linux-kernel - Re: kdbus: add code for buses, domains and endpoints

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Message-ID: <CALCETrXbwFUR1fj8SnGMQ6VpTV9=5t+bWxWs3abx0XXORg0TAQ@mail.gmail.com>
Date:	Thu, 30 Oct 2014 15:00:57 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Alex Elsayed <eternaleye@...il.com>
Cc:	Linux API <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: kdbus: add code for buses, domains and endpoints

On Thu, Oct 30, 2014 at 2:47 PM, Alex Elsayed <eternaleye@...il.com> wrote:
> Andy Lutomirski wrote:
>
>> On Thu, Oct 30, 2014 at 11:08 AM, Djalal Harouni
>> <tixxdz@...ndz.org> wrote:
>>> Hi Andy,
>>>
>>> 2) To get the creds of the sender of the message during send time. This
>>> is specially relevent to authorize specific D-Bus method calls, by
>>> checking the creds of the caller, not the one who created the kdbus
>>> connection.
>>
>> Please humor me here: can you describe, concretely, a case where
>> authorization of the principal issuing a method call is more correct
>> than authorization of the principal who connected to the object being
>> acted on?
>>
>> I suspect that such examples are actually quite difficult to find.
>>
>> --Andy
>
> The simple answer is that this is a misaimed question - you don't connect to
> the object being acted on.
>
> You connect to the _same bus_ as other clients have connected to. You then
> act on objects they have made available on the bus.
>
> You might have connected to a restricted endpoint, which provides a narrowed
> view of the bus, but that's neither the same thing nor mandatory.

OK, but this doesn't answer the question.  It is not an example of a
case where checking credentials at the time of connection to the bus
is actually worse from a security standpoint than checking for
credentials at the time of the send.

--Andy
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