manager_luo_serialize_fd_stores() refuses to serialize a unit fd store
entry that holds a child LUO session named like PID 1's own ("systemd"),
to stop a service from hijacking PID 1's reserved session namespace
across kexec. That guard had no test coverage.
Add a test-luo store-hijack/check-hijack subcommand pair: on the first
boot a system service preserves a child LUO session named "systemd" in
its fd store; after kexec the test asserts the entry was not restored --
the unit's NFileDescriptorStore is 0, and check-hijack, run as the unit's
own second-boot ExecStart, confirms the hijack fd is absent from its
restored LISTEN_FDNAMES -- proving PID 1 skipped it during serialization.
The restore-side guards (corrupt mapping, reserved token 0, invalid unit
name, missing child session) are intentionally not covered: they only run
against PID 1's own "systemd" session built by luo_preserve_fd_stores(),
which a cooperating userspace helper cannot corrupt without racing or
displacing PID 1 (it single-owns /dev/liveupdate at shutdown). Triggering
them reliably would need kernel fault injection.
Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>
Rocker Zhang
851ee29a54