Build Housecarl 0.1.0: the nftables firewall manager

Zones, address sets (IPv4 and IPv6 mixed, dynamic sets with timeouts) and
services, ordered rules in the early, input, forward and output chains,
port forwards with hairpin NAT and IPv6 pinholes, source NAT, redirects,
and switchable built-ins (loopback, conntrack, ICMPv6, antispoofing, MSS
clamping, DHCPv6 client, flowtable). Every change is validated, checked
with nft -c and applied in one transaction to Housecarl's own table,
inet housecarl; changes made over the network roll back unless
confirmed, and the confirmed ruleset is loaded at boot by
housecarl-ruleset.service. An empty configuration applies nothing.

Also: hit counters and the drop log (nflog), 'hc import' of an existing
nftables ruleset and 'hc takeover', the hc CLI, the REST API and the web
UI, users, scoped tokens (sets:write:NAME), the audit log, the web UI's
certificate through Jarl, Debian packages, docs, unit tests with real
nft 1.1.3, and an e2e test with real traffic (71 checks).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

deploy/systemd/housecarl-backup.service

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+# Housecarl: one database backup, run daily by housecarl-backup.timer.
+# Installed as /etc/systemd/system/housecarl-backup.service (see
+# docs/operations.md#backups). What to keep, and where, is in the backup:
+# section of /etc/housecarl/housecarl.yaml.
+[Unit]
+Description=Housecarl database backup
+Documentation=file:///usr/local/share/doc/housecarl/docs/operations.md
+# Nothing to back up before 'housecarld init'.
+ConditionPathExists=/var/lib/housecarl/housecarl.db
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/bin/housecarld --config /etc/housecarl/housecarl.yaml backup
+User=housecarl
+Group=housecarl
+UMask=0077
+Nice=10
+IOSchedulingClass=idle
+
+# If you change backup.dir in housecarl.yaml, allow the new one too:
+# 'systemctl edit housecarl-backup.service' and add ReadWritePaths=/new/dir.
+ProtectSystem=strict
+ReadWritePaths=/var/lib/housecarl -/var/backups/housecarl
+ProtectHome=yes
+PrivateTmp=yes
+PrivateDevices=yes
+PrivateNetwork=yes
+NoNewPrivileges=yes
+CapabilityBoundingSet=
+ProtectKernelTunables=yes
+ProtectKernelModules=yes
+ProtectKernelLogs=yes
+ProtectControlGroups=yes
+ProtectClock=yes
+ProtectHostname=yes
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+RestrictAddressFamilies=AF_UNIX
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallErrorNumber=EPERM

deploy/systemd/housecarl-backup.timer

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+# Housecarl: runs housecarl-backup.service (a database backup) every day.
+# Installed as /etc/systemd/system/housecarl-backup.timer. Change the schedule
+# with 'systemctl edit housecarl-backup.timer', e.g.
+#   [Timer]
+#   OnCalendar=
+#   OnCalendar=*-*-* 02:30
+# and keep backup.retention in housecarl.yaml above the new interval.
+[Unit]
+Description=Daily Housecarl database backup
+Documentation=file:///usr/local/share/doc/housecarl/docs/operations.md
+
+[Timer]
+OnCalendar=daily
+# Spread the start over an hour, and catch up on a run missed while the
+# machine was off.
+RandomizedDelaySec=1h
+Persistent=true
+
+[Install]
+WantedBy=timers.target

deploy/systemd/housecarl-ruleset.service

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+# Housecarl: loads the last confirmed ruleset at boot, before the network
+# comes up and whether or not housecarld starts.
+# Installed as /etc/systemd/system/housecarl-ruleset.service.
+[Unit]
+Description=Housecarl firewall ruleset
+Documentation=file:///usr/local/share/doc/housecarl/README.md
+DefaultDependencies=no
+Before=network-pre.target shutdown.target
+Wants=network-pre.target
+# Debian's nftables.service flushes the whole ruleset: Housecarl's loads after it.
+After=nftables.service local-fs.target
+Conflicts=shutdown.target
+ConditionPathExists=/var/lib/housecarl/ruleset.nft
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/sbin/nft -f /var/lib/housecarl/ruleset.nft
+
+[Install]
+WantedBy=sysinit.target

deploy/systemd/housecarl.service

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+# Housecarl: keeps the firewall's nftables ruleset; its REST API and web UI.
+# Installed as /etc/systemd/system/housecarl.service (see docs/install.md).
+[Unit]
+Description=Housecarl firewall manager (with web UI and API)
+Documentation=file:///usr/local/share/doc/housecarl/README.md
+# The confirmed ruleset is already in force from housecarl-ruleset.service.
+After=housecarl-ruleset.service network-online.target
+Wants=network-online.target
+
+[Service]
+Type=notify
+NotifyAccess=main
+ExecStart=/usr/local/bin/housecarld --config /etc/housecarl/housecarl.yaml serve
+# SIGHUP rereads the TLS certificate.
+ExecReload=/bin/kill -HUP $MAINPID
+Restart=on-failure
+RestartSec=2s
+
+User=housecarl
+Group=housecarl
+UMask=0027
+
+# /var/lib/housecarl: the database and the confirmed ruleset (ruleset.nft).
+StateDirectory=housecarl
+StateDirectoryMode=0750
+ConfigurationDirectory=housecarl
+ConfigurationDirectoryMode=0750
+# /run/housecarl: the local API socket (housecarl.sock), for root and the
+# housecarl user.
+RuntimeDirectory=housecarl
+RuntimeDirectoryMode=0750
+
+# Sandboxing: housecarld writes only its own state.
+ProtectSystem=strict
+ProtectHome=yes
+PrivateTmp=yes
+PrivateDevices=yes
+NoNewPrivileges=yes
+# The only privilege housecarld gets: changing nftables (it runs nft) and
+# reading logged packets (nfnetlink_log), both CAP_NET_ADMIN.
+CapabilityBoundingSet=CAP_NET_ADMIN
+AmbientCapabilities=CAP_NET_ADMIN
+ProtectKernelTunables=yes
+ProtectKernelModules=yes
+ProtectKernelLogs=yes
+ProtectControlGroups=yes
+ProtectClock=yes
+ProtectHostname=yes
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+# AF_NETLINK: nftables, logged packets, the interfaces and their addresses.
+RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6 AF_NETLINK
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallErrorNumber=EPERM
+
+[Install]
+WantedBy=multi-user.target
+# 'systemctl restart housecarld' works too (the daemon's binary is housecarld).
+Alias=housecarld.service