Issue 6969 - Implement abort-on-property-read snippet

lib/content/snippets.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 34 matching lines @@
  */
 function toRegExp(pattern)
 {
   if (pattern.length >= 2 && pattern[0] == "/" &&
       pattern[pattern.length - 1] == "/")
   {
     return new RegExp(pattern.substring(1, pattern.length - 1));
   }
 
   return new RegExp(regexEscape(pattern));
+}
+
+/**
+ * Returns the value of the <code>cssText</code> property of the object
+ * returned by <code>getComputedStyle</code> for the given element. If the
+ * value of the <code>cssText</code> property is blank, this function computes
+ * the value out of the properties available in the object.
+ *
+ * @param {Element} element The element for which to get the computed CSS text.
+ *
+ * @returns {string} The computed CSS text.
+ */
+function getComputedCSSText(element)
+{
+  let style = getComputedStyle(element);
+  let {cssText} = style;
+
+  if (cssText)
+    return cssText;
+
+  for (let property of style)
+    cssText += `${property}: ${style[property]}; `;
+
+  return cssText.trim();
 }
 
 /**
  * Injects JavaScript code into the document using a temporary
  * <code>script</code> element.
  *
  * @param {string} code The code to inject.
  * @param {Array.<function|string>} [dependencies] A list of dependencies
  *   to inject along with the code. A dependency may be either a function or a
  *   string containing some executable code.
@@ skipping 295 matching lines @@
 
   let styleRegExp = style ? toRegExp(style) : null;
   let searchStyleRegExp = searchStyle ? toRegExp(searchStyle) : null;
 
   new MutationObserver(() =>
   {
     for (let element of document.querySelectorAll(searchSelector))
     {
       if (searchRegExp.test(element.textContent) &&
           (!searchStyleRegExp ||
-           searchStyleRegExp.test(getComputedStyle(element).cssText)))
+           searchStyleRegExp.test(getComputedCSSText(element))))
       {
         let closest = element.closest(selector);
         if (closest && (!styleRegExp ||
-                        styleRegExp.test(getComputedStyle(closest).cssText)))
+                        styleRegExp.test(getComputedCSSText(closest))))
         {
           hideElement(closest);
         }
       }
     }
   })
   .observe(document, {childList: true, characterData: true, subtree: true});
 }
 
 exports["hide-if-contains-and-matches-style"] = hideIfContainsAndMatchesStyle;
@@ skipping 45 matching lines @@
     for (let i = 0; i < times; i++)
       object + "";
 
     if (typeof dir == "function")
       dir.call(this, object);
   };
 }
 
 exports["dir-string"] = makeInjector(dirString);
 
+/**
+ * Prevents the execution of inline scripts.
+ *
+ * Only on Firefox.
+ *
+ * @param {string} [search] If specified, only scripts containing the given
+ *   string are prevented from executing. If the string begins and ends with a
+ *   slash (<code>/</code>), the text in between is treated as a regular
+ *   expression.
+ * @param {string} [selector] If specified, only scripts whose HTML element
+ *   matches the given CSS selector are prevented from executing.
+ */
+function preventInlineScripts(search = null, selector = null)
+{
+  let re = search ? toRegExp(search) : null;
+
+  document.addEventListener("beforescriptexecute", event =>
+  {
+    let {target} = event;
+
+    if ((!selector || target.matches(selector)) &&
+        (!re || re.test(target.textContent)))
+    {
+      event.preventDefault();
+    }
+  },
+  true);
+}
+
+exports["prevent-inline-scripts"] = preventInlineScripts;
+
+/**
+ * Generates a random alphanumeric ID consisting of 6 base-36 digits
+ * from the range 100000..zzzzzz (both inclusive).
+ *
+ * @returns {string} The random ID.
+ */
 function randomId()
 {
   // 2176782336 is 36^6 which mean 6 chars [a-z0-9]
   // 60466176 is 36^5
-  // 2176782336 - 60466176 = 2116316160. This ensure always 6 chars
-  // for when Math.random() returns 0.0
-  return (Math.floor(Math.random() * 2116316160 + 60466176)).toString(36);

[Manish Jethani, 2018/09/25 12:25:22]

Nit: The parentheses around `Math.foor(...)` are unnecessary.

[hub, 2018/09/25 15:40:43]

Done.

-}
-
-/**
- * Will patch a property on the window object to abort when read.
- * It will intercept the onerror callback and block it if tagged.
- *
- * @todo handle properties of properties.
- *
- * @param {string} prop the name of the property.
- */
-function abortOnPropertyRead(...props)
-{
-  if (props.length == 0)
+  // 2176782336 - 60466176 = 2116316160. This ensure to always have 6
+  // chars even if Math.random() returns its minimum value 0.0
+  //
+  return Math.floor(Math.random() * 2116316160 + 60466176).toString(36);
+}
+
+function wrapPropertyAccess(object, property, descriptor)
+{
+  let currentDescriptor = Object.getOwnPropertyDescriptor(object, property);
+  if (currentDescriptor && !currentDescriptor.configurable)
+    return false;
+
+  Object.defineProperty(object, property, descriptor);
+  return true;
+}
+
+/**
+ * Patches a property on the window object to abort execution when the
+ * property is read.
+ *
+ * No error is be printed to the console.
+ *
+ * The idea originates from
+ * {@link https://github.com/uBlockOrigin/uAssets/blob/80b195436f8f8d78ba713237bfc268ecfc9d9d2b/filters/resources.txt#L1703 uBlock Origin}.
+ *
+ * @param {string} property The name of the property.
+ */
+function abortOnPropertyRead(property)
+{
+  if (!property)
     return;
 
-  let magic = randomId();
-
-  let abort = function()
-  {
-    throw new ReferenceError(magic);
-  };
+  let rid = randomId();
+
+  function abort()
+  {
+    throw new ReferenceError(rid);
+  }
 
   let {onerror} = window;
-  window.onerror = (message, ...rest) =>
-  {
-    if (typeof message == "string" && message.includes(magic))
-      return true;
-    if (onerror && typeof onerro == "function")
-      return onerror(this, message, ...rest);
-  };
-
-  let patch = function(o, p)
-  {
-    // simple property
-    let d = Object.getOwnPropertyDescriptor(o, p);
-    if (!d || d.get != abort)
-      Object.defineProperty(o, p, {get: abort, set() {}});
-  };
-  for (let prop of props)
-    patch(window, prop);
-}
-
-exports["abort-on-property-read"] = makeInjector(abortOnPropertyRead, randomId);
+  if (wrapPropertyAccess(window, property, {get: abort, set() {}}))
+  {
+    window.onerror = (message, ...rest) =>
+    {
+      if (typeof message == "string" && message.includes(rid))
+        return true;
+      if (typeof onerror == "function")
+        return (() => {}).call.call(onerror, this, message, ...rest);
+    };
+  }
+}
+
+exports["abort-on-property-read"] = makeInjector(abortOnPropertyRead,
+                                                 wrapPropertyAccess,
+                                                 randomId);