Replaces the systemd-run --scope + bwrap composition with systemd-run in
service-unit mode (--pipe --wait, transient .service unit). Same cgroup
limits and walltime kill, plus the hardening directives that --scope
units cannot carry: NoNewPrivileges, ProtectSystem=strict, ProtectHome,
ProtectKernel{Tunables,Modules,Logs,ControlGroups}, RestrictNamespaces,
RestrictAddressFamilies, RestrictSUIDSGID, LockPersonality,
MemoryDenyWriteExecute, SystemCallFilter (seccomp), and an empty
CapabilityBoundingSet (drops all caps). UID drop via User=/Group=.
The TemporaryFileSystem="/etc /var/lib" pair is the gotcha:
ProtectSystem=strict makes /var/lib *read-only* but visible, so the host
DB at /var/lib/left4me/left4me.db (mode 0644) was readable from inside.
Masking /var/lib with tmpfs hides the entire subtree; the BindPaths bind
to /overlay is at a different path and unaffected.
The Python side (ScriptBuilder, run_sandboxed_script, routes) is
unchanged — same sudo-helper invocation, same argv shape.
Loses PID-namespace isolation (no PrivatePID= directive in systemd).
Host PIDs are visible via /proc and ps -ef but not signal-able due to
UID mismatch — information disclosure only, not a privilege boundary.
Smoke-tested on ckn@10.0.4.128 prior to this commit; all isolation
invariants reproduced and the hardening directives provably blocked
unshare(2), mount(2), personality(2), bpf(2), and sysctl writes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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