[mutter] xwayland: Protect against crash on x11->wayland transfer cancellation

[Carlos Garnacho <carlosg src gnome org>]

commit da0aac665f9f18647af894e296586f3ff3fbc3fa
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri Sep 11 15:35:07 2015 +0200

    xwayland: Protect against crash on x11->wayland transfer cancellation
    
    If the transfer is cancelled, the X11SelectionData will be cleared from
    the MetaSelectionBridge, although x11_data_write_cb() was invariably
    expecting it to be non-NULL.
    
    If the write was cancelled, all the actions done in x11_data_write_cb()
    are moot, so just return early. If there's other errors happening
    (eg. "connection closed" if the target client happens to crash), we
    should still attempt at clearing the data anyway.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=754357

 src/wayland/meta-xwayland-selection.c |   28 +++++++++++++++++-----------
 1 files changed, 17 insertions(+), 11 deletions(-)
---
diff --git a/src/wayland/meta-xwayland-selection.c b/src/wayland/meta-xwayland-selection.c
index 3a97a40..081a244 100644
--- a/src/wayland/meta-xwayland-selection.c
+++ b/src/wayland/meta-xwayland-selection.c
@@ -410,27 +410,33 @@ x11_data_write_cb (GObject      *object,
   MetaSelectionBridge *selection = user_data;
   X11SelectionData *data = selection->x11_selection;
   GError *error = NULL;
+  gboolean success = TRUE;
 
   g_output_stream_write_finish (G_OUTPUT_STREAM (object), res, &error);
 
-  if (data->incr)
+  if (error)
+    {
+      if (g_error_matches (error, G_IO_ERROR, G_IO_ERROR_CANCELLED))
+        {
+          g_error_free (error);
+          return;
+        }
+
+      g_warning ("Error writing from X11 selection: %s\n", error->message);
+      g_error_free (error);
+      success = FALSE;
+    }
+
+  if (success && data->incr)
     {
       Display *xdisplay = GDK_DISPLAY_XDISPLAY (gdk_display_get_default ());
       XDeleteProperty (xdisplay, selection->window,
                        gdk_x11_get_xatom_by_name ("_META_SELECTION"));
     }
-
-  if (error)
+  else
     {
-      if (error->domain != G_IO_ERROR ||
-          error->code != G_IO_ERROR_CANCELLED)
-        g_warning ("Error writing from X11 selection: %s\n", error->message);
-
-      g_error_free (error);
+      x11_selection_data_finish (selection, success);
     }
-
-  if (!data->incr)
-    x11_selection_data_finish (selection, TRUE);
 }
 
 static void