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 didnt 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).

Affected Software

References

• https://git.kernel.org/stable/c/5f537664e705b0bf8b7e329861f20128534f6a83
• https://git.kernel.org/stable/c/780ab8329672464984cf1344bd5c3993af0226c7
• https://git.kernel.org/stable/c/7d6405c13b0d8a8367cd8df63f118b619a3f0dd2
• https://git.kernel.org/stable/c/97153a05077f618f7471f50a78158602badccb30