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

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Date:	Wed, 12 Aug 2015 10:11:29 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.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

Oleg Nesterov <oleg@...hat.com> writes:

> 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)".

So it was.  I must have tired when I read the git log last night.

Eric
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