Re: [PATCH] gpio: mockup: allocate lines with main struct

[Kees Cook <kees@kernel.org>]

On Wed, Mar 18, 2026 at 05:05:58PM -0700, Rosen Penev wrote:
> Remove no longer needed kcalloc to simplify allocation.
> 
> Added __counted_by along with a counting variable to get extra runtime
> analysis.
> 
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  drivers/gpio/gpio-mockup.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpio/gpio-mockup.c b/drivers/gpio/gpio-mockup.c
> index a7d69f3835c1..a907ce28cbbb 100644
> --- a/drivers/gpio/gpio-mockup.c
> +++ b/drivers/gpio/gpio-mockup.c
> @@ -52,10 +52,11 @@ struct gpio_mockup_line_status {
>  
>  struct gpio_mockup_chip {
>  	struct gpio_chip gc;
> -	struct gpio_mockup_line_status *lines;
>  	struct irq_domain *irq_sim_domain;
>  	struct dentry *dbg_dir;
>  	struct mutex lock;
> +	int nr_lines;
> +	struct gpio_mockup_line_status lines[] __counted_by(nr_lines);
>  };

In the cases where a new counter variable is being added to the struct,
I think it might be better to have those be unsigned.

>  
>  struct gpio_mockup_dbgfs_private {
> @@ -436,15 +437,18 @@ static int gpio_mockup_probe(struct platform_device *pdev)
>  	if (rv)
>  		name = dev_name(dev);
>  
> -	chip = devm_kzalloc(dev, sizeof(*chip), GFP_KERNEL);
> +	chip = devm_kzalloc(dev, struct_size(chip, lines, ngpio), GFP_KERNEL);
>  	if (!chip)
>  		return -ENOMEM;
>  
> -	mutex_init(&chip->lock);
> +	chip->nr_lines = ngpio;

Besides the new variable being meaningless for negative values, there's
a strong hint about its type even from the counter used to perform the
calculation (u16):

static int gpio_mockup_probe(struct platform_device *pdev)
{
	...
        u16 ngpio;
	...
        rv = device_property_read_u16(dev, "nr-gpios", &ngpio);
	...
        gc->ngpio = ngpio;
	...
        chip->lines = devm_kcalloc(dev, gc->ngpio,
                                   sizeof(*chip->lines), GFP_KERNEL);

But this begs the question: why add nr_lines when ngpio is already part
of the struct:

struct gpio_chip {
	...
        u16                     ngpio;


?

-Kees

-- 
Kees Cook