LibWeb: Make frames nesting-aware and disallow deep nesting

A Frame now knows about its nesting-level.

The FrameLoader checks whether the recursion level of the current
frame allows it to be displayed and if not doesn't even load the
requested resource.

The nesting-check is done on a per-URL-basis, so there can be many many
nested Frames as long as they have different URLs.
If there are however Frames with the same URL nested inside each other
we only allow this to happen 3 times.

This mitigates infinetely recursing <iframe>s in an HTML-document
crashing the browser with an OOM.

Userland/Libraries/LibWeb/HTML/FrameHostElement.cpp

@@ -26,8 +26,11 @@ void FrameHostElement::inserted()
     HTMLElement::inserted();
     if (!is_connected())
         return;
-    if (auto* frame = document().frame())
+    if (auto* frame = document().frame()) {
         m_content_frame = Frame::create_subframe(*this, frame->main_frame());
+        m_content_frame->set_frame_nesting_levels(frame->frame_nesting_levels());
+        m_content_frame->register_frame_nesting(document().url());
+    }
 }
 
 Origin FrameHostElement::content_origin() const

Userland/Libraries/LibWeb/Loader/FrameLoader.cpp

@@ -136,6 +136,11 @@ bool FrameLoader::load(const LoadRequest& request, Type type)
         return false;
     }
 
+    if (!m_frame.is_frame_nesting_allowed(request.url())) {
+        dbgln("No further recursion is allowed for the frame, abort load!");
+        return false;
+    }
+
     auto& url = request.url();
 
     set_resource(ResourceLoader::the().load_resource(Resource::Type::Generic, request));

Userland/Libraries/LibWeb/Page/Frame.cpp

@@ -286,4 +286,14 @@ void Frame::unregister_viewport_client(ViewportClient& client)
     VERIFY(was_removed);
 }
 
+void Frame::register_frame_nesting(URL const& url)
+{
+    m_frame_nesting_levels.ensure(url)++;
+}
+
+bool Frame::is_frame_nesting_allowed(URL const& url) const
+{
+    return m_frame_nesting_levels.get(url).value_or(0) < 3;
+}
+
 }

Userland/Libraries/LibWeb/Page/Frame.h

@@ -81,6 +81,12 @@ public:
 
     void did_edit(Badge<EditEventHandler>);
 
+    void register_frame_nesting(URL const&);
+    bool is_frame_nesting_allowed(URL const&) const;
+
+    void set_frame_nesting_levels(const HashMap<URL, size_t> frame_nesting_levels) { m_frame_nesting_levels = move(frame_nesting_levels); };
+    HashMap<URL, size_t> const& frame_nesting_levels() const { return m_frame_nesting_levels; }
+
 private:
     explicit Frame(DOM::Element& host_element, Frame& main_frame);
     explicit Frame(Page&);
@@ -105,6 +111,8 @@ private:
     bool m_cursor_blink_state { false };
 
     HashTable<ViewportClient*> m_viewport_clients;
+
+    HashMap<URL, size_t> m_frame_nesting_levels;
 };
 
 }