[mutter] wayland: Preserve the event mask on the root window

[Olivier Fourdan <ofourdan src gnome org>]

commit 76012506ff40bb4791c1796004382eec4f44367d
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Thu Dec 15 11:16:49 2016 +0100

    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

 src/wayland/meta-xwayland-selection.c |   13 +++++++++----
 1 files changed, 9 insertions(+), 4 deletions(-)
---
diff --git a/src/wayland/meta-xwayland-selection.c b/src/wayland/meta-xwayland-selection.c
index a8806f1..d2a6e94 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);