The hardening refactor that just landed closes the same-uid attack
surface (FS view, ptrace, /proc visibility, signals) for the web +
gameserver units via systemd directives plus system-wide
kernel.yama.ptrace_scope=2. Keeping the script-sandbox on a separate
uid was the inconsistent half-step — defense-in-depth only, with
build-time-idmap complexity attached. One principle wins: harden
once, share the uid.
scripts/libexec/left4me-script-sandbox: drop the idmap block (uid
lookups, STAGING setup, cleanup_staging trap, mount --bind
--map-users), switch User=/Group= to left4me, point BindPaths at
\$OVERLAY_DIR directly. Header comment updated to reflect
hardening-not-uid as the same-uid defense. nsenter self-wrap kept —
it's about mount-namespace escape, not uid.
Tests + comments + companion docs updated. Build-time-idmap and
overlay-idmap plans marked SUPERSEDED; user-uid-split spec revised
to "1 user is correct"; one-line update notes on the hardening
specs and the build-overlay-unit-design.
Companion ckn-bw commit removes the l4d2-sandbox user + group and
tightens /var/lib/left4me from 0711 → 0755 (the traverse-only mode
was specifically for the sandbox uid).
The script content lives in the overlays.script DB column and the
unit's %i is the row id, so the worker-writes-script-to-fs step in
the original sketch is duplication. Document three options (worker
writes / unit fetches via helper / pipe to stdin) and recommend the
unit-fetches variant with RuntimeDirectory= auto-cleanup. Promote
this to the top of the open-decisions list since it shapes the
worker, the unit, and whether a fetch-script helper is added.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
The build-time idmap landing today required a nsenter self-wrap in
left4me-script-sandbox to escape the web app's PrivateTmp namespace
before pre-creating the idmapped staging bind. Working but band-aid:
the helper is reinventing what a systemd template unit would do
declaratively. Mirror the left4me-server@.service pattern with a
build-overlay@.service template — ExecStartPre does the idmap bind in
PID 1's namespace by default, the hardening flags live in the unit
file, ExecStopPost tears down. Worker switches to sudo systemctl start.
Doc captures full proposed unit, worker rewrite sketch, sudoers
update, migration order, verification steps, and the ~5h estimate
so a future session can pick this up cold and execute.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
