Use about:blank as the failback URL if the filter denies a navigation.

content/browser/renderer_host/render_view_host_impl.cc

Index: content/browser/renderer_host/render_view_host_impl.cc
===================================================================
--- content/browser/renderer_host/render_view_host_impl.cc	(revision 127913)
+++ content/browser/renderer_host/render_view_host_impl.cc	(working copy)
@@ -495,7 +495,7 @@
   // The URL could have been cobbled together from any highlighted text string,
   // and can't be interpreted as a capability.
   WebDropData filtered_data(drop_data);
-  FilterURL(policy, renderer_id, &filtered_data.url);
+  FilterURL(policy, renderer_id, false, &filtered_data.url);
 
   // The filenames vector, on the other hand, does represent a capability to
   // access the given files.
@@ -1039,15 +1039,15 @@
   // renderer to load the URL and grant the renderer the privileges to request
   // the URL.  To prevent this attack, we block the renderer from inserting
   // banned URLs into the navigation controller in the first place.
-  FilterURL(policy, renderer_id, &validated_params.url);
-  FilterURL(policy, renderer_id, &validated_params.referrer.url);
+  FilterURL(policy, renderer_id, false, &validated_params.url);
+  FilterURL(policy, renderer_id, true, &validated_params.referrer.url);
   for (std::vector<GURL>::iterator it(validated_params.redirects.begin());
       it != validated_params.redirects.end(); ++it) {
-    FilterURL(policy, renderer_id, &(*it));
+    FilterURL(policy, renderer_id, false, &(*it));
   }
-  FilterURL(policy, renderer_id, &validated_params.searchable_form_url);
-  FilterURL(policy, renderer_id, &validated_params.password_form.origin);
-  FilterURL(policy, renderer_id, &validated_params.password_form.action);
+  FilterURL(policy, renderer_id, true, &validated_params.searchable_form_url);
+  FilterURL(policy, renderer_id, true, &validated_params.password_form.origin);
+  FilterURL(policy, renderer_id, true, &validated_params.password_form.action);
 
   delegate_->DidNavigate(this, validated_params);
 }
@@ -1139,10 +1139,10 @@
 
   // We don't validate |unfiltered_link_url| so that this field can be used
   // when users want to copy the original link URL.
-  FilterURL(policy, renderer_id, &validated_params.link_url);
-  FilterURL(policy, renderer_id, &validated_params.src_url);
-  FilterURL(policy, renderer_id, &validated_params.page_url);
-  FilterURL(policy, renderer_id, &validated_params.frame_url);
+  FilterURL(policy, renderer_id, true, &validated_params.link_url);
+  FilterURL(policy, renderer_id, true, &validated_params.src_url);
+  FilterURL(policy, renderer_id, false, &validated_params.page_url);
+  FilterURL(policy, renderer_id, true, &validated_params.frame_url);
 
   view->ShowContextMenu(validated_params);
 }
@@ -1159,7 +1159,7 @@
                                       int64 source_frame_id) {
   GURL validated_url(url);
   FilterURL(ChildProcessSecurityPolicyImpl::GetInstance(),
-            GetProcess()->GetID(), &validated_url);
+            GetProcess()->GetID(), false, &validated_url);
 
   delegate_->RequestOpenURL(
       validated_url, referrer, disposition, source_frame_id);
@@ -1244,8 +1244,8 @@
 
   // Allow drag of Javascript URLs to enable bookmarklet drag to bookmark bar.
   if (!filtered_data.url.SchemeIs(chrome::kJavaScriptScheme))
-    FilterURL(policy, GetProcess()->GetID(), &filtered_data.url);
-  FilterURL(policy, GetProcess()->GetID(), &filtered_data.html_base_url);
+    FilterURL(policy, GetProcess()->GetID(), false, &filtered_data.url);
+  FilterURL(policy, GetProcess()->GetID(), false, &filtered_data.html_base_url);
   view->StartDragging(filtered_data, drag_operations_mask, image, image_offset);
 }
 
@@ -1448,10 +1448,20 @@
 
 void RenderViewHostImpl::FilterURL(ChildProcessSecurityPolicyImpl* policy,
                                    int renderer_id,
+                                   bool empty_allowed,
                                    GURL* url) {
-  if (!url->is_valid())
-    return;  // We don't need to block invalid URLs.
+  if (empty_allowed && url->is_empty())
+    return;
 
+  if (!url->is_valid()) {
+    // Have to use about:blank for the denied case, instead of an empty GURL.
+    // This is because the browser treats navigation to an empty GURL as a
+    // navigation to the home page. This is often a privileged page
+    // (chrome://newtab/) which is exactly what we don't want.
+    *url = GURL(chrome::kAboutBlankURL);
+    return;
+  }
+
   if (url->SchemeIs(chrome::kAboutScheme)) {
     // The renderer treats all URLs in the about: scheme as being about:blank.
     // Canonicalize about: URLs to about:blank.
@@ -1463,7 +1473,7 @@
     // URL.  This prevents us from storing the blocked URL and becoming confused
     // later.
     VLOG(1) << "Blocked URL " << url->spec();
-    *url = GURL();
+    *url = GURL(chrome::kAboutBlankURL);
   }
 }