#!/usr/sbin/nft -f
#
# nftables ruleset for an End Node acting as a workstation in a LAN.
#
# Copyright (C) 2018  Antonio Ospite <ao2@ao2.it>
# SPDX-License-Identifier: MIT
#
# Based on:
# https://wiki.nftables.org/wiki-nftables/index.php/Quick_reference-nftables_in_10_minutes#Simple_IP.2FIPv6_Firewall
# https://wiki.archlinux.org/index.php/Nftables#Workstation
# https://stosb.com/blog/explaining-my-configs-nftables/

flush ruleset

table inet filter {

    define common_open_ports = {
            xmpp-client,
            xmpp-server,
            5298, # Link-local XMPP, for backward compatibility, XEP-0174
    }

    set tcp_open_ports {
        type inet_service
        flags interval

        elements = {
            $common_open_ports,
        }
    }

    set udp_open_ports {
        type inet_service
        flags interval

        elements = {
            $common_open_ports,
        }
    }

    chain input {
        type filter hook input priority 0
        policy drop

        iif lo accept

        ip protocol icmp icmp type {
            echo-reply,
            echo-request,
            time-exceeded,
            parameter-problem,
            destination-unreachable
        } accept

        # ICMPv6 configuration based on:
        # https://github.com/intel/intel-iot-refkit/blob/master/meta-refkit-core/recipes-security/nftables-settings-default/files/firewall.template
        ip6 nexthdr ipv6-icmp icmpv6 type {
            echo-reply,
            echo-request,
            time-exceeded,
            parameter-problem,
            destination-unreachable,
            packet-too-big
        } accept

        # Allow IPv6 Neighbor Discovery (RFC4861).
        ip6 nexthdr ipv6-icmp icmpv6 type {
            nd-router-advert,
            nd-router-solicit,
            nd-neighbor-advert,
            nd-neighbor-solicit
        } ip6 hoplimit 255 accept

        # Allow multicast listener discovery on link-local addresses.
        # RFC2710 specifies that a Hop-by-Hop Options header is used.
        hbh nexthdr ipv6-icmp icmpv6 type {
            mld-listener-query,
            mld-listener-report,
            mld-listener-reduction
        } ip6 saddr fe80::/10 accept

        # Allow multicast router discovery messages on link-local addresses (hop limit 1).
        ip6 nexthdr ipv6-icmp icmpv6 type {
            nd-router-advert,
            nd-router-solicit
        } ip6 hoplimit 1 ip6 saddr fe80::/10 accept

        # Allow IGMPv3 queries.
        ip protocol igmp ip daddr 224.0.0.1 accept

        # Stateful filtering for anything else.
        ct state established,related accept
        ct state invalid drop
        ct state new jump in-new

        # Silently drop other incoming broadcast and multicast traffic.
        meta pkttype {broadcast, multicast} drop

        limit rate 3/minute burst 10 packets log prefix "[INPUT]: "
        counter reject
    }

    chain in-new {
        # Silently drop DHCPv4 Discover and Request packets from other clients.
        ip saddr 0.0.0.0 ip daddr 255.255.255.255 udp sport bootpc udp dport bootps drop

        # Silently drop DHCPv6 from other clients.
        ip6 saddr fe80::/64 ip6 daddr fe80::/64 udp sport dhcpv6-client udp dport dhcpv6-server drop

        # mDNS (ZeroConf/Bonjour)
        ip  daddr 224.0.0.251 udp dport mdns accept
        ip6 daddr ff02::fb    udp dport mdns accept

        # SSDP: https://en.wikipedia.org/wiki/Simple_Service_Discovery_Protocol
        ip daddr 239.255.255.250 udp dport 1900 accept
        ip6 daddr {
            ff02::c,
            ff05::c,
            ff08::c,
            ff0e::c
        } udp dport 1900 accept

        tcp dport @tcp_open_ports tcp flags & (fin | syn | rst | ack) == syn accept
        udp dport @udp_open_ports accept
    }

    chain forward {
        type filter hook forward priority 0
        policy drop

        limit rate 3/minute burst 10 packets log prefix "[FORWARD]: "
        counter reject
    }

    chain output {
        type filter hook output priority 0
        policy drop

        counter accept
    }
}