Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1756280Ab2B1Qc0 (ORCPT <rfc822;w@1wt.eu>);
	Tue, 28 Feb 2012 11:32:26 -0500
Received: from bhuna.collabora.co.uk ([93.93.135.160]:50287 "EHLO
	bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754864Ab2B1QcZ (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 28 Feb 2012 11:32:25 -0500
Message-ID: <4F4D01C0.3050808@collabora.co.uk>
Date: Tue, 28 Feb 2012 17:33:04 +0100
From: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1
MIME-Version: 1.0
To: David Lamparter <equinox@diac24.net>
CC: Rodrigo Moya <rodrigo.moya@collabora.co.uk>,
        David Miller <davem@davemloft.net>, javier@collabora.co.uk,
        eric.dumazet@gmail.com, lennart@poettering.net, kay.sievers@vrfy.org,
        alban.crequy@collabora.co.uk, bart.cerneels@collabora.co.uk,
        sjoerd.simons@collabora.co.uk, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/10] af_unix: add multicast and filtering features to
 AF_UNIX
References: <1329753455-1106-1-git-send-email-javier@collabora.co.uk> <20120224.153616.117399887784547022.davem@davemloft.net> <4F4B8C66.5060206@collabora.co.uk> <20120227.140535.1623396420455657443.davem@davemloft.net> <1330426059.2139.21.camel@megeve> <20120228142846.GD187520@jupiter.n2.diac24.net> <4F4CF1BF.7080503@collabora.co.uk>
In-Reply-To: <4F4CF1BF.7080503@collabora.co.uk>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2352
Lines: 58

On 02/28/2012 04:24 PM, Javier Martinez Canillas wrote:
> On 02/28/2012 03:28 PM, David Lamparter wrote:
>> On Tue, Feb 28, 2012 at 11:47:39AM +0100, Rodrigo Moya wrote:
>>> > - slow readers: dropping packets vs blocking the sender. Although
>>> >   datagrams are not reliable on IP, datagrams on Unix sockets are
>>> never
>>> >   lost. So if one receiver has its buffer full the sender is blocked
>>> > instead of dropping packets. That way we guarantee a reliable
>>> > communication channel.
>> 
>> This sounds like a terribly nice way to f*ck the entire D-Bus system by
>> having one broken (or malicious) desktop application. What's the
>> intended way of coping with users that block the socket by not reading?
>> 
>> 
>> -David L.
> 
> The problem is that D-bus expects a reliable transport method (TCP or
> SOCK_STREAM Unix socks) but this is not the case with multicast Unix
> sockets. Since our implementation is for SOCK_SEQPACKET and SOCK_DGRAM
> socket types.
> 
> So, you have to either add another layer to the D-bus protocol to make
> it reliable (acks, retransmissions, flow control, etc) or avoid losing
> D-bus messages (by blocking the sender if one of the receivers has its
> buffer full).
> 

Also, this problem exists with current D-bus implementation. If a
malicious desktop application doesn't read its socket then the messages
sent to it will be buffered in the daemon:
https://bugs.freedesktop.org/show_bug.cgi?id=33606

dbus-daemon memory usage will ballooning until
max_incoming_bytes/max_outgoing_bytes limit is reached (1GB for session
bus in default configuration)

<limit name="max_incoming_bytes">1000000000</limit>
<limit name="max_outgoing_bytes">1000000000</limit>

It only works because not many applications are broken and user-space
memory is virtualized. But if you bypass the daemon and use a multicast
transport layer (as in our multicast Unix socket implementation) you
don't have that much memory to buffer the packets.

So you have to either block the senders or:

- drop the slow reader
- kill the spammer
- have an infinite amount of memory

Regards,
Javier
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/