Nftables

1. Overview
2. Role Variables
   • OS Specific Variables
   • Rules Dictionaries
3. Example Playbook
4. Known Issue
5. Configuration
6. Development
7. License
8. 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… ^^

Role Variables

• nft_pkg_manage : If nftables package(s) should be managed with this role [default : true].
• nft_pkg_state : State of new nftables package(s) [default : installed].
• 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_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_group_rules : You can add global rules or override those defined by nft_global_default_rules for a group.
• nft_global_host_rules: : Hosts can also add or override global rules.
• nft_input_default_rules : Set default rules for input chain.
• nft_input_group_rules : You can add input rules or override those defined by nft_input_default_rules for a group.
• nft_input_host_rules: : Hosts can also add or override input rules.
• nft_output_default_rules : Set default rules for output chain.
• nft_output_group_rules : You can add output rules or override those defined by nft_output_default_rules for a group.
• nft_output_host_rules: : Hosts can also add or override output rules.
• nft_define_default : Set default vars available in all rules.
• nft_define_group : You can add vars or override those defined by nft_define_default for groups.
• nft_define_host : You can add or override existant 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].

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.

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_*_group_rules : Can add rules and override those defined by nft_*_default_rules. You can define it in group_vars/webservers.
• nft_*_host_rules : Can add rules and override those define by nft_*_default_rules and nft_*_group_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_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
  200 input udp accepted:
    - udp dport @input_udp_accept ct state new accept
  210 input tcp accepted:
    - tcp dport @input_tcp_accept ct state new accept
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
  200 output udp accepted:
    - udp dport @output_udp_accept ct state new accept
  210 output tcp accepted:
    - tcp dport @output_tcp_accept ct state new accept
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: input_tcp_accept
    value: '{ ssh }'
  input udp accepted:
    name: input_udp_accept
    value: 'none'
  output tcp accepted:
    name: output_tcp_accept
    value: '{ http, https, hkp }'
  output udp accepted:
    name: output_udp_accept
    value: '{ bootps, domain, ntp }'
nft_define_group: {}
nft_define_host: {}

# sets and maps
nft_set_default:
  blackhole:
    - type ipv4_addr;
    - elements = $badcast_addr
  input_tcp_accept:
    - type inet_service; flags interval;
    - elements = $input_tcp_accept
  input_udp_accept:
    - type inet_service; flags interval;
  output_tcp_accept:
    - type inet_service; flags interval;
    - elements = $output_tcp_accept
  output_udp_accept:
    - type inet_service; flags interval;
    - elements = $output_udp_accept
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 firewall {
	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 firewall {
	set blackhole {
		type ipv4_addr
		elements = { 255.255.255.255, 224.0.0.1, 224.0.0.251}
	}

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

	set output_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
		udp dport @input_udp_accept ct state new accept
		tcp dport @input_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 @output_udp_accept ct state new accept
		tcp dport @output_tcp_accept ct state new accept
	}
}

Example Playbook

• Manage Nftables with defaults vars :

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

• Use default rules with allow incoming ICMP and count dropped input packets :

group_vars/first_group :

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

Known Issue

• The first run of a playbook may be long (~8 minutes) just after the (re)start of nftables service.
  • Probably due to Ansible/OpenSSH Specific default Settings, the outgoing connections for Ansible/SSH will be blocked :

trace id d7c3a8dc inet firewall output packet: oif "ens18" ip saddr REMOTE_HOST ip daddr MY_HOST ip dscp 0x02 ip ecn not-ect ip ttl 64 ip id 56799 ip length 420 tcp sport ssh tcp dport 53922 tcp flags == 0x18 tcp window 1452

• This only happen at the first run on new clean host. The next runs will works without any delay.

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.
• Restart nftables service.

Development

This source code comes from our Gogs 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 Gogs instance :)

License

WTFPL

Author Information

Jérémy Gardais

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