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* Put the NixOS firewall ruleset in its own chain (‘nixos-fw’). This
should make it easier to compose with packages that set their own firewall rules, such as Nova or Libvirt. * Provide a chain for accepted packets (‘nixos-fw-accept’), requested by Nicolas Pierron. svn path=/nixos/trunk/; revision=27607
This commit is contained in:
Eelco Dolstra
parent
1d09ad240a
commit
3bc3dc3940
@ -1,4 +1,24 @@
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# This module enables a simple firewall.
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/* This module enables a simple firewall.
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The firewall can be customised in arbitrary ways by setting
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‘networking.firewall.extraCommands’. For modularity, the firewall
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uses several chains:
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- ‘nixos-fw-input’ is the main chain for input packet processing.
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- ‘nixos-fw-log-refuse’ and ‘nixos-fw-refuse’ are called for
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refused packets. (The former jumps to the latter after logging
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the packet.) If you want additional logging, or want to accept
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certain packets anyway, you can insert rules at the start of
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these chain.
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- ‘nixos-fw-accept’ is called for accepted packets. If you want
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additional logging, or want to reject certain packets anyway, you
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can insert rules at the start of this chain.
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*/
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{ config, pkgs, ... }:
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@ -8,6 +28,15 @@ let
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cfg = config.networking.firewall;
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helpers =
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''
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# Helper command to manipulate both the IPv4 and IPv6 tables.
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ip46tables() {
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iptables "$@"
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ip6tables "$@"
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}
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'';
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in
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{
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@ -36,7 +65,7 @@ in
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};
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networking.firewall.logRefusedPackets = mkOption {
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default = false;
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default = true;
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description =
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''
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Whether to log all rejected or dropped incoming packets.
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@ -45,6 +74,17 @@ in
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'';
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};
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networking.firewall.logRefusedUnicastsOnly = mkOption {
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default = true;
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description =
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''
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If <option>networking.firewall.logRefusedPackets</option>
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and this option are enabled, then only log packets
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specifically directed at this machine, i.e., not broadcasts
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or multicasts.
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'';
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};
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networking.firewall.rejectPackets = mkOption {
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default = false;
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description =
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@ -124,50 +164,72 @@ in
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preStart =
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''
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# Helper command to manipulate both the IPv4 and IPv6 tables.
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ip46tables() {
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iptables "$@"
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ip6tables "$@"
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}
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${helpers}
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set -x
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ip46tables -F INPUT
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ip46tables -F FW_REFUSE || true
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ip46tables -X # flush unused chains
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ip46tables -P INPUT ACCEPT
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# Flush the old firewall rules. !!! Ideally, updating the
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# firewall would be atomic. Apparently that's possible
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# with iptables-restore.
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ip46tables -D INPUT -j nixos-fw || true
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for chain in nixos-fw nixos-fw-accept nixos-fw-log-refuse nixos-fw-refuse FW_REFUSE; do
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ip46tables -F "$chain" || true
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ip46tables -X "$chain" || true
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done
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# The "FW_REFUSE" chain performs logging and
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# rejecting/dropping of packets.
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ip46tables -N FW_REFUSE
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# The "nixos-fw-accept" chain just accepts packets.
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ip46tables -N nixos-fw-accept
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ip46tables -A nixos-fw-accept -j ACCEPT
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${optionalString cfg.logRefusedConnections ''
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ip46tables -A FW_REFUSE -p tcp --syn -j LOG --log-level info --log-prefix "rejected connection: "
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''}
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${optionalString cfg.logRefusedPackets ''
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ip46tables -A FW_REFUSE -j LOG --log-level info --log-prefix "rejected packet: "
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''}
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# The "nixos-fw-refuse" chain rejects or drops packets.
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ip46tables -N nixos-fw-refuse
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${if cfg.rejectPackets then ''
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# Send a reset for existing TCP connections that we've
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# somehow forgotten about. Send ICMP "port unreachable"
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# for everything else.
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ip46tables -A FW_REFUSE -p tcp ! --syn -j REJECT --reject-with tcp-reset
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ip46tables -A FW_REFUSE -j REJECT
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ip46tables -A nixos-fw-refuse -p tcp ! --syn -j REJECT --reject-with tcp-reset
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ip46tables -A nixos-fw-refuse -j REJECT
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'' else ''
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ip46tables -A FW_REFUSE -j DROP
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ip46tables -A nixos-fw-refuse -j DROP
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''}
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# The "nixos-fw-log-refuse" chain performs logging, then
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# jumps to the "nixos-fw-refuse" chain.
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ip46tables -N nixos-fw-log-refuse
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${optionalString cfg.logRefusedConnections ''
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ip46tables -A nixos-fw-log-refuse -p tcp --syn -j LOG --log-level info --log-prefix "rejected connection: "
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''}
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${optionalString (cfg.logRefusedPackets && !cfg.logRefusedUnicastsOnly) ''
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ip46tables -A nixos-fw-log-refuse -m pkttype --pkt-type broadcast \
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-j LOG --log-level info --log-prefix "rejected broadcast: "
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ip46tables -A nixos-fw-log-refuse -m pkttype --pkt-type multicast \
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-j LOG --log-level info --log-prefix "rejected multicast: "
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''}
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ip46tables -A nixos-fw-log-refuse -m pkttype ! --pkt-type unicast -j nixos-fw-refuse
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${optionalString cfg.logRefusedPackets ''
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ip46tables -A nixos-fw-log-refuse \
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-j LOG --log-level info --log-prefix "rejected packet: "
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''}
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ip46tables -A nixos-fw-log-refuse -j nixos-fw-refuse
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# The "nixos-fw" chain does the actual work.
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ip46tables -N nixos-fw
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# Accept all traffic on the loopback interface.
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ip46tables -A INPUT -i lo -j ACCEPT
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ip46tables -A nixos-fw -i lo -j nixos-fw-accept
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# Accept packets from established or related connections.
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ip46tables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
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ip46tables -A nixos-fw -m conntrack --ctstate ESTABLISHED,RELATED -j nixos-fw-accept
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# Accept connections to the allowed TCP ports.
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${concatMapStrings (port:
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''
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ip46tables -A INPUT -p tcp --dport ${toString port} -j ACCEPT
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ip46tables -A nixos-fw -p tcp --dport ${toString port} -j nixos-fw-accept
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''
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) cfg.allowedTCPPorts
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}
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@ -175,39 +237,42 @@ in
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# Accept packets on the allowed UDP ports.
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${concatMapStrings (port:
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''
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ip46tables -A INPUT -p udp --dport ${toString port} -j ACCEPT
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ip46tables -A nixos-fw -p udp --dport ${toString port} -j nixos-fw-accept
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''
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) cfg.allowedUDPPorts
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}
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# Accept IPv4 multicast. Not a big security risk since
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# probably nobody is listening anyway.
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iptables -A INPUT -d 224.0.0.0/4 -j ACCEPT
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#iptables -A nixos-fw -d 224.0.0.0/4 -j nixos-fw-accept
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# Optionally respond to ICMPv4 pings.
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${optionalString cfg.allowPing ''
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iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
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iptables -A nixos-fw -p icmp --icmp-type echo-request -j nixos-fw-accept
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''}
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# Accept all ICMPv6 messages except redirects and node
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# information queries (type 139). See RFC 4890, section
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# 4.4.
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ip6tables -A INPUT -p icmpv6 --icmpv6-type redirect -j DROP
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ip6tables -A INPUT -p icmpv6 --icmpv6-type 139 -j DROP
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ip6tables -A INPUT -p icmpv6 -j ACCEPT
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ip6tables -A nixos-fw -p icmpv6 --icmpv6-type redirect -j DROP
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ip6tables -A nixos-fw -p icmpv6 --icmpv6-type 139 -j DROP
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ip6tables -A nixos-fw -p icmpv6 -j nixos-fw-accept
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${cfg.extraCommands}
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# Reject/drop everything else.
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ip46tables -A INPUT -j FW_REFUSE
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ip46tables -A nixos-fw -j nixos-fw-log-refuse
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# Enable the firewall.
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ip46tables -A INPUT -j nixos-fw
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'';
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postStop =
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''
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iptables -F INPUT
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iptables -P INPUT ACCEPT
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ip6tables -F INPUT
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ip6tables -P INPUT ACCEPT
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${helpers}
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ip46tables -D INPUT -j nixos-fw || true
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#ip46tables -P INPUT ACCEPT
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'';
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};
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