Ensure the permissions DOMTokenList is initialized before access

third_party/WebKit/Source/core/html/HTMLIFrameElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Simon Hausmann (hausmann@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2006, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Ericsson AB. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 43 matching lines @@
 
 HTMLIFrameElement::~HTMLIFrameElement()
 {
 }
 
 DOMTokenList* HTMLIFrameElement::sandbox() const
 {
     return m_sandbox.get();
 }
 
-DOMTokenList* HTMLIFrameElement::permissions() const
+DOMTokenList* HTMLIFrameElement::permissions()
 {
+    if (!initializePermissionsAttribute())

[esprehn, 2016/07/27 06:05:56]

How can this fail? Does the spec say it can be null?

I'm confused if null below can cause a crash why is returning null ever okay
here?

[raymes, 2016/07/27 06:13:45]

Sorry my description was inaccurate. It doesn't actually crash - it just doesn't
work properly if the attribute is initially accessed via JS. I've updated the
description. It did crash in the new test I added (without this change) because
it assumes this will be non-null.

+        return nullptr;
     return m_permissions.get();
 }
 
 bool HTMLIFrameElement::isPresentationAttribute(const QualifiedName& name) const
 {
     if (name == widthAttr || name == heightAttr || name == alignAttr || name == frameborderAttr)
         return true;
     return HTMLFrameElementBase::isPresentationAttribute(name);
 }
 
@@ skipping 110 matching lines @@
 {
     if (!RuntimeEnabledFeatures::permissionDelegationEnabled())
         return false;
 
     if (!m_permissions)
         m_permissions = HTMLIFrameElementPermissions::create(this);
     return true;
 }
 
 } // namespace blink