rm: --preserve-root bypassed via a symlink to / (string check instead of dev/inode)

The --preserve-root check uses a path-string test (path.has_root() && path.parent().is_none()) rather than comparing device/inode. A symlink to / (e.g. /tmp/rootlink -> /) has a parent component, so it passes the check. GNU caches /'s dev/inode at startup and compares every traversed directory against it.

Impact: rm -rf --preserve-root on a path that resolves through a symlink to / bypasses protection and can delete system directories. Recommendation: compare each entered directory's dev/inode against cached /.

Remediation: Acknowledged by Canonical; fixed in commit 5e5968cd.

Reported by Zellic in the uutils coreutils Program Security Assessment (prepared for Canonical, Jan 20 2026), audited commit 3a07ffc5a9bd4c283e75afa548ba1f1957bad242. Finding 3.44. Credit: Zellic.