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LibJS: Guard against stack overflow in ProxyObject has_property()

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If proxy has an undefined trap, it will fallback to target's
internal_has_property, which will then check target's prototype for
the requested property. If Proxy's prototype is set to the Proxy itself,
it will check in itself in a loop, causing a stack overflow.
This commit is contained in:
Maciej 2023-05-04 14:32:37 +02:00 • committed by Tim Flynn
parent e7502d4d6d
commit 52a5a42147
2 changed files with 30 additions and 0 deletions
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13
Userland/Libraries/LibJS/Runtime/ProxyObject.cpp
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@ -402,6 +402,19 @@ ThrowCompletionOr<bool> ProxyObject::internal_has_property(PropertyKey const& pr
// 3. Assert: Type(handler) is Object.
// 4. Let target be O.[[ProxyTarget]].
// NOTE: We need to protect ourselves from a Proxy with the handler's prototype set to the
// Proxy itself, which would by default bounce between these functions indefinitely and lead to
// a stack overflow when the Proxy's (p) or Proxy handler's (h) Object::get() is called and the
// handler doesn't have a `has` trap:
//
// 1. p -> ProxyObject::internal_has_property() <- you are here
// 2. target -> Object::internal_has_property()
// 3. target.[[Prototype]] (which is internal_has_property) -> Object::internal_has_property()
//
// In JS code: `const proxy = new Proxy({}, {}); proxy.__proto__ = Object.create(proxy); "foo" in proxy;`
if (vm.did_reach_stack_space_limit())
return vm.throw_completion<InternalError>(ErrorType::CallStackSizeExceeded);
// 5. Let trap be ? GetMethod(handler, "has").
auto trap = TRY(Value(m_handler).get_method(vm, vm.names.has));