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

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Date:	Wed, 13 May 2009 10:35:58 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	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

On Wed, 2009-05-13 at 16:20 +0200, Kay Sievers wrote:
> On Wed, May 13, 2009 at 15:34, Kay Sievers <kay.sievers@...y.org> wrote:
> 
> >>> +     kern_cred = prepare_kernel_cred(NULL);
> >>
> >> If you have no intention of altering the credentials you create, you might
> >> want to use &init_cred instead of kern_cred.  That said, you might want to
> >> allocate it and let the security module alter it before you use it.
> >
> > Ah, didn't know that it was exported. It's the one in
> > include/linux/init_task.h, right? I'll give that a try.
> 
> That seems to work fine here. Thanks a lot for the help.
> 
> Maybe we could do the same credential swap in sysfs, and get rid of:
> /**
>  * lookup_one_noperm - bad hack for sysfs
>  * @name:       pathname component to lookup
>  * @base:       base directory to lookup from
>  *
>  * This is a variant of lookup_one_len that doesn't perform any permission
>  * checks.   It's a horrible hack to work around the braindead sysfs
>  * architecture and should not be used anywhere else.
>  *
>  * DON'T USE THIS FUNCTION EVER, thanks.
>  */
> 
> in fs/namei.c?
> 
> 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.

-- 
Stephen Smalley
National Security Agency

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