diff options
Diffstat (limited to 'nixos/modules/services/networking/firewall.nix')
| -rw-r--r-- | nixos/modules/services/networking/firewall.nix | 588 |
1 files changed, 0 insertions, 588 deletions
diff --git a/nixos/modules/services/networking/firewall.nix b/nixos/modules/services/networking/firewall.nix deleted file mode 100644 index 4c3052e9e53..00000000000 --- a/nixos/modules/services/networking/firewall.nix +++ /dev/null @@ -1,588 +0,0 @@ -/* This module enables a simple firewall. - - The firewall can be customised in arbitrary ways by setting - ‘networking.firewall.extraCommands’. For modularity, the firewall - uses several chains: - - - ‘nixos-fw’ is the main chain for input packet processing. - - - ‘nixos-fw-accept’ is called for accepted packets. If you want - additional logging, or want to reject certain packets anyway, you - can insert rules at the start of this chain. - - - ‘nixos-fw-log-refuse’ and ‘nixos-fw-refuse’ are called for - refused packets. (The former jumps to the latter after logging - the packet.) If you want additional logging, or want to accept - certain packets anyway, you can insert rules at the start of - this chain. - - - ‘nixos-fw-rpfilter’ is used as the main chain in the raw table, - called from the built-in ‘PREROUTING’ chain. If the kernel - supports it and `cfg.checkReversePath` is set this chain will - perform a reverse path filter test. - - - ‘nixos-drop’ is used while reloading the firewall in order to drop - all traffic. Since reloading isn't implemented in an atomic way - this'll prevent any traffic from leaking through while reloading - the firewall. However, if the reloading fails, the ‘firewall-stop’ - script will be called which in return will effectively disable the - complete firewall (in the default configuration). - -*/ - -{ config, lib, pkgs, ... }: - -with lib; - -let - - cfg = config.networking.firewall; - - inherit (config.boot.kernelPackages) kernel; - - kernelHasRPFilter = ((kernel.config.isEnabled or (x: false)) "IP_NF_MATCH_RPFILTER") || (kernel.features.netfilterRPFilter or false); - - helpers = import ./helpers.nix { inherit config lib; }; - - writeShScript = name: text: let dir = pkgs.writeScriptBin name '' - #! ${pkgs.runtimeShell} -e - ${text} - ''; in "${dir}/bin/${name}"; - - defaultInterface = { default = mapAttrs (name: value: cfg.${name}) commonOptions; }; - allInterfaces = defaultInterface // cfg.interfaces; - - startScript = writeShScript "firewall-start" '' - ${helpers} - - # Flush the old firewall rules. !!! Ideally, updating the - # firewall would be atomic. Apparently that's possible - # with iptables-restore. - ip46tables -D INPUT -j nixos-fw 2> /dev/null || true - for chain in nixos-fw nixos-fw-accept nixos-fw-log-refuse nixos-fw-refuse; do - ip46tables -F "$chain" 2> /dev/null || true - ip46tables -X "$chain" 2> /dev/null || true - done - - - # The "nixos-fw-accept" chain just accepts packets. - ip46tables -N nixos-fw-accept - ip46tables -A nixos-fw-accept -j ACCEPT - - - # The "nixos-fw-refuse" chain rejects or drops packets. - ip46tables -N nixos-fw-refuse - - ${if cfg.rejectPackets then '' - # Send a reset for existing TCP connections that we've - # somehow forgotten about. Send ICMP "port unreachable" - # for everything else. - ip46tables -A nixos-fw-refuse -p tcp ! --syn -j REJECT --reject-with tcp-reset - ip46tables -A nixos-fw-refuse -j REJECT - '' else '' - ip46tables -A nixos-fw-refuse -j DROP - ''} - - - # The "nixos-fw-log-refuse" chain performs logging, then - # jumps to the "nixos-fw-refuse" chain. - ip46tables -N nixos-fw-log-refuse - - ${optionalString cfg.logRefusedConnections '' - ip46tables -A nixos-fw-log-refuse -p tcp --syn -j LOG --log-level info --log-prefix "refused connection: " - ''} - ${optionalString (cfg.logRefusedPackets && !cfg.logRefusedUnicastsOnly) '' - ip46tables -A nixos-fw-log-refuse -m pkttype --pkt-type broadcast \ - -j LOG --log-level info --log-prefix "refused broadcast: " - ip46tables -A nixos-fw-log-refuse -m pkttype --pkt-type multicast \ - -j LOG --log-level info --log-prefix "refused multicast: " - ''} - ip46tables -A nixos-fw-log-refuse -m pkttype ! --pkt-type unicast -j nixos-fw-refuse - ${optionalString cfg.logRefusedPackets '' - ip46tables -A nixos-fw-log-refuse \ - -j LOG --log-level info --log-prefix "refused packet: " - ''} - ip46tables -A nixos-fw-log-refuse -j nixos-fw-refuse - - - # The "nixos-fw" chain does the actual work. - ip46tables -N nixos-fw - - # Clean up rpfilter rules - ip46tables -t raw -D PREROUTING -j nixos-fw-rpfilter 2> /dev/null || true - ip46tables -t raw -F nixos-fw-rpfilter 2> /dev/null || true - ip46tables -t raw -X nixos-fw-rpfilter 2> /dev/null || true - - ${optionalString (kernelHasRPFilter && (cfg.checkReversePath != false)) '' - # Perform a reverse-path test to refuse spoofers - # For now, we just drop, as the raw table doesn't have a log-refuse yet - ip46tables -t raw -N nixos-fw-rpfilter 2> /dev/null || true - ip46tables -t raw -A nixos-fw-rpfilter -m rpfilter --validmark ${optionalString (cfg.checkReversePath == "loose") "--loose"} -j RETURN - - # Allows this host to act as a DHCP4 client without first having to use APIPA - iptables -t raw -A nixos-fw-rpfilter -p udp --sport 67 --dport 68 -j RETURN - - # Allows this host to act as a DHCPv4 server - iptables -t raw -A nixos-fw-rpfilter -s 0.0.0.0 -d 255.255.255.255 -p udp --sport 68 --dport 67 -j RETURN - - ${optionalString cfg.logReversePathDrops '' - ip46tables -t raw -A nixos-fw-rpfilter -j LOG --log-level info --log-prefix "rpfilter drop: " - ''} - ip46tables -t raw -A nixos-fw-rpfilter -j DROP - - ip46tables -t raw -A PREROUTING -j nixos-fw-rpfilter - ''} - - # Accept all traffic on the trusted interfaces. - ${flip concatMapStrings cfg.trustedInterfaces (iface: '' - ip46tables -A nixos-fw -i ${iface} -j nixos-fw-accept - '')} - - # Accept packets from established or related connections. - ip46tables -A nixos-fw -m conntrack --ctstate ESTABLISHED,RELATED -j nixos-fw-accept - - # Accept connections to the allowed TCP ports. - ${concatStrings (mapAttrsToList (iface: cfg: - concatMapStrings (port: - '' - ip46tables -A nixos-fw -p tcp --dport ${toString port} -j nixos-fw-accept ${optionalString (iface != "default") "-i ${iface}"} - '' - ) cfg.allowedTCPPorts - ) allInterfaces)} - - # Accept connections to the allowed TCP port ranges. - ${concatStrings (mapAttrsToList (iface: cfg: - concatMapStrings (rangeAttr: - let range = toString rangeAttr.from + ":" + toString rangeAttr.to; in - '' - ip46tables -A nixos-fw -p tcp --dport ${range} -j nixos-fw-accept ${optionalString (iface != "default") "-i ${iface}"} - '' - ) cfg.allowedTCPPortRanges - ) allInterfaces)} - - # Accept packets on the allowed UDP ports. - ${concatStrings (mapAttrsToList (iface: cfg: - concatMapStrings (port: - '' - ip46tables -A nixos-fw -p udp --dport ${toString port} -j nixos-fw-accept ${optionalString (iface != "default") "-i ${iface}"} - '' - ) cfg.allowedUDPPorts - ) allInterfaces)} - - # Accept packets on the allowed UDP port ranges. - ${concatStrings (mapAttrsToList (iface: cfg: - concatMapStrings (rangeAttr: - let range = toString rangeAttr.from + ":" + toString rangeAttr.to; in - '' - ip46tables -A nixos-fw -p udp --dport ${range} -j nixos-fw-accept ${optionalString (iface != "default") "-i ${iface}"} - '' - ) cfg.allowedUDPPortRanges - ) allInterfaces)} - - # Accept IPv4 multicast. Not a big security risk since - # probably nobody is listening anyway. - #iptables -A nixos-fw -d 224.0.0.0/4 -j nixos-fw-accept - - # Optionally respond to ICMPv4 pings. - ${optionalString cfg.allowPing '' - iptables -w -A nixos-fw -p icmp --icmp-type echo-request ${optionalString (cfg.pingLimit != null) - "-m limit ${cfg.pingLimit} " - }-j nixos-fw-accept - ''} - - ${optionalString config.networking.enableIPv6 '' - # Accept all ICMPv6 messages except redirects and node - # information queries (type 139). See RFC 4890, section - # 4.4. - ip6tables -A nixos-fw -p icmpv6 --icmpv6-type redirect -j DROP - ip6tables -A nixos-fw -p icmpv6 --icmpv6-type 139 -j DROP - ip6tables -A nixos-fw -p icmpv6 -j nixos-fw-accept - - # Allow this host to act as a DHCPv6 client - ip6tables -A nixos-fw -d fe80::/64 -p udp --dport 546 -j nixos-fw-accept - ''} - - ${cfg.extraCommands} - - # Reject/drop everything else. - ip46tables -A nixos-fw -j nixos-fw-log-refuse - - - # Enable the firewall. - ip46tables -A INPUT -j nixos-fw - ''; - - stopScript = writeShScript "firewall-stop" '' - ${helpers} - - # Clean up in case reload fails - ip46tables -D INPUT -j nixos-drop 2>/dev/null || true - - # Clean up after added ruleset - ip46tables -D INPUT -j nixos-fw 2>/dev/null || true - - ${optionalString (kernelHasRPFilter && (cfg.checkReversePath != false)) '' - ip46tables -t raw -D PREROUTING -j nixos-fw-rpfilter 2>/dev/null || true - ''} - - ${cfg.extraStopCommands} - ''; - - reloadScript = writeShScript "firewall-reload" '' - ${helpers} - - # Create a unique drop rule - ip46tables -D INPUT -j nixos-drop 2>/dev/null || true - ip46tables -F nixos-drop 2>/dev/null || true - ip46tables -X nixos-drop 2>/dev/null || true - ip46tables -N nixos-drop - ip46tables -A nixos-drop -j DROP - - # Don't allow traffic to leak out until the script has completed - ip46tables -A INPUT -j nixos-drop - - ${cfg.extraStopCommands} - - if ${startScript}; then - ip46tables -D INPUT -j nixos-drop 2>/dev/null || true - else - echo "Failed to reload firewall... Stopping" - ${stopScript} - exit 1 - fi - ''; - - canonicalizePortList = - ports: lib.unique (builtins.sort builtins.lessThan ports); - - commonOptions = { - allowedTCPPorts = mkOption { - type = types.listOf types.port; - default = [ ]; - apply = canonicalizePortList; - example = [ 22 80 ]; - description = - '' - List of TCP ports on which incoming connections are - accepted. - ''; - }; - - allowedTCPPortRanges = mkOption { - type = types.listOf (types.attrsOf types.port); - default = [ ]; - example = [ { from = 8999; to = 9003; } ]; - description = - '' - A range of TCP ports on which incoming connections are - accepted. - ''; - }; - - allowedUDPPorts = mkOption { - type = types.listOf types.port; - default = [ ]; - apply = canonicalizePortList; - example = [ 53 ]; - description = - '' - List of open UDP ports. - ''; - }; - - allowedUDPPortRanges = mkOption { - type = types.listOf (types.attrsOf types.port); - default = [ ]; - example = [ { from = 60000; to = 61000; } ]; - description = - '' - Range of open UDP ports. - ''; - }; - }; - -in - -{ - - ###### interface - - options = { - - networking.firewall = { - enable = mkOption { - type = types.bool; - default = true; - description = - '' - Whether to enable the firewall. This is a simple stateful - firewall that blocks connection attempts to unauthorised TCP - or UDP ports on this machine. It does not affect packet - forwarding. - ''; - }; - - package = mkOption { - type = types.package; - default = pkgs.iptables; - defaultText = literalExpression "pkgs.iptables"; - example = literalExpression "pkgs.iptables-legacy"; - description = - '' - The iptables package to use for running the firewall service." - ''; - }; - - logRefusedConnections = mkOption { - type = types.bool; - default = true; - description = - '' - Whether to log rejected or dropped incoming connections. - Note: The logs are found in the kernel logs, i.e. dmesg - or journalctl -k. - ''; - }; - - logRefusedPackets = mkOption { - type = types.bool; - default = false; - description = - '' - Whether to log all rejected or dropped incoming packets. - This tends to give a lot of log messages, so it's mostly - useful for debugging. - Note: The logs are found in the kernel logs, i.e. dmesg - or journalctl -k. - ''; - }; - - logRefusedUnicastsOnly = mkOption { - type = types.bool; - default = true; - description = - '' - If <option>networking.firewall.logRefusedPackets</option> - and this option are enabled, then only log packets - specifically directed at this machine, i.e., not broadcasts - or multicasts. - ''; - }; - - rejectPackets = mkOption { - type = types.bool; - default = false; - description = - '' - If set, refused packets are rejected rather than dropped - (ignored). This means that an ICMP "port unreachable" error - message is sent back to the client (or a TCP RST packet in - case of an existing connection). Rejecting packets makes - port scanning somewhat easier. - ''; - }; - - trustedInterfaces = mkOption { - type = types.listOf types.str; - default = [ ]; - example = [ "enp0s2" ]; - description = - '' - Traffic coming in from these interfaces will be accepted - unconditionally. Traffic from the loopback (lo) interface - will always be accepted. - ''; - }; - - allowPing = mkOption { - type = types.bool; - default = true; - description = - '' - Whether to respond to incoming ICMPv4 echo requests - ("pings"). ICMPv6 pings are always allowed because the - larger address space of IPv6 makes network scanning much - less effective. - ''; - }; - - pingLimit = mkOption { - type = types.nullOr (types.separatedString " "); - default = null; - example = "--limit 1/minute --limit-burst 5"; - description = - '' - If pings are allowed, this allows setting rate limits - on them. If non-null, this option should be in the form of - flags like "--limit 1/minute --limit-burst 5" - ''; - }; - - checkReversePath = mkOption { - type = types.either types.bool (types.enum ["strict" "loose"]); - default = kernelHasRPFilter; - defaultText = literalDocBook "<literal>true</literal> if supported by the chosen kernel"; - example = "loose"; - description = - '' - Performs a reverse path filter test on a packet. If a reply - to the packet would not be sent via the same interface that - the packet arrived on, it is refused. - - If using asymmetric routing or other complicated routing, set - this option to loose mode or disable it and setup your own - counter-measures. - - This option can be either true (or "strict"), "loose" (only - drop the packet if the source address is not reachable via any - interface) or false. Defaults to the value of - kernelHasRPFilter. - ''; - }; - - logReversePathDrops = mkOption { - type = types.bool; - default = false; - description = - '' - Logs dropped packets failing the reverse path filter test if - the option networking.firewall.checkReversePath is enabled. - ''; - }; - - connectionTrackingModules = mkOption { - type = types.listOf types.str; - default = [ ]; - example = [ "ftp" "irc" "sane" "sip" "tftp" "amanda" "h323" "netbios_sn" "pptp" "snmp" ]; - description = - '' - List of connection-tracking helpers that are auto-loaded. - The complete list of possible values is given in the example. - - As helpers can pose as a security risk, it is advised to - set this to an empty list and disable the setting - networking.firewall.autoLoadConntrackHelpers unless you - know what you are doing. Connection tracking is disabled - by default. - - Loading of helpers is recommended to be done through the - CT target. More info: - https://home.regit.org/netfilter-en/secure-use-of-helpers/ - ''; - }; - - autoLoadConntrackHelpers = mkOption { - type = types.bool; - default = false; - description = - '' - Whether to auto-load connection-tracking helpers. - See the description at networking.firewall.connectionTrackingModules - - (needs kernel 3.5+) - ''; - }; - - extraCommands = mkOption { - type = types.lines; - default = ""; - example = "iptables -A INPUT -p icmp -j ACCEPT"; - description = - '' - Additional shell commands executed as part of the firewall - initialisation script. These are executed just before the - final "reject" firewall rule is added, so they can be used - to allow packets that would otherwise be refused. - ''; - }; - - extraPackages = mkOption { - type = types.listOf types.package; - default = [ ]; - example = literalExpression "[ pkgs.ipset ]"; - description = - '' - Additional packages to be included in the environment of the system - as well as the path of networking.firewall.extraCommands. - ''; - }; - - extraStopCommands = mkOption { - type = types.lines; - default = ""; - example = "iptables -P INPUT ACCEPT"; - description = - '' - Additional shell commands executed as part of the firewall - shutdown script. These are executed just after the removal - of the NixOS input rule, or if the service enters a failed - state. - ''; - }; - - interfaces = mkOption { - default = { }; - type = with types; attrsOf (submodule [ { options = commonOptions; } ]); - description = - '' - Interface-specific open ports. - ''; - }; - } // commonOptions; - - }; - - - ###### implementation - - # FIXME: Maybe if `enable' is false, the firewall should still be - # built but not started by default? - config = mkIf cfg.enable { - - networking.firewall.trustedInterfaces = [ "lo" ]; - - environment.systemPackages = [ cfg.package ] ++ cfg.extraPackages; - - boot.kernelModules = (optional cfg.autoLoadConntrackHelpers "nf_conntrack") - ++ map (x: "nf_conntrack_${x}") cfg.connectionTrackingModules; - boot.extraModprobeConfig = optionalString cfg.autoLoadConntrackHelpers '' - options nf_conntrack nf_conntrack_helper=1 - ''; - - assertions = [ - # This is approximately "checkReversePath -> kernelHasRPFilter", - # but the checkReversePath option can include non-boolean - # values. - { assertion = cfg.checkReversePath == false || kernelHasRPFilter; - message = "This kernel does not support rpfilter"; } - ]; - - systemd.services.firewall = { - description = "Firewall"; - wantedBy = [ "sysinit.target" ]; - wants = [ "network-pre.target" ]; - before = [ "network-pre.target" ]; - after = [ "systemd-modules-load.service" ]; - - path = [ cfg.package ] ++ cfg.extraPackages; - - # FIXME: this module may also try to load kernel modules, but - # containers don't have CAP_SYS_MODULE. So the host system had - # better have all necessary modules already loaded. - unitConfig.ConditionCapability = "CAP_NET_ADMIN"; - unitConfig.DefaultDependencies = false; - - reloadIfChanged = true; - - serviceConfig = { - Type = "oneshot"; - RemainAfterExit = true; - ExecStart = "@${startScript} firewall-start"; - ExecReload = "@${reloadScript} firewall-reload"; - ExecStop = "@${stopScript} firewall-stop"; - }; - }; - - }; - -} |