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# Copyright 2020 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
from typing import List, Optional, Union
from netaddr import IPAddress, IPSet
from zope.interface import provider
from twisted.internet.endpoints import HostnameEndpoint
from twisted.internet.interfaces import (
IAddress,
IHostResolution,
IReactorPluggableNameResolver,
IResolutionReceiver,
)
logger = logging.getLogger(__name__)
def check_against_blacklist(
ip_address: IPAddress, ip_whitelist: Optional[IPSet], ip_blacklist: IPSet
) -> bool:
"""
Compares an IP address to allowed and disallowed IP sets.
Args:
ip_address: The IP address to check
ip_whitelist: Allowed IP addresses.
ip_blacklist: Disallowed IP addresses.
Returns:
True if the IP address is in the blacklist and not in the whitelist.
"""
if ip_address in ip_blacklist:
if ip_whitelist is None or ip_address not in ip_whitelist:
return True
return False
class BlacklistingHostnameEndpoint(HostnameEndpoint):
def __init__(
self,
reactor: IReactorPluggableNameResolver,
host: Union[str, bytes],
port: int,
timeout: int = 30,
bindAddress=None,
attemptDelay=None,
ip_whitelist: Optional[IPSet] = None,
ip_blacklist: Optional[IPSet] = None,
):
super().__init__(reactor, host, port, timeout, bindAddress, attemptDelay)
self._ip_whitelist = ip_whitelist
self._ip_blacklist = ip_blacklist
# Calling super().__init__ sets up _nameResolver, wrap that so the
# results can be filtered before being returned.
#
# Note that the nameResolver is called even if the passed in host is an
# IP address (which will resolve to itself).
self._real_nameResolver = self._nameResolver
self._nameResolver = self._filteringNameResolver
def _filteringNameResolver(
self, recv: IResolutionReceiver, hostname: str, portNumber: int = 0
) -> IResolutionReceiver:
r = recv()
addresses = [] # type: List[IAddress]
def _callback() -> None:
r.resolutionBegan(None)
has_bad_ip = False
for i in addresses:
ip_address = IPAddress(i.host)
if check_against_blacklist(
ip_address, self._ip_whitelist, self._ip_blacklist
):
logger.info(
"Dropped %s from DNS resolution to %s due to blacklist"
% (ip_address, hostname)
)
has_bad_ip = True
# if we have a blacklisted IP, we'd like to raise an error to block the
# request, but all we can really do from here is claim that there were no
# valid results.
if not has_bad_ip:
for i in addresses:
r.addressResolved(i)
r.resolutionComplete()
@provider(IResolutionReceiver)
class EndpointReceiver:
@staticmethod
def resolutionBegan(resolutionInProgress: IHostResolution) -> None:
pass
@staticmethod
def addressResolved(address: IAddress) -> None:
addresses.append(address)
@staticmethod
def resolutionComplete() -> None:
_callback()
self._real_nameResolver.resolveHostName(
EndpointReceiver, hostname, portNumber=portNumber
)
return r
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