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overlay-idmap plans marked SUPERSEDED; user-uid-split spec revised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).
Architectural cleanup: the uid translation is a build-time concern
(the sandbox produces sandbox-uid files); having the gameserver path
unwind that producer-side decision on every mount means the mount
helper carries idmap lifecycle code it shouldn't need. Moving the
idmap into the script-sandbox bind makes files land left4me-owned on
disk, drops ~140 lines from left4me-overlay, and makes all overlay
content (workshop + script-built) consistent on-disk.
Verified on left4.me kernel 6.12.86 that the kernel idmap propagates
through plain re-bind, so systemd-run's BindPaths can wrap a
pre-created idmapped staging path.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
