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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, cmd
from vyos import ConfigError
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 _check_kmod():
""" load required Kernel modules """
modules = ['nft_nat', 'nft_chain_nat_ipv4']
for module in modules:
if not os.path.exists(f'/sys/module/{module}'):
if call(f'modprobe {module}') != 0:
raise ConfigError(f'Loading Kernel module {module} failed')
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 parse_source_destination(conf, source_dest):
""" Common wrapper to read in both NAT source and destination CLI """
tmp = []
base_level = ['nat', source_dest]
conf.set_level(base_level)
for number in conf.list_nodes(['rule']):
rule = {
'description': '',
'dest_address': '',
'dest_port': '',
'disable': False,
'exclude': False,
'interface_in': '',
'interface_out': '',
'log': False,
'protocol': '',
'number': number,
'source_address': '',
'source_port': '',
'translation_address': '',
'translation_port': ''
}
conf.set_level(base_level + ['rule', number])
if conf.exists(['description']):
rule['description'] = conf.return_value(['description'])
if conf.exists(['destination', 'address']):
rule['dest_address'] = conf.return_value(['destination', 'address'])
if conf.exists(['destination', 'port']):
rule['dest_port'] = conf.return_value(['destination', 'port'])
if conf.exists(['disable']):
rule['disable'] = 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']):
rule['source_address'] = conf.return_value(['source', 'address'])
if conf.exists(['source', 'port']):
rule['source_port'] = conf.return_value(['source', 'port'])
if conf.exists(['translation', 'address']):
rule['translation_address'] = conf.return_value(['translation', 'address'])
if conf.exists(['translation', 'port']):
rule['translation_port'] = conf.return_value(['translation', 'port'])
tmp.append(rule)
return tmp
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']:
nat[tgt] = parse_source_destination(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']
if interface and interface not in interfaces():
print(f'NAT configuration warning: interface {interface} does not exist on this system')
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}')
return None
if __name__ == '__main__':
try:
_check_kmod()
c = get_config()
verify(c)
generate(c)
apply(c)
except ConfigError as e:
print(e)
exit(1)

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