Public bug reported:
On Ubuntu 26.04, the Displays panel of gnome-control-center crashes when
the laptop lid is closed and no external monitor is connected.
Environment:
- Ubuntu 26.04
- Official gnome-control-center package: 1:50.3-0ubuntu0.2
- gnome-control-center-data: 1:50.3-0ubuntu0.2
- GNOME Wayland session
- Laptop with a built-in display and no external monitor
Steps to reproduce:
1. Keep the GNOME session running with the laptop lid closed.
2. With no external monitor connected, run:
gnome-control-center display
Actual result:
gnome-control-center terminates with SIGSEGV. The backtrace shows
cc_display_monitor_set_active() at frame #0, with GTK switch notifications in
the call chain.
Expected result:
The settings application should remain open, even if there is no display
available for configuration. I understand that a closed built-in display may be
excluded from configuration; this report concerns the crash in that state.
Investigation and local fix:
In panels/display/cc-display-settings.c, on_enabled_row_active_changed_cb()
only checks self->updating before passing self->selected_output to
cc_display_monitor_set_active().
I applied the following patch:
```diff
--- a/panels/display/cc-display-settings.c
+++ b/panels/display/cc-display-settings.c
@@ -686,7 +686,7 @@
on_enabled_row_active_changed_cb (CcDisplaySettings *self)
{
- if (self->updating)
+ if (self->updating || self->selected_output == NULL)
return;
cc_display_monitor_set_active (self->selected_output,
adw_switch_row_get_active
(self->enabled_row));
```
Verification:
I rebuilt the Ubuntu source package and installed gnome-control-center and
gnome-control-center-data as 1:50.3-0ubuntu0.2+local1. After applying this
patch, the Displays panel no longer crashes with the laptop lid closed.
The attached backtrace was collected from the unmodified official
package, 1:50.3-0ubuntu0.2, before installing the local fix.
Previous occurrence:
I previously encountered a similar crash on Ubuntu 24.04 with package
1:46.7-0ubuntu0.24.04.6 in an X11 session. In that investigation, the backtrace
showed cc_display_monitor_set_active(self=0x0), and the same NULL guard
prevented the crash.
The Ubuntu 26.04 backtrace does not show argument values, so a NULL
dereference in this version is inferred from the previous investigation,
the source code, and the successful local fix.
Related upstream report:
https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/2077
I have not tested upstream main and cannot confirm whether this has
exactly the same cause as the original upstream report.
** Affects: gnome-control-center (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "Official package crash backtrace"
https://bugs.launchpad.net/bugs/2169467/+attachment/6005499/+files/gnome-control-center-50.3-backtrace.txt
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https://bugs.launchpad.net/bugs/2169467
Title:
gnome-control-center Displays panel crashes with laptop lid closed and
no external monitor; NULL guard fixes crash
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