linux-kernel - Re: [PATCH] user_ns: use correct check for single-threadedness

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Date:	Wed, 12 Aug 2015 16:40:25 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Ricky Zhou <rickyz@...omium.org>,
	Julien Tinnes <jln@...gle.com>
Subject: Re: [PATCH] user_ns: use correct check for single-threadedness

On 08/11, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...hat.com> writes:
>
> >> Then why we can't simply check thread_group_empty() == T ? Why should we
> >> worry about CLONE_SIGHAND at all?
> >
> > The same for clone() actually... I forgot why we decided to check
> > CLONE_SIGHAND, iirc I suggested CLONE_THREAD initially then we switched
> > to CLONE_SIGHAND "just in case", to make it as strict as possible.
>
> I do agree that making the test be for CLONE_THREAD is safe, makes
> sense, and is less confusing than what we have now.x

Good,

> > How about the patch below?
> >
> > (note that the "or parent" part of the comment is wrong in any case).
>
> It was correct.

Yes, I know,

> You failed to removed it when you removed CLONE_PARENT
> from that test.

Cough... it was you ;) 1f7f4dde5c945f41a7abc2285be43d918029ecc5
"fork:  Allow CLONE_PARENT after setns(CLONE_NEWPID)".

Oleg.

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