[Webkit-unassigned] [Bug 161534] Regression(r197648): JSObject::setPrototypeWithCycleCheck() allows for cycles but the rest of the code base does not

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=161534

--- Comment #3 from Chris Dumez <cdumez at apple.com> ---
(In reply to comment #2)
> > Yeah, we should teach the rest of the engine that it's OK to have cycles
> > in the "getPrototypeDirect" chain.
> > Currently, inside JSC itself, this will never happen. However, I guess we
> > need to
> > teach it this w.r.t the HTML spec.
> 
> That's a pretty big change. Are we sure we need to allow cycles? What's the
> expected behavior if you find a cycle? Is it specified?

Note that even without my patch, it is fairly trivial to end up with an infinite loop since r197648 allows for cycles:

<script>
var target = {
  __proto__: null
};
var proxy = new Proxy(target, {});
Object.prototype.__proto__ = {
   __proto__: proxy,
};

var a = {};
a.test;
</script>

This seems to infinite loop for me on ToT, no DOM involved.

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