Nftables

1. Overview
2. Role Variables
   • OS Specific Variables
   • Rules Dictionaries
3. Examples
   • With playbooks
   • With group_vars and host_vars
4. Configuration
   • Fail2ban integration
5. Development
6. License
7. Author Information

Overview

A role to manage Nftables rules and packages.

Highly inspired by Mike Gleason firewall role (3 levels of rules definition and template), thanks ! I hope i haven't complexify his philosophy… (I'm pretty sure, i now did complexify it :D) ^^

Role Variables

• nft_enabled : Enable or disable support for Nftables [default : true].
• nft_pkg_state : State of new nftables package(s) [default : present].
• nft_old_pkg_list : The list of useless packages to remove (such as Iptables,…) [default : iptables].
• nft_old_pkg_state : State of old package(s) [default : absent].
• nft_old_pkg_manage : If old package(s) should be managed with this role [default : true].
• nft_conf_dir_path : Directory to store the differents Nftables configuration files [default : /etc/nftables.d].
• nft_main_conf_path : Main configuration file loaded by systemd unit [default : /etc/nftables.conf].
• nft_main_conf_content : Template used to generate the previous main configuration file [default : etc/nftables.conf.j2].
• nft_input_conf_path : Input configuration file include in main configuration file [default : {{ nft_conf_dir_path }}/filter-input.nft].
• nft_input_conf_content : Template used to generate the previous input configuration file [default : etc/nftables.d/filter-input.nft.j2].
• nft_output_conf_path : Output configuration file include in main configuration file [default : {{ nft_conf_dir_path }}/filter-output.nft].
• nft_output_conf_content : Template used to generate the previous output configuration file [default : etc/nftables.d/filter-output.nft.j2].
• nft_forward_conf_path : forward configuration file include in main configuration file [default : {{ nft_conf_dir_path }}/filter-forward.nft].
• nft_forward_conf_content : Template used to generate the previous forward configuration file [default : etc/nftables.d/filter-forward.nft.j2].
• nft_define_conf_path : Vars definition file include in main configuration file [default : {{ nft_conf_dir_path }}/defines.nft].
• nft_define_conf_content : Template used to generate the previous vars definition file [default : etc/nftables.d/defines.nft.j2].
• nft_sets_conf_path : Sets and maps definition file include in main configuration file [default : {{ nft_conf_dir_path }}/sets.nft].
• nft_sets_conf_content : Template used to generate the previous sets and maps definition file [default : etc/nftables.d/sets.nft.j2].
• nft_global_default_rules : Set default rules for global chain. Other chains will jump to global before apply their specific rules.
• nft_global_rules : You can add global rules or override those defined by nft_global_default_rules for all hosts.
• nft_global_group_rules : You can add global rules or override those defined by nft_global_default_rules and nft_global_rules for a group.
• nft_global_host_rules : Hosts can also add or override all previours rules.
• nft__custom_content : Custom content (tables, include,…) to add in Nftables configuration [default : ''].
• nft_input_default_rules : Set default rules for input chain.
• nft_input_rules : You can add input rules or override those defined by nft_input_default_rules for all hosts.
• nft_input_group_rules : You can add input rules or override those defined by nft_input_default_rules and nft_input_rules for a group.
• nft_input_host_rules: : Hosts can also add or override all previous input rules.
• nft_output_default_rules : Set default rules for output chain.
• nft_output_rules : You can add output rules or override those defined by nft_output_default_rules for all hosts.
• nft_output_group_rules : You can add output rules or override those defined by nft_output_default_rules and nft_output_rules for a group.
• nft_output_host_rules : Hosts can also add or override all previous output rules.
• nft_forward_default_rules : Set default rules for forward chain.
• nft_forward_rules : You can add forward rules or override those defined by nft_forward_default_rules for all hosts.
• nft_forward_group_rules : You can add forward rules or override those defined by nft_forward_default_rules and nft_forward_rules for a group.
• nft_forward_host_rules : Hosts can also add or override all previous forward rules.
• nft__forward_table_manage : If the forward table should be managed [default : False].
• nft__nat_table_manage : If the nat table should be managed [default : False].
• nft__nat_default_prerouting_rules : Set default rules for prerouting chain of nat table.
• nft__nat_prerouting_rules : Set rules for prerouting chain of nat table for all hosts in the Ansible inventory.
• nft__nat_group_prerouting_rules : Set rules for prerouting chain of nat table for hosts in specific Ansible inventory group.
• nft__nat_host_prerouting_rules : Set rules for prerouting chain of nat table for specific hosts the Ansible inventory.
• nft__nat_prerouting_conf_path : Prerouting configuration file include in the main configuration [default : {{ nft_conf_dir_path }}/nat-prerouting.nft].
• nft__nat_prerouting_conf_content : Template used to generate the previous prerouting configuration file [default : etc/nftables.d/nat-prerouting.nft.j2].
• nft__nat_default_postrouting_rules : Set default rules for postrouting chain of nat table.
• nft__nat_postrouting_rules : Set rules for postrouting chain of nat table for all hosts in the Ansible inventory.
• nft__nat_group_postrouting_rules : Set rules for postrouting chain of nat table for hosts in specific Ansible inventory group.
• nft__nat_host_postrouting_rules : Set rules for postrouting chain of nat table for specific hosts the Ansible inventory.
• nft__nat_postrouting_conf_path : postrouting configuration file include in the main configuration [default : {{ nft_conf_dir_path }}/nat-postrouting.nft].
• nft__nat_postrouting_conf_content : Template used to generate the previous postrouting configuration file [default : etc/nftables.d/nat-postrouting.nft.j2].
• nft_define_default : Set default vars available in all rules.
• nft_define : You can add vars or override those defined by nft_define_default for all hosts.
• nft_define_group : You can add vars or override those defined by nft_define_default and nft_define for a group.
• nft_define_host : You can add or override all previous vars.
• nft_service_manage : If nftables service should be managed with this role [default : true].
• nft_service_name : nftables service name [default : nftables].
• nft_service_enabled : Set nftables service available at startup [default : true].
• nft__service_protect : If systemd unit should protect system and home [default : true].
• nft_merged_groups : If variables from the hosts Ansible groups should be merged [default : false].
• nft_merged_groups_dir : The dictionary where the nftables group rules, named like the Ansible groups, are located in [default : vars/].
• nft_debug : Toggle more verbose output on/off. [default: 'false'].

OS Specific Variables

Please see default value by Operating System file in [vars][vars directory] directory.

• nft_pkg_list : The list of package(s) to provide nftables.
• nft__bin_location : Path to nftables executable. [default : /usr/sbin/nft]

Rules Dictionaries

Each type of rules dictionaries will be merged and rules will be applied in the alphabetical order of the keys (the reason to use 000 to 999 as prefix). So :

• nft_*_default_rules : Define default rules for all nodes. You can define it in group_vars/all.
• nft_*_rules : Can add rules and override those defined by nft_*_default_rules. You can define it in group_vars/all.
• nft_*_group_rules : Can add rules and override those defined by nft_*_default_rules and nft_*_rules. You can define it in group_vars/webservers.
  • If 'nft_merged_groups' is set to true, multiple group rules from the ansible groups will also be merged together.
• nft_*_host_rules : Can add rules and override those define by nft_*_default_rules, nft_*_group_rules and nft_*_rules. You can define it in host_vars/www.local.domain.

defaults/main.yml:

# rules
nft_global_default_rules:
  005 state management:
    - ct state established,related accept
    - ct state invalid drop
nft_global_rules: {}
nft_merged_groups: false
nft_merged_groups_dir: vars/
nft_global_group_rules: {}
nft_global_host_rules: {}

nft_input_default_rules:
  000 policy:
    - type filter hook input priority 0; policy drop;
  005 global:
    - jump global
  010 drop unwanted:
    - ip daddr @blackhole counter drop
  015 localhost:
    - iif lo accept
  210 input tcp accepted:
    - tcp dport @in_tcp_accept ct state new accept
nft_input_rules: {}
nft_input_group_rules: {}
nft_input_host_rules: {}

nft_output_default_rules:
  000 policy:
    - type filter hook output priority 0; policy drop;
  005 global:
    - jump global
  015 localhost:
    - oif lo accept
  050 icmp:
    - ip protocol icmp accept
    - ip6 nexthdr icmpv6 counter accept
  200 output udp accepted:
    - udp dport @out_udp_accept ct state new accept
  210 output tcp accepted:
    - tcp dport @out_tcp_accept ct state new accept
nft_output_rules: {}
nft_output_group_rules: {}
nft_output_host_rules: {}

# define nft vars
nft_define_default:
  broadcast and multicast:
    desc: 'broadcast and multicast'
    name: badcast_addr
    value: '{ 255.255.255.255, 224.0.0.1, 224.0.0.251 }'
  input tcp accepted:
    name: in_tcp_accept
    value: '{ ssh }'
  output tcp accepted:
    name: out_tcp_accept
    value: '{ http, https, hkp }'
  output udp accepted:
    name: out_udp_accept
    value: '{ bootps, domain, ntp }'
nft_define: {}
nft_define_group: {}
nft_define_host: {}

# sets and maps
nft_set_default:
  blackhole:
    - type ipv4_addr;
    - elements = $badcast_addr
  in_tcp_accept:
    - type inet_service; flags interval;
    - elements = $in_tcp_accept
  out_tcp_accept:
    - type inet_service; flags interval;
    - elements = $out_tcp_accept
  out_udp_accept:
    - type inet_service; flags interval;
    - elements = $out_udp_accept
nft_set: {}
nft_set_group: {}
nft_set_host: {}

Those default will generate the following configuration :

#!/usr/sbin/nft -f
# Ansible managed

# clean
flush ruleset

include "/etc/nftables.d/defines.nft"

table inet filter {
	chain global {
		# 000 state management
		ct state established,related accept
		ct state invalid drop
	}
	include "/etc/nftables.d/sets.nft"
	include "/etc/nftables.d/filter-input.nft"
	include "/etc/nftables.d/filter-output.nft"
}

And you can get all rules and definitons by displaying the ruleset on the host : $ nft list ruleset :

table inet filter {
	set blackhole {
		type ipv4_addr
		elements = { 255.255.255.255, 224.0.0.1, 224.0.0.251}
	}

	set out_tcp_accept {
		type inet_service
		flags interval
		elements = { http, https, hkp}
	}

	set out_udp_accept {
		type inet_service
		flags interval
		elements = { domain, bootps, ntp}
	}

	chain global {
		ct state established,related accept
		ct state invalid drop
	}

	chain input {
		type filter hook input priority 0; policy drop;
		jump global
		ip daddr @blackhole counter packets 0 bytes 0 drop
		iif "lo" accept
		tcp dport @in_tcp_accept ct state new accept
	}

	chain output {
		type filter hook output priority 0; policy drop;
		jump global
		oif "lo" accept
		ip protocol icmp accept
		udp dport @out_udp_accept ct state new accept
		tcp dport @out_tcp_accept ct state new accept
	}
}

Examples

With playbooks

- hosts: serverXYZ
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
      nft_input_rules:
        400 input torrent accepted:
          - udp dport 6881 ct state new accept
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
      nft_input_rules:
        400 input http accepted:
          - tcp dport { 80, 443, 8080-8082 } ct state new accept
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
    - nft_define_group:
        input http accepted:
          desc: HTTP and HTTPS
          name: in_http_accept
          value: '{ 80, 443 }'
      nft_input_group_rules:
        400 input http accepted:
          - tcp dport $in_http_accept ct state new accept
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
      nft_set_group:
        in_udp_accept:
          - type inet_service; flags interval;
          - elements = { 6881-6887, 6889 }
      nft_input_group_rules:
        200 input udp accepted:
          - udp dport @in_udp_accept ct state new accept
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
      nft_input_host_rules:
        050 icmp:⏎
          - ip protocol icmp  ip saddr != 192.168.0.0/24  counter  drop⏎
          - ip protocol icmp  icmp type echo-request  ip length <= 84  counter  limit rate 10/minute  accept
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
    - nft_define:
      input tcp accepted:
        desc: Custom SSH port and torrent
        name: in_tcp_accept
        value: '{ 2201, 6881 }'
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
      nft_output_default_rules:
        000 policy:
          - type filter hook output priority 0; policy drop;
        005 state management:
          - ct state established,related accept
          - ct state invalid drop
        015 localhost:
          - oif lo accept
        050 my rule for XXX hosts and services:
          - tcp dport 2000  ip saddr { xxx.xxx.xxx.xxx, yyy.yyy.yyy.yyy }  ct state new  accept
        250 reset-ssh:  # allow the host to reset SSH connections to avoid 10 min delay from Ansible controller
          - tcp sport ssh tcp flags { rst, psh | ack } counter accept
  roles:
    - role: ipr-cnrs.nftables

- hosts: serverXYZ
  vars:
      nft_output_host_rules:
        210 output tcp accepted:
          -
  roles:
    - role: ipr-cnrs.nftables

With group_vars and host_vars

nft_input_group_rules:
  020 icmp:
    - ip protocol icmp icmp type echo-request ip length <= 84 counter limit rate 1/minute accept
  999 count policy packet:
    - counter

Configuration

This role will :

• Install nftables on the system.
• Enable nftables service by default at startup.
• Generate a default configuration file which include all following files and loaded by systemd unit.
• Generate input and output rules files include called by the main configuration file.
• Generate vars in a file and sets and maps in another file.
• (re)Start nftables service at first run.
• Reload nftables service at next runs to avoid to let the host without firewall rules due to invalid syntax.

Fail2ban integration

Before Debian Bullseye, systemd unit for Fail2ban doesn't come with a decent integration with Nftables. So this role will create override file for fail2ban unit, even if it's not (yet) available on the host, in order to :

• Start fail2ban unit after nftables.
• Restart fail2ban unit when nftables unit restart.

Development

This source code comes from our Gitea instance and the Github repo exist just to be able to send the role to Ansible Galaxy…

But feel free to send issue/PR here :)

Thanks to this hook, Github automatically got updates from our Gitea instance :)

License

WTFPL

Author Information

Jérémy Gardais

• Source : on IPR's Gitea
• IPR (Institut de Physique de Rennes)