[PATCH] omapfb: Use devm_kcalloc() in vrfb_probe()

[PATCH] omapfb: Use devm_kcalloc() in vrfb_probe()

[SF Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Wed, 26 Apr 2017 11:08:30 +0200

* A multiplication for the size determination of a memory allocation
  indicated that an array data structure should be processed.
  Thus use the corresponding function "devm_kcalloc".

* Replace the specification of a data structure by a pointer dereference
  to make the corresponding size determination a bit safer according to
  the Linux coding style convention.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/video/fbdev/omap2/omapfb/vrfb.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/video/fbdev/omap2/omapfb/vrfb.c b/drivers/video/fbdev/omap2/omapfb/vrfb.c
index f346b02eee1d..54b51a7a290a 100644
--- a/drivers/video/fbdev/omap2/omapfb/vrfb.c
+++ b/drivers/video/fbdev/omap2/omapfb/vrfb.c
@@ -358,11 +358,7 @@ static int __init vrfb_probe(struct platform_device *pdev)
 		return PTR_ERR(vrfb_base);
 
 	num_ctxs = pdev->num_resources - 1;
-
-	ctxs = devm_kzalloc(&pdev->dev,
-			sizeof(struct vrfb_ctx) * num_ctxs,
-			GFP_KERNEL);
-
+	ctxs = devm_kcalloc(&pdev->dev, num_ctxs, sizeof(*ctxs), GFP_KERNEL);
 	if (!ctxs)
 		return -ENOMEM;
 
-- 
2.12.2

Re: [PATCH] omapfb: Use devm_kcalloc() in vrfb_probe()

[Bartlomiej Zolnierkiewicz]

Hi,

On Wednesday, April 26, 2017 11:20:07 AM SF Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Wed, 26 Apr 2017 11:08:30 +0200
> 
> * A multiplication for the size determination of a memory allocation
>   indicated that an array data structure should be processed.
>   Thus use the corresponding function "devm_kcalloc".
> 
> * Replace the specification of a data structure by a pointer dereference
>   to make the corresponding size determination a bit safer according to
>   the Linux coding style convention.
> 
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>  drivers/video/fbdev/omap2/omapfb/vrfb.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/video/fbdev/omap2/omapfb/vrfb.c b/drivers/video/fbdev/omap2/omapfb/vrfb.c
> index f346b02eee1d..54b51a7a290a 100644
> --- a/drivers/video/fbdev/omap2/omapfb/vrfb.c
> +++ b/drivers/video/fbdev/omap2/omapfb/vrfb.c
> @@ -358,11 +358,7 @@ static int __init vrfb_probe(struct platform_device *pdev)
>  		return PTR_ERR(vrfb_base);
>  
>  	num_ctxs = pdev->num_resources - 1;
> -
> -	ctxs = devm_kzalloc(&pdev->dev,
> -			sizeof(struct vrfb_ctx) * num_ctxs,
> -			GFP_KERNEL);
> -
> +	ctxs = devm_kcalloc(&pdev->dev, num_ctxs, sizeof(*ctxs), GFP_KERNEL);

This change makes the resulting binary larger by 24 bytes (probably
because of the need to have an additional function argument) and
I don't see an improvement from a security POV (pdev->num_resources
is based on the size of static tables from arch/arm/mach-omap2/fb.c).

I'm sorry but I'm not applying this patch.

>  	if (!ctxs)
>  		return -ENOMEM;

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

Re: [PATCH] omapfb: Use devm_kcalloc() in vrfb_probe()

[Bartlomiej Zolnierkiewicz]

On Thursday, May 11, 2017 04:27:19 PM Bartlomiej Zolnierkiewicz wrote:

> > @@ -358,11 +358,7 @@ static int __init vrfb_probe(struct platform_device *pdev)
> >  		return PTR_ERR(vrfb_base);
> >  
> >  	num_ctxs = pdev->num_resources - 1;
> > -
> > -	ctxs = devm_kzalloc(&pdev->dev,
> > -			sizeof(struct vrfb_ctx) * num_ctxs,
> > -			GFP_KERNEL);
> > -
> > +	ctxs = devm_kcalloc(&pdev->dev, num_ctxs, sizeof(*ctxs), GFP_KERNEL);
> 
> This change makes the resulting binary larger by 24 bytes (probably
> because of the need to have an additional function argument) and

24 bytes seemed too much for just an additional function argument
so I've checked the source:

static inline void *devm_kzalloc(struct device *dev, size_t size, gfp_t gfp)
{
	return devm_kmalloc(dev, size, gfp | __GFP_ZERO);
}
static inline void *devm_kmalloc_array(struct device *dev,
				       size_t n, size_t size, gfp_t flags)
{
	if (size != 0 && n > SIZE_MAX / size)
		return NULL;
	return devm_kmalloc(dev, n * size, flags);
}
static inline void *devm_kcalloc(struct device *dev,
				 size_t n, size_t size, gfp_t flags)
{
	return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
}

The extra kcalloc() checks are inlined currently into each instance.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

Re: [PATCH] omapfb: Use devm_kcalloc() in vrfb_probe()

[Geert Uytterhoeven]

On Thu, May 11, 2017 at 5:22 PM, Bartlomiej Zolnierkiewicz
<b.zolnierkie@samsung.com> wrote:
> On Thursday, May 11, 2017 04:27:19 PM Bartlomiej Zolnierkiewicz wrote:
>
>> > @@ -358,11 +358,7 @@ static int __init vrfb_probe(struct platform_device *pdev)
>> >             return PTR_ERR(vrfb_base);
>> >
>> >     num_ctxs = pdev->num_resources - 1;
>> > -
>> > -   ctxs = devm_kzalloc(&pdev->dev,
>> > -                   sizeof(struct vrfb_ctx) * num_ctxs,
>> > -                   GFP_KERNEL);
>> > -
>> > +   ctxs = devm_kcalloc(&pdev->dev, num_ctxs, sizeof(*ctxs), GFP_KERNEL);
>>
>> This change makes the resulting binary larger by 24 bytes (probably
>> because of the need to have an additional function argument) and
>
> 24 bytes seemed too much for just an additional function argument
> so I've checked the source:
>
> static inline void *devm_kzalloc(struct device *dev, size_t size, gfp_t gfp)
> {
>         return devm_kmalloc(dev, size, gfp | __GFP_ZERO);
> }
> static inline void *devm_kmalloc_array(struct device *dev,
>                                        size_t n, size_t size, gfp_t flags)
> {
>         if (size != 0 && n > SIZE_MAX / size)
>                 return NULL;
>         return devm_kmalloc(dev, n * size, flags);
> }
> static inline void *devm_kcalloc(struct device *dev,
>                                  size_t n, size_t size, gfp_t flags)
> {
>         return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
> }
>
> The extra kcalloc() checks are inlined currently into each instance.

And in this case the compiler cannot optimize them away as n is not
known at compile time.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds