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
@@ skipping 332 matching lines @@
   var observer = new MutationObserver(function()
   {
     if (style.parentNode != parentNode)
       parentNode.appendChild(style);
   });
 
   observer.observe(parentNode, {childList: true});
   return observer;
 }
 
-function injectJS(f)
-{
-  var args = JSON.stringify(Array.prototype.slice.call(arguments, 1));
-  args = args.substring(1, args.length - 1);
-  var codeString = "(" + f.toString() + ")(" + args + ");";
-
+function runInPage(fn, arg)
+{
   var script = document.createElement("script");
+  script.type = "application/javascript";
   script.async = false;
-  script.textContent = codeString;
+  script.textContent = "(" + fn + ")(" + JSON.stringify(arg) + ");";
   document.documentElement.appendChild(script);
   document.documentElement.removeChild(script);
 }
 
 function protectStyleSheet(document, style)
 {
   style.id = id;
 
-  var protector = function(id)
+  runInPage(function(id)
   {
     var style = document.getElementById(id) ||
                 document.documentElement.shadowRoot.getElementById(id);
     style.removeAttribute("id");
 
-    var i;
     var disableables = [style, style.sheet];
-    for (i = 0; i < disableables.length; i += 1)
+    for (var i = 0; i < disableables.length; i++)
       Object.defineProperty(disableables[i], "disabled",
                             {value: false, enumerable: true});
 
-    var methods = ["deleteRule", "removeRule"];
-    for (i = 0; i < methods.length; i += 1)
-    {
-      if (methods[i] in CSSStyleSheet.prototype)
-      {
-        (function(method)
-        {
-          var original = CSSStyleSheet.prototype[method];
-          CSSStyleSheet.prototype[method] = function(index)
-          {
-            if (this != style.sheet)
-              original.call(this, index);
-          };
-        }(methods[i]));
-      }
-    }
-  };
-
-  injectJS(protector, id);
+    ["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. We go to some lengths to avoid breaking code
-// using WebSockets, circumvention and as far as possible detection.
+// connections from being opened.
 // [1] - https://bugs.chromium.org/p/chromium/issues/detail?id=129353
 function wrapWebSocket()
 {
-  if (typeof WebSocket == "undefined" ||
-      typeof WeakMap == "undefined" ||
-      typeof Proxy == "undefined")
+  if (typeof WebSocket == "undefined")
     return;
 
   var eventName = "abpws-" + id;
 
   document.addEventListener(eventName, function(event)
   {
     ext.backgroundPage.sendMessage({
       type: "websocket-request",
       url: event.detail.url
     }, function (block)
     {
       document.dispatchEvent(
         new CustomEvent(eventName + "-" + event.detail.url, {detail: block})
       );
     });
   });
 
-  function wrapper(eventName)
-  {
+  runInPage(function(eventName)
+  {
+    // 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;
-
-    function checkRequest(url, protocols, callback)
+    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 incomingEventName = eventName + "-" + url;
       function listener(event)
       {
         callback(event.detail);
-        document.removeEventListener(incomingEventName, listener);
-      }
-      document.addEventListener(incomingEventName, listener);
-
-      document.dispatchEvent(new CustomEvent(eventName, {
-        detail: {url: url, protocols: protocols}
+        removeEventListener(incomingEventName, listener);
+      }
+      addEventListener(incomingEventName, listener);
+
+      dispatchEvent(new CustomEvent(eventName, {
+        detail: {url: url}
       }));
     }
 
-    // We need to store state for our wrapped WebSocket instances, that webpages
-    // can't access. We use a WeakMap to avoid leaking memory in the case that
-    // all other references to a WebSocket instance have been deleted.
-    var instanceStorage = new WeakMap();
-
-    var eventNames = ["close", "open", "message", "error"];
-    var eventAttrNames = ["onclose", "onopen", "onmessage", "onerror"];
-
-    function addRemoveEventListener(storage, key, type, listener)

[kzar, 2016/07/12 11:34:32]

Should we care about the useCapture parameter for addEventListener? So far I
just ignore it.

-    {
-      if (typeof listener == "object")
-        listener = listener.handleEvent;
-
-      if (!(eventNames.indexOf(type) > -1 && typeof listener == "function"))
-        return;
-
-      var listeners = storage.listeners[type];
-      var listenerIndex = listeners.indexOf(listener);
-
-      if (key == "addEventListener")
-      {
-        if (listenerIndex == -1)
-          listeners.push(listener);
-      }
-      else if (listenerIndex > -1)
-        listeners.splice(listenerIndex, 1);
-    }
-
-    // We check if a WebSocket should be blocked before actually creating it. As
-    // this is done asynchonously we must queue up any actions (method calls and
-    // assignments) that happen in the mean time.
-    // Once we have a result, we create the WebSocket (if allowed) and perform
-    // the queued actions.
-    function processQueue(storage)

[kzar, 2016/07/12 11:34:33]

Queuing up assignments and method calls seems rather pointless now that we
manage events ourselves. In my testing I couldn't find any website which use
this, it's usual to wait for a connection to be opened before attempting to send
for example. I'd like to remove storage.queue and all related logic, any
opinions?

-    {
-      for (var i = 0; i < storage.queue.length; i += 1)
-      {
-        var action = storage.queue[i][0];
-        var key = storage.queue[i][1];
-        var value = storage.queue[i][2];
-
-        if (action == "set")
-          storage.websocket[key] = value;
-        else if (action == "call")
-          storage.websocket[key].apply(storage.websocket, value);
-      }
-    }
-
-    var defaults = {
-      readyState: RealWebSocket.CONNECTING,
-      bufferedAmount: 0,
-      extensions: "",
-      binaryType: "blob"
-    };
-
-    // We cannot dispatch WebSocket events directly to their listeners since
-    // event.target would give a way back to the original WebSocket constructor.
-    // Instead we must listen for events ourselves and pass them on, taking care
-    // to spoof the event target and isTrusted flag.
-    function wrappedEventListener(name, me)
-    {
-      var storage = instanceStorage.get(me);
-      return function(event)
-      {
-        var eventProxy = new Proxy(event, {
-          get: function(target, key)
-          {
-            if (key == "isTrusted" && "isTrusted" in target)
-              return true;
-            if (key == "target" || key == "srcElement" || key == "currentTarget")
-              return me;
-            return target[key];
-          }
-        });
-
-        var listeners = storage.listeners[name];
-        for (var i = 0; i < listeners.length; i += 1)
-          listeners[i].call(me, eventProxy);
-        var listener = storage.listeners["on" + name];
-        if (typeof listener == "function")
-          listener.call(me, eventProxy);
-      };
-    }
-
-    WebSocket = function(url, protocols)

[kzar, 2016/07/12 11:34:33]

So far I don't intercept WebSocket.toString() so it could be used to detect us.
I'm inclined to wrap WebSocket in a Proxy to fix that. On the other hand this
code is already too complex for my taste. Opinions?

[lainverse, 2016/07/12 12:22:20]

If we going all the way to avoid detection then we have to. However, make sure
to handle chained toString calls and calls on functions, like
ws.toString.toString(), ws.close.toString(). Also, there is toLocaleString
function with the same output (not sure if some specificl locale parameters
provided, but should be the same).

-    {
-      var me = this;
-      var storage = {
-        url: url,
-        protocol: protocols || "",
-        queue: [],
-        websocket: null,
-        blocked: false,
-        listeners: {
-          onclose: null,
-          onopen: null,
-          onmessage: null,
-          onerror: null,
-          close: [],
-          open: [],
-          message: [],
-          error: []
-        }
-      };
-      instanceStorage.set(me, storage);
-
-      checkRequest(url, protocols, function(blocked)
+    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 websocket = new RealWebSocket(url, protocols);
+
+      checkRequest(websocket.url, function(blocked)
       {
         if (blocked)
-        {
-          storage.blocked = true;
-          wrappedEventListener("error", me)(new Error("error"));
-        }
-        else
-        {
-          storage.websocket = new RealWebSocket(url, protocols);
-          for (var i = 0; i < eventNames.length; i += 1)

[kzar, 2016/07/12 11:34:32]

If a website creates a WebSocket (which manages to connect), doesn't add a close
event listener and then deletes all references to it the WebSocket should be
garbage collected.

As we always add a close event listener here the (actual, not wrapper of)
WebSocket wouldn't be garbage collected until the connection was closed.
Personally I don't think this is a big deal, and certainly not worth the extra
logic to fix. Any opinions?

-            storage.websocket.addEventListener(
-              eventNames[i],
-              wrappedEventListener(eventNames[i], me)
-            );
-          processQueue(storage);
-        }
-        delete storage.queue;
+          closeWebSocket(websocket);
       });
-    };
+
+      return websocket;
+    }.bind();
+
     Object.defineProperties(WebSocket, {
-      CONNECTING: {value: 0, enumerable: true},
-      OPEN: {value: 1, enumerable: true},
-      CLOSING: {value: 2, enumerable: true},
-      CLOSED: {value: 3, enumerable: true}
+      CONNECTING: {value: RealWebSocket.CONNECTING, enumerable: true},
+      OPEN: {value: RealWebSocket.OPEN, enumerable: true},
+      CLOSING: {value: RealWebSocket.CLOSING, enumerable: true},
+      CLOSED: {value: RealWebSocket.CLOSED, enumerable: true},
+      prototype: {value: RealWebSocket.prototype}
     });
-    WebSocket.prototype = new Proxy(RealWebSocket.prototype,{
-      set: function(target, key, value, me)
-      {
-        var storage = instanceStorage.get(me);
-
-        if (!storage)
-          target[key] = value;
-        else if (eventAttrNames.indexOf(key) > -1)
-          storage.listeners[key] = value;
-        else if (storage.websocket)
-          storage.websocket[key] = value;
-        else if (!storage.blocked)
-          storage.queue.push(["set", key, value]);
-
-        return true;
-      },
-      get: function(target, key, me)
-      {
-        if (key == "__proto__" && me != WebSocket.prototype)
-          return WebSocket.prototype;
-
-        if (key == "constructor")
-          return WebSocket;
-
-        var storage = instanceStorage.get(me);
-        if (!storage)
-          return target[key];
-
-        if (key == "addEventListener" || key == "removeEventListener")
-          return function()
-          {
-            if (arguments.length > 1)
-              addRemoveEventListener(storage, key, arguments[0], arguments[1]);
-          };
-
-        if (eventAttrNames.indexOf(key) > -1)
-          return storage.listeners[key];
-
-        var desc = Object.getOwnPropertyDescriptor(target, key);
-        if (desc && typeof desc.value == "function")
-          return function()
-          {
-            if (storage.websocket)
-              storage.websocket[key].apply(storage.websocket, arguments);
-            else if (!storage.blocked)
-              storage.queue.push(["call", key, arguments]);
-          };
-
-        if (storage.websocket)
-          return storage.websocket[key];
-        if (key == "url" || key == "protocol")
-          return storage[key];
-        if (storage.blocked && key == "readyState")
-          return WebSocket.CLOSED;
-        if (key in defaults)
-          return defaults[key];
-        return undefined;
-      }
-    });
-  }
-
-  injectJS(wrapper, eventName);
+
+    RealWebSocket.prototype.constructor = WebSocket;
+  }, eventName);
 }
 
 function init(document)
 {
   var shadow = null;
   var style = null;
   var observer = null;
   var tracer = null;
 
   wrapWebSocket();
@@ skipping 161 matching lines @@
   }, true);
 
   return updateStylesheet;
 }
 
 if (document instanceof HTMLDocument)
 {
   checkSitekey();
   window.updateStylesheet = init(document);
 }