nixos/usbguard: add USBGuard dbus daemon option

The usbguard package includes the dbus daemon, but the NixOS config
option does not provide a service file or its necessary polkit rules.

Enabling the dbus daemon allows use of Gnome's USBGuard support.

nixos/modules/services/security/usbguard.nix

@@ -150,6 +150,8 @@ in
           Generate device specific rules including the "via-port" attribute.
         '';
       };
+
+      dbus.enable = mkEnableOption (lib.mdDoc "USBGuard dbus daemon");
     };
   };
 
@@ -160,49 +162,90 @@ in
 
     environment.systemPackages = [ cfg.package ];
 
-    systemd.services.usbguard = {
-      description = "USBGuard daemon";
+    systemd.services = {
+      usbguard = {
+        description = "USBGuard daemon";
 
-      wantedBy = [ "basic.target" ];
-      wants = [ "systemd-udevd.service" ];
+        wantedBy = [ "basic.target" ];
+        wants = [ "systemd-udevd.service" ];
 
-      # make sure an empty rule file exists
-      preStart = ''[ -f "${ruleFile}" ] || touch ${ruleFile}'';
+        # make sure an empty rule file exists
+        preStart = ''[ -f "${ruleFile}" ] || touch ${ruleFile}'';
 
-      serviceConfig = {
-        Type = "simple";
-        ExecStart = "${cfg.package}/bin/usbguard-daemon -P -k -c ${daemonConfFile}";
-        Restart = "on-failure";
+        serviceConfig = {
+          Type = "simple";
+          ExecStart = "${cfg.package}/bin/usbguard-daemon -P -k -c ${daemonConfFile}";
+          Restart = "on-failure";
 
-        StateDirectory = [
-          "usbguard"
-          "usbguard/IPCAccessControl.d"
-        ];
+          StateDirectory = [
+            "usbguard"
+            "usbguard/IPCAccessControl.d"
+          ];
 
-        AmbientCapabilities = "";
-        CapabilityBoundingSet = "CAP_CHOWN CAP_FOWNER";
-        DeviceAllow = "/dev/null rw";
-        DevicePolicy = "strict";
-        IPAddressDeny = "any";
-        LockPersonality = true;
-        MemoryDenyWriteExecute = true;
-        NoNewPrivileges = true;
-        PrivateDevices = true;
-        PrivateTmp = true;
-        ProtectControlGroups = true;
-        ProtectHome = true;
-        ProtectKernelModules = true;
-        ProtectSystem = true;
-        ReadOnlyPaths = "-/";
-        ReadWritePaths = "-/dev/shm -/tmp";
-        RestrictAddressFamilies = [ "AF_UNIX" "AF_NETLINK" ];
-        RestrictNamespaces = true;
-        RestrictRealtime = true;
-        SystemCallArchitectures = "native";
-        SystemCallFilter = "@system-service";
-        UMask = "0077";
+          AmbientCapabilities = "";
+          CapabilityBoundingSet = "CAP_CHOWN CAP_FOWNER";
+          DeviceAllow = "/dev/null rw";
+          DevicePolicy = "strict";
+          IPAddressDeny = "any";
+          LockPersonality = true;
+          MemoryDenyWriteExecute = true;
+          NoNewPrivileges = true;
+          PrivateDevices = true;
+          PrivateTmp = true;
+          ProtectControlGroups = true;
+          ProtectHome = true;
+          ProtectKernelModules = true;
+          ProtectSystem = true;
+          ReadOnlyPaths = "-/";
+          ReadWritePaths = "-/dev/shm -/tmp";
+          RestrictAddressFamilies = [ "AF_UNIX" "AF_NETLINK" ];
+          RestrictNamespaces = true;
+          RestrictRealtime = true;
+          SystemCallArchitectures = "native";
+          SystemCallFilter = "@system-service";
+          UMask = "0077";
+        };
+      };
+
+      usbguard-dbus = mkIf cfg.dbus.enable {
+        description = "USBGuard D-Bus Service";
+
+        wantedBy = [ "multi-user.target" ];
+        requires = [ "usbguard.service" ];
+
+        serviceConfig = {
+          Type = "dbus";
+          BusName = "org.usbguard1";
+          ExecStart = "${cfg.package}/bin/usbguard-dbus --system";
+          Restart = "on-failure";
+        };
+
+        aliases = [ "dbus-org.usbguard.service" ];
       };
     };
+
+    security.polkit.extraConfig =
+      let
+        groupCheck = (lib.concatStrings (map
+          (g: "subject.isInGroup(\"${g}\") || ")
+          cfg.IPCAllowedGroups))
+        + "false";
+      in
+      optionalString cfg.dbus.enable ''
+        polkit.addRule(function(action, subject) {
+            if ((action.id == "org.usbguard.Policy1.listRules" ||
+                 action.id == "org.usbguard.Policy1.appendRule" ||
+                 action.id == "org.usbguard.Policy1.removeRule" ||
+                 action.id == "org.usbguard.Devices1.applyDevicePolicy" ||
+                 action.id == "org.usbguard.Devices1.listDevices" ||
+                 action.id == "org.usbguard1.getParameter" ||
+                 action.id == "org.usbguard1.setParameter") &&
+                subject.active == true && subject.local == true &&
+                (${groupCheck})) {
+                    return polkit.Result.YES;
+            }
+        });
+      '';
   };
   imports = [
     (mkRemovedOptionModule [ "services" "usbguard" "ruleFile" ] "The usbguard module now uses ${defaultRuleFile} as ruleFile. Alternatively, use services.usbguard.rules to configure rules.")