[PATCH] lkdtm: reduce stack size

[PATCH] lkdtm: reduce stack size

[Frank Seidel]

From: Frank Seidel <frank@f-seidel.de>

Reduce stack memory footprint of lkdtm
(recursive_loop). From 1024 bytes on i386 down
to <10.

Signed-off-by: Frank Seidel <frank@f-seidel.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)

Re: [PATCH] lkdtm: reduce stack size

[Ankita Garg]

Hi Frank,

On Sun, Mar 01, 2009 at 09:00:14PM +0100, Frank Seidel wrote:
> From: Frank Seidel <frank@f-seidel.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@f-seidel.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@in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs, 
Bangalore, India   

Re: [PATCH] lkdtm: reduce stack size

[Frank Seidel]

Ankita Garg wrote:
> 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.

Oh, i see. Then this patch of course doesn't make sense.

Thanks,
Frank

Re: [PATCH] lkdtm: reduce stack size

[Bernd Petrovitsch]

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@f-seidel.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@f-seidel.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
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services

Re: [PATCH] lkdtm: reduce stack size

[Ankita Garg]

Hi Bernd,

On Mon, Mar 02, 2009 at 10:51:30AM +0100, Bernd Petrovitsch wrote:
> 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@f-seidel.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.
>

There is some text at the head of the module file that explains what the
module does and the usage, etc. I suppose that would be sufficient ?
 
-- 
Regards,
Ankita Garg (ankita@in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs, 
Bangalore, India