linux-kernel - Re: [patch 1/4] Add routine for generating an ID for kernel pointer

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Date:	Mon, 2 Jan 2012 13:18:13 +0100
From:	bastien ROUCARIES <roucaries.bastien@...il.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [patch 1/4] Add routine for generating an ID for kernel pointer

Le Saturday 31 December 2011 08:51:02, Cyrill Gorcunov a écrit :
> On Fri, Dec 30, 2011 at 06:51:37PM -0500, KOSAKI Motohiro wrote:
> ...
> 
> > >Guys, this become more and more complex, finally I fear someone
> > >propose to do ideal hashing run-time ;) Maybe we can step back and
> > >live with root-only and plain pointers here? I'm not sure who else
> > >might need such facility except us, and if once there will be a
> > >candidate -- we could take a look on hashing again and provide safe
> > >hashes there. No?
> > 
> > But recently kernel security fashion are, we don't expose a kernel
> > pointer at all even though the file is root only. I'm not sure how
> > much effective such fashion. but you seems run opposite way.
> > 
> > I doubt user land can implement good comparison way. Why you gave up
> > Andrew's sys_are_these_files_the_same() idea?

By memory, it seems that fuse expose kernel pointer encrypting it with tea. Tea is simple and quick you should get a glimpse at 
it.

> Because of speed, as Pavel mentioned
> 
>  | With this the complexity of determining sharing for N files scattered
>  | across several tasks would be N^2, since we'll have to compare each
>  | file to each file.
>  | 
>  | On the other hand having just N IDs at hands would allow us to use more
>  | efficient algorithms resulting in e.g. N*log(N) complexity.



> 	Cyrill
> --
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