Local privilege escalation via unchecked helper failure

Local privilege escalation in util-linux 2.39 through 2.41.5 and 2.42 through 2.42.2 allows local users to obtain root privileges. In libmount's exec_helper path, a nonzero external mount-helper exit is stored but treated as success, so idmap and owner hooks act on the pre-existing target. Exploitation requires a usable root-controlled fstab entry, a failing external helper, and X-mount.idmap or ownership options; successful use exposes root data or changes privileged inode permissions.