The Linux kernel's cifs_setsize() function previously called truncate_pagecache() but omitted a call to pagecache_isize_extended() when extending a file's size. The correct sequence, as shown in truncate_setsize(), includes calling pagecache_isize_extended() to zero the tail of the page that crosses the old EOF boundary. Without this call, dirty bytes beyond the old EOF could be written back to the CIFS server, exposing stale data in the extended file region. This vulnerability has been resolved by adding the missing call to pagecache_isize_extended() in cifs_setsize().

This vulnerability could lead to stale or unintended data being sent back to the CIFS server when a file is extended, potentially exposing outdated or sensitive information in the newly allocated file space. There is no indication of active exploitation in the wild.

A fix has been implemented in the Linux kernel to call pagecache_isize_extended() in cifs_setsize() when extending files. Users should apply the official Linux kernel updates that include this fix. No additional mitigation steps are indicated.