nixos/pretalx: set up hardening

nixos/modules/services/web-apps/pretalx.nix

@@ -337,6 +337,39 @@ in
           LogsDirectory = "pretalx";
           WorkingDirectory = cfg.settings.filesystem.data;
           SupplementaryGroups = [ "redis-pretalx" ];
+          AmbientCapabilities = "";
+          CapabilityBoundingSet = [ "" ];
+          DevicePolicy = "closed";
+          LockPersonality = true;
+          MemoryDenyWriteExecute = true;
+          NoNewPrivileges = true;
+          PrivateDevices = true;
+          PrivateTmp = true;
+          ProcSubset = "pid";
+          ProtectControlGroups = true;
+          ProtectHome = true;
+          ProtectHostname = true;
+          ProtectKernelLogs = true;
+          ProtectKernelModules = true;
+          ProtectKernelTunables = true;
+          ProtectProc = "invisible";
+          ProtectSystem = "strict";
+          RemoveIPC = true;
+          RestrictAddressFamilies = [
+            "AF_INET"
+            "AF_INET6"
+            "AF_UNIX"
+          ];
+          RestrictNamespaces = true;
+          RestrictRealtime = true;
+          RestrictSUIDSGID = true;
+          SystemCallArchitectures = "native";
+          SystemCallFilter = [
+            "@system-service"
+            "~@privileged"
+            "@chown"
+          ];
+          UMask = "0027";
         };
       };
     in {
@@ -399,6 +432,8 @@ in
         wantedBy = [ "multi-user.target" ];
         serviceConfig.ExecStart = "${lib.getExe' pythonEnv "celery"} -A pretalx.celery_app worker ${cfg.celery.extraArgs}";
       });
+
+      nginx.serviceConfig.SupplementaryGroups = lib.mkIf cfg.nginx.enable [ "pretalx" ];
     };
 
     systemd.sockets.pretalx-web.socketConfig = {