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

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Date:	Sat, 10 Mar 2012 01:52:17 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Matt Helsley <matthltc@...ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.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 01:46:37PM -0800, Matt Helsley wrote:
> > > 
> > > I simply do not understand what mm->num_exe_file_vmas means after
> > > PR_SET_MM_EXE_FILE.
> 
> I think it should fail if the num_exe_file_vmas is not 0 when
> PR_SET_MM_EXE_FILE is used. It's simple, keeps things clear, might
> catch userspace bugs (harder to accidentally leave a mapping of the original
> executable), and could avoid kernel bugs too.

Yes, and in last version (whuch I just sent out) we have at the very beginning
of the function

+	if (mm->num_exe_file_vmas)
+               return -EBUSY;

> > 
> > Wait, Oleg, I'm confused, in case if there *is* exitsting VM_EXECUTABLEs
> > then we jump into first banch and simply replace old exe_file.
> 
> What happens if multiple prctl calls are made? We'll have a mix of N
> executable files that've been mapped n_i times. I think we're better off
> just returning an error in that case -- -EBUSY or something.
> 
> > If there is no VM_EXECUTABLEs, then we simply setup new exe_file
> > and num_exe_file_vmas remains zero.
> 
> Which is fine.
> 

Matt, please check the last version, and tell me if it's fine for you.

	Cyrill
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