GHSA-5QR9-X6VC-9RX2
Vulnerability from github – Published: 2026-09-17 18:32 – Updated: 2026-09-17 18:32In 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.
{
"affected": [],
"aliases": [
"CVE-2026-92487"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-17T17:17:50Z",
"severity": null
},
"details": "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.",
"id": "GHSA-5qr9-x6vc-9rx2",
"modified": "2026-09-17T18:32:06Z",
"published": "2026-09-17T18:32:06Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-92487"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1135704ed22f54873eb0498a232611d9eca30dd4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/24f20986b253c3e4eb13ebe3c2007d1d352408a6"
}
],
"schema_version": "1.4.0",
"severity": []
}
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