CVE-2026-92487 (GCVE-0-2026-92487)
Vulnerability from cvelistv5
Published
2026-09-17 16:10
Modified
2026-10-19 09:03
Severity ?
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.
Impacted products
Vendor Product Version
Linux Linux Version: 82a81a7352bcf5f2756ac33d47ee0582737e9a85
Version: 82a81a7352bcf5f2756ac33d47ee0582737e9a85
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/exfat/exfat_fs.h",
            "fs/exfat/file.c",
            "fs/exfat/iomap.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "24f20986b253c3e4eb13ebe3c2007d1d352408a6",
              "status": "affected",
              "version": "82a81a7352bcf5f2756ac33d47ee0582737e9a85",
              "versionType": "git"
            },
            {
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              "status": "affected",
              "version": "82a81a7352bcf5f2756ac33d47ee0582737e9a85",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/exfat/exfat_fs.h",
            "fs/exfat/file.c",
            "fs/exfat/iomap.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.2"
            },
            {
              "lessThan": "7.2",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.6",
                  "versionStartIncluding": "7.2",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "7.2",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nexfat: fix valid_size extension over a shared writable mapping\n\nWhen a shared writable mapping has its valid_size extended by a buffered\nwrite or a page fault, exfat zeroes the page-cache gap below the new\nvalid_size. A store through the mapping can race with this zeroing and be\noverwritten.\n\nFix this by zeroing the gap lazily. Drop -\u003emap_pages so that every first\nwrite fault goes through exfat_page_mkwrite(), which advances valid_size to\ncover the faulting page. With fault-around enabled, a store could install a\nwritable PTE, skip -\u003epage_mkwrite(), and land past valid_size without\nadvancing it. Extending valid_size one faulting page at a time also leaves\nnever-written pages in a large mapping alone.\n\nThe gap is filled with block granularity, zeroing only the not-uptodate\nblocks and preserving blocks that may hold data stored through the mapping.\nOn the buffered-write path the invalidate lock is held and the gap is\nunmapped before zeroing, so a racing store re-faults and, under the inode\nlock, completes only after the gap has been zeroed and valid_size covers\nit."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:03:53.813Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/24f20986b253c3e4eb13ebe3c2007d1d352408a6"
        },
        {
          "url": "https://git.kernel.org/stable/c/1135704ed22f54873eb0498a232611d9eca30dd4"
        }
      ],
      "title": "exfat: fix valid_size extension over a shared writable mapping",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-92487",
    "datePublished": "2026-09-17T16:10:02.317Z",
    "dateReserved": "2026-09-16T12:21:13.870Z",
    "dateUpdated": "2026-10-19T09:03:53.813Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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