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

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Date:	Fri, 9 Mar 2012 14:02:44 -0800
From:	Matt Helsley <matthltc@...ibm.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	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 Fri, Mar 09, 2012 at 07:42:24PM +0400, Cyrill Gorcunov wrote:
> On Fri, Mar 09, 2012 at 04:21:22PM +0100, Oleg Nesterov wrote:

<snip>

> > Just one note for the record, prctl_set_mm_exe_file() does
> > 
> > 	if (mm->num_exe_file_vmas)
> > 		return -EBUSY;
> > 
> > We could do
> > 
> > 	if (mm->exe_file)
> > 		return -EBUSY;
> > 
> > This way "because this feature is a special to C/R" becomes
> > really true. IOW, you can't do PR_SET_MM_EXE_FILE twice.
> > 
> 
> Sure, i'll make it this way. Thanks a lot, Oleg!!!

Sorry about the other email -- hadn't full caught up on this thread.
This is even better, yes.

Of course I'd prefer it if there was a way to keep num_exe_file_vmas
correct and not special-case c/r. The first approximation of a solution
might be to increment the count whenever a new mmap filp == mm->exe_file
and decrement on unmap. I think there are a bunch of details needed to
make that work but my feeling is it's do-able. Have you investigated this
already and rejected it for some reason (did I miss that discussion
somehow?)?

Cheers,
	-Matt Helsley

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