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Re: ISSUE-111 - Exceptions are broken

From: Sid Stamm <sid@mozilla.com>
Date: Mon, 12 Mar 2012 10:06:55 -0700
Message-ID: <4F5E2D2F.9030303@mozilla.com>
To: Nicholas Doty <npdoty@w3.org>
CC: Kevin Smith <kevsmith@adobe.com>, "VINCENT (VINCENT) TOUBIANA" <Vincent.Toubiana@alcatel-lucent.com>, Tracking Protection Working Group WG <public-tracking@w3.org>
Hey Nick,

Sorry for the late reply.

On 3/8/12 3:53 PM, Nicholas Doty wrote:

>> I am not sure how to do this using current methodologies.  Take a
>> simple example.  Site A has an exception for all 3rd parties and
>> includes 3rd Party B which then includes 3rd Party C.  3rd Party C is
>> requested from 3rd Party B, not Site A.  How does the browser know
>> that 3rd Party C's request originated from Site A?  Certainly 3rd
>> Part C probably knows from customized request parameters, but how
>> does the browser map the request to its list of exceptions to even
>> see the '*' associated with site A?  I think this would be new
>> functionality.

> We opened ISSUE-110 I believe specifically for this question (will
> user agents always be able to determine corresponding
> top-level-origin for all outgoing requests?) as Vincent was concerned
> that browsers or browser extensions might not be able to do this. I
> believe Sid informed us that browsers always could (whether it's a
> redirect, embedded iframe, XHR request, etc.) which is why it was
> closed -- Sid, can you confirm?

Confirmed.

The key here is that *all* subordinate loads are subject to some
top-level policy regardless of which element is their parent.  It is
perhaps new functionality to apply a policy based on the top frame only,
but as far as I can tell there's no reason Browsers shouldn't be able to
do this.  We draw the stuff on the screen, and there's *always* a causal
chain of requests starting with the top level site.  We had to work in
part of this space when implementing a "frame-ancestors" part of CSP in
Firefox, one that checked all frame/iframe ancestors of an element, and
in fact we have to at the very least keep track of at least one level of
"ancestry" for iframes due to the same origin policy.

Now, that's not saying there are bugs in specific bits of browser code
that make this hard or impossible for extensions, but due to the way
requests are initiated, browser vendors should indeed be able to keep
track of the whole chain of loads (redirect, subordinate or otherwise).
 The catch here is that it may not be trivial to implement, but it *can*
be engineered.

-Sid
Received on Monday, 12 March 2012 17:07:17 UTC

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