wayland: Preserve the event mask on the root window

A window manager must select the SubstructureRedirect mask on the root
window to receive the MapRequest from the X11 clients and manage the
windows. Without this event mask set, a window manager won't be able to
map any new window.

The Wayland selection code in mutter can change/clear the event mask on
the requestor window from a XSelectionRequest event when the window is
not managed by mutter/gnome-shell.

A rogue or simply buggy X11 client may send a XConvertSelection() on the
root window and mutter will happily change/clear its own event mask on
the root window, effectively turning itself into a regular X11 client
unable to map any new X11 window from the other X11 clients.

To avoid this, simply check that the requestor window is not the root
window prior to change/clear the event mask on that window.

https://bugzilla.gnome.org/show_bug.cgi?id=776128

1 files changed, 9 insertions, 4 deletions

diff --git a/src/wayland/meta-xwayland-selection.c b/src/wayland/meta-xwayland-selection.c
index a8806f17e..d2a6e9421 100644
--- a/src/wayland/meta-xwayland-selection.c
+++ b/src/wayland/meta-xwayland-selection.c
@@ -546,6 +546,8 @@ static WaylandSelectionData *
 wayland_selection_data_new (XSelectionRequestEvent *request_event,
                             MetaWaylandCompositor  *compositor)
 {
+  MetaDisplay *display = meta_get_display ();
+  MetaScreen *screen = display->screen;
   MetaWaylandDataDevice *data_device;
   MetaWaylandDataSource *wayland_source;
   MetaSelectionBridge *selection;
@@ -595,7 +597,8 @@ wayland_selection_data_new (XSelectionRequestEvent *request_event,
   data->window = meta_display_lookup_x_window (meta_get_display (),
                                                data->request_event.requestor);
 
-  if (!data->window)
+  /* Do *not* change the event mask on the root window, bugger! */
+  if (!data->window && data->request_event.requestor != screen->xroot)
     {
       /* Not a managed window, set the PropertyChangeMask
        * for INCR deletion notifications.
@@ -629,10 +632,12 @@ reply_selection_request (XSelectionRequestEvent *request_event,
 static void
 wayland_selection_data_free (WaylandSelectionData *data)
 {
-  if (!data->window)
-    {
-      MetaDisplay *display = meta_get_display ();
+  MetaDisplay *display = meta_get_display ();
+  MetaScreen *screen = display->screen;
 
+  /* Do *not* change the event mask on the root window, bugger! */
+  if (!data->window && data->request_event.requestor != screen->xroot)
+    {
       meta_error_trap_push (display);
       XSelectInput (GDK_DISPLAY_XDISPLAY (gdk_display_get_default ()),
                     data->request_event.requestor, NoEventMask);