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

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."""