From 8519bada6086dd48e55cbd8b74f2a74cdeb36368 Mon Sep 17 00:00:00 2001
From: Simon Bruder <simon@sbruder.de>
Date: Mon, 23 Oct 2023 23:23:37 +0200
Subject: [PATCH] authoritative-dns: Init

---
 modules/authoritative-dns.nix | 177 ++++++++++++++++++++++++++++++++++
 modules/default.nix           |   1 +
 modules/wireguard/home.nix    |  42 +++-----
 3 files changed, 189 insertions(+), 31 deletions(-)
 create mode 100644 modules/authoritative-dns.nix

diff --git a/modules/authoritative-dns.nix b/modules/authoritative-dns.nix
new file mode 100644
index 0000000..97c0cad
--- /dev/null
+++ b/modules/authoritative-dns.nix
@@ -0,0 +1,177 @@
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.sbruder.knot;
+
+  primaryHost = "vueko";
+  secondaryHosts = [ "okarin" ];
+
+  isPrimaryHost = config.networking.hostName == primaryHost;
+  isSecondaryHost = lib.elem config.networking.hostName secondaryHosts;
+
+  addresses = {
+    vueko = [ "168.119.176.53" "2a01:4f8:c012:2f4::1" ];
+    okarin = [ "82.165.242.252" "2001:8d8:1800:8627::1" ];
+  };
+in
+{
+  options = {
+    sbruder.knot.generated-zones = lib.mkOption {
+      type = lib.types.attrsOf lib.types.path;
+      default = { };
+      description = "List of zones generated by a nix expression";
+    };
+  };
+
+  config = lib.mkIf (isPrimaryHost || isSecondaryHost) {
+    services.knot = {
+      enable = true;
+      keyFiles = [
+        # Managed in separate repository.
+        # It includes all statically managed zones.
+        # Even though it is not a key,
+        # it needs to be included here
+        # so the module disables configuration checks.
+        "/var/lib/knot/static.conf"
+      ];
+      extraConfig = ''
+        server:
+        ${lib.concatStringsSep "\n" (map (address: "    listen: ${address}@53") addresses.${config.networking.hostName})}
+            automatic-acl: on
+
+        log:
+          - target: syslog
+            any: info
+        remote:
+        ${lib.concatStrings (lib.mapAttrsToList (host: hostAddresses: ''
+          - id: ${host}
+            address: [${lib.concatStringsSep ", " hostAddresses}]
+        '') addresses)}
+      '' + (lib.optionalString isPrimaryHost ''
+        # HACK: this string just continues the previous section
+          - id: inwx
+            # INWX only allows the specification of one primary DNS,
+            # which limits the IP protocol usable for zone transfers to one.
+            address: [185.181.104.96]
+
+        policy:
+          - id: default
+            nsec3: on
+
+        template:
+          - id: default
+            storage: /var/lib/knot/zones/
+            semantic-checks: on
+            # auto increment serial
+            zonefile-sync: -1
+            zonefile-load: difference-no-serial
+            journal-content: all
+            # secondary
+            notify: [inwx, ${lib.concatStringsSep ", " secondaryHosts}]
+            # dnssec
+            dnssec-signing: on
+            dnssec-policy: default
+          - id: nix-generated
+            storage: /var/lib/knot/nix-zones/
+            semantic-checks: on
+            # auto increment serial
+            zonefile-sync: -1
+            zonefile-load: difference-no-serial
+            journal-content: all
+
+        zone:
+        ${lib.concatMapStrings (domain: ''
+          - domain: ${domain}
+            template: nix-generated
+        '') (lib.attrNames cfg.generated-zones)}
+      '') + (lib.optionalString isSecondaryHost ''
+        acl:
+          - id: primary_notify
+            address: [${lib.concatStringsSep ", " (lib.flatten addresses.${primaryHost})}]
+            action: notify
+
+        template:
+          - id: default
+            master: [${primaryHost}]
+            acl: [primary_notify]
+      '');
+    };
+
+    users.users.knot = {
+      openssh.authorizedKeys.keys = config.sbruder.pubkeys.trustedKeys;
+      shell = pkgs.bashInteractive;
+    };
+
+    systemd.tmpfiles.rules = [
+      "f /var/lib/knot/static.conf 0644 knot knot - -"
+    ] ++ (lib.optionals isPrimaryHost [
+      "d /var/lib/knot/nix-zones 0755 knot knot - -"
+    ]);
+
+    systemd.services.knot-generated-zones = lib.mkIf isPrimaryHost {
+      wantedBy = [ "knot.service" ];
+      after = [ "knot.service" ];
+      path = with pkgs; [ knot-dns ];
+      script = ''
+        set -euo pipefail
+        ${lib.concatStringsSep "\n" (lib.mapAttrsToList (domain: zonefile: ''
+          kzonecheck -o ${lib.escapeShellArg domain} ${lib.escapeShellArg zonefile}
+          target=/var/lib/knot/nix-zones/${lib.escapeShellArg domain}.zone
+          if [ -h "$target" ]; then
+            pre_target="$(readlink "$target")"
+          else
+            pre_target="/invalid/path"
+          fi
+          ln -sf ${lib.escapeShellArg zonefile} "$target"
+          if [ "$pre_target" != ${lib.escapeShellArg domain} ]; then
+            echo -n "Zone for ${lib.escapeShellArg domain} changed, reloading… "
+            knotc zone-reload ${lib.escapeShellArg domain}
+          fi
+        '') cfg.generated-zones)}
+      '';
+      restartTriggers = lib.attrValues cfg.generated-zones;
+      serviceConfig = {
+        Type = "oneshot";
+        RemainAfterExit = true;
+        User = "knot";
+
+        BindReadOnlyPaths = [ "/run/knot/knot.sock" ];
+        CapabilityBoundingSet = ""; # clear
+        LockPersonality = true;
+        MemoryDenyWriteExecute = true;
+        NoNewPrivileges = true;
+        PrivateDevices = true;
+        PrivateNetwork = true;
+        PrivateTmp = true;
+        PrivateUsers = true;
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = true;
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        ProtectProc = "invisible";
+        ProtectSystem = true;
+        RemoveIPC = true;
+        RestrictAddressFamilies = [ "AF_UNIX" ]; # knot socket
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+        RestrictSUIDSGID = true;
+        SystemCallArchitectures = "native";
+        SystemCallFilter = [ "@system-service" "~@privileged" "~@resources" ];
+      };
+    };
+
+    networking.firewall = {
+      allowedTCPPorts = [ 53 ];
+      allowedUDPPorts = [ 53 ];
+    };
+
+    assertions = [
+      {
+        assertion = isPrimaryHost -> (lib.hasAttr "vpn.sbruder.de" cfg.generated-zones);
+        message = "The authoritative DNS module requires the server the wg-home wireguard server to run on the same host.";
+      }
+    ];
+  };
+}
diff --git a/modules/default.nix b/modules/default.nix
index b8b5e15..10dee35 100644
--- a/modules/default.nix
+++ b/modules/default.nix
@@ -20,6 +20,7 @@
   imports = [
     ../pkgs/modules.nix
     ./ausweisapp.nix
+    ./authoritative-dns.nix
     ./cups.nix
     ./docker.nix
     ./fancontrol.nix
diff --git a/modules/wireguard/home.nix b/modules/wireguard/home.nix
index 9cbed29..67172a1 100644
--- a/modules/wireguard/home.nix
+++ b/modules/wireguard/home.nix
@@ -126,38 +126,18 @@ in
 
     networking.firewall = {
       trustedInterfaces = [ "wg-home" ];
-      allowedUDPPorts = lib.optionals enableServer [
-        serverPort
-        53
-      ];
+      allowedUDPPorts = lib.optional enableServer serverPort;
     };
 
-    services.bind = lib.mkIf enableServer {
-      enable = true;
-      zones = lib.singleton {
-        name = "vpn.sbruder.de";
-        master = true;
-        file =
-          let
-            # !!! very hacky
-            hexStringToInt = hex: (builtins.fromTOML "int = 0x${hex}").int;
-
-            peerRecords = lib.concatStrings
-              (lib.mapAttrsToList
-                (peer: peerConfig: ''
-                  ${peer} IN A ${peerConfig.address}
-                '')
-                peers);
-
-            peerRecordsHash = builtins.hashString "sha256" peerRecords;
-            serial = hexStringToInt (lib.substring 0 8 peerRecordsHash);
-          in
-          pkgs.writeText "vpn.sbruder.de.zone" (''
-            $TTL 3600
-            @ IN SOA ${serverHostName}.sbruder.de. hostmaster.sbruder.de. ${toString serial} 28800 3600 604800 3600
-            @ IN NS ${serverHostName}.sbruder.de.
-          '' + peerRecords);
-      };
-    };
+    sbruder.knot.generated-zones."vpn.sbruder.de" = pkgs.writeText "vpn.sbruder.de.zone" (''
+      ; having $ORIGIN set here fails
+      @ IN SOA ${serverHostName}.sbruder.de. hostmaster.sbruder.de. 1 86400 10800 3600000 3600
+      @ IN NS ${serverHostName}.sbruder.de.
+    '' + lib.concatStrings
+      (lib.mapAttrsToList
+        (peer: peerConfig: ''
+          ${peer} IN A ${peerConfig.address}
+        '')
+        peers));
   };
 }