linux-kernel - Re: [PATCH 1/1][2nd resend] sys_unshare: remove the dead CLONE

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Date:	Tue, 9 Nov 2010 18:17:54 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Ying Han <yinghan@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Roland McGrath <roland@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	JANAK DESAI <janak@...ibm.com>
Subject: Re: [PATCH 1/1][2nd resend] sys_unshare: remove the dead
	CLONE_THREAD/SIGHAND/VM code

On 11/09, KOSAKI Motohiro wrote:
>
> > -static void check_unshare_flags(unsigned long *flags_ptr)
> > +static int check_unshare_flags(unsigned long unshare_flags)
> >  {
> > +	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
> > +				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
> > +				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))
> > +		return -EINVAL;
>
> Please put WARN_ON_ONCE() explicitly. That's good way to find hidden
> user if exist and getting better bug report.

Perhaps... but this needs a separate change.

Please note that this check was simply moved from sys_unshare(), this
patch shouldn't have any visible effect.

Personally, I think it would be even better if, say, unshare(CLONE_THREAD)
returned -EINVAL unconditionally.

> And, I've reveied this patch and I've found no fault. but I will not put
> my ack because I think I haven't understand original intention perhaps.

Thanks!

IIRC, the main (only?) motivation for sys_unshare() was unshare_fs().
Most probably unshare_thread/vm were added as placeholders.

Oleg.

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