chromeos-base/chromeos-firewall-init/files/iptables.conf

# Copyright 2011 The ChromiumOS Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

description     "Set iptables policies and add rules"
author          "chromium-os-dev@chromium.org"

start on starting network-services
task

script
{
  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 icmp echo (NB: icmp echo ratelimiting is done by the kernel)
  iptables -A INPUT -p icmp -j ACCEPT -w

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

  # Accept inbound mDNS traffic
  iptables -A INPUT -p udp --destination 224.0.0.251 --dport 5353 -j ACCEPT -w

  # Accept inbound SSDP traffic
  iptables -A INPUT -p udp --destination 239.255.255.250 --dport 1900 -j ACCEPT -w

  # netfilter-queue-helper is used for Linux < 3.12.
  # For Linux >= 3.12, conntrackd.conf is used instead.
  if [ -e /usr/sbin/netfilter-queue-helper ]; then
    . /usr/sbin/netfilter-common

    # Filter outgoing SSDP traffic for the DIAL protocol through a user-space
    # filter (netfilter-queue-helper) which will open up a port for reply
    # traffic.
    iptables -I OUTPUT -p udp --destination 239.255.255.250 --dport 1900 \
        -j NFQUEUE --queue-num ${NETFILTER_OUTPUT_NFQUEUE} -w

    # Ditto for outbound mDNS legacy unicast replies (source port != 5353).
    iptables -I OUTPUT -p udp --destination 224.0.0.251 --dport 5353 \
        -j NFQUEUE --queue-num ${NETFILTER_OUTPUT_NFQUEUE} -w

    # Send incoming UDP traffic (which has not passed any other rules) to the
    # user-space filter to test whether it was a reply to outgoing DIAL protocol
    # traffic.
    iptables -A INPUT -p udp -j NFQUEUE \
        --queue-num ${NETFILTER_INPUT_NFQUEUE} -w
  fi
} 2>&1 | logger --priority daemon.info -t ${UPSTART_JOB}
end script