On Tue, Nov 8, 2011 at 11:29 AM, Andreas Rossberg <rossb...@google.com>wrote:
> On 8 November 2011 19:13, Mark S. Miller <erig...@google.com> wrote: > > The reason Proxy.attach may not be fatal is that it only allows > attachment > > to extensible objects. Our hypothesis is that any ES5 object that is > > interested in defending itself has already made itself non-extensible. > This > > is why we must key this off of non-extensibility, rather than > introducing a > > new orthogonal bit -- to avoid breaching the defenses of those ES5 era > > objects that tried to defend themselves. > > I don't think that addresses the issue I was describing. The problem > is: the object itself can all be frozen, non-extensible, > non-attachable just fine, but that doesn't achieve much by itself > anymore because an attacker can still attach to each individual > method, since they are entirely separate objects! > > So instead of just freezing an object, you _additionally_ would have > to make all its _individual methods_ non-attachable (by whatever > means). AFAICS, that affects assumptions of existing ES5 code quite > severely. In general, for an object to be defensive, much of the surface reachable from it by transitive prototype and reflective property traversal should usually be frozen, and at least non-extensible. This is possible to express in ES5 < http://code.google.com/p/google-caja/source/browse/trunk/src/com/google/caja/ses/startSES.js#623>, but inconvenient and expensive. That's why I have been advocating better defensive abstractions for ES6: "const functions", "const classes", "traitsjs" or its syntactic derivatives, etc. Nevertheless, I see your point. Many defensive ES5 abstractions will be less defensive than this. If I understand you correctly, your point is specifically about the [[Call]] and [[Construct]] traps. Perhaps we should be more conservative here, without necessarily backing away from the whole Proxy.attach idea? -- Cheers, --MarkM
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