nixos/memcached: Isolate the service

memcached is (as the name suggests) an in-memory database so FS access
is not required.

nixos/modules/services/databases/memcached.nix

@@ -86,7 +86,25 @@ in
         in "${memcached}/bin/memcached ${networking} -m ${toString cfg.maxMemory} -c ${toString cfg.maxConnections} ${concatStringsSep " " cfg.extraOptions}";
 
         User = cfg.user;
+
+        # Filesystem access
+        ProtectSystem = "strict";
+        ProtectHome = true;
+        PrivateTmp = true;
+        PrivateDevices = true;
+        ProtectKernelTunables = true;
+        ProtectKernelModules = true;
+        ProtectControlGroups = true;
         RuntimeDirectory = "memcached";
+        # Caps
+        CapabilityBoundingSet = "";
+        NoNewPrivileges = true;
+        # Misc.
+        LockPersonality = true;
+        RestrictRealtime = true;
+        PrivateMounts = true;
+        PrivateUsers = true;
+        MemoryDenyWriteExecute = true;
       };
     };
   };