feat: added support for running the VPN router on a host with Docker Community Edition.

ADR.md

@@ -0,0 +1,28 @@
+# Architecture Decision Records
+
+## ADR-1: Docker's published ports are filtered in DOCKER-USER by the package
+
+Status: Accepted
+
+Context: Docker adds its own iptables rules for published ports. They are evaluated before
+UFW's, so a published port is reachable from the external interface whatever UFW says. Docker
+reserves the `DOCKER-USER` chain, evaluated first in `FORWARD`, for rules of the operator. The
+router is an internet-facing host, and Docker is installed on it for services run alongside the
+router.
+
+Decision: The package secures Docker itself. A `docker` configuration section has `mode`
+(`auto`, `on`, `off`) and `exposed_ports`. In `auto` mode the rules are applied when
+`docker.service` is installed, which is what the package looks up; `on` requires Docker and
+`off` removes the rules. The rules are in a chain of their own, `VPN-ROUTER-DOCKER`, entered by
+one jump at the top of `DOCKER-USER`. For traffic from the external interface they accept IPsec
+protected traffic, TCP to `exposed_ports` and established connections, and drop the rest. The
+`vpn-router-docker` unit applies them after `docker.service` starts and removes them when it
+stops; `vpn-router-setup` restarts it while Docker runs.
+
+Consequences: Installing Docker first is recommended; `auto` mode then finds it as soon as the
+package is configured. When Docker is installed after the package, the rules are applied by
+restarting `vpn-router-setup`, a reboot or a restart of Docker, not by Docker's first start,
+because `vpn-router-docker` is already active. A published
+port is reachable from the external interface only when it is in `exposed_ports`. Other rules
+in `DOCKER-USER` are not touched, because the package owns only its own chain. Restarting Docker
+restores the rules. The rules cover IPv4 only.

README.md

@@ -6,6 +6,7 @@ A Debian package that configures a Linux host or virtual machine as a VPN router
 - road-warrior (P2S) access using IKEv2 EAP-TLS, with a bundled certificate authority
 - optional WireGuard endpoint
 - routing and NAT for a protected subnet, TCP MSS clamping, and UFW firewall rules
+- firewall rules for the ports Docker publishes, when Docker is installed
 
 Nothing in the package is specific to a cloud provider. It is built on the external and
 internal NIC names, and a `mode` setting says how much of the rest you are supplying and
@@ -28,6 +29,10 @@ service that applies it.
 systemctl restart vpn-router-setup   apply it
 ```
 
+If the host runs Docker, the recommended order is Docker first and the package second. The
+package secures the ports Docker publishes when it finds the Docker service; the steps for a
+host that already runs Docker, and for installing Docker later, are under [Docker](#docker).
+
 ### By hand
 
 ```sh
@@ -108,6 +113,8 @@ must have the type shown below; an unknown section or setting is an error.
 | `wireguard` | `enabled` | boolean | `false` | WireGuard endpoint |
 | `wireguard` | `address` | string | | Address and prefix for `wg0`, for example `192.168.200.1/24` |
 | `wireguard` | `listen_port` | integer | `51820` | UDP port |
+| `docker` | `mode` | string | `auto` | `auto` secures Docker when its service is installed, `on` requires it, `off` removes the rules |
+| `docker` | `exposed_ports` | list | | TCP ports and port ranges (`8000:8100`) reachable from the external interface; at most 15, a range counting as two |
 
 A minimal site-to-site configuration in `auto` mode:
 
@@ -153,6 +160,56 @@ interface does not exist the service stops and says so. In `interfaces` and `aut
 the internal gateway is taken from the routing table, falling back to the first host
 address of the connected subnet with a warning when the routing table has nothing to say.
 
+## Docker
+
+Docker publishes container ports in its own firewall rules, which bypass UFW and can expose
+ports on the external interface. Docker evaluates the `DOCKER-USER` chain before its own
+rules, so the package filters there. With `docker.mode` set to `auto`, the package secures
+Docker when `docker.service` is installed, and does nothing otherwise.
+
+### On a host that already runs Docker
+
+Installing Docker first is the recommended order. After installing the package:
+
+1. Set `general.platform` in `/etc/vpn-router/vpn-router.json`. While it is `none`, nothing is
+   configured, the Docker rules included.
+2. List the TCP ports the running containers must expose to the internet, for example
+   `"docker": { "exposed_ports": ["443"] }`. The default is none: once the rules are applied,
+   every published port that is not listed is unreachable from the external interface, and
+   remains reachable through the IPsec tunnel.
+3. Apply the configuration with `systemctl restart vpn-router-setup`. Docker is running, so
+   this also restarts `vpn-router-docker`, which installs the rules.
+4. Check the result:
+
+   ```sh
+   iptables -S DOCKER-USER        # "-j VPN-ROUTER-DOCKER" is the first rule
+   iptables -S VPN-ROUTER-DOCKER  # the rules of the external interface
+   ```
+
+### When Docker is installed after the package
+
+The Docker rules are not applied when Docker starts for the first time, so run
+`systemctl restart vpn-router-setup` after installing Docker, then check as above. A reboot or a
+restart of Docker applies them as well.
+
+The rules sit in their own chain, `VPN-ROUTER-DOCKER`, entered by one jump at the top of
+`DOCKER-USER`; other rules in `DOCKER-USER` are left alone. For traffic that arrives on the
+external interface, in this order:
+
+1. IPsec protected traffic is accepted.
+2. TCP to the ports in `docker.exposed_ports` is accepted; none by default.
+3. Packets of established and related connections are accepted.
+4. Everything else is dropped.
+
+Traffic from every other interface, including the internal one and the Docker bridges, is
+not affected. The rules cover IPv4 only.
+
+The `vpn-router-docker` service applies the rules after `docker.service` starts and removes
+them when Docker stops, so restarting Docker restores them. `systemctl restart
+vpn-router-setup` applies a changed configuration while Docker runs. With `docker.mode` set to
+`on`, the service fails when Docker is not installed or its daemon is not running; with
+`off` it removes the rules.
+
 ## Applying changes
 
 ```sh
@@ -256,7 +313,8 @@ modules shipped with the package; the configuration file accepts any module inst
 
 ## Removal
 
-`apt-get remove` terminates the tunnels and takes `wg-quick@wg0` down, but leaves the
+`apt-get remove` stops `vpn-router-docker`, which removes the Docker rules. It terminates the
+tunnels and takes `wg-quick@wg0` down, but leaves the
 configuration in place. `strongswan` is left enabled, since it is a shared service that
 may be in use by something else.
 

debian-package/debian/changelog

@@ -1,3 +1,22 @@
+vpn-router (0.3.0-1) unstable; urgency=medium
+
+  * Secure the ports Docker publishes. Rules in a chain of their own,
+    VPN-ROUTER-DOCKER, entered by a jump at the top of DOCKER-USER, accept
+    IPsec protected traffic, TCP to docker.exposed_ports and established
+    connections from the external interface and drop the rest of it. Other
+    rules in DOCKER-USER are left alone. The rules cover IPv4 only.
+  * Add the docker configuration section. docker.mode is auto (the default,
+    secures Docker when docker.service is installed), on (requires Docker) or
+    off (removes the rules); docker.exposed_ports lists the TCP ports and port
+    ranges reachable from the external interface, none by default.
+  * Add the vpn-router-docker service, which applies the Docker rules after
+    docker.service starts and removes them when it stops. vpn-router-setup
+    restarts it while Docker runs, so a changed configuration takes effect.
+  * Installing Docker before this package is recommended. When Docker is
+    installed later, restart vpn-router-setup to apply the rules.
+
+ -- Sławomir Koszewski <slawek@koszewscy.waw.pl>  Fri, 23 Oct 2026 12:44:45 +0200
+
 vpn-router (0.2.0-1) unstable; urgency=medium
 
   * Change the configuration file to JSON, /etc/vpn-router/vpn-router.json.

debian-package/debian/install

@@ -2,6 +2,7 @@ src/etc/sysctl.d/99-vpn-router.conf                   etc/sysctl.d/
 src/usr/lib/vpn-router/vpnrouter.py                   usr/lib/vpn-router/
 src/usr/lib/vpn-router/simple-ca                      usr/lib/vpn-router/
 src/usr/lib/vpn-router/configure                      usr/lib/vpn-router/
+src/usr/lib/vpn-router/docker-rules                   usr/lib/vpn-router/
 src/usr/lib/vpn-router/setup                          usr/lib/vpn-router/
 src/usr/lib/vpn-router/generate-config                usr/lib/vpn-router/
 src/usr/lib/vpn-router/vpnrouter_platforms/*.py       usr/lib/vpn-router/vpnrouter_platforms/

debian-package/debian/rules

@@ -4,3 +4,4 @@
 
 override_dh_installsystemd:
 	dh_installsystemd --name=vpn-router-setup
+	dh_installsystemd --name=vpn-router-docker

debian-package/debian/vpn-router.vpn-router-docker.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=VPN Router rules for Docker published ports
+Documentation=file:/usr/share/doc/vpn-router/README.md
+After=docker.service vpn-router-setup.service
+PartOf=docker.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/lib/vpn-router/docker-rules apply
+ExecStop=/usr/lib/vpn-router/docker-rules remove
+
+[Install]
+WantedBy=docker.service

debian-package/src/usr/lib/vpn-router/docker-rules

@@ -0,0 +1,114 @@
+#!/usr/bin/python3
+"""Secure the ports Docker publishes, with rules in the DOCKER-USER chain.
+
+Usage: docker-rules apply|remove
+
+Docker evaluates DOCKER-USER in FORWARD before its own rules, which makes it the
+place to filter traffic to containers. The rules live in their own chain,
+VPN-ROUTER-DOCKER, entered by one jump at the top of DOCKER-USER, so anything
+else in DOCKER-USER is left alone. Traffic arriving on the external interface is
+accepted when it is IPsec protected, when it is TCP to docker.exposed_ports, or
+when it belongs to an established connection; all other traffic from the
+external interface is dropped. Traffic from other interfaces is not affected.
+
+docker.mode decides whether this runs: auto applies the rules when the Docker
+service is installed, on requires it, off removes the rules. The vpn-router-docker
+unit runs apply after docker.service starts and remove when it stops.
+"""
+
+import os
+import subprocess
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.realpath(__file__)))
+
+import vpnrouter
+from vpnrouter import fail, warn
+
+CHAIN = 'VPN-ROUTER-DOCKER'
+USER_CHAIN = 'DOCKER-USER'
+
+
+def iptables(*args, check=True):
+    result = subprocess.run(['iptables', *args], capture_output=True, text=True)
+    if check and result.returncode != 0:
+        fail(f'iptables {" ".join(args)} failed: {result.stderr.strip()}')
+    return result
+
+
+def docker_installed():
+    """True when systemd knows the docker.service unit."""
+    result = subprocess.run(
+        ['systemctl', 'list-unit-files', '--no-legend', 'docker.service'],
+        capture_output=True, text=True)
+    return result.returncode == 0 and result.stdout.strip() != ''
+
+
+def remove():
+    """Take the jump and the chain out; nothing happens when they are absent."""
+    while iptables('-D', USER_CHAIN, '-j', CHAIN, check=False).returncode == 0:
+        pass
+    iptables('-F', CHAIN, check=False)
+    iptables('-X', CHAIN, check=False)
+
+
+def apply(cfg):
+    mode = cfg['docker']['mode']
+    if mode == 'off':
+        remove()
+        return
+
+    if not docker_installed():
+        if mode == 'on':
+            fail('docker.mode is on but the docker service is not installed; '
+                 'install Docker before vpn-router')
+        return
+
+    if iptables('-S', USER_CHAIN, check=False).returncode != 0:
+        if mode == 'on':
+            fail(f'docker.mode is on but there is no {USER_CHAIN} chain; '
+                 'is the Docker daemon running?')
+        warn(f'no {USER_CHAIN} chain, the Docker daemon is not running; '
+             'the rules are applied when it starts')
+        return
+
+    ctx = vpnrouter.build_context(cfg)
+    wan = ctx['wan_iface']
+    if not wan:
+        fail('the external interface is not known; set interfaces.external '
+             'or use mode auto or interfaces')
+
+    ports = ','.join(item.strip() for item in cfg['docker']['exposed_ports'])
+
+    remove()
+    iptables('-N', CHAIN)
+    iptables('-A', CHAIN, '-i', wan, '-m', 'policy', '--dir', 'in', '--pol', 'ipsec', '-j', 'ACCEPT')
+    if ports:
+        iptables('-A', CHAIN, '-i', wan, '-p', 'tcp', '-m', 'multiport', '--dports', ports, '-j', 'ACCEPT')
+    iptables('-A', CHAIN, '-i', wan, '-m', 'conntrack', '--ctstate', 'ESTABLISHED,RELATED', '-j', 'ACCEPT')
+    iptables('-A', CHAIN, '-i', wan, '-j', 'DROP')
+    iptables('-I', USER_CHAIN, '1', '-j', CHAIN)
+
+
+def main():
+    if len(sys.argv) != 2 or sys.argv[1] not in ('apply', 'remove'):
+        print('usage: docker-rules apply|remove', file=sys.stderr)
+        return 2
+
+    if sys.argv[1] == 'remove':
+        remove()
+        return 0
+
+    cfg = vpnrouter.load_config()
+    if vpnrouter.deferred(cfg):
+        return 0
+    try:
+        vpnrouter.validate(cfg)
+        apply(cfg)
+    except vpnrouter.ConfigError as exc:
+        fail(str(exc))
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())

debian-package/src/usr/lib/vpn-router/setup

@@ -299,6 +299,16 @@ def run_platform_setup(cfg, ctx):
         fail(f'platform module {module.__name__} failed: {exc}')
 
 
+def refresh_docker_rules():
+    """Apply the new settings to the Docker rules while Docker is running.
+
+    When Docker is not running, vpn-router-docker applies them after
+    docker.service starts.
+    """
+    if unit_is_active('docker.service'):
+        run(['systemctl', 'restart', 'vpn-router-docker.service'], check=False)
+
+
 def main():
     cfg = vpnrouter.load_config()
     ctx, changed = vpnrouter.configure(cfg)
@@ -337,6 +347,7 @@ def main():
         run(['systemctl', 'restart', 'systemd-resolved'], check=False)
 
     run_platform_setup(cfg, ctx)
+    refresh_docker_rules()
     return 0
 
 

debian-package/src/usr/lib/vpn-router/vpnrouter.py

@@ -8,6 +8,7 @@ import ipaddress
 import json
 import os
 import pathlib
+import re
 import shutil
 import subprocess
 import sys
@@ -46,8 +47,17 @@ SCHEMA = {
     'remote':     {'addrs': [], 'id': '', 'cidrs': [], 'psk': '', 'psk_file': ''},
     'p2s':        {'enabled': False, 'address_pool': '', 'ca_name': 'VPN Router CA'},
     'wireguard':  {'enabled': False, 'address': '', 'listen_port': 51820},
+    'docker':     {'mode': 'auto', 'exposed_ports': []},
 }
 
+DOCKER_MODES = ('auto', 'on', 'off')
+
+#: A port or a port range as iptables multiport takes it: 443 or 8000:8100.
+DOCKER_PORT = re.compile(r'^\d{1,5}(:\d{1,5})?$')
+
+#: The multiport match takes at most 15 ports, and a range counts as two.
+DOCKER_PORT_LIMIT = 15
+
 TYPE_NAMES = {str: 'a string', list: 'a list of strings', bool: 'a boolean',
               int: 'an integer'}
 
@@ -212,6 +222,24 @@ def validate(cfg):
     if not 1 <= port <= 65535:
         raise ConfigError(f'wireguard.listen_port: {port} is not a valid port')
 
+    docker_mode = _get(cfg, 'docker', 'mode')
+    if docker_mode not in DOCKER_MODES:
+        raise ConfigError(
+            f'docker.mode: {docker_mode!r} is not one of {", ".join(DOCKER_MODES)}')
+
+    ports = _get_list(cfg, 'docker', 'exposed_ports')
+    weight = 0
+    for item in ports:
+        if not DOCKER_PORT.match(item) or any(
+                not 1 <= int(part) <= 65535 for part in item.split(':')):
+            raise ConfigError(
+                f'docker.exposed_ports: {item!r} is not a port or a port range')
+        weight += 2 if ':' in item else 1
+    if weight > DOCKER_PORT_LIMIT:
+        raise ConfigError(
+            f'docker.exposed_ports: at most {DOCKER_PORT_LIMIT} ports are allowed, '
+            'a range counting as two')
+
 
 def resolve_psk(cfg):
     """Return the pre-shared key, or '' when none is configured."""

debian-package/src/usr/share/doc/vpn-router/vpn-router.json.example

@@ -32,5 +32,9 @@
     "enabled": false,
     "address": "192.168.200.1/24",
     "listen_port": 51820
+  },
+  "docker": {
+    "mode": "auto",
+    "exposed_ports": ["443"]
   }
 }