fleet-agent reports clock health via 'chronyc -n tracking', but the hardened
unit runs with NoNewPrivileges (explicit + forced by DynamicUser/SystemCallFilter/
MemoryDenyWriteExecute). SELinux transitions the exec'd chronyc into chronyc_t,
and NNP forbids that domain change without process2:nnp_transition — which the
base policy doesn't grant for unconfined_service_t -> chronyc_t. Under enforcing
the exec is denied (avc: denied { nnp_transition } comm=fleet-agent, seen on
comet-beacon-54), so chronyc never runs and every chrony_* health field stays
empty (Monitor chrony row shows '—'). uptime/cpu/mem are unaffected (no exec).
Ship a minimal local module (files/stig/fleet-agent-chronyc.te) granting only
that one nnp_transition to the MORE-confined chronyc_t domain — the safe
direction the permission exists to gate — loosening nothing else in the agent
sandbox. Built + semodule -i'd in 2c-STIG alongside the existing
chrony_dhcp_dispatcher / fapolicyd_tmpfs modules. Justified in
docs/stig-deviations.md #16. Needs a workstation image rebuild + reboot; same
policy-store-rebuild reproducibility re-check as #14/#15.
fapolicyd is the app-allowlisting exec guard for the writable RAM overlay
(dm-verity covers only the read-only erofs lower). It statfs's mounts to decide
which to watch, and tmpfs is in its default watch_fs. This image's root is
systemd.volatile=overlay, so statfs("/") returns the overlay upper — a tmpfs —
and the shipped policy has no 'fapolicyd_t tmpfs_t:filesystem getattr' (no
ordinary host roots on tmpfs). Under enforcing the getattr is DENIED (audit:
dev=tmpfs ino=1 name="/", permissive=0, seen 2026-07-03 on comet-beacon-54),
so fapolicyd can't fully mark the tmpfs mounts (/, /tmp, /dev/shm) and its guard
over the writable overlay is incomplete — a real exec-guard gap, not just SIEM
noise.
Ship a minimal local allow module (allow, not dontaudit — we want fapolicyd to
see the tmpfs), compiled + semodule -i'd in 2c-STIG right after the chrony one.
Registered as deviation #15.
BENCH-VERIFY: the AVC is gone on an enforcing boot AND fapolicyd blocks a non-RPM
executable dropped in /tmp (proves the guard now covers the overlay), trusted
kiosk/appliance binaries still run, and the verity hash is reproducible across
two builds (semodule rebuilds the policy store).
The build failed: checkmodule rejected `policy_module(chrony_dhcp_dispatcher,
1.0.0)` with "Building a policy module, but no module specification found".
policy_module() is a refpolicy m4 macro expanded only by the refpolicy Makefile
(/usr/share/selinux/devel), not by checkmodule. Use the raw module-policy
declaration `module chrony_dhcp_dispatcher 1.0.0;`, which is exactly what
checkmodule -M -m parses. require{} + allow rule unchanged.
The NM dispatcher 10-chrony-dhcp-ntp runs `chronyc reload sources` to load DHCP
option-42 NTP servers. That chronyc runs in the confined custom-dispatcher
domain (NetworkManager_dispatcher_custom_t), so its reply socket carries that
label and the shipped policy has no rule for chronyd_t to sendto it. Under
enforcing, chronyd does the reload but its ack is denied — chronyc reports
failure and the AVC floods the SIEM (seen 2026-07-03; permissive=1 only because
the box was booted enforcing=0).
Ship a minimal local allow module (files/stig/chrony-dhcp-dispatcher.te):
allow chronyd_t NetworkManager_dispatcher_custom_t:unix_dgram_socket sendto;
Built + semodule -i'd in the 2c-STIG provisioner (checkpolicy installed if
absent), with an install assertion. `allow` not `dontaudit` — it also lets the
reload ack succeed so chronyc returns cleanly. Documented as
docs/stig-deviations.md #14 (not a rule waiver — a local functional allow).
BENCH-VERIFY: enforcing boot shows no AVC, chronyc reload returns 0, a
DHCP-handed NTP server appears in `chronyc sources`; and re-check verity-hash
reproducibility (semodule rebuilds the policy store, like the semanage step).
Audiobuzz