nfsd: fix posix_acl leak and ignored error in nfsd4_create_file

{
  "id": "ea36b287d0a904128e0d756284aa3f392df899d98ca53fc6e7bf4b7475b16742",
  "url": "https://osv.dev/vulnerability/CVE-2026-53396",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "nfsd: fix posix_acl leak and ignored error in nfsd4_create_file",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: nfsd: fix posix_acl leak and ignored error in nfsd4_create_file nfsd4_create_file() has two bugs in its ACL handling: The return value of nfsd4_acl_to_attr() is silently discarded. When the NFSv4-to-POSIX ACL conversion fails (e.g., -EINVAL for unsupported ACE types), the file is created without any ACL and the client receives NFS4_OK. This violates RFC 7530/8881 which require the server to reject unsupported attributes on CREATE. When start_creating() fails after ACL attributes have been populated in attrs (either via nfsd4_acl_to_attr or via ownership transfer from open->op_dpacl/op_pacl), the function jumps to out_write which skips nfsd_attrs_free(). The posix_acl allocations are leaked. A client can trigger this repeatedly with OPEN(CREATE), ACL attributes, and an invalid filename (e.g., longer than NAME_MAX). Fix both by capturing the nfsd4_acl_to_attr() return value and by changing the early error paths to jump to out instead of out_write. Initialize child to ERR_PTR(-EINVAL) so that end_creating() is safe to call even if start_creating() was never reached.",
    "evidence": "osv:CVE-2026-53396",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.1.3",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-53396",
      "aliases": [
        "CVE-2026-53396"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "7ab96df840e60eb933abfe65fc5fe44e72f16dc0"
                },
                {
                  "fixed": "18cf006a08babec0bbac2a3784f8f28e56e47490"
                },
                {
                  "fixed": "24c975bbdd564d7d0ad90294bfa69729830345de"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53396.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.1.3"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-53396.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.926124380Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/18cf006a08babec0bbac2a3784f8f28e56e47490",
        "https://git.kernel.org/stable/c/24c975bbdd564d7d0ad90294bfa69729830345de",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53396.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-53396",
        "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/2026/53xxx/CVE-2026-53396.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-53396",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 490409,
  "published_at": "2026-07-19T12:01:58.375+00:00"
}