Fix popunders spawned from a subframe.

content/browser/web_contents/web_contents_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/web_contents/web_contents_impl.h"
 
 #include <stddef.h>
 
 #include <cmath>
 #include <utility>
@@ skipping 582 matching lines @@
 
 WebContentsImpl* WebContentsImpl::CreateWithOpener(
     const WebContents::CreateParams& params,
     FrameTreeNode* opener) {
   TRACE_EVENT0("browser", "WebContentsImpl::CreateWithOpener");
   WebContentsImpl* new_contents = new WebContentsImpl(params.browser_context);
 
   FrameTreeNode* new_root = new_contents->GetFrameTree()->root();
 
   if (opener) {
-    new_root->SetOriginalOpener(opener);
+    // For the "original opener", track the opener's main frame instead, because
+    // if the opener is a subframe, the opener tracking could be easily bypassed
+    // by spawning from a subframe and deleting the subframe.
+    // https://crbug.com/705316
+    new_root->SetOriginalOpener(opener->frame_tree()->root());
+
     if (!params.opener_suppressed) {
       new_root->SetOpener(opener);
       new_contents->created_with_opener_ = true;
     }
   }
 
   // If the opener is sandboxed, a new popup must inherit the opener's sandbox
   // flags, and these flags take effect immediately.  An exception is if the
   // opener's sandbox flags lack the PropagatesToAuxiliaryBrowsingContexts
   // bit (which is controlled by the "allow-popups-to-escape-sandbox" token).
@@ skipping 4784 matching lines @@
     RenderViewHost* render_view_host = RenderViewHost::From(render_widget_host);
     if (!render_view_host)
       continue;
     render_view_host_set.insert(render_view_host);
   }
   for (RenderViewHost* render_view_host : render_view_host_set)
     render_view_host->OnWebkitPreferencesChanged();
 }
 
 }  // namespace content