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

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Date:	Thu, 8 Mar 2012 20:25:59 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	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 03/08, Cyrill Gorcunov wrote:
>
> On Thu, Mar 08, 2012 at 08:05:34PM +0100, Oleg Nesterov wrote:
> ...
> > >
> > > Yes, exactly, I need to remove old mappings first (because VMAs
> > > we're about to restore may intersect with current map the host
> > > program has). And yes, once they all are removed I don't have
> > > /proc/pid/exe anymore. That's why I need num_exe_file_vmas == 0
> > > case.
> >
> > OK, in this case PR_SET_MM_EXE_FILE should probably fail if
> > mm->num_exe_file_vmas != 0 ? This way it would be more or less
> > consistent or at least understandable. Just we add the new
> > special case: num_exe_file_vmas == 0 but exe_file != NULL
> > because c/r people are crazy.
> >
>
> Sure, I can drop num_exe_file_vmas != 0 case and refuse to
> setup new exe symlink if there some VM_EXECUTABLE remains
> unmapped. Sounds good?

Personally I like this. This is simple and _understable_, even
if ->num_exe_file_vmas has no meaning after PR_SET_MM_EXE.

But please-please document the new special case in the changelog.

Oleg.

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