#
# /etc/pf.conf
# ------------
# PF rules for DragonFly BSD
#
#
# Introduction
# ------------
# PF selectively passes or blocks data packets on a network interface
# based on the Layer 3 (IPv4 and IPv6) and Layer 4 (TCP, UDP, ICMP, and
# ICMPv6) headers.  The most often used criteria are source and
# destination address, source and destination port, and protocol.
# A series of rules specify matching criteria and the action block or
# pass.  PF is a *last-matching-rule-wins* firewall.
# An implicit `pass all` at the beginning of the ruleset means that if a
# packet does not match any filter rule the packet passes.  A best practice
# is to add an explicit `block all` as the first rule of a ruleset.
#
#
# References
# ----------
# [1] OpenBSD PF - User's Guide
#     https://www.openbsd.org/faq/pf/index.html
# [2] Firewalling with OpenBSD's PF packet filter
#     https://home.nuug.no/~peter/pf/en/index.html
# [3] The Book of PF (3rd Edition, 2015)
#     http://nostarch.com/pf3
# [4] PF Firewall Tutorial (FreeBSD and OpenBSD)
#     https://calomel.org/pf_config.html
# [5] OpenBSD PF (brief introduction)
#     https://paulgorman.org/technical/openbsd-pf.txt
# [6] FreeBSD Handbook - 29.3 PF
#     https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/firewalls-pf.html
# [7] PF - A baseline configuration for a web server with IPv6 and TLS/SSL
#     https://forums.freebsd.org/threads/56470/
# [8] How to secure FreeBSD with PF firewall
#     https://www.vultr.com/docs/how-to-secure-freebsd-with-pf-firewall
# [9] OpenBSD packet filter (PF): Real life example
#     http://daemon-notes.com/articles/network/pf
# [10] A simple VPN tunnel with FreeBSD
#      https://cyprio.net/wtf/2014-03-21-a-simple-vpn-tunnel-with-freebsd.html
# [11] A Barebones PF IPv6 Firewall Ruleset
#      https://content.pivotal.io/blog/a-barebones-pf-ipv6-firewall-ruleset
# [12] FreeBSD-PF: urpf-failed & IPv6
#      https://lists.freebsd.org/pipermail/freebsd-pf/2010-July/005724.html
# [13] DIY VPN with DragonFly, PF and OpenVPN
#      http://rampke.de/diyvpn/
# [14] OpenVPN with IPv6 and OpenBSD on a cheap VPS
#      http://rampke.de/ipv6-openvpn/
#
#
# Configurations
# --------------
# * Enable PF service, see pfctl(8) for additional options:
#       pf_enable="YES"
#       pf_flags=""    # additional flags for "pfctl" startup
# * Specify the ruleset configuration file for PF:
#       pf_rules="/etc/pf.conf"   # default
# * Enable logging support provided by pflog(4):
#       pflog_enable="YES"
# * Further configure the pflog:
#       pflog_flags=""   # additional flags for "pflogd" startup
#       pflog_logfile="/var/log/pflog"   # default
#
#
# Usage Examples
# --------------
# * pfctl -vnf /etc/pf.conf
#   Check "/etc/pf.conf" for errors, but do not load ruleset.
# * pfctl -F all -f /etc/pf.conf
#   Flush all NAT, filter, state, and table rules, and reload ruleset.
# * pfctl -e
#   Enable PF.
# * pfctl -d
#   Disable PF.
# * pfctl -s [ rules | nat | states ]
#   Report on the filter rules, NAT rules, or state table.
# * pfctl -k host
#   Kill all state entries originating from "host".
# * pfctl -s states -vv
#   Show state ID's, ages, and rule numbers.
# * pfctl -s rules -vv
#   Show rules with stats and rule numbers.
# * pfctl -s Tables
#   List tables.
# * pfctl -s info
#   Show filter stats and counters.
# * pfctl -s all
#   Show everything.
# * pfctl -t foo -T show
#   Show the contents of table "foo".
# * pfctl -t foo -T add xx.xx.xx.xx
#   Add address "xx.xx.xx.xx" to table "foo".
# * pfctl -t foo -T delete xx.xx.xx.xx
#   Delete address "xx.xx.xx.xx" from table "foo".
#
# * tcpdump -n -e -ttt -i pflog0
#   Get PF logging messages from the "pflog0" interface.
# * tcpdump -n -e -ttt -r /var/log/pflog
#   Read PF logging from the "pflog" file.
#
#
# Aaron LI
# 2017-05-08
#


##
## NOTE:
##
#
# * Avoid negated lists (e.g. "{ 10.0.0.0/8, !10.1.2.3 }"), because each
#   list item expands to add another rule, which causes undesirable results.
#
# * persist : (table)
#   Force the kernel to keep the table even when no rules refer to it.
#   If this flag is not set, the kernel will automatically remove the
#   table when the last rule referring to it is flushed.
# * quick : (rule)
#   If the rule is matched, no further rules will be evaluated!
# * self : (rule)
#   Expands to all addresses assigned to all interfaces.
#
# * egress : (interface group)
#   The kernel automatically creates an `egress` group for the interface(s)
#   that hold the default route(s).
# * Interface (group) names, and `self` can have *modifiers* appended:
#   + `:0` : Do not include interface aliases.
#   + `:broadcast` : Translates to the interface's broadcast address(es).
#   + `:network` : Translates to the network(s) attached to the interface.
#   + `:peer` : Translates to the point-to-point interface's peer address(es).
# * Host names may also have the `:0` modifier appended to restrict the
#   name resolution to the first of each v4 and v6 address found.
# * Host name resolution and interface to address translation are done at
#   ruleset *load-time*.  By surrounding the interface name (and optional
#   modifiers) in *parentheses* makes PF update the rules whenever the
#   interface changes its address, avoiding manual reloading, which is
#   especially useful with NAT. 
#
# * VPN (e.g., OpenVPN) requires a tunnel interface (e.g., tun0) on which
#   the NAT and corresponding filtering rules are needed; however, it is
#   required that the interface exists when loading the rules to make them
#   effective.  Therefore, a script to reload the PF rules after OpenVPN
#   startup is recommended (see, /usr/local/etc/openvpn/server-up.sh).
#


##
## Macros & Lists
##

# External interface
ext_if = "{{ network.interface }}"
# Tunnel interface used by VPN
vpn_if = "{{ vpn.interface }}"
# Network used by VPN on $vpn_if
vpn_net  = "{{ vpn.network4 }}/24"

# Allowed Services (incoming & outgoing)
#   * {{ ansible_ssh_port }}: SSH on custom port
#   * {{ ansible_ssh_port+1 }}: UDP port for Mosh connection
#   * domain: DNS resolution
#   * ntp: NTP daemon
#   * smtp: mail server (incoming & outgoing)
#   * submission: mail server (accept mail from MUA/user)
#   * imaps: IMAP server
#   * http & https: web service
#   * git: Git clone etc.
#   * {{ shadowsocks.port }}: ShadowSocks server
#   * {{ vpn.port }}: OpenVPN service (tcp & udp)
#
# For restrictive incoming rules
in_tcp_services_restricted = "{ {{ ansible_ssh_port }}, smtp, submission, imaps }"
# For non-restrictive incoming rules
in_tcp_services = "{ domain, http, https, {{ vpn.port }}, {{ shadowsocks.port }} }"
# For incoming UDP rules
in_udp_services = "{ domain, {{ vpn.port }}, {{ ansible_ssh_port+1 }} }"
# For outgoing rules
# NOTE: allow outgoing SMTP connections for remote mail delivery!
out_tcp_services = "{ domain, smtp, http, https, git, ssh }"
out_udp_services = "{ domain, ntp }"

# IPv4 ICMP:
#   * echoreq :
#     Echo request; used by "ping(8)" and "traceroute(8)"
#     NOTE: also open the UDP ports 33433-33626 for "traceroute(8)"
#   * unreach :
#     Destination unreachable; allow for path MTU discovery
# See also OpenBSD's icmp(4): https://man.openbsd.org/icmp
icmp_types = "{ echoreq, unreach }"

# IPv6 ICMP (i.e., icmp6)
#
# The updated "icmp6" protocol plays a more crucial role than ever in
# parameter passing and even host configuration, and its misconfiguration
# will cause significant problems for the IPv6 traffic.
#
# Generally, the ICMPv6 types "unreach", "toobig", "neighbradv", and
# "neighbrsol" should be allowed to make IPv6 work normally!
#
# NOTE:
# ICMPv6 Neighbor Solicitation (NS) sends packets to the local network
# segment multicast address.  If you don't accept those multicast
# packets, your neighbors (including your upstream router) won't be able
# to discover you, and your external interface's IPv6 address will be
# unreachable from other machines.
# Credit: https://content.pivotal.io/blog/a-barebones-pf-ipv6-firewall-ruleset
#
#   * toobig : Packet too big
#   * timex : Time exceeded
#   * paramprob : Invalid IPv6 header
#   * routeradv & routersol :
#     For getting address using IPv6 autoconfiguration from router.
#   * neighbradv & neighbrsol :
#     For getting neighbor addresses.
# See also OpenBSD's icmp6(4): https://man.openbsd.org/icmp6
icmp6_types = "{ echoreq, unreach, toobig, timex, paramprob, \
                 routeradv, routersol, neighbradv, neighbrsol }"


##
## Tables
##

# Bruteforce protection (e.g., SSH)
table <bruteforce> persist

# Martians: non-routables addresses as defined by stantards
# https://www.iana.org/assignments/iana-ipv4-special-registry/
# https://www.iana.org/assignments/iana-ipv6-special-registry/
# http://en.wikipedia.org/wiki/Reserved_IP_addresses
table <martians> const { \
      0.0.0.0/8, 10.0.0.0/8, 100.64.0.0/10, 127.0.0.0/8, \
      169.254.0.0/16, 172.16.0.0/12, 192.0.0.0/24, 192.0.2.0/24, \
      192.168.0.0/16, 198.18.0.0/15, 198.51.100.0/24, \
      203.0.113.0/24, 240.0.0.0/4, 255.255.255.255/32, \
      ::1/128, ::/128, ::/96, ::ffff:0:0/96, 100::/64, \
      2001::/32, 2001:2::/48, 2001:db8::/32, fc00::/7, fe80::/10 \
}


##
## Options
##

# Play nicely to return with status codes
set block-policy return

# Disable all filtering (with NAT & redirection) on loopback interface
set skip on lo0

# Enable collection of packet and byte count statistics for the external
# interface, which can be viewed using `pfctl -s info`.
set loginterface $ext_if


##
## Rules
##

# Network packet normalization
# Enabling scrub provides a measure of protection against certain kinds of
# attacks based on incorrect handling of packet fragments
scrub in all

# NAT for the VPN network
nat on $ext_if inet from $vpn_net to any -> ($ext_if:0)

# Block all incoming & outgoing traffics by default
# XXX: need to figure out how to allow all VPN outgoing traffic!
#block log all
#
# Block all incoming traffic while allow all outgoing traffic
block in log all
pass  out    all keep state

# Allow all VPN traffics
pass quick on $vpn_if

# The antispoof mechanism protects against activity from spoofed or
# forged IP addresses, mainly by blocking packets appearing on
# interfaces and in directions which are logically not possible.
# Use "antispoof" only on interfaces with an IP address.
#
antispoof log quick for $ext_if

# Mandatory rules for the link-local IPv6 traffics
#
# Credit:
# * https://lists.freebsd.org/pipermail/freebsd-pf/2010-July/005724.html
# * FreeBSD: /etc/rc.firewall
anchor "ipv6-link-local" quick inet6 {
    # Duplicate address detection (DAD)
    pass proto icmp6 from :: to ff02::/16
    # RS, RA, NS, NA, redirect ...
    pass proto icmp6 from fe80::/10 to { fe80::/10, ff02::/16 }
    # Link-local multicast traffic
    pass from { fe80::/10, (self:network) } to ff02::/16
    # DHCPv6
    pass proto udp from fe80::/10 to (self) port dhcpv6-client
}

# Block non-routables addresses.
#
# WARNING: Make sure the above IPv6 link-local traffic is allowed!
#
# NOTE: Using "return" action to prevent annoying timeouts for users.
block drop   in  quick on $ext_if from <martians> to any
block return out quick on $ext_if from any to <martians>

# Block packets whose ingress interface does not match the
# one the route back to their source address.
#
# WARNING:
# Without the above "ipv6-link-local" anchor ruleset, this rule will
# cause problems for the IPv6 traffic!  (see also the links above)
block in log quick from urpf-failed to any

# Block anything coming form source we have no back routes for.
block in log quick from no-route to any

# Block bruteforce on all connections (both in and out)
block log quick from <bruteforce>

# Get rid quick of Internet noises (e.g., broadcast, multicast):
block drop in quick on $ext_if proto { tcp, udp } from any to any \
      port { netbios-ns, netbios-dgm, netbios-ssn, microsoft-ds, nfsd }

# Use overload tables to protect restrictive services (e.g., SSH)
#
#   * max-src-conn :
#     number of simultaneous connections allowed from one host
#   * max-src-conn-rate :
#     rate of new connections allowed from any single host
#     per number of seconds (here: 4 connections every 30 seconds).
#   * overload <bruteforce> :
#     any host which exceeds these limits gets its address added to
#     the "bruteforce" table.
#   * flush global :
#     when a host reaches the limit, that all (global) of that host's
#     connections will be terminated (flush).
#
# NOTE:
# Over time, tables will be filled by overload rules and their size
# will grow incrementally, taking up more memory.  Sometimes an IP
# address that is blocked is a dynamically assigned one, which has
# since been assigned to a host who has a legitimate reason to communicate
# with hosts.  Therefore, the expired entries should get flushed,
# e.g., this command will remove "bruteforce" table entries which
# have not been referenced for 86400 seconds (i.e., 1 day):
#     pfctl -t bruteforce -T expire 86400
# It is convenient to add such clean command to root's cron table.
#
pass in on $ext_if proto tcp to ($ext_if) port $in_tcp_services_restricted \
     flags S/SA keep state \
     (max-src-conn 8, max-src-conn-rate 4/30, \
      overload <bruteforce> flush global)

# Pass traffic for allowed non-restricted services
pass in on $ext_if proto tcp to ($ext_if) port $in_tcp_services
pass in on $ext_if proto udp to ($ext_if) port $in_udp_services

# Allow outgoing connection while retaining state information on those
# connections.  This state information allows return traffic for those
# connections to pass back and should only be used on machines that can
# be trusted.
pass out on $ext_if proto tcp to any port $out_tcp_services keep state
pass out on $ext_if proto udp to any port $out_udp_services keep state

# ICMP: allow only specified ICMP types (in & out)
pass on $ext_if inet  proto icmp      all icmp-type  $icmp_types
pass on $ext_if inet6 proto ipv6-icmp all icmp6-type $icmp6_types

# Allow out the default port range for traceroute(8) & traceroute6(8):
# base (33434) => base+nhops*nqueries-1 (33434+64*3-1=33625)
pass out on $ext_if proto udp to port 33433 >< 33626 keep state

# vim: set ts=8 sw=4 tw=0 fenc=utf-8 ft=pf: #