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

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Message-ID: <20120309125735.GB13346@moon>
Date:	Fri, 9 Mar 2012 16:57:35 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Oleg Nesterov <oleg@...hat.com>
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 Fri, Mar 09, 2012 at 01:48:11PM +0100, Oleg Nesterov wrote:
...
> > +
> > +	/*
> > +	 * Setting new mm::exe_file is only allowed
> > +	 * when no executable VMAs left. This is
>                    ^^^^^^^^^^
> Perhaps this is just me, but imho "executable" is not clear enough.
> I'd suggest VM_EXECUTABLE to avoid the confusion with VM_EXEC.

OK

> 
> > +	 * special C/R case when a restored program
> > +	 * need to change own /proc/$pid/exe symlink.
> > +	 * After this call mm::num_exe_file_vmas become
> > +	 * meaningless.
> > +	 */
> > +	down_write(&mm->mmap_sem);
> > +	if (mm->num_exe_file_vmas == 0) {
> 
> You can check this at the very start lockless and simplify the code.
> Once it is zero, it can never grow (or we have a bug anyway).

sure

> 
> > +		set_mm_exe_file(mm, exe_file);
> > +		exe_file = NULL;
> > +	} else
> > +		err = -EBUSY;
> > +	up_write(&mm->mmap_sem);
> > +
> > +exit:
> > +	if (exe_file)
> > +		fput(exe_file);
> 
> This doesn't look correct, you need fput() in any case.
> set_mm_exe_file() does another get_file().

yeah, thanks, will update.

	Cyrill
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