exfat: fix valid_size extension over a shared writable mapping

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-92487
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-17 17:17:50 UTC
Updated2026-09-17 17:17:50 UTC
DescriptionIn 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.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 82a81a7352bcf5f2756ac33d47ee0582737e9a85 24f20986b253c3e4eb13ebe3c2007d1d352408a6 git Not specified
CNA Linux Linux affected 82a81a7352bcf5f2756ac33d47ee0582737e9a85 1135704ed22f54873eb0498a232611d9eca30dd4 git Not specified
CNA Linux Linux affected 7.2 Not specified
CNA Linux Linux unaffected 7.2 semver Not specified
CNA Linux Linux unaffected 7.2.6 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/24f20986b253c3e4eb13ebe3c2007d1d352408a6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1135704ed22f54873eb0498a232611d9eca30dd4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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