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#!/usr/sbin/nft -f

define in-tcp-ports = {
    {{ ansible_port|default(22) }}
{% if 'MX' in group_names %}
  , 25      # SMTP
{% endif %}
{% if 'LDAP_provider' in group_names %}
  , 636     # ldaps
{% endif %}
{% if 'IMAP' in group_names %}
  , 993     # imaps
  , 4190    # ManageSieve
{% endif %}
{% if 'MSA' in group_names %}
  , 587     # submission [RFC4409]
  , 465     # submission over TLS [RFC8314]
{% endif %}
{% if 'webmail' in group_names or 'lists' in group_names or 'wiki' in group_names or 'nextcloud' in group_names %}
  , 80      # HTTP
  , 443     # HTTP over SSL/TLS
{% endif %}
}

define out-tcp-ports = {
    22
  , 80      # HTTP
  , 443     # HTTP over SSL/TLS
{% if 'out' in group_names or 'MSA' in group_names %}
  , 25      # SMTP
{% endif %}
{% if 'LDAP_provider' in group_names %}
  , 11371   # OpenPGP HTTP Keyserver
  , 43      # whois
{% elif 'MX' in group_names or 'lists' in group_names or 'nextcloud' in group_names %}
  , 636     # ldaps
{% endif %}
{% if 'IMAP' in group_names %}
  , 2703    # Razor2
{% endif %}
}


###############################################################################

flush ruleset

table inet filter {
    # blackholes
    set fail2ban  { type ipv4_addr; timeout 10m; }
    set fail2ban6 { type ipv6_addr; timeout 10m; }

    chain input {
        type filter hook input priority 0
        policy drop

        iif lo accept

        # XXX Bullseye: this is a rather crude match as nftables 0.9.0 lacks support for ipsec expressions
        # to match match inbound resp. outbound policies and source resp. destination tunnel addresses.
        # https://serverfault.com/questions/971735/how-to-match-reqid-in-nftables
        # https://blog.fraggod.net/2016/09/25/nftables-re-injected-ipsec-matching-without-xt_policy.html
        # (We can't use marks to match post-ESP decapsulation here because that doesn't work well with UDP
        # encapsulation.)  We'll also pin the reqid to the lowest address byte in ipsec.conf(5); that way
        # peers can't impersonate each other.
        meta l4proto esp accept
        # ip saddr {{ ipsec_subnet }} ip daddr {{ ipsec[inventory_hostname_short] }} ipsec in reqid $i accept
        ip saddr {{ ipsec_subnet }} ip daddr {{ ipsec[inventory_hostname_short] }} meta secpath exists accept

        # rate-limiting is done directly by the kernel (net.ipv4.icmp_{ratelimit,ratemask} runtime options)
        icmp   type { echo-reply, echo-request, destination-unreachable } counter accept
        icmpv6 type { echo-reply, echo-request, destination-unreachable,
                      packet-too-big, time-exceeded, parameter-problem } counter accept

        # accept neighbour discovery for autoconfiguration, RFC 4890 sec. 4.4.1
        icmpv6 type { 133,134,135,136,141,142 } ip6 hoplimit 255 counter accept

        jump martian
        jump invalid

        udp sport  123 udp dport  123 ct state     related,established accept
{% if groups.all | length > 1 %}
        udp sport  500 udp dport  500 ct state new,related,established accept
{% if groups.NATed | length > 0 %}
        udp sport 4500 udp dport 4500 ct state new,related,established accept
{% endif %}
{% endif %}

        udp sport 53 ct state related,established accept
        tcp sport 53 ct state related,established accept
{% if 'dhclient' in group_names %}
        ip  version 4 udp sport  67 udp dport  68 ct state related,established accept
        ip6 version 6 udp sport 547 udp dport 546 ct state related,established accept
{% endif %}

        meta l4proto tcp ip  saddr @fail2ban  counter drop
        meta l4proto tcp ip6 saddr @fail2ban6 counter drop

        tcp dport $in-tcp-ports  ct state related,established accept
        tcp dport $in-tcp-ports  ct state new counter accept
        tcp sport $out-tcp-ports ct state related,established accept
    }

    chain output {
        type filter hook output priority 0
        policy drop

        oif lo accept

        # XXX Bullseye: unlike for input we can't use marks or test for
        # secpath existence here, because by the time we see a packet to
        # 172.16.0.0/24 we don't know if it'll be encapsulated
        meta l4proto esp accept
        # ip saddr {{ ipsec[inventory_hostname_short] }} ip daddr {{ ipsec_subnet }} ipsec out reqid $i accept
        ip saddr {{ ipsec[inventory_hostname_short] }} ip daddr {{ ipsec_subnet }} accept

        meta l4proto { icmp, icmpv6 } accept

        jump martian
        jump invalid

        udp sport  123 udp dport  123 ct state new,related,established accept
{% if groups.all | length > 1 %}
        udp sport  500 udp dport  500 ct state new,related,established accept
{% if groups.NATed | length > 0 %}
        udp sport 4500 udp dport 4500 ct state new,related,established accept
{% endif %}
{% endif %}

        udp dport 53 ct state new,related,established accept
        tcp dport 53 ct state new,related,established accept
{% if 'dhclient' in group_names %}
        ip  version 4 udp sport  68 udp dport  67 ct state new,related,established accept
        ip6 version 6 udp sport 546 udp dport 547 ct state new,related,established accept
{% endif %}

        tcp sport $in-tcp-ports  ct state related,established accept
        tcp dport $out-tcp-ports ct state related,established accept
        tcp dport $out-tcp-ports ct state new counter accept

        meta l4proto tcp counter reject with tcp reset
        meta l4proto udp counter reject
        counter reject
    }

    chain martian {
        # bogon filter (cf. RFC 6890 for non-global ip addresses)
        define invalid-ip = {
            0.0.0.0/8          # this host, on this network (RFC 1122 sec. 3.2.1.3)
{% if not ansible_default_ipv4.address | ipaddr('10.0.0.0/8') %}
          , 10.0.0.0/8         # private-use (RFC 1918)
{% endif %}
          , 100.64.0.0/10      # shared address space (RFC 6598)
          , 127.0.0.0/8        # loopback (RFC 1122, sec. 3.2.1.3)
          , 169.254.0.0/16     # link local (RFC 3927)
{% if not ansible_default_ipv4.address | ipaddr('172.16.0.0/12') %}
          , 172.16.0.0/12      # private-use (RFC 1918)
{% endif %}
          , 192.0.0.0/24       # IETF protocol assignments (RFC 6890 sec. 2.1)
          , 192.0.2.0/24       # documentation (RFC 5737)
{% if not ansible_default_ipv4.address | ipaddr('192.168.0.0/16') %}
          , 192.168.0.0/16     # private-use (RFC 1918)
{% endif %}
          , 198.18.0.0/15      # benchmarking (RFC 2544)
          , 198.51.100.0/24    # documentation (RFC 5737)
          , 203.0.113.0/24     # documentation (RFC 5737)
          , 240.0.0.0/4        # reserved (RFC 1112, sec. 4)
          , 255.255.255.255/32 # limited broadcast (RFC 0919, section 7)
        }

        define invalid-ip6 = {
            ::1/128         # loopback address (RFC 4291)
          , ::/128          # unspecified (RFC 4291)
          , ::ffff:0:0/96   # IPv4-mapped address (RFC 4291)
          , 100::/64        # discard-only address block (RFC 6666)
          , 2001::/23       # IETF protocol assignments (RFC 2928)
          , 2001::/32       # TEREDO (RFC 4380)
          , 2001:2::/48     # benchmarking (RFC 5180)
          , 2001:db8::/32   # documentation (RFC 3849)
          , 2001:10::/28    # ORCHID (RFC 4843)
          , 2002::/16       # 6to4 (RFC 3056)
          , fc00::/7        # unique-local (RFC 4193)
          , fe80::/10       # linked-scoped unicast (RFC 4291)
        }

        ip saddr $invalid-ip counter drop
        ip daddr $invalid-ip counter drop

        ip6 saddr $invalid-ip6 counter drop
        ip6 daddr $invalid-ip6 counter drop
    }

    chain invalid {
        ct state invalid counter reject

        # drop bogus TCP packets
        tcp flags & (fin|syn|rst|psh|ack|urg) == 0x0         counter drop # null packets
        tcp flags != syn ct state new                        counter drop # SYN-flood attacks
        tcp flags & (fin|syn|rst|psh|ack|urg) == fin|psh|urg counter drop # XMAS packets
        tcp flags & (fin|syn) == fin|syn                     counter drop # bogus
        tcp flags & (syn|rst) == syn|rst                     counter drop # bogus
    }
}