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deployed.

VULNERABILITY DETAILS
There's an integer overflow in computing the required allocation size when instantiating a new javascript object. 

See the following code in objects.cc

// static
bool JSFunction::CalculateInstanceSizeForDerivedClass(
    Handle<JSFunction> function, InstanceType instance_type,
    int requested_embedder_fields, int* instance_size,
    int* in_object_properties) {
  Isolate* isolate = function->GetIsolate();
  int expected_nof_properties = 0;
  bool result = true;
  for (PrototypeIterator iter(isolate, function, kStartAtReceiver);
       !iter.IsAtEnd(); iter.Advance()) {
    Handle<JSReceiver> current =
        PrototypeIterator::GetCurrent<JSReceiver>(iter);
    if (!current->IsJSFunction()) break;
    Handle<JSFunction> func(Handle<JSFunction>::cast(current));
    // The super constructor should be compiled for the number of expected
    // properties to be available.
    Handle<SharedFunctionInfo> shared(func->shared());
    if (shared->is_compiled() ||
        Compiler::Compile(func, Compiler::CLEAR_EXCEPTION)) {
      DCHECK(shared->is_compiled());
      expected_nof_properties += shared->expected_nof_properties(); // <--- overflow here!
    } else if (!shared->is_compiled()) {
      // In case there was a compilation error for the constructor we will
      // throw an error during instantiation. Hence we directly return 0;
      result = false;
      break;
    }
    if (!IsDerivedConstructor(shared->kind())) {
      break;
    }
  }
  CalculateInstanceSizeHelper(instance_type, true, requested_embedder_fields,
                              expected_nof_properties, instance_size,
                              in_object_properties);
  return result;
}

By supplying a long prototype chain of objects with a large expected_nof_properties we can control the resulting value of instance_size by causing (requested_embedder_fields + requested_in_object_properties) << kPointerSizeLog2 to be overflown to a small negative value, resulting in an allocation smaller than header_size, which is the minimum required size for the base object class being allocated. This results in memory corruption when the object is initialised/used.

void JSFunction::CalculateInstanceSizeHelper(InstanceType instance_type,
                                             bool has_prototype_slot,
                                             int requested_embedder_fields,
                                             int requested_in_object_properties,
                                             int* instance_size,
                                             int* in_object_properties) {
  int header_size = JSObject::GetHeaderSize(instance_type, has_prototype_slot);
  DCHECK_LE(requested_embedder_fields,
            (JSObject::kMaxInstanceSize - header_size) >> kPointerSizeLog2);
  *instance_size =
      Min(header_size +
              ((requested_embedder_fields + requested_in_object_properties)
               << kPointerSizeLog2),
          JSObject::kMaxInstanceSize);
  *in_object_properties = ((*instance_size - header_size) >> kPointerSizeLog2) -
                          requested_embedder_fields;
}

The attached PoC crashes current stable on linux.

See crash report ID: 307546648ba8a84a

This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.


VERSION
Chrome Version: Version 64.0.3282.119 (Official Build) (64-bit)
Operating System: Linux

REPRODUCTION CASE
Please include a demonstration of the security bug, such as an attached
HTML or binary file that reproduces the bug when loaded in Chrome. PLEASE
make the file as small as possible and remove any content not required to
demonstrate the bug.

FOR CRASHES, PLEASE INCLUDE THE FOLLOWING ADDITIONAL INFORMATION
Type of crash: renderer
Crash State: crash id 307546648ba8a84a
Client ID (if relevant): [see link above]

 

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