247 lines
9.8 KiB
Nix
247 lines
9.8 KiB
Nix
# debugging:
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# - `journalctl -u systemd-networkd`
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#
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# docs:
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# - wireguard (nixos): <https://nixos.wiki/wiki/WireGuard#Setting_up_WireGuard_with_systemd-networkd>
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# - wireguard (arch): <https://wiki.archlinux.org/title/WireGuard>
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#
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# to route all internet traffic through a VPN endpoint, run `systemctl start vpn-${vpnName}`
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# to show the routing table: `ip rule`
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# to show the NAT rules used for bridging: `sudo iptables -t nat --list-rules -v`
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#
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# the rough idea here is:
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# 1. each VPN has an IP address: if we originate a packet, and the source address is the VPN's address, then it gets routed over the VPN trivially.
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# 2a. create a bridge device for each VPN. traffic exiting that bridge is source-NAT'd to the VPN's address.
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# 2b. to route all traffic for a specific application (or container), give it access to only the bridge device.
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# 3a. create a separate routing table for each VPN, with table id = ID.
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# 3b. if a packet enters the VPN's table then it will be routed via the VPN.
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# 3c. to apply a VPN to all internet traffic, system-wide, a rule is added that forces each packet to enter that VPN's routing table.
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# - that's done with `systemctl start vpn-$VPN`.
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# - the VPN acts as the default route. so traffic destined to e.g. a LAN device do not traverse the VPN in this case. only internet traffic is VPN'd.
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{ config, lib, pkgs, sane-lib, ... }:
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let
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cfg = config.sane.vpn;
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vpnOpts = with lib; types.submodule ({ name, config, ... }: {
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options = {
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name = mkOption {
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type = types.str;
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description = ''
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read-only value: must match the attrName of this vpn.
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'';
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};
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id = mkOption {
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type = types.ints.between 1 99;
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description = ''
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unique integer identifier for this VPN.
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lower number = higher priority, in many senses.
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lowest number = default VPN to use when no other is specified, or when multiple are enabled in the same circumstance.
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'';
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};
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fwmark = mkOption {
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type = types.int;
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};
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priorityMain = mkOption {
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type = types.int;
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};
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priorityWgTable = mkOption {
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type = types.int;
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};
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priorityFwMark = mkOption {
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type = types.int;
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};
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isDefault = mkOption {
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type = types.bool;
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description = ''
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read-only value: set based on whichever VPN has the lowest id.
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'';
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};
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endpoint = mkOption {
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type = types.str;
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description = ''
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host:port which hosts the other end of the VPN.
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e.g. "vpn.example.com:55280"
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'';
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};
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publicKey = mkOption {
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type = types.str;
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description = ''
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pubkey of the remote peer.
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'';
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};
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addrV4 = mkOption {
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type = types.str;
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description = ''
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IP address of my end of the VPN.
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e.g. "172.27.12.34"
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'';
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};
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dns = mkOption {
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type = types.listOf types.str;
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default = [
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"46.227.67.134"
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"192.165.9.158"
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];
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description = ''
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dns servers to use for traffic associated with this VPN.
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'';
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};
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bridgeDevice = mkOption {
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type = types.str;
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default = "br-${name}";
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description = ''
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name of the bridge net device which will be created and configured so as to route all its outbound traffic over the VPN.
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'';
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};
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privateKeyFile = mkOption {
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type = types.either types.str types.path;
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description = ''
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path to the private key for my end of the VPN.
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e.g. "/run/secrets/wg-home.priv"
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'';
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};
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};
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config = {
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inherit name;
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isDefault = builtins.all (other: config.id <= other.id) (builtins.attrValues cfg);
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fwmark = config.id + 10000;
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priorityMain = config.id + 100;
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priorityWgTable = config.id + 200;
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priorityFwMark = config.id + 300;
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};
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});
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mkVpnConfig = name: { id, dns, endpoint, publicKey, addrV4, privateKeyFile, bridgeDevice, priorityMain, priorityWgTable, priorityFwMark, fwmark, ... }: let
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bridgeAddrV4 = "10.20.${builtins.toString id}.1/24";
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in {
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assertions = [
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{
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assertion = (lib.count (c: c.id == id) (builtins.attrValues cfg)) == 1;
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message = "multiple VPNs share id ${id}";
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}
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];
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systemd.network.netdevs."98-${name}" = {
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# see: `man 5 systemd.netdev`
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netdevConfig = {
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Kind = "wireguard";
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Name = name;
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};
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wireguardConfig = {
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PrivateKeyFile = privateKeyFile;
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FirewallMark = fwmark;
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};
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wireguardPeers = [{
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wireguardPeerConfig = {
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AllowedIPs = [
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"0.0.0.0/0"
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"::/0"
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];
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Endpoint = endpoint;
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PublicKey = publicKey;
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};
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}];
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};
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systemd.network.networks."50-${name}" = {
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# see: `man 5 systemd.network`
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matchConfig.Name = name;
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networkConfig.Address = [ addrV4 ];
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networkConfig.DNS = dns;
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# TODO: `sane-vpn up <vpn>` should configure DNS to be sent over the VPN
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# DNSDefaultRoute: system DNS queries are sent to this link's DNS server
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# networkConfig.DNSDefaultRoute = true;
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# Domains = ~.: system DNS queries are sent to this link's DNS server
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# networkConfig.Domains = "~.";
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routingPolicyRules = [
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{
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routingPolicyRuleConfig = {
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# send traffic from the container bridge out over the VPN.
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# the bridge itself does source nat (SNAT) to rewrite the packet source address to that of the VPNs
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# -- but that happens in POSTROUTING: *after* the kernel decides which interface to give the packet to next.
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# therefore, we have to route here based on the packet's address as it is in PREROUTING, i.e. the bridge address. weird!
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Priority = priorityWgTable;
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From = bridgeAddrV4;
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Table = id;
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};
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}
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];
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routes = [{
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routeConfig.Table = id;
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routeConfig.Scope = "link";
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routeConfig.Destination = "0.0.0.0/0";
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routeConfig.Source = addrV4;
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}];
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# RequiredForOnline => should `systemd-networkd-wait-online` fail if this network can't come up?
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linkConfig.RequiredForOnline = false;
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};
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systemd.network.netdevs."99-${bridgeDevice}" = {
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netdevConfig.Kind = "bridge";
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netdevConfig.Name = bridgeDevice;
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};
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systemd.network.networks."51-${bridgeDevice}" = {
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matchConfig.Name = bridgeDevice;
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networkConfig.Description = "NATs inbound traffic to ${name}, intended for container isolation";
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networkConfig.Address = [ bridgeAddrV4 ];
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networkConfig.DNS = dns;
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# ConfigureWithoutCarrier: a bridge with no attached interface has no carrier (this is to be expected).
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# systemd ordinarily waits for a carrier to be present before "configuring" the bridge.
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# i tell it to not do that, so that i can assign an IP address to the bridge before i connect it to anything.
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# alternative may be to issue the bridge a static MACAddress?
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# see: <https://github.com/systemd/systemd/issues/9252#issuecomment-808710185>
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networkConfig.ConfigureWithoutCarrier = true;
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# networkConfig.DHCPServer = true;
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linkConfig.RequiredForOnline = false;
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};
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networking.localCommands = with pkgs; ''
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# view rules with:
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# - `sudo iptables -t nat --list-rules -v`
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# rewrite the source address of every packet leaving the container so that it's routable by the wg tunnel.
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# note that this alone doesn't get it routed *to* the wg device. we can't, since SNAT is POSTROUTING (not PREROUTING).
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# that part's done by an `ip rule` entry.
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${iptables}/bin/iptables -A POSTROUTING -t nat -s ${bridgeAddrV4} -j SNAT --to-source ${addrV4}
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'';
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# linux will drop inbound packets if it thinks a reply to that packet wouldn't exit via the same interface (rpfilter).
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# wg-quick has a solution via `iptables -j CONNMARK`, and that does work for system-wide VPNs,
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# but i couldn't get that to work for firejail/netns with SNAT, so set rpfilter to "loose".
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networking.firewall.checkReversePath = "loose";
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# networking.firewall.extraCommands = with pkgs; ''
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# # wireguard packet marking. without this, rpfilter drops responses from a wireguard VPN
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# # because the "reverse path check" fails (i.e. it thinks a response to the packet would go out via a different interface than what the wireguard packet arrived at).
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# # debug with e.g. `iptables --list -v -n -t mangle`
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# # - and `networking.firewall.logReversePathDrops = true;`, `networking.firewall.logRefusedPackets = true;`
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# # - and `journalctl -k` to see dropped packets
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# #
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# # note that wg-quick also adds a rule to reject non-local traffic from all interfaces EXCEPT the tunnel.
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# # that may protect against actors trying to probe us: actors we connect to via wireguard who send their response packets (speculatively) to our plaintext IP to see if we accept them.
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# # but that's fairly low concern, and firewalling by the gateway/NAT helps protect against that already.
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# ${iptables}/bin/iptables -t mangle -I PREROUTING 1 -i ${name} -m mark --mark 0 -j CONNMARK --restore-mark
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# ${iptables}/bin/iptables -t mangle -A POSTROUTING -o ${name} -m mark --mark ${builtins.toString id} -j CONNMARK --save-mark
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# '';
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};
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in
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{
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options = with lib; {
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sane.vpn = mkOption {
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type = types.attrsOf vpnOpts;
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default = {};
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};
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};
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config = let
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configs = lib.mapAttrsToList mkVpnConfig cfg;
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take = f: {
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assertions = f.assertions;
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networking.firewall.checkReversePath = f.networking.firewall.checkReversePath;
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networking.localCommands = f.networking.localCommands;
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systemd.network = f.systemd.network;
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systemd.services = f.systemd.services;
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};
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in take (sane-lib.mkTypedMerge take configs);
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}
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