Make gdk_event_apply_filters safe against changes in filter list

An event filter may add or remove filters itself.  This patch does
two things to address this case.  The first is to take a temporary
reference to the filter while it is being used.  The second is
to wait until after the filter function is run before determining
the next node in the list to process.  This guards against
changes to the next node.  It also does not run functions
that have been marked as removed.  Though I'm not sure if this
case can arise.

https://bugzilla.gnome.org/show_bug.cgi?id=635380

5 files changed, 96 insertions, 18 deletions

diff --git a/gdk/gdkinternals.h b/gdk/gdkinternals.h
index e1b458e..c425447 100644
--- a/gdk/gdkinternals.h
+++ b/gdk/gdkinternals.h
@@ -59,9 +59,15 @@ struct _GdkColorInfo
   guint ref_count;
 };
 
+typedef enum {
+  GDK_EVENT_FILTER_REMOVED = 1 << 0
+} GdkEventFilterFlags;
+
 struct _GdkEventFilter {
   GdkFilterFunc function;
   gpointer data;
+  GdkEventFilterFlags flags;
+  guint ref_count;
 };
 
 struct _GdkClientFilter {
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index c248598..87d9d55 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -2577,13 +2577,18 @@ gdk_window_add_filter (GdkWindow     *window,
     {
       filter = (GdkEventFilter *)tmp_list->data;
       if ((filter->function == function) && (filter->data == data))
-	return;
+        {
+          filter->ref_count++;
+          return;
+        }
       tmp_list = tmp_list->next;
     }
 
   filter = g_new (GdkEventFilter, 1);
   filter->function = function;
   filter->data = data;
+  filter->ref_count = 1;
+  filter->flags = 0;
 
   if (private)
     private->filters = g_list_append (private->filters, filter);
@@ -2626,6 +2631,11 @@ gdk_window_remove_filter (GdkWindow     *window,
 
       if ((filter->function == function) && (filter->data == data))
 	{
+          filter->flags |= GDK_EVENT_FILTER_REMOVED;
+          filter->ref_count--;
+          if (filter->ref_count != 0)
+            return;
+
 	  if (private)
 	    private->filters = g_list_remove_link (private->filters, node);
 	  else
diff --git a/gdk/quartz/gdkevents-quartz.c b/gdk/quartz/gdkevents-quartz.c
index 2f8b0c8..c6512fc 100644
--- a/gdk/quartz/gdkevents-quartz.c
+++ b/gdk/quartz/gdkevents-quartz.c
@@ -171,19 +171,40 @@ append_event (GdkEvent *event,
 static gint
 gdk_event_apply_filters (NSEvent *nsevent,
 			 GdkEvent *event,
-			 GList *filters)
+			 GList **filters)
 {
   GList *tmp_list;
   GdkFilterReturn result;
   
-  tmp_list = filters;
+  tmp_list = *filters;
 
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter*) tmp_list->data;
-      
-      tmp_list = tmp_list->next;
+      GList *node;
+
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (nsevent, event, filter->data);
+
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
       if (result !=  GDK_FILTER_CONTINUE)
 	return result;
     }
@@ -1165,7 +1186,7 @@ gdk_event_translate (GdkEvent *event,
       /* Apply global filters */
       GdkFilterReturn result;
 
-      result = gdk_event_apply_filters (nsevent, event, _gdk_default_filters);
+      result = gdk_event_apply_filters (nsevent, event, &_gdk_default_filters);
       if (result != GDK_FILTER_CONTINUE)
         {
           return_val = (result == GDK_FILTER_TRANSLATE) ? TRUE : FALSE;
@@ -1206,7 +1227,7 @@ gdk_event_translate (GdkEvent *event,
 	{
 	  g_object_ref (window);
 
-	  result = gdk_event_apply_filters (nsevent, event, filter_private->filters);
+	  result = gdk_event_apply_filters (nsevent, event, &filter_private->filters);
 
 	  g_object_unref (window);
 
diff --git a/gdk/win32/gdkevents-win32.c b/gdk/win32/gdkevents-win32.c
index fb8a7d0..bea28a8 100644
--- a/gdk/win32/gdkevents-win32.c
+++ b/gdk/win32/gdkevents-win32.c
@@ -1025,7 +1025,7 @@ fill_key_event_string (GdkEvent *event)
 static GdkFilterReturn
 apply_event_filters (GdkWindow  *window,
 		     MSG        *msg,
-		     GList      *filters)
+		     GList     **filters)
 {
   GdkFilterReturn result = GDK_FILTER_CONTINUE;
   GdkEvent *event;
@@ -1043,13 +1043,34 @@ apply_event_filters (GdkWindow  *window,
    */
   node = _gdk_event_queue_append (_gdk_display, event);
   
-  tmp_list = filters;
+  tmp_list = *filters;
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter *) tmp_list->data;
-      
-      tmp_list = tmp_list->next;
+      GList *node;
+
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (msg, event, filter->data);
+
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
       if (result !=  GDK_FILTER_CONTINUE)
 	break;
     }
@@ -1756,7 +1777,7 @@ gdk_event_translate (MSG  *msg,
     {
       /* Apply global filters */
 
-      GdkFilterReturn result = apply_event_filters (NULL, msg, _gdk_default_filters);
+      GdkFilterReturn result = apply_event_filters (NULL, msg, &_gdk_default_filters);
       
       /* If result is GDK_FILTER_CONTINUE, we continue as if nothing
        * happened. If it is GDK_FILTER_REMOVE or GDK_FILTER_TRANSLATE,
@@ -1822,7 +1843,7 @@ gdk_event_translate (MSG  *msg,
     {
       /* Apply per-window filters */
 
-      GdkFilterReturn result = apply_event_filters (window, msg, ((GdkWindowObject *) window)->filters);
+      GdkFilterReturn result = apply_event_filters (window, msg, &((GdkWindowObject *) window)->filters);
 
       if (result == GDK_FILTER_REMOVE || result == GDK_FILTER_TRANSLATE)
 	{
diff --git a/gdk/x11/gdkeventsource.c b/gdk/x11/gdkeventsource.c
index f3b850e..7a23b59 100644
--- a/gdk/x11/gdkeventsource.c
+++ b/gdk/x11/gdkeventsource.c
@@ -57,20 +57,40 @@ static GList *event_sources = NULL;
 static gint
 gdk_event_apply_filters (XEvent   *xevent,
 			 GdkEvent *event,
-			 GList    *filters)
+			 GList   **filters)
 {
   GList *tmp_list;
   GdkFilterReturn result;
 
-  tmp_list = filters;
+  tmp_list = *filters;
 
   while (tmp_list)
     {
       GdkEventFilter *filter = (GdkEventFilter*) tmp_list->data;
+      GList *node;
 
-      tmp_list = tmp_list->next;
+      if ((filter->flags & GDK_EVENT_FILTER_REMOVED) != 0)
+        {
+          tmp_list = tmp_list->next;
+          continue;
+        }
+
+      filter->ref_count++;
       result = filter->function (xevent, event, filter->data);
 
+      /* get the next node after running the function since the
+         function may add or remove a next node */
+      node = tmp_list;
+      tmp_list = tmp_list->next;
+
+      filter->ref_count--;
+      if (filter->ref_count == 0)
+        {
+          *filters = g_list_remove_link (*filters, node);
+          g_list_free_1 (node);
+          g_free (filter);
+        }
+
       if (result != GDK_FILTER_CONTINUE)
 	return result;
     }
@@ -143,7 +163,7 @@ gdk_event_source_translate_event (GdkEventSource *event_source,
       /* Apply global filters */
 
       result = gdk_event_apply_filters (xevent, event,
-                                        _gdk_default_filters);
+                                        &_gdk_default_filters);
 
       if (result == GDK_FILTER_REMOVE)
         {
@@ -167,7 +187,7 @@ gdk_event_source_translate_event (GdkEventSource *event_source,
       if (filter_private->filters)
 	{
 	  result = gdk_event_apply_filters (xevent, event,
-					    filter_private->filters);
+					    &filter_private->filters);
 
           if (result == GDK_FILTER_REMOVE)
             {