Local privilege escalation via kernfs xattr race

Race condition in the Linux kernel 7.1 through 7.1.4 allows local users to escalate privileges through concurrent kernfs xattr operations. The kernfs_xattr_set and kernfs_vfs_user_xattr_set paths call simple_xattr_set while relying only on per-inode VFS locks, so namespace-distinct superblocks can concurrently replace or remove entries in the same kernfs_node->iattr->xattrs structure. Reachability requires shared kernfs nodes across multiple namespace-tagged superblocks and concurrent xattr writes; successful exploitation can disclose or modify kernel memory or panic the host.