-2026-89675"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/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": "e0639dc5805a9d4faaa2c07ad98fa853b9529dd3"
                },
                {
                  "fixed": "9031493ef7369d5c59c4bacc96f0c85965f09a98"
                },
                {
                  "fixed": "a385cf5e016b748babf94cc664e43a26e17db117"
                },
                {
                  "fixed": "62c0f6eaf050bb9284c1f9cac6ed1770092e6b95"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89675.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "4.20.0"
                },
                {
                  "fixed": "6.18.51"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.2.4"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89675.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:43.587228627Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/62c0f6eaf050bb9284c1f9cac6ed1770092e6b95",
        "https://git.kernel.org/stable/c/9031493ef7369d5c59c4bacc96f0c85965f09a98",
        "https://git.kernel.org/stable/c/a385cf5e016b748babf94cc664e43a26e17db117",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89675.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89675",
        "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/2026/89xxx/CVE-2026-89675.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-89675",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 511549,
  "published_at": "2026-09-11T19:45:59.635+00:00"
}