mm/MADV_COLLAPSE: catch !none !huge !bad pmd lookups

{
  "id": "b754711b001ddcf322a2edc6c72a2887a7c29931fa577624b87f0113f9995d57",
  "url": "https://osv.dev/vulnerability/CVE-2023-52934",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mm/MADV_COLLAPSE: catch !none !huge !bad pmd lookups",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: mm/MADV_COLLAPSE: catch !none !huge !bad pmd lookups In commit 34488399fa08 (\"mm/madvise: add file and shmem support to MADV_COLLAPSE\") we make the following change to find_pmd_or_thp_or_none(): - if (!pmd_present(pmde)) - return SCAN_PMD_NULL; + if (pmd_none(pmde)) + return SCAN_PMD_NONE; This was for-use by MADV_COLLAPSE file/shmem codepaths, where MADV_COLLAPSE might identify a pte-mapped hugepage, only to have khugepaged race-in, free the pte table, and clear the pmd. Such codepaths include: A) If we find a suitably-aligned compound page of order HPAGE_PMD_ORDER already in the pagecache. B) In retract_page_tables(), if we fail to grab mmap_lock for the target mm/address. In these cases, collapse_pte_mapped_thp() really does expect a none (not just !present) pmd, and we want to suitably identify that case separate from the case where no pmd is found, or it's a bad-pmd (of course, many things could happen once we drop mmap_lock, and the pmd could plausibly undergo multiple transitions due to intervening fault, split, etc). Regardless, the code is prepared install a huge-pmd only when the existing pmd entry is either a genuine pte-table-mapping-pmd, or the none-pmd. However, the commit introduces a logical hole; namely, that we've allowed !none- && !huge- && !bad-pmds to be classified as genuine pte-table-mapping-pmds. One such example that could leak through are swap entries. The pmd values aren't checked a",
    "evidence": "osv:CVE-2023-52934",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.11",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2023-52934",
      "aliases": [
        "CVE-2023-52934"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/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": "34488399fa08faaf664743fa54b271eb6f9e1321"
                },
                {
                  "fixed": "96aaaf8666010a39430cecf8a65c7ce2908a030f"
                },
                {
                  "fixed": "edb5d0cf5525357652aff6eacd9850b8ced07143"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2023-52934.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.1.0"
                },
                {
                  "fixed": "6.1.11"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2023-52934.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:29.231035505Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/96aaaf8666010a39430cecf8a65c7ce2908a030f",
        "https://git.kernel.org/stable/c/edb5d0cf5525357652aff6eacd9850b8ced07143",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/52xxx/CVE-2023-52934.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2023-52934",
        "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/2023/52xxx/CVE-2023-52934.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2023-52934",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 496036,
  "published_at": "2025-03-27T16:37:14.857+00:00"
}