linux-kernel - Re: [PATCH] lkdtm: reduce stack size

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Date:	Mon, 02 Mar 2009 10:51:30 +0100
From:	Bernd Petrovitsch <bernd@...mix.at>
To:	Ankita Garg <ankita@...ibm.com>
Cc:	Frank Seidel <fseidel@...e.de>,
	linux kernel <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org, Adrian Bunk <bunk@...nel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Frank Seidel <frank@...eidel.de>, kernalert.de@...il.com
Subject: Re: [PATCH] lkdtm: reduce stack size

Hi!

On Mon, 2009-03-02 at 09:41 +0530, Ankita Garg wrote:
> Hi Frank,
> 
> On Sun, Mar 01, 2009 at 09:00:14PM +0100, Frank Seidel wrote:
> > From: Frank Seidel <frank@...eidel.de>
> > 
> > Reduce stack memory footprint of lkdtm
> > (recursive_loop). From 1024 bytes on i386 down
> > to <10.
> >
> 
> The intention here is infact to trigger a stack overflow. This module is
> used to test kernel dumping mechanism like kdump. So the expectation is
> that the kernel will dump as soon as the stack overflows.

That answers why the variable exists at all. It is only zeroed and never
else used.
Hmm, adding the above as a comment makes probably sense.

> > Signed-off-by: Frank Seidel <frank@...eidel.de>
> > ---
> >  drivers/misc/lkdtm.c |   16 +++++++++++++---
> >  1 file changed, 13 insertions(+), 3 deletions(-)
> > 
> > --- a/drivers/misc/lkdtm.c
> > +++ b/drivers/misc/lkdtm.c
> > @@ -225,14 +225,24 @@ static int lkdtm_parse_commandline(void)
> > 
> >  static int recursive_loop(int a)
> >  {
> > -	char buf[1024];
> > +	char *buf;
> > +	int ret;
> > +
> > +	buf = kmalloc(1024, GFP_KERNEL);
> > +	if (!buf) {
> > +		printk(KERN_ERR "lkdtm : couldn't allocate buffer\n");
> > +		return -ENOMEM;
> > +	}
> > 
> >  	memset(buf,0xFF,1024);
> >  	recur_count--;
> >  	if (!recur_count)
> > -		return 0;
> > +		ret = 0;
> >  	else
> > -        	return recursive_loop(a);
> > +		ret = recursive_loop(a);
> > +
> > +	kfree(buf);
> > +	return ret;
> >  }
> > 
> >  void lkdtm_handler(void)

	Bernd
-- 
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