#!/bin/bash
# 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.
#
iptables -P INPUT DROP -w
iptables -P FORWARD DROP -w
iptables -P OUTPUT DROP -w

# Accept everything on the loopback
iptables -I INPUT -i lo -j ACCEPT -w
iptables -I OUTPUT -o lo -j ACCEPT -w

# Accept return traffic inbound
iptables -I INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT -w

# Accept all inbound TCP/UDP/ICMP/SCTP packets
iptables -A INPUT -p tcp -j ACCEPT -w
iptables -A INPUT -p udp -j ACCEPT -w
iptables -A INPUT -p icmp -j ACCEPT -w
iptables -A INPUT -p sctp -j ACCEPT -w

# Accept all forwarded TCP/UDP/ICMP/SCTP packets
iptables -A FORWARD -p tcp -j ACCEPT -w
iptables -A FORWARD -p udp -j ACCEPT -w
iptables -A FORWARD -p icmp -j ACCEPT -w
iptables -A FORWARD -p sctp -j ACCEPT -w

# Accept new and return traffic outbound
iptables -I OUTPUT -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT -w