nat.py
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nat.py
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	#!/usr/bin/env python3
	#
	# Copyright (C) 2020 VyOS maintainers and contributors
	#
	# This program is free software; you can redistribute it and/or modify
	# it under the terms of the GNU General Public License version 2 or later as
	# published by the Free Software Foundation.
	#
	# This program is distributed in the hope that it will be useful,
	# but WITHOUT ANY WARRANTY; without even the implied warranty of
	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	# GNU General Public License for more details.
	#
	# You should have received a copy of the GNU General Public License
	# along with this program. If not, see <http://www.gnu.org/licenses/>.

	import jmespath
	import json
	import os

	from copy import deepcopy
	from sys import exit
	from netifaces import interfaces

	from vyos.config import Config
	from vyos.template import render
	from vyos.util import call
	from vyos.util import cmd
	from vyos.util import check_kmod
	from vyos.validate import is_addr_assigned
	from vyos import ConfigError

	from vyos import airbag
	airbag.enable()

	k_mod = ['nft_nat', 'nft_chain_nat_ipv4']

	default_config_data = {
	'deleted': False,
	'destination': [],
	'helper_functions': None,
	'pre_ct_helper': '',
	'pre_ct_conntrack': '',
	'out_ct_helper': '',
	'out_ct_conntrack': '',
	'source': []
	}

	iptables_nat_config = '/tmp/vyos-nat-rules.nft'

	def get_handler(json, chain, target):
	""" Get nftable rule handler number of given chain/target combination.
	Handler is required when adding NAT/Conntrack helper targets """
	for x in json:
	if x['chain'] != chain:
	continue
	if x['target'] != target:
	continue
	return x['handle']

	return None


	def verify_rule(rule, err_msg):
	""" Common verify steps used for both source and destination NAT """
	if rule['translation_port'] or rule['dest_port'] or rule['source_port']:
	if rule['protocol'] not in ['tcp', 'udp', 'tcp_udp']:
	proto = rule['protocol']
	raise ConfigError(f'{err_msg} ports can only be specified when protocol is "tcp", "udp" or "tcp_udp" (currently "{proto}")')

	if '/' in rule['translation_address']:
	raise ConfigError(f'{err_msg}\n' \
	'Cannot use ports with an IPv4net type translation address as it\n' \
	'statically maps a whole network of addresses onto another\n' \
	'network of addresses')


	def parse_configuration(conf, source_dest):
	""" Common wrapper to read in both NAT source and destination CLI """
	ruleset = []
	base_level = ['nat', source_dest]
	conf.set_level(base_level)
	for number in conf.list_nodes(['rule']):
	rule = {
	'description': '',
	'dest_address': '',
	'dest_port': '',
	'disabled': False,
	'exclude': False,
	'interface_in': '',
	'interface_out': '',
	'log': False,
	'protocol': 'all',
	'number': number,
	'source_address': '',
	'source_prefix': '',
	'source_port': '',
	'translation_address': '',
	'translation_prefix': '',
	'translation_port': ''
	}
	conf.set_level(base_level + ['rule', number])

	if conf.exists(['description']):
	rule['description'] = conf.return_value(['description'])

	if conf.exists(['destination', 'address']):
	tmp = conf.return_value(['destination', 'address'])
	if tmp.startswith('!'):
	tmp = tmp.replace('!', '!=')
	rule['dest_address'] = tmp

	if conf.exists(['destination', 'port']):
	tmp = conf.return_value(['destination', 'port'])
	if tmp.startswith('!'):
	tmp = tmp.replace('!', '!=')
	rule['dest_port'] = tmp

	if conf.exists(['disable']):
	rule['disabled'] = True

	if conf.exists(['exclude']):
	rule['exclude'] = True

	if conf.exists(['inbound-interface']):
	rule['interface_in'] = conf.return_value(['inbound-interface'])

	if conf.exists(['outbound-interface']):
	rule['interface_out'] = conf.return_value(['outbound-interface'])

	if conf.exists(['log']):
	rule['log'] = True

	if conf.exists(['protocol']):
	rule['protocol'] = conf.return_value(['protocol'])

	if conf.exists(['source', 'address']):
	tmp = conf.return_value(['source', 'address'])
	if tmp.startswith('!'):
	tmp = tmp.replace('!', '!=')
	rule['source_address'] = tmp

	if conf.exists(['source', 'prefix']):
	rule['source_prefix'] = conf.return_value(['source', 'prefix'])

	if conf.exists(['source', 'port']):
	tmp = conf.return_value(['source', 'port'])
	if tmp.startswith('!'):
	tmp = tmp.replace('!', '!=')
	rule['source_port'] = tmp

	if conf.exists(['translation', 'address']):
	rule['translation_address'] = conf.return_value(['translation', 'address'])

	if conf.exists(['translation', 'prefix']):
	rule['translation_prefix'] = conf.return_value(['translation', 'prefix'])

	if conf.exists(['translation', 'port']):
	rule['translation_port'] = conf.return_value(['translation', 'port'])

	ruleset.append(rule)

	return ruleset

	def get_config():
	nat = deepcopy(default_config_data)
	conf = Config()

	# read in current nftable (once) for further processing
	tmp = cmd('nft -j list table raw')
	nftable_json = json.loads(tmp)

	# condense the full JSON table into a list with only relevand informations
	pattern = 'nftables[?rule].rule[?expr[].jump].{chain: chain, handle: handle, target: expr[].jump.target \| [0]}'
	condensed_json = jmespath.search(pattern, nftable_json)

	if not conf.exists(['nat']):
	nat['helper_functions'] = 'remove'

	# Retrieve current table handler positions
	nat['pre_ct_ignore'] = get_handler(condensed_json, 'PREROUTING', 'VYATTA_CT_HELPER')
	nat['pre_ct_conntrack'] = get_handler(condensed_json, 'PREROUTING', 'NAT_CONNTRACK')
	nat['out_ct_ignore'] = get_handler(condensed_json, 'OUTPUT', 'VYATTA_CT_HELPER')
	nat['out_ct_conntrack'] = get_handler(condensed_json, 'OUTPUT', 'NAT_CONNTRACK')

	nat['deleted'] = True

	return nat

	# check if NAT connection tracking helpers need to be set up - this has to
	# be done only once
	if not get_handler(condensed_json, 'PREROUTING', 'NAT_CONNTRACK'):
	nat['helper_functions'] = 'add'

	# Retrieve current table handler positions
	nat['pre_ct_ignore'] = get_handler(condensed_json, 'PREROUTING', 'VYATTA_CT_IGNORE')
	nat['pre_ct_conntrack'] = get_handler(condensed_json, 'PREROUTING', 'VYATTA_CT_PREROUTING_HOOK')
	nat['out_ct_ignore'] = get_handler(condensed_json, 'OUTPUT', 'VYATTA_CT_IGNORE')
	nat['out_ct_conntrack'] = get_handler(condensed_json, 'OUTPUT', 'VYATTA_CT_OUTPUT_HOOK')

	# set config level for parsing in NAT configuration
	conf.set_level(['nat'])

	# use a common wrapper function to read in the source / destination
	# tree from the config - thus we do not need to replicate almost the
	# same code :-)
	for tgt in ['source', 'destination', 'nptv6']:
	nat[tgt] = parse_configuration(conf, tgt)

	return nat

	def verify(nat):
	if nat['deleted']:
	# no need to verify the CLI as NAT is going to be deactivated
	return None

	if nat['helper_functions']:
	if not (nat['pre_ct_ignore'] or nat['pre_ct_conntrack'] or nat['out_ct_ignore'] or nat['out_ct_conntrack']):
	raise Exception('could not determine nftable ruleset handlers')

	for rule in nat['source']:
	interface = rule['interface_out']
	err_msg = f'Source NAT configuration error in rule "{rule["number"]}":'

	if interface and interface not in 'any' and interface not in interfaces():
	print(f'Warning: rule "{rule["number"]}" interface "{interface}" does not exist on this system')

	if not rule['interface_out']:
	raise ConfigError(f'{err_msg} outbound-interface not specified')

	if rule['translation_address']:
	addr = rule['translation_address']
	if addr != 'masquerade' and not is_addr_assigned(addr):
	print(f'Warning: IP address {addr} does not exist on the system!')
	elif not rule['exclude']:
	raise ConfigError(f'{err_msg} translation address not specified')

	# common rule verification
	verify_rule(rule, err_msg)

	for rule in nat['destination']:
	interface = rule['interface_in']
	err_msg = f'Destination NAT configuration error in rule "{rule["number"]}":'

	if interface and interface not in 'any' and interface not in interfaces():
	print(f'Warning: rule "{rule["number"]}" interface "{interface}" does not exist on this system')

	if not rule['interface_in']:
	raise ConfigError(f'{err_msg} inbound-interface not specified')

	if not rule['translation_address'] and not rule['exclude']:
	raise ConfigError(f'{err_msg} translation address not specified')

	# common rule verification
	verify_rule(rule, err_msg)

	return None

	def generate(nat):
	render(iptables_nat_config, 'firewall/nftables-nat.tmpl', nat, trim_blocks=True, permission=0o755)
	return None

	def apply(nat):
	cmd(f'{iptables_nat_config}')
	if os.path.isfile(iptables_nat_config):
	os.unlink(iptables_nat_config)

	return None

	if __name__ == '__main__':
	try:
	check_kmod(k_mod)
	c = get_config()
	verify(c)
	generate(c)
	apply(c)
	except ConfigError as e:
	print(e)
	exit(1)

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