reject fuse_notify pagecache ops on directories

Summary

In the Linux kernel, the following vulnerability has been resolved: fuse: reject fuse_notify() pagecache ops on directories The operations FUSE_NOTIFY_STORE and FUSE_NOTIFY_RETRIEVE allow the FUSE daemon to actively write/read pagecache contents. For directories with FOPEN_CACHE_DIR, the pagecache is used as kernel-internal cache storage, and userspace is not supposed to have direct access to this cache - in particular, fuse_parse_cache() will hit WARN_ON() if the cache contains bogus data. Reject FUSE_NOTIFY_STORE and FUSE_NOTIFY_RETRIEVE on anything other than regular files with -EINVAL. A flaw was found in the Linux kernel's Filesystem in Userspace (FUSE) component. When these operations are performed on directories configured with `FOPEN_CACHE_DIR`, userspace can improperly access and manipulate kernel-internal cache storage. This could lead to system instability or a denial of service if the cache contains invalid data, potentially triggering a kernel warning. Red Hat severity: Moderate — CVSS 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H). Weakness: CWE-266. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9. Red Hat does not currently list a fixing RHSA for this CVE.