linux-kernel - Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe

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Message-ID: <20120314003642.GH19584@count0.beaverton.ibm.com>
Date:	Tue, 13 Mar 2012 17:36:42 -0700
From:	Matt Helsley <matthltc@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Matt Helsley <matthltc@...ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3

On Tue, Mar 13, 2012 at 04:43:37PM +0100, Oleg Nesterov wrote:
> 
> Matt, is it really possible to hit mm->exe_file = NULL in
> removed_exe_file_vma ? Unless I missed something, this check just
> hides the potentional problem, no?
> 
> IOW, shouldn't it do
> 
> 	void removed_exe_file_vma(struct mm_struct *mm)
> 	{
> 		WARN_ON(!mm->exe_file);
> 		WARN_ON(mm->num_exe_file_vmas <= 0);
> 
> 		if (!--mm->num_exe_file_vmas) {
> 			fput(mm->exe_file);
> 			mm->exe_file = NULL;
> 		}
> 	}
> 
> ?

I think you're spot-on about hiding the problem. I'm not sure the
WARN_ON() would be welcome in the mm's VMA paths though.
Also, it's a nit but I'd keep the decrement out of the condition like in
the original.

Cheers,
	-Matt

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