linux-kernel - Re: [PATCH 00/12] Add kdbus implementation

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Date:	Thu, 30 Oct 2014 12:28:56 +0000
From:	Simon McVittie <simon.mcvittie@...labora.co.uk>
To:	Tom Gundersen <teg@...m.no>, Andy Lutomirski <luto@...capital.net>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Linux API <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
	Marcel Holtmann <marcel@...tmann.org>,
	Ryan Lortie <desrt@...rt.ca>,
	Bastien Nocera <hadess@...ess.net>,
	David Herrmann <dh.herrmann@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Daniel Mack <daniel@...que.org>,
	"alban.crequy" <alban.crequy@...labora.co.uk>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Subject: Re: [PATCH 00/12] Add kdbus implementation

On 30/10/14 11:52, Tom Gundersen wrote:
> For example, if you want to get the audit identity
> bits, you can now get this attached securely by the kernel, at the
> time the message is sent, rather than having to firest get the peer's
> $PID from SCM_CREDENTIALS and then read the audit identity bits racily
> from /proc/$PID/loginuid and /proc/$PID/sessionid

... which dbus-daemon (traditional D-Bus) deliberately doesn't offer as
a feature, because we are not aware of any way to do that over Unix
sockets without a race condition; and if we can't have it securely, we
don't want to have it at all.
<https://bugs.freedesktop.org/show_bug.cgi?id=83499>
It would be great if kdbus can fix that omission.

Capabilities are in the same boat, and as a result, systemd can't
currently have D-Bus methods that can only be called with CAP_WHATEVER.

> * fewer userspace context switches
[...]
> * fewer message copies in userspace

Readers are probably already aware of this, but note that D-Bus is
designed to be usable between mutually distrusting processes, which is
why we use Unix sockets and a lot of copies, rather than mmap or something.

    S

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