linux-kernel - Re: [PATCH] leds: pwm: Use struct

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Date:   Thu, 29 Aug 2019 22:40:42 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: pwm: Use struct_size() helper

On Thu, Aug 29, 2019 at 07:53:20PM -0500, Gustavo A. R. Silva wrote:
> One of the more common cases of allocation size calculations is finding
> the size of a structure that has a zero-sized array at the end, along
> with memory for some number of elements for that array. For example:
> 
> struct led_pwm_priv {
> 	...
>         struct led_pwm_data leds[0];
> };
> 
> Make use of the struct_size() helper instead of an open-coded version
> in order to avoid any potential type mistakes.
> 
> So, replace the following function:
> 
> static inline size_t sizeof_pwm_leds_priv(int num_leds)
> {
>        return sizeof(struct led_pwm_priv) +
>                      (sizeof(struct led_pwm_data) * num_leds);
> }
> 
> with:
> 
> struct_size(priv, leds, count)
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  drivers/leds/leds-pwm.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
> index d0e1f2710351..8b6965a563e9 100644
> --- a/drivers/leds/leds-pwm.c
> +++ b/drivers/leds/leds-pwm.c
> @@ -65,12 +65,6 @@ static int led_pwm_set(struct led_classdev *led_cdev,
>  	return 0;
>  }
>  
> -static inline size_t sizeof_pwm_leds_priv(int num_leds)
> -{
> -	return sizeof(struct led_pwm_priv) +
> -		      (sizeof(struct led_pwm_data) * num_leds);
> -}
> -
>  static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
>  		       struct led_pwm *led, struct fwnode_handle *fwnode)
>  {
> @@ -174,7 +168,7 @@ static int led_pwm_probe(struct platform_device *pdev)
>  	if (!count)
>  		return -EINVAL;
>  
> -	priv = devm_kzalloc(&pdev->dev, sizeof_pwm_leds_priv(count),
> +	priv = devm_kzalloc(&pdev->dev, struct_size(priv, leds, count),
>  			    GFP_KERNEL);
>  	if (!priv)
>  		return -ENOMEM;
> -- 
> 2.23.0
> 

-- 
Kees Cook