exfat: fix valid_size extension over a shared writable mapping

{
  "id": "63beb97c79f8995625a4f93a8d02488c703e911a2896d807a9239c5eda8939f7",
  "url": "https://osv.dev/vulnerability/CVE-2026-92487",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "exfat: fix valid_size extension over a shared writable mapping",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: exfat: fix valid_size extension over a shared writable mapping When a shared writable mapping has its valid_size extended by a buffered write or a page fault, exfat zeroes the page-cache gap below the new valid_size. A store through the mapping can race with this zeroing and be overwritten. Fix this by zeroing the gap lazily. Drop ->map_pages so that every first write fault goes through exfat_page_mkwrite(), which advances valid_size to cover the faulting page. With fault-around enabled, a store could install a writable PTE, skip ->page_mkwrite(), and land past valid_size without advancing it. Extending valid_size one faulting page at a time also leaves never-written pages in a large mapping alone. The gap is filled with block granularity, zeroing only the not-uptodate blocks and preserving blocks that may hold data stored through the mapping. On the buffered-write path the invalidate lock is held and the gap is unmapped before zeroing, so a racing store re-faults and, under the inode lock, completes only after the gap has been zeroed and valid_size covers it.",
    "evidence": "osv:CVE-2026-92487",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.6",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-92487",
      "aliases": [
        "CVE-2026-92487"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "82a81a7352bcf5f2756ac33d47ee0582737e9a85"
                },
                {
                  "fixed": "24f20986b253c3e4eb13ebe3c2007d1d352408a6"
                },
                {
                  "fixed": "1135704ed22f54873eb0498a232611d9eca30dd4"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-92487.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "7.2.0"
                },
                {
                  "fixed": "7.2.6"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-92487.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:28.820286934Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/1135704ed22f54873eb0498a232611d9eca30dd4",
        "https://git.kernel.org/stable/c/24f20986b253c3e4eb13ebe3c2007d1d352408a6",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/92xxx/CVE-2026-92487.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-92487",
        "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/2026/92xxx/CVE-2026-92487.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-92487",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 495830,
  "published_at": "2026-09-17T16:10:02.317+00:00"
}