Hi,
Half a million times the following meta-exchange happened on es-discuss:
- if an attacker modifies Object.prototype, then you're doomed in all
sorts of ways
- Don't let anyone modify it. Just do Object.freeze(Object.prototype)!
I've done it on client-side projects with reasonable success. I've just
tried on a Node project and lots of dependencies started throwing
errors. (I imagine the difference is that in Node, it's easy to create
projects with a big tree of dependencies which I haven't done too much
on the client side).
I tracked down a few of these errors and they all seem to relate to the
override mistake [1].
* In jsdom [2], trying to add a "constructor" property to an object
fails because Object.prototype.constructor is configurable: false,
writable: false
* in tough-cookie [3] (which is a dependency of the popular 'request'
module), trying to set Cookie.prototype.toString fails because
Object.prototype.toString is configurable: false, writable: false
Arguably, they could use Object.defineProperty, but they won't because
it's less natural and it'd be absurd to try to fix npm. The
Cookie.prototype.toString case is interesting. Of all the methods being
added, only toString causes a problem. Using Object.defineProperty for
this one would be an awkward inconsistency.
So, we're in a state where no module needs to modify Object.prototype,
but I cannot freeze it because the override mistake makes throw any
script that tries to set a toString property to an object.
Because of the override mistake, either I have to let Object.prototype
mutable (depite no module needing it to be mutable) or freeze it first
hand and not use popular modules like jsdom or request.
It's obviously possible to replace all built-in props by accessors [4],
of course, but this is a bit ridiculous.
Can the override mistake be fixed? I imagine no web compat issues would
occur since this change is about throwing less errors.
David
[1] http://wiki.ecmascript.org/doku.php?id=strawman:fixing_override_mistake
[2]
https://github.com/tmpvar/jsdom/blob/6c5fe5be8cd01e0b4e91fa96d025341aff1db291/lib/jsdom/utils.js#L65-L95
[3]
https://github.com/goinstant/tough-cookie/blob/c66bebadd634f4ff5d8a06519f9e0e4744986ab8/lib/cookie.js#L694
[4]
https://github.com/rwaldron/tc39-notes/blob/c61f48cea5f2339a1ec65ca89827c8cff170779b/es6/2012-07/july-25.md#fix-override-mistake-aka-the-can-put-check
_______________________________________________
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss
