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

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Message-Id: <20101114161354.BEDB.A69D9226@jp.fujitsu.com>
Date:	Sun, 14 Nov 2010 16:14:01 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	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.

Ah, OK. you are right.



> > 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.





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