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Date: Thu, 19 Jan 2012 10:55:41 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: david@lang.hm, "H. Peter Anvin" <hpa@zytor.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Pavel Emelyanov <xemul@parallels.com>,
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        Andi Kleen <andi@firstfloor.org>, Tejun Heo <tj@kernel.org>,
        Matt Helsley <matthltc@us.ibm.com>, Pekka Enberg <penberg@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Vasiliy Kulikov <segoon@openwall.com>,
        Andrew Morton <akpm@linux-foundation.org>, Valdis.Kletnieks@vt.edu
Subject: Re: [RFC] syscalls, x86: Add __NR_kcmp syscall
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On Wed, Jan 18, 2012 at 03:29:50PM -0800, Eric W. Biederman wrote:
> >
> > It doesn't matter. Even if we take a list of objects the kernel either
> > should return us some ordering info or find duplicates, in any case it
> > makes things more complex i think. So we wanted to bring some minimum
> > into kernel leaving the rest of work to user-space.
> 
> Agreed a syscall does the duplication is probably not the way to go.
> 
>  A syscall that takes a huge list of objects would solve any security
> concerns that we have with returning the object order to user space if
> done carefully, but it would require a bunch of additional user space
> and kernel memory.
> 

yes, an it increase syscall time itself since we will have to provide
this memory dynamically

> Sometimes taking a data structure transforming it into a weird form for
> a specific task and then transforming the data structure back to it's
> original form is a useful way to go.  So I think a general kernel object
> deduplicating system call is an interesting plan B, but a straight
> comparison function if we can make it work is a lot more flexible and
> useful.
> 

I hope the root-only restriction would resolve the potential security
problem, since as I mentioned if I've hijacked the machine and already
goot root -- mem order is not that interesting info I could obtain from
such computer :)

	Cyrill