1 files changed, 259 insertions, 0 deletions
diff --git a/src/conf_mode/nat.py b/src/conf_mode/nat.py
new file mode 100755
index 000000000..5cb1af1f1
--- /dev/null
+++ b/src/conf_mode/nat.py
@@ -0,0 +1,259 @@
+#!/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.validate import is_addr_assigned
+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 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')
+
+    if not rule['translation_address']:
+        raise ConfigError(f'{err_msg} translation address not specified')
+    else:
+        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!')
+
+
+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': '',
+            'disabled': False,
+            'exclude': False,
+            'interface_in': '',
+            'interface_out': '',
+            'log': False,
+            'protocol': 'all',
+            '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['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']):
+            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']
+        err_msg = f"Source NAT configuration error in rule {rule['number']}:"
+
+        if interface and interface not in interfaces():
+            print(f'NAT configuration warning: interface {interface} does not exist on this system')
+
+        if not rule['interface_out']:
+            raise ConfigError(f'{err_msg} outbound-interface 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 interfaces():
+            print(f'NAT configuration warning: interface {interface} does not exist on this system')
+
+        if not rule['interface_in']:
+            raise ConfigError(f'{err_msg} inbound-interface 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()
+        c = get_config()
+        verify(c)
+        generate(c)
+        apply(c)
+    except ConfigError as e:
+        print(e)
+        exit(1)