inspec/lib/resources/iptables.rb

# encoding: utf-8
# author: Christoph Hartmann
# author: Dominik Richter

# Usage:
# describe iptables do
#   it { should have_rule('-P INPUT ACCEPT') }
# end
#
# The following serverspec sytax is not implemented:
# describe iptables do
#   it { should have_rule('-P INPUT ACCEPT').with_table('mangle').with_chain('INPUT') }
# end
# Please use the new sytax:
# describe iptables(table:'mangle', chain: 'input') do
#   it { should have_rule('-P INPUT ACCEPT') }
# end
#
# Note: Docker containers normally do not have iptables installed
#
# @see http://ipset.netfilter.org/iptables.man.html
# @see http://ipset.netfilter.org/iptables.man.html
# @see https://www.frozentux.net/iptables-tutorial/iptables-tutorial.html
class IpTables < Inspec.resource(1)
  name 'iptables'
  desc 'Use the iptables InSpec audit resource to test rules that are defined in iptables, which maintains tables of IP packet filtering rules. There may be more than one table. Each table contains one (or more) chains (both built-in and custom). A chain is a list of rules that match packets. When the rule matches, the rule defines what target to assign to the packet.'
  example "
    describe iptables do
      it { should have_rule('-P INPUT ACCEPT') }
    end
  "

  def initialize(params = {})
    @table = params[:table]
    @chain = params[:chain]

    # we're done if we are on linux
    return if inspec.os.linux?

    # ensures, all calls are aborted for non-supported os
    @iptables_cache = []
    skip_resource 'The `iptables` resource is not supported on your OS yet.'
  end

  def has_rule?(rule = nil, _table = nil, _chain = nil)
    # checks if the rule is part of the ruleset
    # for now, we expect an exact match
    retrieve_rules.any? { |line| line.casecmp(rule) == 0 }
  end

  def retrieve_rules
    return @iptables_cache if defined?(@iptables_cache)

    # construct iptables command to read all rules
    table_cmd = "-t #{@table}" if @table
    iptables_cmd = format('iptables %s -S %s', table_cmd, @chain).strip

    cmd = inspec.command(iptables_cmd)
    return [] if cmd.exit_status.to_i != 0

    # split rules, returns array or rules
    @iptables_cache = cmd.stdout.split("\n").map(&:strip)
  end

  def to_s
    format('Iptables %s %s', @table && "table: #{@table}", @chain && "chain: #{@chain}").strip
  end
end