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Re: Referrer value for resources fetched from CSS

From: Jochen Eisinger <eisinger@google.com>
Date: Tue, 29 Sep 2015 06:54:03 +0000
Message-ID: <CALjhuidc0HHwij-LzVtUNOFTvzsmjJoFENunwBjHbWog7kGKkQ@mail.gmail.com>
To: Tanvi Vyas <tanvi@mozilla.com>, Mike West <mkwst@google.com>, Yoav Weiss <yoav@yoav.ws>, Boris Zbarsky <bzbarsky@mit.edu>
Cc: "public-webappsec@w3.org" <public-webappsec@w3.org>
On Mon, Sep 28, 2015 at 8:03 PM Tanvi Vyas <tanvi@mozilla.com> wrote:

> Hi Jochen,
> Have you updated the spec?

Not yet, no.

> In Firefox we have a concept of a "triggering principal" and a "loading
> principal"[1].  The triggering principal is like the referrer and points to
> the context that triggered the load.  While the "loading principal" should
> be the principal for the context in which the resource is loaded.  Does
> Chrome have a similar distinction?

No, Chrome doesn't have such a clear distinction. We have a FetchContext
which I guess corresponds to the loading principal, but a resource can
ignore the referrer and origin from the FetchContext which is what e.g.
CSSImageValue does.

> In your font example, the stylesheet was the one who triggered the font
> load into the main document.  So the stylesheet is the trigger/referrer and
> the main document is the loading context.
> Thanks!
> ~Tanvi
> [1]
> https://mxr.mozilla.org/mozilla-central/source/netwerk/base/nsILoadInfo.idl#130
> On 9/8/15 4:59 AM, Jochen Eisinger wrote:
> Chrome uses the CSS file as referrer since quite a while. I agree that the
> spec should reflect that.
> On Tue, Sep 8, 2015 at 1:19 PM Mike West < <mkwst@google.com>
> mkwst@google.com> wrote:
>> +jochen, bz
>> I remember talking with Boris about this, but I can't find the thread at
>> the moment. My vague recollection was that Chrome used the URL of the
>> document that loaded the CSS file, and Firefox used the CSS file. It sounds
>> like that might have changed in the relatively recent past.
>> If that's the case, we should update the spec. And by "we", I mean
>> Jochen. :)
>> -mike
>> --
>> Mike West <mkwst@google.com>, @mikewest
>> Google Germany GmbH, Dienerstrasse 12, 80331 München,
>> Germany, Registergericht und -nummer: Hamburg, HRB 86891, Sitz der
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>> Flores
>> (Sorry; I'm legally required to add this exciting detail to emails. Bleh.)
>> On Tue, Sep 8, 2015 at 1:01 PM, Yoav Weiss <yoav@yoav.ws> wrote:
>>> Hi,
>>> When going through the definitions and values of the Referer header in
>>> the referrer policy
>>> <https://w3c.github.io/webappsec/specs/referrer-policy/> spec, I see
>>> that the "No referrer when downgrade" policy (which is the default) is
>>> defined as "sends a full URL", but it's not clear to me what that URL
>>> should be. My default assumption would be that it is the URL of the
>>> settings object/main document.
>>> However, when looking at font resources fetched cross-origin that were
>>> defined by an external stylesheet, I see that the "referer" value is that
>>> of the stylesheet, rather than that of the main document, in both Firefox
>>> and Chrome.
>>> So, I guess my questions are:
>>> * Are I missing something regarding the definitions? Is an external
>>> stylesheet defined as a settings object of its own?
>>> * When the referrer policy is defined as "origin", what should the
>>> referer on such a font resource be?
>>> Cheers :)
>>> Yoav
Received on Tuesday, 29 September 2015 06:54:44 UTC

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