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

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Message-ID: <20090302041148.GA7410@in.ibm.com>
Date:	Mon, 2 Mar 2009 09:41:48 +0530
From:	Ankita Garg <ankita@...ibm.com>
To:	Frank Seidel <fseidel@...e.de>
Cc:	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 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.
 
> 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)

-- 
Regards,
Ankita Garg (ankita@...ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs, 
Bangalore, India   
--
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