linux-kernel - Re: clone() with CLONE_NEWNET breaks kobject_uevent

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Date:	Fri, 19 Aug 2011 09:52:07 +0200
From:	Milan Broz <mbroz@...hat.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	device-mapper development <dm-devel@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>,
	"David S. Miller" <davem@...emloft.net>, containers@...ts.osdl.org
Subject: Re: clone() with CLONE_NEWNET breaks kobject_uevent_env()

(added cc to containers list)

On 08/18/2011 11:45 AM, Milan Broz wrote:
> Hi,
> 
> after analysing very strange report (with running chromium
> some device-mapper ioctl functions started to fail) I found
> interesting problem:
> 
> If you run clone() with CLONE_NEWNET (which is chromium using
> for sanboxing), udev namespace is cloned too (newly registered
> in uevent_sock_list) and netlink send (except the first in list)
> fails with -ESRCH.
> 
> This causes that _every_ call of kobject_uevent_env() return failure.
> 
> Most of users silently ignores  kobject_uevent() return value,
> so the problem was invisible for long time.
> 
> Unfortunately dm checks return value and reports failure,
> taking the wrong error path.
> 
> How is this supposed to work?
> 
> Why cloning net namespace breaks the udev netlink subsystem?
> 
> Is it bug or we need to do something differently?
> (I do not think ignoring return value is the proper way...)

I forgot to explicitly mention that running clone with CLONE_NEWNET
causes kobject_uevent_env() to fail _outside_ of cloned namespace
(for all kernel users in fact).

(The former problem is described here
http://article.gmane.org/gmane.linux.kernel.device-mapper.dm-crypt/5256
but it is IMHO generic problem. Instrumenting  kobject_uevent() shows
that it returns send failure really to all events.)

Can anyone please explain this behavior?

Milan
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