Audiobuzz
5294860e74
Second bench defect after removing the distro 20-chrony-dhcp clobberer (secure-ntp-5a3eaed, comet-beacon-54): the dispatcher wrote the correct `server ntp.fleet.lab iburst nts` line, but chrony loaded ZERO sources -- `chronyc reload sources` returned 200 OK yet authdata/sources stayed empty. Root cause (AVC): chronyd_t was DENIED read on the .sources files because they and /run/chrony-dhcp itself were labeled generic var_run_t; chronyd_t may only read its own chronyd_var_run_t. The dispatcher's `mkdir -p` creates the dir as var_run_t and files inherit it. The distro 20-chrony-dhcp we removed had been restorecon-ing them to the readable label, so removing it exposed a latent labelling gap. Stock RHEL policy already maps /run/chrony-dhcp -> chronyd_var_run_t (a restorecon relabels it and chrony immediately reaches NTS Cook 8). Fix: ship /etc/tmpfiles.d/chrony-dhcp.conf so systemd-tmpfiles pre-creates the dir with that fcontext at sysinit, before any NM event -- the dispatcher's files then inherit chronyd_var_run_t and chronyd can read them. No SELinux allow rules needed (bench-verified: after the fix a real NM event wrote the source as chronyd_var_run_t, no AVC, authdata -> NTS Cook 8). Applies in both secure_ntp modes. Also: the dispatcher now skips `lo` -- it was writing a spurious lo.sources duplicate of the same server (the distro script had skipped loopback). BENCH-VERIFY on the next clean build: a normal boot leaves the source file labeled chronyd_var_run_t (ls -Z), no lo.sources, and authdata reaches NTS/cookies>0 with no manual step.
86 lines
4.1 KiB
Bash
86 lines
4.1 KiB
Bash
#!/bin/bash
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# NetworkManager dispatcher: point chrony at the fleet NTP server, learned from
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# DHCP at runtime (no FQDN baked into the image). Two modes, baked at build time:
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#
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# nts (secure_ntp=true, default): AUTHENTICATED time. Derive the server NAME
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# from the DHCP-provided domain as <PREFIX>.<domain> and write
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# `server NAME iburst nts`. chrony verifies the NTS-KE TLS cert against the
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# fleet CA (chrony.conf: ntstrustedcerts). Because the domain comes from
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# DHCP, a domain change needs only a new DHCP domain + reissued NTS cert —
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# no image rebuild. A DHCP/NTP/DNS spoofer can only DoS (no fleet-CA-signed
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# cert for the name it redirects to => NTS fails => no sync); it cannot
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# shift the clock. See docs/secure-ntp-design.md (F-03/P-18).
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#
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# dhcp (secure_ntp=false): LEGACY, UNAUTHENTICATED. Write the DHCP option-42
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# server IPs as plain `server <ip> iburst`. Lab/interop only.
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#
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# We use NetworkManager's internal DHCP (the network-manager dracut port); NM
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# exports the lease's domain as $DHCP4_DOMAIN_NAME (option 15) / $DHCP4_DOMAIN_SEARCH
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# (option 119) and NTP servers as $DHCP4_NTP_SERVERS (option 42). chrony.conf
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# carries `sourcedir /run/chrony-dhcp`, so writing <iface>.sources there and
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# reloading makes chronyd use them. The baked public pool is stripped (provisioner).
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#
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# Installed 0755 root:root. Lenient on purpose: a hiccup here must never break
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# networking. @NTP_MODE@/@NTP_PREFIX@ are substituted at build time.
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#
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# NB: the chrony package ships its OWN dispatcher at
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# /usr/lib/NetworkManager/dispatcher.d/20-chrony-dhcp writing option-42 servers to
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# the SAME <iface>.sources. NM merges /etc + /usr/lib sorted by name, so it runs
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# AFTER us and would clobber the NTS line — the provisioner removes it (it defeated
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# NTS on the bench: chrony fell back to plain NTP). This script supersedes it. It
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# was ALSO (accidentally) labelling the sources chronyd_var_run_t so chronyd could
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# read them; we restore that via /etc/tmpfiles.d/chrony-dhcp.conf (see the dir note
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# below) — without it, under enforcing SELinux chronyd can't read the sources and
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# loads nothing (bench 2026-07-12).
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MODE="@NTP_MODE@" # nts | dhcp
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PREFIX="@NTP_PREFIX@" # nts: server name = <PREFIX>.<dhcp-domain>
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interface="$1"
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action="$2"
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case "$action" in
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up|dhcp4-change|reapply) ;;
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*) exit 0 ;;
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esac
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# Loopback carries no DHCP NTP config; acting on it just writes a spurious
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# lo.sources duplicate of the same server (the distro 20-chrony-dhcp skipped lo —
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# we must too, or chrony sees two files for one server). Skip it.
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[ "$interface" = lo ] && exit 0
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# /run/chrony-dhcp is pre-created with the chronyd_var_run_t SELinux label by
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# /etc/tmpfiles.d/chrony-dhcp.conf at boot, so the files we write below inherit a
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# label chronyd_t can READ (else, under enforcing, chronyd is denied and loads no
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# sources — bench 2026-07-12). This mkdir is just a fallback if tmpfiles didn't run.
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dir=/run/chrony-dhcp
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file="$dir/${interface}.sources"
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mkdir -p "$dir"
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if [ "$MODE" = nts ]; then
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# Prefer option 15 (domain-name); fall back to the first option-119 search
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# domain; finally fall back to resolv.conf's search/domain. NM does not export
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# $DHCP4_DOMAIN_NAME on every dispatcher event — at boot the source wasn't
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# written because the firing event carried no DHCP domain in env, yet
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# resolv.conf already had `search <domain>` (bench 2026-07-11). Reading it here
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# makes the NTS source get written reliably regardless of which event fires.
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domain="${DHCP4_DOMAIN_NAME:-}"
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[ -z "$domain" ] && domain="${DHCP4_DOMAIN_SEARCH%% *}"
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[ -z "$domain" ] && domain=$(awk '/^(search|domain)[[:space:]]/{print $2; exit}' /etc/resolv.conf 2>/dev/null)
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if [ -n "$domain" ]; then
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printf 'server %s.%s iburst nts\n' "$PREFIX" "$domain" > "$file"
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# Pick up the new source without restarting chronyd.
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chronyc reload sources >/dev/null 2>&1 || true
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fi
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else
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if [ -n "${DHCP4_NTP_SERVERS:-}" ]; then
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: > "$file"
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for s in $DHCP4_NTP_SERVERS; do
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printf 'server %s iburst\n' "$s" >> "$file"
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done
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chronyc reload sources >/dev/null 2>&1 || true
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fi
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fi
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exit 0
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