CVE-2025-40072 fanotify: Validate the return value of mnt_ns_from_dentry() before dereferencing

In the Linux kernel, the following vulnerability has been resolved: fanotify: Validate the return value of mntnsfromdentry before dereferencing The function dofanotifymark does not validate if mntnsfromdentry returns NULL before dereferencing mntns-userns. This causes a NULL pointer dereference i...