CVE-2025-21691

In the Linux kernel, the following vulnerability has been resolved:

cachestat: fix page cache statistics permission checking

When the 'cachestat()' system call was added in commit cf264e1329fb ("cachestat: implement cachestat syscall"), it was meant to be a much more convenient (and performant) version of mincore() that didn't need mapping things into the user virtual address space in order to work.

But it ended up missing the "check for writability or ownership" fix for mincore(), done in commit 134fca9063ad ("mm/mincore.c: make mincore() more conservative").

This just adds equivalent logic to 'cachestat()', modified for the file context (rather than vma).

This vulnerability is rated as Moderate because exploitation requires local access and is limited to unauthorized information disclosure via page cache timing, without allowing privilege escalation or data manipulation. In affected Red Hat Enterprise Linux environments, an authenticated local attacker can invoke the cachestat system call on files without having write privileges or ownership. This allows monitoring whether file pages are resident in memory, potentially facilitating side-channel attacks against other workloads on multi-tenant systems.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.