util-linux mount target TOCTOU allows local privilege escalation

util-linux is a random collection of Linux utilities. In util-linux 2.17 through 2.41.6 and 2.42 through 2.42.3, and in 2.42.4 when the legacy mount(2) path is used without /proc, restricted non-root mount requests validate an /etc/fstab target before the mount operation re-resolves that pathname. A local low-privileged user authorized by an fstab user or users entry whose target has an attacker-writable ancestor can use renameat2(RENAME_EXCHANGE) to swap a path component and redirect an authorized mount to a root-owned location, such as mounting attacker-controlled content over /etc/sudoers.d, and thereby gain root privileges. Versions 2.41.5 and 2.42.2 pin targets for the new mount API, and 2.42.4 pins legacy targets through /proc/self/fd; the documented legacy fallback without /proc remains affected.