nfsd: cap decoded POSIX ACL count to bound sort cost

{
  "id": "5a262f0ffc67ce2eb840bae5513eb2a3630814ed19b21b618fc778b9fb8c6b68",
  "url": "https://osv.dev/vulnerability/CVE-2026-89695",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "nfsd: cap decoded POSIX ACL count to bound sort cost",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: nfsd: cap decoded POSIX ACL count to bound sort cost nfsd4_decode_posixacl() reads a u32 entry count off the wire and passes it straight to posix_acl_alloc() and sort_pacl_range(). The latter is an O(n^2) bubble sort, so a client-chosen count drives unbounded CPU in the server's compound processing path. nfsd4_decode_posixacl() xdr_stream_decode_u32(&count) /* uncapped u32 */ posix_acl_alloc(count, GFP_KERNEL) sort_pacl_range(*acl, 0, count - 1) /* O(n^2) bubble sort */ The encoder side in the same file already rejects ACLs whose a_count exceeds NFS_ACL_MAX_ENTRIES, but the decoder introduced in commit 5fc51dfc2eb1 (\"NFSD: Add support for XDR decoding POSIX draft ACLs\") omitted the symmetric check. Fix by rejecting a wire count greater than NFS_ACL_MAX_ENTRIES with nfserr_inval, before any allocation, so the sort is bounded by NFS_ACL_MAX_ENTRIES^2 comparisons. While we're in here, also fix the nfserr_resource return if posix_acl_alloc() fails. That's not a legal error code for v4.1+. Change it to return nfserr_jukebox as that's more appropriate for memory allocation failures.",
    "evidence": "osv:CVE-2026-89695",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-89695",
      "aliases": [
        "CVE-2026-89695"
      ],
      "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": [
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                  "introduced": "5fc51dfc2eb160bd7ab3251ab1767cacf9c8bf05"
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                {
                  "fixed": "ea14d71d6ecb925673761bcf79f781f7dc9042cc"
                },
                {
                  "fixed": "4bc1108e876153a2dd6d874052b99182c3603135"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89695.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "7.0.0"
                },
                {
                  "fixed": "7.2.4"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89695.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:35.550114141Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/4bc1108e876153a2dd6d874052b99182c3603135",
        "https://git.kernel.org/stable/c/ea14d71d6ecb925673761bcf79f781f7dc9042cc",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89695.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89695",
        "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-2026-89695.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-89695",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 502991,
  "published_at": "2026-09-11T19:46:14.258+00:00"
}