linux-kernel - Re: kdbus: credential faking

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Message-ID: <2655319.HiHStWqHEi@merkaba>
Date:	Fri, 10 Jul 2015 16:20:44 +0200
From:	Martin Steigerwald <martin@...htvoll.de>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	Stephen Smalley <sds@...ho.nsa.gov>,
	Greg KH <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	Djalal Harouni <tixxdz@...ndz.org>,
	lkml <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>,
	Paul Osmialowski <p.osmialowsk@...sung.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Paul Moore <paul@...l-moore.com>
Subject: Re: kdbus: credential faking

Am Freitag, 10. Juli 2015, 15:43:08 schrieb David Herrmann:
> Hi

Hi,

> On Fri, Jul 10, 2015 at 3:25 PM, Stephen Smalley <sds@...ho.nsa.gov> 
> wrote:
> > On 07/09/2015 06:22 PM, David Herrmann wrote:
> >> To be clear, faking metadata has one use-case, and one use-case only:
> >> dbus1 compatibility
> >> 
> >> In dbus1, clients connect to a unix-socket placed in the file-system
> >> hierarchy. To avoid breaking ABI for old clients, we support a
> >> unix-kdbus proxy. This proxy is called systemd-bus-proxyd. It is
> >> spawned once for each bus we proxy and simply remarshals messages from
> >> the client to kdbus and vice versa.
> > 
> > Is this truly necessary?  Can't the distributions just update the client
> > side libraries to use kdbus if enabled and be done with it?  Doesn't
> > this proxy undo many of the benefits of using kdbus in the first place?
> 
> We need binary compatibility to dbus1. There're millions of
> applications and language bindings with dbus1 compiled in, which we
> cannot suddenly break.

Wow, do I get this right, that this credential faking – I do think that the 
last two words are already completely sufficient to show the insanity of it 
at least when I apply something to it that is commonly called common sense, 
credential *what*? – is just for supporting something that is broken in 
userspace already?

I do get the "never break userspace" mantra for anything *already* 
implemented in the kernel. But this is more like "userspace is broken, lets 
port it into the kernel and keep the brokenness while doing so thus setting 
the brokenness in stone" due to the first mantra.

I did not look at the actual code, but from the mere reading of this, I 
shudder.

I am happy that you digged this out of the larger thread with a descriptive 
thread title, so that this may get some attention, Stephen.

Ciao,
-- 
Martin
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