Message-ID: <54522F08.7080005@collabora.co.uk>
Date: Thu, 30 Oct 2014 12:28:56 +0000
From: Simon McVittie <simon.mcvittie@collabora.co.uk>
Organization: Collabora Ltd.
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To: Tom Gundersen <teg@jklm.no>, Andy Lutomirski <luto@amacapital.net>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Kosina <jkosina@suse.cz>, Linux API <linux-api@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        John Stultz <john.stultz@linaro.org>, Arnd Bergmann <arnd@arndb.de>,
        Tejun Heo <tj@kernel.org>, Marcel Holtmann <marcel@holtmann.org>,
        Ryan Lortie <desrt@desrt.ca>, Bastien Nocera <hadess@hadess.net>,
        David Herrmann <dh.herrmann@gmail.com>,
        Djalal Harouni <tixxdz@opendz.org>, Daniel Mack <daniel@zonque.org>,
        "alban.crequy" <alban.crequy@collabora.co.uk>,
        Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Subject: Re: [PATCH 00/12] Add kdbus implementation
References: <1414620056-6675-1-git-send-email-gregkh@linuxfoundation.org> <alpine.LRH.2.00.1410292354480.11562@twin.jikos.cz> <20141029231106.GB16548@kroah.com> <alpine.LRH.2.00.1410300019570.11562@twin.jikos.cz> <20141029234001.GB16520@kroah.com> <CALCETrXY90YAXA9-GLc0EowmRCtWZzh8br8seiqrzOkmNn8_Hw@mail.gmail.com> <CAG-2HqX9RUQHiF1U_CXiDVVLS-7aUOQdYn7EVNSMZNdbe38cTA@mail.gmail.com>
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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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