In the Linux kernel, the following vulnerability has been resolved: netfs: clear post-EOF pagecache when extending a file via write Fix netfs to… (CVE-2026-98844)

The Linux kernel netfs vulnerability (CVE-2026-98844) involved improper clearing of the post-EOF pagecache when extending a file via write operations. Specifically, stale data could remain in the pagecache if dirty data was previously written through an mmapped region, as neither buffered nor direct I/O write paths cleared this stale cache. The fix zeroes the tail of the folio overlapping the EOF before extending writes, ensuring no stale data is exposed. It also manages concurrent extending writes by re-reading the file size under folio lock and clamps zeroing accordingly, and waits for any ongoing writeback to complete before zeroing. This prevents data races and ensures data integrity during concurrent file extension and writeback operations. The fix includes a helper function to handle cases where exclusive locks are held for file resize operations, used by the CIFS client to address related issues.

The vulnerability could result in stale or unintended data being exposed or written beyond the EOF during file extension operations, potentially leading to data corruption or leakage of previously written data through memory-mapped files. This affects the integrity and confidentiality of file data handled by netfs in the Linux kernel. No known exploits in the wild have been reported.

A fix for this vulnerability has been implemented in the Linux kernel netfs subsystem. Users and administrators should apply the official kernel updates that include this patch to ensure the issue is resolved. Since this is a kernel-level fix, upgrading to a kernel version containing this patch is the recommended remediation. Patch status is not explicitly stated in the provided data; therefore, check the vendor or Linux kernel advisory for the exact fixed version and update accordingly.