futex: Fix private hash use-after-free on resize

{
  "id": "c67618568ce36bd7df4895927ebd3e2b49dc17a8687eee4665d850b836d53c1b",
  "url": "https://osv.dev/vulnerability/CVE-2026-98788",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "futex: Fix private hash use-after-free on resize",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: futex: Fix private hash use-after-free on resize poll_state_synchronize_rcu(mm->futex.phash.batches) is used by futex_ref_drop() to check that a grace period has passed since the current hash was published. This relies on batches referencing a grace period which started after the hash pointer was assigned. __futex_pivot_hash() sets mmph->batches before it replaces mmph->hash: scoped_guard(rcu) { mmph->batches = get_state_synchronize_rcu(); rcu_assign_pointer(mmph->hash, new); } The scoped_guard(rcu) doesn't stop new grace periods from starting, and if one starts between those two assignments, futex_ref_drop() can move forward while a reader still holds a pointer to the old hash. Fix things by setting mmph->batches after assigning mmph->hash. The scoped_guard(rcu) isn't needed, so let's drop that as well.",
    "evidence": "osv:CVE-2026-98788",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.10",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-98788",
      "aliases": [
        "CVE-2026-98788"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "56180dd20c19e5b0fa34822997a9ac66b517e7b3"
                },
                {
                  "fixed": "5d5dc18b3a9ac011619b7d3af4514bf9e9b6a6af"
                },
                {
                  "fixed": "f35e3b5784221654f9cdbd6222275a7fa203f6c3"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98788.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.17.0"
                },
                {
                  "fixed": "7.2.10"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98788.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:53.343864739Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/5d5dc18b3a9ac011619b7d3af4514bf9e9b6a6af",
        "https://git.kernel.org/stable/c/f35e3b5784221654f9cdbd6222275a7fa203f6c3",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98788.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98788",
        "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/2026/98xxx/CVE-2026-98788.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98788",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 522338,
  "published_at": "2026-10-18T15:48:24.833+00:00"
}