linux-kernel - Re: [PATCH 2/4] check_unsafe_exec: kill the dead -EAGAIN and clear_in

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Date:	Fri, 22 Nov 2013 16:00:24 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	oleg@...hat.com
CC:	kosaki.motohiro@...fujitsu.com, akpm@...ux-foundation.org,
	viro@...IV.linux.org.uk, keescook@...omium.org, mhocko@...e.cz,
	snanda@...omium.org, dserrg@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] check_unsafe_exec: kill the dead -EAGAIN and clear_in_exec
 logic

>> I have found no problem in this patch. However, I have a very basic question.
>> Why do we need to keep fs->in_exec?
> 
> To ensure that a sub-thread can't create a new process with the same
> ->fs while we are doing exec without LSM_UNSAFE_SHARE, I guess. This
> is only for security/ code.

But in LSM_UNSAFE_SHARE case, we have no check, right? I'm amazing why
we don't need anything.


> 
>> If it is correct,
>> can't we move it it to signal->in_exec?
> 
> Yes, perhaps, I am thinking about more cleanups too. But not that this
> will add the subtle change. CLONE_THREAD doesn't require CLONE_FS, so
> copy_fs() can fail even it the caller doesn't share ->fs with the execing
> thread. And we still need fs->lock to set signal->in_exec, this looks
> a bit strange.

Oops. Yes, this is totally odd. Sorry, we need to stop off topic discussion.
Anyway

Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

> 
>> I am not expert in this area and I may overlook something.
> 
> Neither me ;) So this patch tries to not change the current logic.
> 
> I feel that perhaps we can do more cleanups, but I am not really sure
> and this needs a separate change.



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