mm: thp: deny THP for files on anonymous inodes

{
  "id": "9e9a53de397dd81c89b8e4a3a5087b61418372e8abfac3162cf681fdff7a308e",
  "url": "https://osv.dev/vulnerability/CVE-2026-23375",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mm: thp: deny THP for files on anonymous inodes",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: mm: thp: deny THP for files on anonymous inodes file_thp_enabled() incorrectly allows THP for files on anonymous inodes (e.g. guest_memfd and secretmem). These files are created via alloc_file_pseudo(), which does not call get_write_access() and leaves inode->i_writecount at 0. Combined with S_ISREG(inode->i_mode) being true, they appear as read-only regular files when CONFIG_READ_ONLY_THP_FOR_FS is enabled, making them eligible for THP collapse. Anonymous inodes can never pass the inode_is_open_for_write() check since their i_writecount is never incremented through the normal VFS open path. The right thing to do is to exclude them from THP eligibility altogether, since CONFIG_READ_ONLY_THP_FOR_FS was designed for real filesystem files (e.g. shared libraries), not for pseudo-filesystem inodes. For guest_memfd, this allows khugepaged and MADV_COLLAPSE to create large folios in the page cache via the collapse path, but the guest_memfd fault handler does not support large folios. This triggers WARN_ON_ONCE(folio_test_large(folio)) in kvm_gmem_fault_user_mapping(). For secretmem, collapse_file() tries to copy page contents through the direct map, but secretmem pages are removed from the direct map. This can result in a kernel crash: BUG: unable to handle page fault for address: ffff88810284d000 RIP: 0010:memcpy_orig+0x16/0x130 Call Trace: collapse_file hpage_collapse_scan_file madvise_collapse Secretmem is not af",
    "evidence": "osv:CVE-2026-23375",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.78",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.17",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.7",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-23375",
      "aliases": [
        "CVE-2026-23375"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "7fbb5e188248c50f737720825da1864ce42536d1"
                },
                {
                  "fixed": "08de46a75f91a6661bc1ce0a93614f4bc313c581"
                },
                {
                  "fixed": "0524ee56af2c9bfbad152a810f1ca95de8ca00d7"
                },
                {
                  "fixed": "f6fa05f0dddd387417d0c28281ddb951582514d6"
                },
                {
                  "fixed": "dd085fe9a8ebfc5d10314c60452db38d2b75e609"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23375.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.8.0"
                },
                {
                  "fixed": "6.12.78"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.17"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "6.19.7"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-23375.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:30.625540512Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0524ee56af2c9bfbad152a810f1ca95de8ca00d7",
        "https://git.kernel.org/stable/c/08de46a75f91a6661bc1ce0a93614f4bc313c581",
        "https://git.kernel.org/stable/c/dd085fe9a8ebfc5d10314c60452db38d2b75e609",
        "https://git.kernel.org/stable/c/f6fa05f0dddd387417d0c28281ddb951582514d6",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/23xxx/CVE-2026-23375.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-23375",
        "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/2026/23xxx/CVE-2026-23375.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-23375",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 497461,
  "published_at": "2026-03-25T10:27:55.754+00:00"
}