util-linux: util-linux: TOCTOU in the mount program when applying post-mount ownership/mode changes

A flaw was found in util-linux. When an /etc/fstab entry uses the user option together with X-mount.owner, X-mount.group, or X-mount.mode, mount8 changes ownership or permissions on the mount target after mounting without re-verifying the path. A local unprivileged user can exploit this...