linux-kernel - Re: [PATCH] video: fbdev: matrox: matroxfb_base.c: Fix for possible null pointer dereference

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Date:	Wed, 2 Jul 2014 18:18:22 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
cc:	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Jingoo Han <jg1.han@...sung.com>,
	Alexandru Juncu <alexj@...edu.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Joe Perches <joe@...ches.com>, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] video: fbdev: matrox: matroxfb_base.c:  Fix for possible
 null pointer dereference



On Wed, 2 Jul 2014, Rickard Strandqvist wrote:

> Fix a possible null pointer dereference, there is otherwise a risk of a 
> possible null pointer dereference
> 
> This was found using a static code analysis program called cppcheck
> 
> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
> ---
>  drivers/video/fbdev/matrox/matroxfb_base.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/fbdev/matrox/matroxfb_base.c b/drivers/video/fbdev/matrox/matroxfb_base.c
> index 7116c53..85ef84b 100644
> --- a/drivers/video/fbdev/matrox/matroxfb_base.c
> +++ b/drivers/video/fbdev/matrox/matroxfb_base.c
> @@ -1971,9 +1971,9 @@ static void matroxfb_register_device(struct matrox_fb_info* minfo) {
>  	int i = 0;
>  	list_add(&minfo->next_fb, &matroxfb_list);
>  	for (drv = matroxfb_driver_l(matroxfb_driver_list.next);
> -	     drv != matroxfb_driver_l(&matroxfb_driver_list);
> +	     drv && drv != matroxfb_driver_l(&matroxfb_driver_list);

The "drv" check is pointless because drv can't be NULL - use the patch 
below.

>  	     drv = matroxfb_driver_l(drv->node.next)) {
> -		if (drv && drv->probe) {
> +		if (drv->probe) {
>  			void *p = drv->probe(minfo);
>  			if (p) {
>  				minfo->drivers_data[i] = p;
> -- 
> 1.7.10.4

matroxfb: delete pointless NULL-pointer check

The for loop walks a double-linked list, so drv cannot be NULL.

This patch deletes the pointless NULL-pointer check. cppcheck warned about
it.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>

---
 drivers/video/fbdev/matrox/matroxfb_base.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/drivers/video/fbdev/matrox/matroxfb_base.c
===================================================================
--- linux-2.6.orig/drivers/video/fbdev/matrox/matroxfb_base.c	2014-06-19 16:41:45.048259897 +0200
+++ linux-2.6/drivers/video/fbdev/matrox/matroxfb_base.c	2014-07-03 00:13:04.299380130 +0200
@@ -1973,7 +1973,7 @@ static void matroxfb_register_device(str
 	for (drv = matroxfb_driver_l(matroxfb_driver_list.next);
 	     drv != matroxfb_driver_l(&matroxfb_driver_list);
 	     drv = matroxfb_driver_l(drv->node.next)) {
-		if (drv && drv->probe) {
+		if (drv->probe) {
 			void *p = drv->probe(minfo);
 			if (p) {
 				minfo->drivers_data[i] = p;
--
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