linux-kernel - Re: [patch 00/13] devtmpfs patches

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Date:	Wed, 13 May 2009 15:43:28 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	Stephen Smalley <sds@...ho.nsa.gov>,
	David Howells <dhowells@...hat.com>,
	"David P. Quigley" <dpquigl@...ho.nsa.gov>,
	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	Greg KH <gregkh@...e.de>, Jan Blunck <jblunck@...e.de>,
	James Morris <jmorris@...ei.org>,
	Eric Paris <eparis@...isplace.org>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [patch 00/13] devtmpfs patches

Kay Sievers <kay.sievers@...y.org> writes:

> On Wed, 2009-05-13 at 10:35 -0400, Stephen Smalley wrote:
>> > Maybe we could do the same credential swap in sysfs, and get rid of:
>> > /**
>> >  * lookup_one_noperm - bad hack for sysfs
>> > 
>> > Seems a bit odd to have a vfs function for a single filesystem, called
>> > from a single location, and annotated as "do not use". Christoph added
>> > the comment a while ago, so adding him to Cc:.
>> 
>> Yes, that makes sense to me as well - we didn't have the credentials
>> infrastructure in place at the time that lookup_one_noperm was
>> introduced, but switching the credentials around a normal lookup_one_len
>> call should work now.
>
> Something like this? It seems to work fine here, but I did not test it with SELinux.

That just masks the problem not fixes it.

The problem is that sysfs attempts to keep the dcache in lock-step with
the sysfs_dentries.

The VFS model is lazy coherency and bringing things in sync on access.
This is important to avoid locking problems.

Eric
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