[gnome-shell] st/texture-cache: Don't overwrite existing bind images on texture reset

[Marge Bot <marge-bot src gnome org>]

commit 606ec25f8b67a88388f12b548b1ad80396371b4c
Author: Sebastian Keller <skeller gnome org>
Date:   Thu Feb 25 17:42:43 2021 +0100

    st/texture-cache: Don't overwrite existing bind images on texture reset
    
    If the icon surface of a window got updated and its type or format no
    longer match what we expect, st_texture_cache_reset_texture() might
    overwrite the existing image in the bind with a new image, while still
    keeping the weak ref on the old image. Due to this the old image might
    trigger a st_texture_cache_on_pixbuf_notify() after the bind has already
    been freed by g_signal_handlers_destroy() in the bind source. While this
    usually would remove the weak ref, the weak ref it tries to remove is
    on the new image, not the old one. The call to
    st_texture_cache_on_pixbuf_notify() then tries to read the already
    free'd memory from the bind which causes the cast to G_OBJECT to fail,
    resulting in the crash.
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3785
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1718>

 src/st/st-texture-cache.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)
---
diff --git a/src/st/st-texture-cache.c b/src/st/st-texture-cache.c
index 07b1166a1b..b27cac4c10 100644
--- a/src/st/st-texture-cache.c
+++ b/src/st/st-texture-cache.c
@@ -776,11 +776,10 @@ st_texture_cache_reset_texture (StTextureCachePropertyBind *bind,
       if (error)
         g_warning ("Failed to allocate texture: %s", error->message);
     }
-  else
-    bind->image = g_object_new (ST_TYPE_IMAGE_CONTENT,
-                                "preferred-width", 0, /* tough luck */
-                                "preferred-height", 0,
-                                NULL);
+  else if (!bind->image)
+    {
+      bind->image = st_image_content_new_with_preferred_size (0, 0);
+    }
 }
 
 static void