left4me-script-sandbox now pre-creates an idmapped bind staging path
(--map-users=<left4me_uid>:<sandbox_uid>:1) and points the sandbox's
BindPaths at that staging instead of the raw overlay dir. Writes from
inside the sandbox (uid l4d2-sandbox) land on disk as left4me, so all
overlay content is uniformly left4me-owned end-to-end.
left4me-overlay loses ~165 lines of idmap-on-mount logic: the per-
lowerdir stat + idmap-bind setup, the bind-umount loop in teardown,
the uid lookup helpers, the _is_mountpoint /proc/self/mountinfo parser,
and the LEFT4ME_TEST_* env-var stubs. It's back to a simple "validate
lowerdirs, mount overlay" shape; gameserver mount path no longer needs
to know about producer-side ownership decisions.
Verified on kernel 6.12 that the kernel idmap propagates through
systemd-run's plain re-bind of the staging path. Tests dropped 4
idmap-on-mount specs and one deploy-artifact regression check; added
test_script_sandbox_uses_idmap_staging to pin the new staging path
+ map flags + trap cleanup.
The post-build world-read chmod kludge in the sandbox is also dropped:
the web app reads overlay files via its primary uid (left4me).
Existing overlays on the test server are sandbox-owned from prior runs
and need a one-shot `chown -R left4me:left4me /var/lib/left4me/overlays`
during deploy. New overlays produced by the refactored sandbox are
left4me-owned from creation.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
os.path.ismount() compares st_dev against the parent dir, which silently
returns False for same-fs bind mounts. The idmap binds at runtime/<n>/
idmap/<basename> are exactly that case, so:
- cmd_umount skipped the bind-umount step every stop, leaving orphan
binds in PID 1's mount namespace.
- cmd_mount's idempotency check then "didn't see" the orphan and
re-bound on top, accumulating one mount per start/stop cycle.
Findmnt nesting like
/var/lib/left4me/runtime/2/idmap/overlays_9
└─/var/lib/left4me/runtime/2/idmap/overlays_9
is the visible symptom. Reboot wipes everything so the bug is invisible
on a fresh boot — only stop/start cycles accumulate.
Replace both ismount sites with a _is_mountpoint() helper that reads
/proc/self/mountinfo (column 5 is the mount point). Keep os.path.ismount
for the overlay merged check, where it's reliable (distinct fs type).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Issue #1: idmap target now uses parent+name (overlays_workshop instead of
workshop) to prevent basename collisions across allowlist roots; explicit
die() on collision detected in the loop.
Issue #2: env-var uid stubs (renamed to LEFT4ME_TEST_SANDBOX_UID etc.) are
only honoured when LEFT4ME_OVERLAY_PRINT_ONLY=1, so a misconfigured systemd
unit override cannot influence real uid mapping.
Issue #3: os.stat(lowerdir) is wrapped in try/except OSError with a die()
that shell-quotes the path and includes the exception, matching the helper's
existing error style.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Insert an idmapped bind mount in front of each lowerdir whose top-level
uid matches l4d2-sandbox at overlay-mount time, so that overlayfs copy-up
produces left4me-owned upperdir entries instead of EACCES.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
systemd's `+` Exec prefix removes sandbox/credentials but does NOT
detach from the unit's per-service mount namespace (created by
PrivateTmp/Protect*). The Python interpreter for the helper was
launched inside that namespace, and even though the helper internally
nsenter'd into PID 1 for the umount syscall, the calling Python
process itself never left the unit's namespace. Its existence pinned
the namespace alive, which kept the slave mount tree alive, which
made PID 1's umount return EBUSY for the entire duration of the
helper's run. The mount became unmountable the moment the helper
exited — empirically verified by polling /proc/*/ns/mnt during stop:
the only PID holding the dying namespace was the helper itself.
Wrap both ExecStartPre and ExecStopPost with `/usr/bin/nsenter
--mount=/proc/1/ns/mnt --` so the helper Python interpreter runs in
PID 1's mount namespace from the start. With the helper out of the
unit's namespace, umount succeeds first try once the cgroup empties.
Reset went from ~25 s with retry/lazy-fallback workarounds to ~0.5 s
clean.
Knock-on cleanups:
- Helper drops internal nsenter for the syscalls (already in PID 1's
namespace), and drops the eager-retry loop + lazy-umount fallback +
inner work_inner retry (no race left to ride out).
- Revert TimeoutStopSec=60s back to 15s.
- Tests updated to expect the new argv shapes.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
New privileged helper at /usr/local/libexec/left4me/left4me-overlay
(Python, system /usr/bin/python3, stdlib only) takes only the instance
name, parses instance.env for L4D2_LOWERDIRS, validates each lowerdir
against an allowlist (installation/, overlays/, global_overlay_cache/,
workshop_cache/), refuses upperdirs tainted with user.fuseoverlayfs.*
xattrs from the prior fuse era, and execs `nsenter --mount=/proc/1/ns/mnt
-- mount -t overlay ...` so the resulting mount lives in the host
namespace. Mirrors the existing left4me-systemctl / left4me-journalctl
pattern; sudoers entry is verb-constrained.
KernelOverlayFSMounter implements the existing OverlayMounter ABC,
deriving the instance name from the merged path. No call sites use it
yet — that's the next commit.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
