148 lines
4 KiB
Nix
148 lines
4 KiB
Nix
{ config, pkgs, ... }:
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with pkgs.lib;
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let
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cfg = config.networking.firewall;
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in
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{
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###### interface
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options = {
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networking.firewall.enable = mkOption {
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default = false;
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description =
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''
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Whether to enable the firewall.
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'';
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};
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networking.firewall.logRefusedConnections = mkOption {
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default = true;
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description =
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''
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Whether to log rejected or dropped incoming connections.
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'';
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};
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networking.firewall.logRefusedPackets = mkOption {
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default = false;
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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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This tends to give a lot of log messages, so it's mostly
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useful for debugging.
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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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''
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If set, forbidden packets are rejected rather than dropped
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(ignored). This means that a ICMP "port unreachable" error
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message is sent back to the client. Rejecting packets makes
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port scanning somewhat easier.
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'';
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};
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networking.firewall.allowedTCPPorts = mkOption {
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default = [];
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example = [22 80];
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type = types.list types.int;
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description =
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''
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List of TCP ports on which incoming connections are
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accepted.
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'';
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};
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};
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###### implementation
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# !!! Maybe if `enable' is false, the firewall should still be built
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# but not started by default. However, currently nixos-rebuild
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# doesn't deal with such Upstart jobs properly (it starts them if
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# they are changed, regardless of whether the start condition
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# holds).
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config = mkIf config.networking.firewall.enable {
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environment.systemPackages = [ pkgs.iptables ];
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jobs.firewall =
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{ startOn = "started network-interfaces";
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path = [ pkgs.iptables ];
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preStart =
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''
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# Helper command to manipulate both the IPv4 and IPv6 filters.
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ip46tables() {
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iptables "$@"
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ip6tables "$@"
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}
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ip46tables -F
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ip46tables -X # flush unused chains
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ip46tables -P INPUT DROP
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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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${optionalString cfg.logRefusedConnections ''
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ip46tables -A FW_REFUSE -p tcp --syn -j LOG --log-level info --log-prefix "rejected connection: "
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''}
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${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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ip46tables -A FW_REFUSE -j ${if cfg.rejectPackets then "REJECT" else "DROP"}
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# Accept all traffic on the loopback interface.
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ip46tables -A INPUT -i lo -j ACCEPT
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# Accept packets from established or related connections.
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ip46tables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
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# Accept connections to the allowed TCP ports.
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${concatMapStrings (port:
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''
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ip46tables -A INPUT -p tcp --dport ${toString port} -j ACCEPT
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''
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) config.networking.firewall.allowedTCPPorts
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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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# Accept IPv6 ICMP packets on the local link. Otherwise
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# stuff like neighbor/router solicitation won't work.
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ip6tables -A INPUT -s fe80::/10 -p icmpv6 -j ACCEPT
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# Reject/drop everything else.
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ip46tables -A INPUT -j FW_REFUSE
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'';
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postStop =
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''
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iptables -F
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iptables -P INPUT ACCEPT
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ip6tables -F
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ip6tables -P INPUT ACCEPT
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'';
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};
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};
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}
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