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deploy/hardening: drop ProcSubset=pid from the server drop-in (regression fix)

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The hardening-extraction subagent (commit just prior) re-introduced
ProcSubset=pid into the server@ drop-in because the design plan's
template had it. The directive had previously been removed from the
live unit by ckn-bw 4339289 — it hides /proc/cpuinfo and breaks
SteamAPI master-server registration, leaving the server in LAN-only
fallback ("LAN servers are restricted to local clients (class C)").

Add a negative assertion in the drop-in test so the regression cannot
sneak back in via a copy-paste edit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
mwiegand 2026-05-15 19:24:34 +02:00
parent e9c172a619
commit 3703749252
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2 changed files with 15 additions and 2 deletions
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10
deploy/files/etc/systemd/system/left4me-server@.service.d/10-hardening.conf
View file

@ -52,7 +52,15 @@ PrivateIPC=true
RestrictNamespaces=true
RestrictRealtime=true
ProtectProc=invisible
ProcSubset=pid
# ProcSubset=pid intentionally OMITTED — it hides /proc/cpuinfo and
# /proc/sys/*, which breaks Source's tier0/cpu.cpp and (downstream)
# SteamAPI_Init's pipe-creation step. Server then registers as LAN-only
# and rejects external clients with "LAN servers are restricted to
# local clients (class C)". PrivatePIDs=true (kernel PID namespace) is
# the load-bearing peer-process isolation; ProtectProc=invisible is the
# foreign-uid /proc hide. Losing ProcSubset=pid only exposes host kernel
# info (cpuinfo, meminfo, sysctls), which is not sensitive in this
# threat model. See ckn-bw commit 4339289 for the original fix.
ProtectKernelTunables=true
ProtectKernelModules=true
ProtectKernelLogs=true

7
deploy/tests/test_example_units.py
View file

@ -286,7 +286,6 @@ def test_server_hardening_dropin_present_with_directives():
"CapabilityBoundingSet=",
"AmbientCapabilities=",
"SystemCallArchitectures=native x86",
"ProcSubset=pid",
"TemporaryFileSystem=/var/lib /etc /opt /home /root /srv /mnt /media",
"BindReadOnlyPaths=/var/lib/left4me/installation",
"BindReadOnlyPaths=/var/lib/left4me/overlays",
@ -299,3 +298,9 @@ def test_server_hardening_dropin_present_with_directives():
assert "SystemCallFilter=~@debug @mount @raw-io @reboot @swap @cpu-emulation @obsolete @privileged" in text
# MemoryDenyWriteExecute must remain absent (Source engine compat).
assert "MemoryDenyWriteExecute" not in text
# ProcSubset=pid must remain absent — hides /proc/cpuinfo and breaks
# SteamAPI master-server registration (LAN-only fallback). See
# ckn-bw 4339289 and the comment block in the drop-in itself.
for line in text.splitlines():
bare = line.split("#", 1)[0].strip()
assert bare != "ProcSubset=pid", "ProcSubset=pid must not be active in the server drop-in"