linux-kernel - Re: [PATCH 2/2] cgroup: add xattr support

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Message-ID: <alpine.LSU.2.00.1201201951100.1448@eggly.anvils>
Date:	Fri, 20 Jan 2012 20:00:58 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Lennart Poettering <mzxreary@...inter.de>
cc:	Tejun Heo <tj@...nel.org>, Kay Sievers <kay.sievers@...y.org>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH 2/2] cgroup: add xattr support

On Sat, 21 Jan 2012, Lennart Poettering wrote:
> On Wed, 18.01.12 18:40, Tejun Heo (tj@...nel.org) wrote:
> > On Wed, Jan 18, 2012 at 06:20:05PM -0800, Tejun Heo wrote:
> > 
> > Also note that tmpfs also implies size limit.  We definitely need some
> > form of control over the amount of memory xattr may consume.
> 
> Good point. But then again we don't even have anything resembling for
> tmpfs either, where it would be much more important... :-(

But although the tmpfs framework for xattrs is general, the validation
function only permits XATTR_SECURITY_PREFIX and XATTR_TRUSTED_PREFIX.

Yes, it would be very necessary to impose size limits if tmpfs went
beyond those to permit XATTR_USER_PREFIX - which the cgroupfs patch
under discussion does permit.

> 
> Given that cgroupfs is probably mostly read-only for normal users, the
> requirement for quotas on it is probably much less important than for tmpfs
> though.

Hugh
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