nftables puppet module

This module manages an opinionated nftables configuration.

By default it sets up a firewall that drops every connection, except outbound ICMP, DNS, NTP, HTTP, and HTTPS, and inbound ICMP and SSH traffic:

include nftables

This can be overridden using parameters, for example, this allows all outbound traffic:

class { 'nftables':
  out_all => true,
}

There are also pre-built rules for specific services, for example this will allow a web server to serve traffic over HTTPS:

include nftables
include nftables::rules::https

Note that the module conflicts with the firewalld system and will stop it in Puppet runs.

Configuration

The main configuration file loaded by the nftables service will be files/config/puppet.nft, all other files created by that module go into files/config/puppet and will also be purged if not managed anymore.

The main configuration file includes dedicated files for the filter and NAT tables, as well as processes any custom-*.nft files before hand.

The filter and NAT tables both have all the master chains (INPUT, OUTPUT, FORWARD in case of filter and PREROUTING and POSTROUTING in case of NAT) configured, to which you can hook in your own chains that can contain specific rules.

All filter masterchains drop by default. By default we have a set of default_MASTERCHAIN chains configured to which you can easily add your custom rules.

For specific needs you can add your own chain.

There is a global chain, that defines the default behavior for all masterchains. This chain is empty by default.

INPUT and OUTPUT to the loopback device is allowed by default, though you could restrict it later.

On the other hand, if you don't want any of the default tables, chains and rules created by the module, you can set nftables::inet_filter and/or nftables::nat to false and build your whole nftables configuration from scratch by using the building blocks provided by this module. Look at nftables::inet_filter for inspiration.

Rules Validation

Initially puppet deploys all configuration to /etc/nftables/puppet-preflight/ and /etc/nftables/puppet-preflight.nft. This is validated with nft -c -I /etc/nftables/puppet-preflight/ -f /etc/nftables/puppet-preflight.nft. If and only if successful the configuration will be copied to the real locations before the service is reloaded.

Un-managed rules

By default, rules added manually by the administrator to the in-memory ruleset will be left untouched. However, nftables::purge_unmanaged_rules can be set to true to revert this behaviour and force a reload of the ruleset during the Puppet run if non-managed changes are detected.

Basic types

nftables::config

Manages a raw file in /etc/nftables/puppet/${name}.nft

Use this for any custom table files.

nftables::chain

Prepares a chain file as a concat file to which you will be able to add dedicated rules through nftables::rule.

The name must be unique for all chains. The inject parameter can be used to directly add a jump to a masterchain. inject must follow the pattern ORDER-MASTERCHAIN, where order references a 2-digit number which defines the rule order (by default use e.g. 20) and masterchain references the chain to hook in the new chain. It's possible to specify the in-interface name and out-interface name for the inject rule.

nftables::rule

A simple way to add rules to any chain. The name must be: CHAIN_NAME-rulename, where CHAIN_NAME refers to your chain and an arbitrary name for your rule. The rule will be a concat::fragment to the chain CHAIN_NAME.

You can define the order by using the order param.

Before defining your own rule, take a look to the list of ready-to-use rules available in the REFERENCE, somebody might have encapsulated a rule definition for you already.

nftables::set

Adds a named set to a given table. It allows composing the set using individual parameters but also takes raw input via the content and source parameters.

nftables::simplerule

Allows expressing firewall rules without having to use nftables's language by adding an abstraction layer a-la-Firewall. It's rather limited how far you can go so if you need rather complex rules or you can speak nftables it's recommended to use nftables::rule directly.

Facts

One structured fact nftables is available

{
  tables => [
    "bridge-filter",
    "bridge-nat",
    "inet-firewalld",
    "ip-firewalld",
    "ip6-firewalld"
  ],
  version => "0.9.3"
}

• nftables.version is the version of the nft command from nft --version.
• nftables.tables is the list of tables installed on the machine from nft list tables.

Editor goodies

If you're using Emacs there are some snippets for Yasnippet available here that could make your life easier when using the module. This is third party configuration that's only included here for reference so changes in the interfaces exposed by this module are not guaranteed to be automatically applied there.

Development

This module relies on CI testing. To ensure the tests and documentation is complete.

The following steps are a blueprint for the necessary work to add a new rule to the module:

1. add a new class for the new rule (there are enough examples)
2. document class and parameters
3. Add a spec test for the new rule to spec/classes/rules
4. add the rule to spec/acceptance/all_rules_spec.rb
5. update the reference with bundle exec rake strings:generate:reference
6. commit, push and open a PR