Merge r186666 - Plugin create can end up destroying its renderer.

https://bugs.webkit.org/show_bug.cgi?id=146824
rdar://problem/18921429

Reviewed by Andreas Kling.

Plugins can run arbitrary code during initialization. If the plugin
happens to destroy the associated node, its renderer becomes invalid.
This patch checks whether the renderer survived the createPlugin() call.
(This WeakPtr pattern is also used in RenderWidget to avoid dangling pointers.)

Speculative fix. Not reproducible.

* loader/SubframeLoader.cpp:
(WebCore::SubframeLoader::loadPlugin):

Source/WebCore/ChangeLog

@@ -1,3 +1,21 @@
+2015-07-09  Zalan Bujtas  <zalan@apple.com>
+
+        Plugin create can end up destroying its renderer.
+        https://bugs.webkit.org/show_bug.cgi?id=146824
+        rdar://problem/18921429
+
+        Reviewed by Andreas Kling.
+
+        Plugins can run arbitrary code during initialization. If the plugin
+        happens to destroy the associated node, its renderer becomes invalid.
+        This patch checks whether the renderer survived the createPlugin() call.
+        (This WeakPtr pattern is also used in RenderWidget to avoid dangling pointers.)
+
+        Speculative fix. Not reproducible.
+
+        * loader/SubframeLoader.cpp:
+        (WebCore::SubframeLoader::loadPlugin):
+
 2015-07-09  Daniel Bates  <dabates@apple.com>
 
         Fetching Content Security Policy report URL should respect same origin policy

Source/WebCore/loader/SubframeLoader.cpp

@@ -386,10 +386,12 @@ Document* SubframeLoader::document() const
 
 bool SubframeLoader::loadPlugin(HTMLPlugInImageElement& pluginElement, const URL& url, const String& mimeType, const Vector<String>& paramNames, const Vector<String>& paramValues, bool useFallback)
 {
-    RenderEmbeddedObject* renderer = pluginElement.renderEmbeddedObject();
+    if (useFallback)
+        return false;
 
+    RenderEmbeddedObject* renderer = pluginElement.renderEmbeddedObject();
     // FIXME: This code should not depend on renderer!
-    if (!renderer || useFallback)
+    if (!renderer)
         return false;
 
     pluginElement.subframeLoaderWillCreatePlugIn(url);
@@ -403,7 +405,11 @@ bool SubframeLoader::loadPlugin(HTMLPlugInImageElement& pluginElement, const URL
         loadManually = false;
 #endif
 
+    WeakPtr<RenderWidget> weakRenderer = renderer->createWeakPtr();
+    // createPlugin *may* cause this renderer to disappear from underneath.
     RefPtr<Widget> widget = m_frame.loader().client().createPlugin(contentSize, &pluginElement, url, paramNames, paramValues, mimeType, loadManually);
+    if (!weakRenderer)
+        return false;
 
     if (!widget) {
         if (!renderer->isPluginUnavailable())