backends: Make uniform checks on remote desktop input dbus methods

They all checked that the remote session service talked with the
correct peer, and some of them did check that there is an associated
screencast session.

Add a new check for the session being started (as it's state is
decoupled with screencast session availability) and move all checks
to a function that is called from all input-oriented DBus methods.

Fixes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1254

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1258


(cherry picked from commit c8837a8de5)

src/backends/meta-remote-desktop-session.c

@@ -253,6 +253,37 @@ check_permission (MetaRemoteDesktopSession *session,
                     g_dbus_method_invocation_get_sender (invocation)) == 0;
 }
 
+static gboolean
+meta_remote_desktop_session_check_can_notify (MetaRemoteDesktopSession *session,
+                                              GDBusMethodInvocation    *invocation)
+{
+  if (!session->started)
+    {
+      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+                                             G_DBUS_ERROR_FAILED,
+                                             "Session not started");
+      return FALSE;
+    }
+
+  if (!check_permission (session, invocation))
+    {
+      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+                                             G_DBUS_ERROR_ACCESS_DENIED,
+                                             "Permission denied");
+      return FALSE;
+    }
+
+  if (!session->screen_cast_session)
+    {
+      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
+                                             G_DBUS_ERROR_FAILED,
+                                             "No screen cast active");
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
 static gboolean
 handle_start (MetaDBusRemoteDesktopSession *skeleton,
               GDBusMethodInvocation        *invocation)
@@ -332,13 +363,8 @@ handle_notify_keyboard_keycode (MetaDBusRemoteDesktopSession *skeleton,
   MetaRemoteDesktopSession *session = META_REMOTE_DESKTOP_SESSION (skeleton);
   ClutterKeyState state;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
 
   if (pressed)
     state = CLUTTER_KEY_STATE_PRESSED;
@@ -364,13 +390,8 @@ handle_notify_keyboard_keysym (MetaDBusRemoteDesktopSession *skeleton,
   MetaRemoteDesktopSession *session = META_REMOTE_DESKTOP_SESSION (skeleton);
   ClutterKeyState state;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
 
   if (pressed)
     state = CLUTTER_KEY_STATE_PRESSED;
@@ -418,13 +439,8 @@ handle_notify_pointer_button (MetaDBusRemoteDesktopSession *skeleton,
   uint32_t button;
   ClutterButtonState state;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
 
   button = translate_to_clutter_button (button_code);
 
@@ -454,13 +470,8 @@ handle_notify_pointer_axis (MetaDBusRemoteDesktopSession *skeleton,
   MetaRemoteDesktopSession *session = META_REMOTE_DESKTOP_SESSION (skeleton);
   ClutterScrollFinishFlags finish_flags = CLUTTER_SCROLL_FINISHED_NONE;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
 
   if (flags & META_REMOTE_DESKTOP_NOTIFY_AXIS_FLAGS_FINISH)
     {
@@ -507,13 +518,8 @@ handle_notify_pointer_axis_discrete (MetaDBusRemoteDesktopSession *skeleton,
   ClutterScrollDirection direction;
   int step_count;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
 
   if (axis > 1)
     {
@@ -558,13 +564,8 @@ handle_notify_pointer_motion_relative (MetaDBusRemoteDesktopSession *skeleton,
 {
   MetaRemoteDesktopSession *session = META_REMOTE_DESKTOP_SESSION (skeleton);
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
 
   clutter_virtual_input_device_notify_relative_motion (session->virtual_pointer,
                                                        CLUTTER_CURRENT_TIME,
@@ -587,21 +588,8 @@ handle_notify_pointer_motion_absolute (MetaDBusRemoteDesktopSession *skeleton,
   MetaScreenCastStream *stream;
   double abs_x, abs_y;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
-
-  if (!session->screen_cast_session)
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_FAILED,
-                                             "No screen cast active");
-      return TRUE;
-    }
 
   stream = meta_screen_cast_session_get_stream (session->screen_cast_session,
                                                 stream_path);
@@ -637,21 +625,8 @@ handle_notify_touch_down (MetaDBusRemoteDesktopSession *skeleton,
   MetaScreenCastStream *stream;
   double abs_x, abs_y;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
-
-  if (!session->screen_cast_session)
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_FAILED,
-                                             "No screen cast active");
-      return TRUE;
-    }
 
   stream = meta_screen_cast_session_get_stream (session->screen_cast_session,
                                                 stream_path);
@@ -688,21 +663,8 @@ handle_notify_touch_motion (MetaDBusRemoteDesktopSession *skeleton,
   MetaScreenCastStream *stream;
   double abs_x, abs_y;
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
-
-  if (!session->screen_cast_session)
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_FAILED,
-                                             "No screen cast active");
-      return TRUE;
-    }
 
   stream = meta_screen_cast_session_get_stream (session->screen_cast_session,
                                                 stream_path);
@@ -734,13 +696,8 @@ handle_notify_touch_up (MetaDBusRemoteDesktopSession *skeleton,
 {
   MetaRemoteDesktopSession *session = META_REMOTE_DESKTOP_SESSION (skeleton);
 
-  if (!check_permission (session, invocation))
+  if (!meta_remote_desktop_session_check_can_notify (session, invocation))
-    {
-      g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR,
-                                             G_DBUS_ERROR_ACCESS_DENIED,
-                                             "Permission denied");
     return TRUE;
-    }
 
   clutter_virtual_input_device_notify_touch_up (session->virtual_touchscreen,
                                                        CLUTTER_CURRENT_TIME,