From 77c8997c20e5b93a56299850ec1ce4216f8f8b3f Mon Sep 17 00:00:00 2001 From: Benjamin Barenblat Date: Mon, 19 Apr 2021 14:19:51 -0400 Subject: localsubnetsetd, a daemon to track the local subnet for nftables --- CONTRIBUTING.md | 28 +++++++ LICENSE | 202 ++++++++++++++++++++++++++++++++++++++++++++++++ README.md | 26 +++++++ localsubnetsetd | 103 ++++++++++++++++++++++++ localsubnetsetd.service | 39 ++++++++++ 5 files changed, 398 insertions(+) create mode 100644 CONTRIBUTING.md create mode 100644 LICENSE create mode 100644 README.md create mode 100755 localsubnetsetd create mode 100644 localsubnetsetd.service diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md new file mode 100644 index 0000000..6272489 --- /dev/null +++ b/CONTRIBUTING.md @@ -0,0 +1,28 @@ +# How to Contribute + +We'd love to accept your patches and contributions to this project. 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The original use case for +localsubnetsetd was to give special access to traffic on an IPv6 subnet with an +unpredictable network number (as is common with prefix delegations from consumer +ISPs). More generally, localsubnetsetd allows you to treat local network traffic +specially without involving a border firewall. + +## Dependencies + +localsubnetsetd is written in Python 3 and requires the nftables and pyroute2 +libraries. On Debian, you want the `python3`, `python3-nftables`, and +`python3-pyroute2` packages. + +## Setup + +localsubnetsetd requires that `local_subnets4` and `local_subnets6` sets exist +in the `inet filter` table. Create them with + + nft add set inet filter local_subnets4 { type ipv4_addr; flags interval; } + nft add set inet filter local_subnets6 { type ipv6_addr; flags interval; } + +--- + +This is not an official Google product. diff --git a/localsubnetsetd b/localsubnetsetd new file mode 100755 index 0000000..d955cca --- /dev/null +++ b/localsubnetsetd @@ -0,0 +1,103 @@ +#!/usr/bin/python3 +# Copyright 2021 Google LLC +# +# 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 +# +# https://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. + +from socket import AF_INET, AF_INET6 + +import nftables +import pyroute2 + + +def send_command(nft, s): + '''Sends a command to nftables. + + Sends the specified command string to the specified nftables instance. Waits + for acknowledgement. Raises RuntimeError if the command fails. + ''' + print(s) + failed, stdout, stderr = nft.cmd(s) + if failed: + raise RuntimeError('nftables command failed: %s' % stderr) + + +def set_name(family): + '''Generates the relevant nftables set name for the specified protocol.''' + if family == AF_INET: + return 'local_subnets4' + elif family == AF_INET6: + return 'local_subnets6' + raise ValueError("don't have a set for family %d" % family) + + +def flush(family): + '''Creates an nftables command to flush the local subnet set.''' + return 'flush set inet filter %s' % set_name(family) + + +def add(msg): + '''Creates an nftables command to add a subnet. + + Processes a netlink message to extract its subnet, and creates an nftables + command to add that subnet to the appropriate set. + ''' + for k, v in msg['attrs']: + if k == 'IFA_ADDRESS': + subnet = v + '/' + str(msg['prefixlen']) + break + else: + raise ValueError("message lacks 'IFA_ADDRESS' attribute") + + return 'add element inet filter %s { %s }' % (set_name( + msg['family']), subnet) + + +def add_current(netlink, family=None): + '''Creates an nftables command to add all current subnets.''' + r = [] + for msg in netlink.get_addr(): + if family and msg['family'] != family: + continue + r.append(add(msg)) + return '; '.join(r) + + +def maintain_sets(nft, netlink): + # Start listening for netlink messages now so we don't miss any while + # we're querying the current IP address set. + netlink.bind() + + # Populate the sets with the initial set of IP addresses. + send_command( + nft, '; '.join([flush(AF_INET), + flush(AF_INET6), + add_current(netlink)])) + + # Watch for changes. + while True: + for msg in netlink.get(): + if msg['event'] == 'RTM_NEWADDR': + send_command(nft, add(msg)) + elif msg['event'] == 'RTM_DELADDR': + # We might still be holding another address on the same subnet, + # so we can't just delete this subnet. Rebuild the subnet set + # from scratch. + fam = msg['family'] + send_command(nft, + flush(fam) + '; ' + add_current(netlink, fam)) + + +if __name__ == '__main__': + nft = nftables.Nftables() + with pyroute2.IPRoute() as netlink: + maintain_sets(nft, netlink) diff --git a/localsubnetsetd.service b/localsubnetsetd.service new file mode 100644 index 0000000..4279569 --- /dev/null +++ b/localsubnetsetd.service @@ -0,0 +1,39 @@ +# Copyright 2021 Google LLC +# +# 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 +# +# https://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. + +[Unit] +Description=local subnet set maintenance daemon +Requires=nftables.service +After=nftables.service + +[Service] +ExecStart=localsubnetsetd +Restart=always +NoNewPrivileges=true +ProtectSystem=strict +ProtectHome=true +PrivateDevices=true +ProtectKernelTunables=true +ProtectKernelModules=true +ProtectControlGroups=true +RestrictAddressFamilies=AF_NETLINK +RestrictNamespaces=true +LockPersonality=true +MemoryDenyWriteExecute=true +RestrictRealtime=true +SystemCallFilter=@system-service +SystemCallArchitectures=native + +[Install] +WantedBy=sysinit.target -- cgit v1.2.3