router(host): add nftables config for basic router functionality

inventories/chaosknoten/host_vars/router.yaml

@@ -1 +1,2 @@
 systemd_networkd__config_dir: 'resources/chaosknoten/router/systemd_networkd/'
+nftables__config: "{{ lookup('ansible.builtin.file', 'resources/chaosknoten/router/nftables/nftables.conf') }}"

inventories/chaosknoten/hosts.yaml

@@ -91,6 +91,9 @@ base_config_hosts:
 systemd_networkd_hosts:
   hosts:
     router:
+nftables_hosts:
+  hosts:
+    router:
 docker_compose_hosts:
   hosts:
     ccchoir:

playbooks/deploy.yaml

@@ -9,6 +9,11 @@
   roles:
     - systemd_networkd
 
+- name: Ensure nftables deployment on nftables_hosts
+  hosts: nftables_hosts
+  roles:
+    - nftables
+
 - name: Ensure deployment of infrastructure authorized keys
   hosts: infrastructure_authorized_keys_hosts
   roles:

resources/chaosknoten/router/nftables/nftables.conf

@@ -0,0 +1,73 @@
+#!/usr/sbin/nft -f
+
+## Variables
+
+# Interfaces
+define if_net1_v4_wan = "net1"
+define if_net2_v6_wan = "net2"
+define if_net0_2_v4_nat = "net0.2"
+define if_net0_3_ci_runner = "net0.3"
+
+# Interface Groups
+define wan_ifs = { $if_net1_v4_wan,
+                   $if_net2_v6_wan }
+define lan_ifs = { $if_net0_2_v4_nat,
+                   $if_net0_3_ci_runner }
+
+
+## Rules
+
+table inet reverse-path-forwarding {
+    chain rpf-filter {
+        type filter hook prerouting priority mangle + 10; policy drop;
+
+        # Only allow packets if their source address is routed via their incoming interface.
+        # https://github.com/NixOS/nixpkgs/blob/d9d87c51960050e89c79e4025082ed965e770d68/nixos/modules/services/networking/firewall-nftables.nix#L100
+        fib saddr . mark . iif oif exists accept
+    }
+}
+
+table inet host {
+    chain input {
+        type filter hook input priority filter; policy drop;
+
+        iifname "lo" accept comment "allow loopback"
+
+        ct state invalid drop
+        ct state established,related accept
+
+		ip protocol icmp accept
+		ip6 nexthdr icmpv6 accept
+
+        # Allow SSH access.
+        tcp dport 22 accept comment "allow ssh access"
+
+        # Allow DHCP server access.
+		iifname $if_net0_3_ci_runner udp dport 67 accept comment "allow dhcp server access"
+    }
+}
+
+table ip v4nat {
+    chain prerouting {
+        type nat hook prerouting priority dstnat; policy accept;
+    }
+
+    chain postrouting {
+        type nat hook postrouting priority srcnat; policy accept;
+
+        oifname $if_net1_v4_wan masquerade
+    }
+}
+
+table inet forward {
+    chain forward {
+        type filter hook forward priority filter; policy drop;
+
+        ct state invalid drop
+        ct state established,related accept
+
+        # Allow internet access.
+		meta nfproto ipv6 iifname $lan_ifs oifname $if_net2_v6_wan accept comment "allow v6 internet access"
+		meta nfproto ipv4 iifname $lan_ifs oifname $if_net1_v4_wan accept comment "allow v4 internet access"
+    }
+}

resources/chaosknoten/router/systemd_networkd/21-net0.2-v4_nat.network

@@ -8,7 +8,7 @@ RequiredForOnline=no
 [Network]
 Description=v4-NAT
 
-IPMasquerade=ipv4
+# Masquerading done in nftables (nftables.conf).
 IPv6SendRA=yes
 
 [Address]

resources/chaosknoten/router/systemd_networkd/21-net0.3-ci_runners.network

@@ -8,7 +8,7 @@ RequiredForOnline=no
 [Network]
 Description=ci-runners
 
-IPMasquerade=ipv4
+# Masquerading done in nftables (nftables.conf).
 IPv6SendRA=yes
 
 DHCPServer=true

roles/nftables/README.md

@@ -0,0 +1,11 @@
+# Role `nftables`
+
+Deploys nftables.
+
+## Support Distributions
+
+Should work on Debian-based distributions.
+
+## Required Arguments
+
+- `nftables__config`: nftables configuration to deploy.

roles/nftables/handlers/main.yaml

@@ -0,0 +1,5 @@
+- name: Restart nftables service
+  ansible.builtin.systemd_service:
+    name: nftables
+    state: restarted
+  become: true

roles/nftables/meta/argument_specs.yaml

@@ -0,0 +1,6 @@
+argument_specs:
+  main:
+    options:
+      nftables__config:
+        type: str
+        required: true

roles/nftables/tasks/main.yaml

@@ -0,0 +1,15 @@
+- name: ensure nftables is installed
+  ansible.builtin.apt:
+    name: nftables
+    state: present
+  become: true
+
+- name: deploy nftables configuration
+  ansible.builtin.copy:
+    content: "{{ nftables__config }}"
+    dest: "/etc/nftables.conf"
+    mode: "0644"
+    owner: root
+    group: root
+  become: true
+  notify: Restart nftables service