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>
Smoke testing on the test host revealed three issues with the helper as
shipped:
1. bwrap 0.11+ rejects --uid without --unshare-user. Switching the UID
drop from inside bwrap to systemd-run (--uid=l4d2-sandbox
--gid=l4d2-sandbox) sidesteps the userns UID-mapping headaches and
keeps file ownership on the bind-mounted /overlay matching
l4d2-sandbox on the host (which the wipe path relies on).
2. bwrap running as an unprivileged uid still needs a user namespace to
set up its mount-namespace bind-mounts. Adding --unshare-user-try
gives it the userns context when needed and is a no-op otherwise.
3. /etc/alternatives wasn't bind-mounted, so symlinked tools like
/usr/bin/awk -> /etc/alternatives/awk fell over inside the sandbox.
Adds the ro-bind.
Also: the helper now chowns the overlay dir to l4d2-sandbox before bwrap
(idempotent — needed because the web app creates the dir as left4me),
and the deploy script chmods /var/lib/left4me to 0711 so l4d2-sandbox
can traverse to the bind-mount source.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
deploy-test-server.sh: provisions the l4d2-sandbox system user (no home,
nologin shell) and installs the bubblewrap apt/dnf package; copies the
left4me-script-sandbox helper into /usr/local/libexec/left4me with mode
0755. Drops the global_overlay_cache directory provisioning, the
refresh-global-overlays unit installation, and the timer enable.
Deletes the orphaned left4me-refresh-global-overlays.{service,timer}
files. Trims the matching paragraph from deploy/README.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Privileged bash helper that wraps user-authored scripts in
systemd-run --scope (cgroup limits + RuntimeMaxSec=3600) inside a
bubblewrap sandbox dropped to the l4d2-sandbox uid. Network is shared
with the host so scripts can fetch from Steam / l4d2center / etc.;
filesystem is RO except for /overlay (rw bind from
/var/lib/left4me/overlays/{id}) and tmpfs /tmp + /run.
Adds a sudoers rule allowing the left4me user to invoke this helper
without restrictions on its arguments. Strict argument validation is
in the helper itself.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Drop MountFlags=shared (the assumption that it propagated fuse mounts
to host was incorrect on systemd 257 with ProtectSystem+ReadWritePaths).
Restore PrivateTmp=true (was dropped in 593611e for fuse propagation
that did not work). Rewrite the comment block to describe the new
model: mounts go through the left4me-overlay helper which nsenters
into PID 1's mount namespace, so the unit's mount-ns layout is no
longer load-bearing.
Update the three user-facing READMEs (root, l4d2host, deploy) to drop
fuse-overlayfs / fusermount3 prereqs and call out the kernel overlayfs
mount path through the privileged helper.
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>
Each SSE log-viewer or job-log stream holds a thread for its full
lifetime. With --threads 8, a handful of open browser tabs could
exhaust the pool. 32 keeps the same single-process scheduler invariant
(_claim_lock in job_worker is process-local) while giving SSE plenty
of headroom on the test box's user count.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Adds two managed system overlays (l4d2center-maps, cedapug-maps) that
fetch curated map archives from upstream sources and reconcile addons
symlinks for non-Steam maps. A daily systemd timer enqueues a coalesced
refresh_global_overlays worker job; downloads, extraction, and rebuilds
run in the existing job worker and surface in the job log UI.
Schema: GlobalOverlaySource / GlobalOverlayItem / GlobalOverlayItemFile
plus nullable Job.user_id so system jobs render as "system" in the UI.
The new builder reconciles symlinks against the per-source vpk cache
and leaves foreign symlinks untouched. Initialize-time guard refuses
to mount a partial overlay if any expected vpk is missing from cache.
Refresh service uses shutil.move to handle EXDEV when /tmp and the
cache live on different filesystems.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
ProtectSystem=full + ReadWritePaths implicitly give the unit a private
mount namespace (systemd needs to remount /usr read-only). The default
namespace propagation is slave, so mounts the worker creates inside
never reach the host. The gameserver units (started via systemctl,
each with their own namespace) then inherit a host that lacks the
overlay, and their CHDIR into /var/lib/left4me/runtime/<name>/merged
fails.
Set MountFlags=shared so mount events propagate from the worker's
namespace back to the host, then onward to gameserver units at their
unshare time.
Verified on test box: nsenter -t <gunicorn-pid> -m mount showed the
fuse-overlayfs mount inside the worker but plain mount on the host
did not, while web unit had ProtectSystem=full + ReadWritePaths.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
PrivateTmp=true gives the unit a private mount namespace. The worker's
fuse-overlayfs mount lives only inside that namespace, so the host
cannot see it and the gameserver unit (started via systemctl, with its
own namespace inherited from the host) also cannot see it. The
gameserver unit then fails CHDIR on
/var/lib/left4me/runtime/<name>/merged/left4dead2.
The mount must land in the host namespace so the gameserver unit
inherits it at unshare time. Remaining hardening: dedicated user,
ProtectSystem=full, ReadWritePaths, sudoers allowlist limited to two
helper scripts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The job worker calls fusermount3 (setuid-root) to mount per-instance
FUSE overlays and sudo to invoke the privileged systemctl wrapper.
NoNewPrivileges=true blocks both, surfacing as
"fusermount3: mount failed: Operation not permitted" the first time a
server is started. Hardening is still enforced via dedicated user,
PrivateTmp, ProtectSystem=full, ReadWritePaths, and the narrow sudoers
allowlist limited to two helper scripts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
