compositor: Guard against untimely calls

It seems that sometimes these functions are called by Javascript in
GNOME Shell during tear down. This causes segfaults and crash reports,
but without any backtraces other than the entry and exit points into
gjs.

In order to get more useful information about where these calls come
from, validate the input passed gracefully, by complaining in the log
and returning NULL values.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/926

1 files changed, 40 insertions, 15 deletions

diff --git a/src/compositor/compositor.c b/src/compositor/compositor.c
index 30a7a3824..f6734da2d 100644
--- a/src/compositor/compositor.c
+++ b/src/compositor/compositor.c
@@ -210,9 +210,14 @@ get_compositor_for_display (MetaDisplay *display)
 ClutterActor *
 meta_get_stage_for_display (MetaDisplay *display)
 {
-  MetaCompositor *compositor = get_compositor_for_display (display);
-  MetaCompositorPrivate *priv =
-    meta_compositor_get_instance_private (compositor);
+  MetaCompositor *compositor;
+  MetaCompositorPrivate *priv;
+
+  g_return_val_if_fail (display, NULL);
+
+  compositor = get_compositor_for_display (display);
+  g_return_val_if_fail (compositor, NULL);
+  priv = meta_compositor_get_instance_private (compositor);
 
   return priv->stage;
 }
@@ -226,9 +231,14 @@ meta_get_stage_for_display (MetaDisplay *display)
 ClutterActor *
 meta_get_window_group_for_display (MetaDisplay *display)
 {
-  MetaCompositor *compositor = get_compositor_for_display (display);
-  MetaCompositorPrivate *priv =
-    meta_compositor_get_instance_private (compositor);
+  MetaCompositor *compositor;
+  MetaCompositorPrivate *priv;
+
+  g_return_val_if_fail (display, NULL);
+
+  compositor = get_compositor_for_display (display);
+  g_return_val_if_fail (compositor, NULL);
+  priv = meta_compositor_get_instance_private (compositor);
 
   return priv->window_group;
 }
@@ -242,9 +252,14 @@ meta_get_window_group_for_display (MetaDisplay *display)
 ClutterActor *
 meta_get_top_window_group_for_display (MetaDisplay *display)
 {
-  MetaCompositor *compositor = get_compositor_for_display (display);
-  MetaCompositorPrivate *priv =
-    meta_compositor_get_instance_private (compositor);
+  MetaCompositor *compositor;
+  MetaCompositorPrivate *priv;
+
+  g_return_val_if_fail (display, NULL);
+
+  compositor = get_compositor_for_display (display);
+  g_return_val_if_fail (compositor, NULL);
+  priv = meta_compositor_get_instance_private (compositor);
 
   return priv->top_window_group;
 }
@@ -258,9 +273,14 @@ meta_get_top_window_group_for_display (MetaDisplay *display)
 ClutterActor *
 meta_get_feedback_group_for_display (MetaDisplay *display)
 {
-  MetaCompositor *compositor = get_compositor_for_display (display);
-  MetaCompositorPrivate *priv =
-    meta_compositor_get_instance_private (compositor);
+  MetaCompositor *compositor;
+  MetaCompositorPrivate *priv;
+
+  g_return_val_if_fail (display, NULL);
+
+  compositor = get_compositor_for_display (display);
+  g_return_val_if_fail (compositor, NULL);
+  priv = meta_compositor_get_instance_private (compositor);
 
   return priv->feedback_group;
 }
@@ -274,9 +294,14 @@ meta_get_feedback_group_for_display (MetaDisplay *display)
 GList *
 meta_get_window_actors (MetaDisplay *display)
 {
-  MetaCompositor *compositor = get_compositor_for_display (display);
-  MetaCompositorPrivate *priv =
-    meta_compositor_get_instance_private (compositor);
+  MetaCompositor *compositor;
+  MetaCompositorPrivate *priv;
+
+  g_return_val_if_fail (display, NULL);
+
+  compositor = get_compositor_for_display (display);
+  g_return_val_if_fail (compositor, NULL);
+  priv = meta_compositor_get_instance_private (compositor);
 
   return priv->windows;
 }