CVE-2026-64514 (GCVE-0-2026-64514)
Vulnerability from cvelistv5
Published
2026-07-25 08:52
Modified
2026-08-17 04:57
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is "is this fault still WP-blocked?". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says "wait", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns "don't wait" and lets the fault path retry.
References
Impacted products
Vendor Product Version
Linux Linux Version: 369cd2121be440543280b91056de187f625d0dbb
Version: 369cd2121be440543280b91056de187f625d0dbb
Version: 369cd2121be440543280b91056de187f625d0dbb
Version: 369cd2121be440543280b91056de187f625d0dbb
Version: 369cd2121be440543280b91056de187f625d0dbb
Version: 369cd2121be440543280b91056de187f625d0dbb
Version: 369cd2121be440543280b91056de187f625d0dbb
Version: 369cd2121be440543280b91056de187f625d0dbb
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{
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      "cpeApplicability": [
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              "cpeMatch": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: gate must_wait writability check on pte_present()\n\nuserfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE\nwithout taking the page table lock and then apply pte_write() /\nhuge_pte_write() to it.  Those accessors decode bits from the present\nencoding only; on a swap or migration entry they read the offset bits that\nhappen to share the same position and return an undefined result.\n\nThe intent of the check is \"is this fault still WP-blocked?\".  A\nnon-marker swap entry means the page is in transit -- the userfault\ncontext the original fault delivered against is no longer the same, and\nthe swap-in or migration completion path will re-deliver a fresh fault if\nuserspace still needs to handle it.  Worst case under the current code the\ngarbage write bit says \"wait\", and the thread stays asleep until a\nUFFDIO_WAKE that may never arrive.\n\nGate the writability check on pte_present() so the lockless re-check only\ninspects present-PTE bits when the entry is actually present.  The\nnon-present, non-marker case returns \"don\u0027t wait\" and lets the fault path\nretry."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:57:05.592Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a5700a4c1c9099ac2ac73fe8a09cf059972e0d2f"
        },
        {
          "url": "https://git.kernel.org/stable/c/d4026417e8184d13850a0bad4d96ceb6ed9f7152"
        },
        {
          "url": "https://git.kernel.org/stable/c/29e6f952c5fb7dc1d6b90fe5b7f36063d44ddae0"
        },
        {
          "url": "https://git.kernel.org/stable/c/5f4dbdb0a87596214076b20b94f2b71b522170b3"
        },
        {
          "url": "https://git.kernel.org/stable/c/a6e9a4939e359599701b1da351e84f72e021443a"
        },
        {
          "url": "https://git.kernel.org/stable/c/60d696a037eeeedfb57756dfe7ec08a1587c8631"
        },
        {
          "url": "https://git.kernel.org/stable/c/710183888174639a15fcec16cd1af766b8480bb7"
        },
        {
          "url": "https://git.kernel.org/stable/c/8e80af52db652fbc41320eee45a4f73bc029faf2"
        }
      ],
      "title": "userfaultfd: gate must_wait writability check on pte_present()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64514",
    "datePublished": "2026-07-25T08:52:05.878Z",
    "dateReserved": "2026-07-19T15:36:31.793Z",
    "dateUpdated": "2026-08-17T04:57:05.592Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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