util-linux: util-linux: restricted bind mounts do not pin the source, allowing X-mount.owner/group/mode redirection

A flaw was found in util-linux. Restricted bind mounts take the source path from fstab but do not pin that source before the privileged mount. A local unprivileged user who can replace the authorized source or a writable ancestor can redirect SUID mount8 to bind another host directory. If the fst...