nixos/firewall: Cleanup in case reload fails
This commit is contained in:
William A. Kennington III
parent
e0b6da1708
commit
ec9c4143a7
@ -37,6 +37,180 @@ let
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}
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'';
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writeShScript = name: text: let dir = pkgs.writeScriptBin name ''
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#! ${pkgs.stdenv.shell} -e
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${text}
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''; in "${dir}/bin/${name}";
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startScript = writeShScript "firewall-start" ''
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${helpers}
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# Flush the old firewall rules. !!! Ideally, updating the
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# firewall would be atomic. Apparently that's possible
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# with iptables-restore.
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ip46tables -D INPUT -j nixos-fw 2> /dev/null || true
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for chain in nixos-fw nixos-fw-accept nixos-fw-log-refuse nixos-fw-refuse FW_REFUSE; do
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ip46tables -F "$chain" 2> /dev/null || true
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ip46tables -X "$chain" 2> /dev/null || true
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done
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# The "nixos-fw-accept" chain just accepts packets.
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ip46tables -N nixos-fw-accept
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ip46tables -A nixos-fw-accept -j ACCEPT
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# The "nixos-fw-refuse" chain rejects or drops packets.
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ip46tables -N nixos-fw-refuse
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${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 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 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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${optionalString cfg.logRefusedPackets ''
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ip46tables -A nixos-fw-log-refuse \
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-j LOG --log-level info --log-prefix "rejected packet: "
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''}
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ip46tables -A nixos-fw-log-refuse -j nixos-fw-refuse
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# The "nixos-fw" chain does the actual work.
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ip46tables -N nixos-fw
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# Perform a reverse-path test to refuse spoofers
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# For now, we just drop, as the raw table doesn't have a log-refuse yet
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${optionalString (kernelHasRPFilter && cfg.checkReversePath) ''
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if ! ip46tables -A PREROUTING -t raw -m rpfilter --invert -j DROP; then
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echo "<2>failed to initialise rpfilter support" >&2
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fi
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''}
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# Accept all traffic on the trusted interfaces.
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${flip concatMapStrings cfg.trustedInterfaces (iface: ''
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ip46tables -A nixos-fw -i ${iface} -j nixos-fw-accept
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'')}
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# Accept packets from established or related connections.
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ip46tables -A nixos-fw -m conntrack --ctstate ESTABLISHED,RELATED -j nixos-fw-accept
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# Accept connections to the allowed TCP ports.
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${concatMapStrings (port:
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''
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ip46tables -A nixos-fw -p tcp --dport ${toString port} -j nixos-fw-accept
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''
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) cfg.allowedTCPPorts
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}
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# Accept connections to the allowed TCP port ranges.
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${concatMapStrings (rangeAttr:
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let range = toString rangeAttr.from + ":" + toString rangeAttr.to; in
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''
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ip46tables -A nixos-fw -p tcp --dport ${range} -j nixos-fw-accept
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''
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) cfg.allowedTCPPortRanges
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}
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# Accept packets on the allowed UDP ports.
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${concatMapStrings (port:
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''
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ip46tables -A nixos-fw -p udp --dport ${toString port} -j nixos-fw-accept
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''
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) cfg.allowedUDPPorts
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}
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# Accept packets on the allowed UDP port ranges.
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${concatMapStrings (rangeAttr:
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let range = toString rangeAttr.from + ":" + toString rangeAttr.to; in
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''
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ip46tables -A nixos-fw -p udp --dport ${range} -j nixos-fw-accept
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''
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) cfg.allowedUDPPortRanges
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}
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# Accept IPv4 multicast. Not a big security risk since
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# probably nobody is listening anyway.
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#iptables -A nixos-fw -d 224.0.0.0/4 -j nixos-fw-accept
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# Optionally respond to ICMPv4 pings.
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${optionalString cfg.allowPing ''
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iptables -w -A nixos-fw -p icmp --icmp-type echo-request ${optionalString (cfg.pingLimit != null)
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"-m limit ${cfg.pingLimit} "
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}-j nixos-fw-accept
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''}
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# Accept all ICMPv6 messages except redirects and node
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# information queries (type 139). See RFC 4890, section
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# 4.4.
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${optionalString config.networking.enableIPv6 ''
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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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''}
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${cfg.extraCommands}
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# Reject/drop everything else.
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ip46tables -A nixos-fw -j nixos-fw-log-refuse
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# Enable the firewall.
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ip46tables -A INPUT -j nixos-fw
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'';
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stopScript = writeShScript "firewall-stop" ''
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${helpers}
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# Clean up in case reload fails
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ip46tables -D INPUT -j nixos-drop 2>/dev/null || true
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# Clean up after added ruleset
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ip46tables -D INPUT -j nixos-fw 2>/dev/null || true
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${cfg.extraStopCommands}
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'';
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reloadScript = writeShScript "firewall-reload" ''
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${helpers}
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# Create a unique drop rule
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ip46tables -D INPUT -j nixos-drop 2>/dev/null || true
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ip46tables -F nixos-drop 2>/dev/null || true
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ip46tables -X nixos-drop 2>/dev/null || true
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ip46tables -N nixos-drop
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ip46tables -A nixos-drop -j DROP
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# Don't allow traffic to leak out until the script has completed
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ip46tables -A INPUT -j nixos-drop
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if ${startScript}; then
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ip46tables -D INPUT -j nixos-drop 2>/dev/null || true
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else
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echo "Failed to reload firewall... Stopping"
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${stopScript}
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exit 1
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fi
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'';
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kernelPackages = config.boot.kernelPackages;
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kernelHasRPFilter = kernelPackages.kernel.features.netfilterRPFilter or false;
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@ -248,7 +422,7 @@ in
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''
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Additional shell commands executed as part of the firewall
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shutdown script. These are executed just after the removal
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of the nixos input rule.
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of the nixos input rule, or if the service enters a failed state.
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'';
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};
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@ -276,177 +450,28 @@ in
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message = "This kernel does not support disabling conntrack helpers"; }
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];
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systemd.services.firewall = rec
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{ description = "Firewall";
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systemd.services.firewall = {
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description = "Firewall";
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wantedBy = [ "network.target" ];
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after = [ "network-interfaces.target" "systemd-modules-load.service" ];
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wantedBy = [ "network.target" ];
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after = [ "network-interfaces.target" "systemd-modules-load.service" ];
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path = [ pkgs.iptables ];
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path = [ pkgs.iptables ];
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# FIXME: this module may also try to load kernel modules, but
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# containers don't have CAP_SYS_MODULE. So the host system had
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# better have all necessary modules already loaded.
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unitConfig.ConditionCapability = "CAP_NET_ADMIN";
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# FIXME: this module may also try to load kernel modules, but
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# containers don't have CAP_SYS_MODULE. So the host system had
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# better have all necessary modules already loaded.
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unitConfig.ConditionCapability = "CAP_NET_ADMIN";
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reloadIfChanged = true;
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reloadIfChanged = true;
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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};
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script =
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''
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${helpers}
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# Flush the old firewall rules. !!! Ideally, updating the
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# firewall would be atomic. Apparently that's possible
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# with iptables-restore.
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ip46tables -D INPUT -j nixos-fw 2> /dev/null || true
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for chain in nixos-fw nixos-fw-accept nixos-fw-log-refuse nixos-fw-refuse FW_REFUSE; do
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ip46tables -F "$chain" 2> /dev/null || true
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ip46tables -X "$chain" 2> /dev/null || true
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done
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# The "nixos-fw-accept" chain just accepts packets.
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ip46tables -N nixos-fw-accept
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ip46tables -A nixos-fw-accept -j ACCEPT
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# The "nixos-fw-refuse" chain rejects or drops packets.
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ip46tables -N nixos-fw-refuse
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${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 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 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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${optionalString cfg.logRefusedPackets ''
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ip46tables -A nixos-fw-log-refuse \
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-j LOG --log-level info --log-prefix "rejected packet: "
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''}
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ip46tables -A nixos-fw-log-refuse -j nixos-fw-refuse
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# The "nixos-fw" chain does the actual work.
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ip46tables -N nixos-fw
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# Perform a reverse-path test to refuse spoofers
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# For now, we just drop, as the raw table doesn't have a log-refuse yet
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${optionalString (kernelHasRPFilter && cfg.checkReversePath) ''
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if ! ip46tables -A PREROUTING -t raw -m rpfilter --invert -j DROP; then
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echo "<2>failed to initialise rpfilter support" >&2
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fi
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''}
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# Accept all traffic on the trusted interfaces.
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${flip concatMapStrings cfg.trustedInterfaces (iface: ''
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ip46tables -A nixos-fw -i ${iface} -j nixos-fw-accept
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'')}
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# Accept packets from established or related connections.
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ip46tables -A nixos-fw -m conntrack --ctstate ESTABLISHED,RELATED -j nixos-fw-accept
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# Accept connections to the allowed TCP ports.
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${concatMapStrings (port:
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''
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ip46tables -A nixos-fw -p tcp --dport ${toString port} -j nixos-fw-accept
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''
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) cfg.allowedTCPPorts
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}
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# Accept connections to the allowed TCP port ranges.
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${concatMapStrings (rangeAttr:
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let range = toString rangeAttr.from + ":" + toString rangeAttr.to; in
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''
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ip46tables -A nixos-fw -p tcp --dport ${range} -j nixos-fw-accept
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''
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) cfg.allowedTCPPortRanges
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}
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# Accept packets on the allowed UDP ports.
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${concatMapStrings (port:
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''
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ip46tables -A nixos-fw -p udp --dport ${toString port} -j nixos-fw-accept
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''
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) cfg.allowedUDPPorts
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}
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# Accept packets on the allowed UDP port ranges.
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${concatMapStrings (rangeAttr:
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let range = toString rangeAttr.from + ":" + toString rangeAttr.to; in
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''
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ip46tables -A nixos-fw -p udp --dport ${range} -j nixos-fw-accept
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''
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) cfg.allowedUDPPortRanges
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}
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# Accept IPv4 multicast. Not a big security risk since
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# probably nobody is listening anyway.
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#iptables -A nixos-fw -d 224.0.0.0/4 -j nixos-fw-accept
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# Optionally respond to ICMPv4 pings.
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${optionalString cfg.allowPing ''
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iptables -w -A nixos-fw -p icmp --icmp-type echo-request ${optionalString (cfg.pingLimit != null)
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"-m limit ${cfg.pingLimit} "
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}-j nixos-fw-accept
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''}
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# Accept all ICMPv6 messages except redirects and node
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# information queries (type 139). See RFC 4890, section
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# 4.4.
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${optionalString config.networking.enableIPv6 ''
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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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''}
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${cfg.extraCommands}
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# Reject/drop everything else.
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ip46tables -A nixos-fw -j nixos-fw-log-refuse
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# Enable the firewall.
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ip46tables -A INPUT -j nixos-fw
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'';
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reload = ''
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${helpers}
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ip46tables -A INPUT -j DROP
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${script}
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ip46tables -D INPUT -j DROP || true # extraCommands might delete the above rule and cause this to fail
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'';
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postStop =
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''
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${helpers}
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ip46tables -D INPUT -j nixos-fw || true
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${cfg.extraStopCommands}
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'';
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serviceConfig = {
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Type = "oneshot";
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RemainAfterExit = true;
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ExecStart = "@${startScript} firewall-start";
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ExecReload = "@${reloadScript} firewall-reload";
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ExecStop = "@${stopScript} firewall-stop";
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};
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};
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};
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Loading…
Reference in New Issue
Block a user