roles/dch-gw: Configure the filter table

The *filter* table is responsible for deciding which packets will be
accepted and which will be rejected. It has three chains, which classify
packets according to whether they are destined for the local machine
(input), passing through this machine (forward) or originating from the
local machine (output).

The *dch-gw* role now configures all three chains in this table. For
now, it defines basic rules, mostly based on TCP/UDP destination port:

* Traffic destined for a service hosted by the local machine (DNS, DHCP,
  SSH), is allowed if it does not come from the Internet
* Traffic passing through the machine is allowed if:
  * It is passing between internal networks
  * It is destined for a host on the FireMon network (VPN)
  * It was NATed to in internal host (marked 323)
  * It is destined for the Internet
* Only DHCP, HTTP, and DNS are allowed to originate from the local
machine

This configuration requires an `internet_iface` variable, which
indicates the name of the network interface connected to the Internet
directly.

group_vars/dch-gw/dch-network.yml

@@ -40,6 +40,11 @@ dch_networks:
     router_iface: vlan254
 
 
+firemon_networks:
+- 192.168.0.0/16
+- 172.28.33.0/24
+
+
 nat_port_forwards:
 - protocol: tcp
   port: http
@@ -62,3 +67,33 @@ nat_port_forwards:
 - protocol: udp
   port: ipsec-nat-t
   destination: 172.31.0.2
+
+
+allow_incoming:
+- protocol: udp
+  port: domain
+- protocol: tcp
+  port: domain
+- protocol: udp
+  port: bootps
+- protocol: tcp
+  port: ssh
+
+
+allow_outgoing:
+- protocol: udp
+  port: ntp
+- protocol: udp
+  port: dhcpv6-server
+- protocol: udp
+  port: bootps
+- protocol: tcp
+  port: https
+- protocol: tcp
+  port: http
+- protocol: udp
+  port: domain
+- protocol: tcp
+  port: domain
+
+trace_dropped: true

host_vars/gw0/network.yml

@@ -1,6 +1,8 @@
+internet_iface: enp4s0
+
 network:
   ignore_interfaces:
-  - enp4s0
+  - '{{ internet_iface }}'
   interfaces:
   - ifname: enp1s0
     enabled: true
@@ -66,7 +68,7 @@ dhcpcd_ntp_servers: false
 dhcpcd_noipv4: true
 dhcpcd_noipv6rs: true
 dhcpcd_interfaces:
-- name: enp4s0
+- name: '{{ internet_iface }}'
   description: Internet
   config:
   - ipv4

roles/dch-gw/defaults/main.yml

@@ -1 +1,3 @@
 nat_port_forwards: []
+allow_incoming: []
+trace_dropped: false

roles/dch-gw/files/inet-filter.nft

@@ -0,0 +1,7 @@
+#! /usr/sbin/nft -f
+
+table inet filter {
+	chain input		{ type filter hook input priority 0; }
+	chain forward		{ type filter hook forward priority 0; }
+	chain output		{ type filter hook output priority 0; }
+}

roles/dch-gw/tasks/main.yml

@@ -31,6 +31,33 @@
     sysctl_file=/etc/sysctl.d/ip-forwarding.conf
     state=present
 
+- name: ensure inet filter rules are configured
+  copy:
+    src=inet-filter.nft
+    dest=/etc/nftables/ruleset.d/10_inet-filter.nft
+    mode=0644
+  notify: reload nftables
+- name: ensure basic rules are defined
+  template:
+    src={{ item }}.nft.j2
+    dest=/etc/nftables/ruleset.d/20_{{ item }}.nft
+    mode=0644
+  with_items:
+  - incoming
+  - forward
+  - outgoing
+  notify: reload nftables
+- name: ensure final reject rules are defined
+  template:
+    src=reject.nft.j2
+    dest=/etc/nftables/ruleset.d/90_{{ item }}-reject.nft
+    mode=0644
+  with_items:
+  - input
+  - forward
+  - output
+  notify: reload nftables
+
 - name: ensure ipv4 nat rules are configured
   copy:
     src=ipv4-nat.nft

roles/dch-gw/templates/forward.nft.j2

@@ -0,0 +1,23 @@
+{#- vim: set sw=4 ts=4 sts=4 et : #}
+table inet filter {
+    set firemon {
+        type ipv4_addr
+        flags interval
+        elements = {
+{% for prefix in firemon_networks %}
+            {{ prefix }},
+{% endfor %}
+        }
+    }
+
+    chain forward {
+        ct state established,related accept
+        iifname {{ dch_networks.guest.router_iface }} oif != {{ internet_iface }} drop
+        iif != {{ internet_iface }} oifname {{ dch_networks.guest.router_iface }} drop
+        iif != {{ internet_iface }} oif != {{ internet_iface }} counter accept
+        ip daddr @firemon counter accept
+        mark 323 counter accept
+        tcp dport smtp counter reject with icmpx type host-unreachable
+        oif {{ internet_iface }} accept
+    }
+}

roles/dch-gw/templates/incoming.nft.j2

@@ -0,0 +1,34 @@
+{#- vim: set sw=4 ts=4 sts=4 et : #}
+table inet filter {
+    set allow_tcp_in {
+        type inet_service
+        flags interval
+        elements = {
+{% for item in allow_incoming if item.protocol|d('tcp') == 'tcp' %}
+            {{ item.port }},
+{% endfor %}
+        }
+    }
+
+    set allow_udp_in {
+        type inet_service
+        flags interval
+        elements = {
+{% for item in allow_incoming if item.protocol|d('tcp') == 'udp' %}
+            {{ item.port }},
+{% endfor %}
+        }
+    }
+
+    chain input {
+        ct state established,related accept
+        iif lo accept
+        ip6 nexthdr ipv6-icmp accept
+        ip protocol icmp accept
+        udp sport dhcpv6-server counter accept
+        iif != {{ internet_iface }} tcp dport @allow_tcp_in ct state new counter accept
+        iif != {{ internet_iface }} udp dport @allow_udp_in ct state new counter accept
+        iif {{ internet_iface }} drop
+        pkttype != host drop
+    }
+}

roles/dch-gw/templates/outgoing.nft.j2

@@ -0,0 +1,31 @@
+{#- vim: set sw=4 ts=4 sts=4 et : #}
+table inet filter {
+    set allow_tcp_out {
+        type inet_service
+        flags interval
+        elements = {
+{% for item in allow_outgoing if item.protocol|d('tcp') == 'tcp' %}
+            {{ item.port }},
+{% endfor %}
+        }
+    }
+
+    set allow_udp_out {
+        type inet_service
+        flags interval
+        elements = {
+{% for item in allow_outgoing if item.protocol|d('tcp') == 'udp' %}
+            {{ item.port }},
+{% endfor %}
+        }
+    }
+
+    chain output {
+        ct state established,related accept
+        oif lo accept
+        ip6 nexthdr ipv6-icmp accept
+        ip protocol icmp accept
+        tcp dport @allow_tcp_out ct state new counter accept
+        udp dport @allow_udp_out ct state new counter accept
+    }
+}

roles/dch-gw/templates/port-forwards.nft.j2

@@ -33,13 +33,13 @@ table ip nat {
     }
 
     chain prerouting {
-        ip daddr $outside_address dnat tcp dport map @tcp_forward
-        ip daddr $outside_address dnat udp dport map @udp_forward
+        ip daddr $outside_address meta mark set 323 dnat tcp dport map @tcp_forward
+        ip daddr $outside_address meta mark set 323 dnat udp dport map @udp_forward
     }
 
     chain postrouting {
 {% for item in nat_port_forwards %}
-        ip saddr @inside_networks ip daddr {{ item.destination }} {{ item.protocol|d('tcp') }} dport {{ item.port }} masquerade
+        ip saddr @inside_networks ip daddr {{ item.destination }} {{ item.protocol|d('tcp') }} dport {{ item.port }} meta mark set 323 masquerade
 {% endfor %}
     }
 }

roles/dch-gw/templates/reject.nft.j2

@@ -0,0 +1,6 @@
+{#- vim: set sw=4 ts=4 sts=4 et : #}
+table inet filter {
+    chain {{ item }} {
+        {% if trace_dropped %}nftrace set 1 {% endif %}counter reject with icmpx type host-unreachable
+    }
+}