[PATCH] Input: applespi - use struct_size() helper

[PATCH] Input: applespi - use struct_size() helper

[Gustavo A. R. Silva]

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 touchpad_protocol {
	...
        struct tp_finger        fingers[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 form:

sizeof(*tp) + tp->number_of_fingers * sizeof(tp->fingers[0]);

with:

struct_size(tp, fingers, tp->number_of_fingers)

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/input/keyboard/applespi.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/input/keyboard/applespi.c b/drivers/input/keyboard/applespi.c
index acf34a5ff571..584289b67fb3 100644
--- a/drivers/input/keyboard/applespi.c
+++ b/drivers/input/keyboard/applespi.c
@@ -1494,8 +1494,7 @@ static void applespi_got_data(struct applespi_data *applespi)
 		size_t tp_len;
 
 		tp = &message->touchpad;
-		tp_len = sizeof(*tp) +
-			 tp->number_of_fingers * sizeof(tp->fingers[0]);
+		tp_len = struct_size(tp, fingers, tp->number_of_fingers);
 
 		if (le16_to_cpu(message->length) + 2 != tp_len) {
 			dev_warn_ratelimited(&applespi->spi->dev,
-- 
2.22.0

Re: [PATCH] Input: applespi - use struct_size() helper

[Dmitry Torokhov]

On Mon, Aug 05, 2019 at 07:06:38PM -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 touchpad_protocol {
> 	...
>         struct tp_finger        fingers[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 form:
> 
> sizeof(*tp) + tp->number_of_fingers * sizeof(tp->fingers[0]);
> 
> with:
> 
> struct_size(tp, fingers, tp->number_of_fingers)
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

Applied, thank you.

> ---
>  drivers/input/keyboard/applespi.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/input/keyboard/applespi.c b/drivers/input/keyboard/applespi.c
> index acf34a5ff571..584289b67fb3 100644
> --- a/drivers/input/keyboard/applespi.c
> +++ b/drivers/input/keyboard/applespi.c
> @@ -1494,8 +1494,7 @@ static void applespi_got_data(struct applespi_data *applespi)
>  		size_t tp_len;
>  
>  		tp = &message->touchpad;
> -		tp_len = sizeof(*tp) +
> -			 tp->number_of_fingers * sizeof(tp->fingers[0]);
> +		tp_len = struct_size(tp, fingers, tp->number_of_fingers);
>  
>  		if (le16_to_cpu(message->length) + 2 != tp_len) {
>  			dev_warn_ratelimited(&applespi->spi->dev,
> -- 
> 2.22.0
> 

-- 
Dmitry