Issue 1727 - Prevent circumvention via WebSocket

include.preload.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
 var SELECTOR_GROUP_SIZE = 200;
+var id = Math.random().toString(36).substr(2);
 
 var typeMap = {
   "img": "IMAGE",
   "input": "IMAGE",
   "picture": "IMAGE",
   "audio": "MEDIA",
   "video": "MEDIA",
   "frame": "SUBDOCUMENT",
   "iframe": "SUBDOCUMENT",
   "object": "OBJECT",
@@ skipping 312 matching lines @@
   var observer = new MutationObserver(function()
   {
     if (style.parentNode != parentNode)
       parentNode.appendChild(style);
   });
 
   observer.observe(parentNode, {childList: true});
   return observer;
 }
 
+function runInPage(fn, arg)
+{
+  var script = document.createElement("script");
+  script.type = "application/javascript";
+  script.async = false;
+  script.textContent = "(" + fn + ")(" + JSON.stringify(arg) + ");";
+  document.documentElement.appendChild(script);
+  document.documentElement.removeChild(script);
+}
+
 function protectStyleSheet(document, style)
 {
-  var id = Math.random().toString(36).substr(2)
   style.id = id;
 
-  var code = [
-    "(function()",
-    "{",
-    '  var style = document.getElementById("' + id + '") ||',
-    '              document.documentElement.shadowRoot.getElementById("' + id + '");',
-    '  style.removeAttribute("id");'
-  ];
+  runInPage(function(id)
+  {
+    var style = document.getElementById(id) ||
+                document.documentElement.shadowRoot.getElementById(id);
+    style.removeAttribute("id");
 
-  var disableables = ["style", "style.sheet"];
-  for (var i = 0; i < disableables.length; i++)
+    var disableables = [style, style.sheet];
+    for (var i = 0; i < disableables.length; i++)
+      Object.defineProperty(disableables[i], "disabled",
+                            {value: false, enumerable: true});
+
+    ["deleteRule", "removeRule"].forEach(function(method)
+    {
+      var original = CSSStyleSheet.prototype[method];
+      CSSStyleSheet.prototype[method] = function(index)
+      {
+        if (this != style.sheet)
+          original.call(this, index);
+      };
+    });
+  }, id);
+}
+
+// Neither Chrome[1] nor Safari allow us to intercept WebSockets, and therefore
+// some ad networks are misusing them as a way to serve adverts and circumvent
+// us. As a workaround we wrap WebSocket, preventing blocked WebSocket
+// connections from being opened.
+// [1] - https://bugs.chromium.org/p/chromium/issues/detail?id=129353
+function wrapWebSocket()
+{
+  if (typeof WebSocket == "undefined")
+    return;
+
+  var eventName = "abpws-" + id;
+
+  document.addEventListener(eventName, function(event)
   {
-    code.push("  Object.defineProperty(" + disableables[i] + ', "disabled", '
-                                         + "{value: false, enumerable: true});");
-  }
+    ext.backgroundPage.sendMessage({
+      type: "websocket-request",
+      url: event.detail.url
+    }, function (block)
+    {
+      document.dispatchEvent(
+        new CustomEvent(eventName + "-" + event.detail.url, {detail: block})
+      );
+    });
+  });
 
-  var methods = ["deleteRule", "removeRule"];
-  for (var j = 0; j < methods.length; j++)
+  runInPage(function(eventName)
   {
-    var method = methods[j];
-    if (method in CSSStyleSheet.prototype)
+    // As far as possible we must track everything we use that could be
+    // sabotaged by the website later in order to circumvent us.
+    var RealWebSocket = WebSocket;
+    var closeWebSocket = Function.prototype.call.bind(RealWebSocket.prototype.close);
+    var addEventListener = document.addEventListener.bind(document);
+    var removeEventListener = document.removeEventListener.bind(document);
+    var dispatchEvent = document.dispatchEvent.bind(document);
+    var CustomEvent = window.CustomEvent;
+
+    function checkRequest(url, callback)
     {
-      var origin = "CSSStyleSheet.prototype." + method;
-      code.push("  var " + method + " = " + origin + ";",
-                "  " + origin + " = function(index)",
-                "  {",
-                "    if (this != style.sheet)",
-                "      " + method + ".call(this, index);",
-                "  }");
+      var incomingEventName = eventName + "-" + url;
+      function listener(event)
+      {
+        callback(event.detail);
+        removeEventListener(incomingEventName, listener);
+      }
+      addEventListener(incomingEventName, listener);
+
+      dispatchEvent(new CustomEvent(eventName, {
+        detail: {url: url}
+      }));
     }
-  }
 
-  code.push("})();");
+    WebSocket = function WrappedWebSocket(url, protocols)
+    {
+      // Throw correct exceptions if the constructor is used improperly.
+      if (!(this instanceof WrappedWebSocket)) return RealWebSocket();
+      if (arguments.length < 1) return new RealWebSocket();
 
-  var script = document.createElement("script");
-  script.async = false;
-  script.textContent = code.join("\n");
-  document.documentElement.appendChild(script);
-  document.documentElement.removeChild(script);
+      var websocket = new RealWebSocket(url, protocols);
+
+      checkRequest(websocket.url, function(blocked)
+      {
+        if (blocked)
+          closeWebSocket(websocket);
+      });
+
+      return websocket;
+    }.bind();
+
+    var properties = Object.getOwnPropertyNames(RealWebSocket);
+    for (var i = 0; i < properties.length; i++)
+    {
+      var name = properties[i];
+      var desc = Object.getOwnPropertyDescriptor(RealWebSocket, name);
+      Object.defineProperty(WebSocket, name, desc);
+    }
+
+    RealWebSocket.prototype.constructor = WebSocket;
+  }, eventName);
 }
 
 function init(document)
 {
   var shadow = null;
   var style = null;
   var observer = null;
   var tracer = null;
 
+  wrapWebSocket();
+
   function getPropertyFilters(callback)
   {
     ext.backgroundPage.sendMessage({
       type: "filters.get",
       what: "cssproperties"
     }, callback);
   }
   var propertyFilters = new CSSPropertyFilters(window, getPropertyFilters,
                                                addElemHideSelectors);
 
@@ skipping 150 matching lines @@
   }, true);
 
   return updateStylesheet;
 }
 
 if (document instanceof HTMLDocument)
 {
   checkSitekey();
   window.updateStylesheet = init(document);
 }