Re: [PATCH 2/3] Input: atmel_mxt_ts - check mem_size before calculating config memory size

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, May 04, 2026 at 11:54:46AM -0700, Dmitry Torokhov wrote:
> In mxt_update_cfg(), the driver calculates the memory size needed to store
> the configuration as data->mem_size - cfg.start_ofs. If data->mem_size is
> less than or equal to cfg.start_ofs, this calculation will underflow or
> result in a zero-size buffer, neither of which is valid for a configuration
> update.
> 
> Add a check to return -EINVAL if data->mem_size is too small. While at it,
> change the types of start_ofs and mem_size in struct mxt_cfg to u16 to
> match the device address space.
> 
> Assisted-by: Gemini:gemini-3.1-pro
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> ---
>  drivers/input/touchscreen/atmel_mxt_ts.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
> index 28b2bd889c70..d660cc5b5fe3 100644
> --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> @@ -275,8 +275,8 @@ struct mxt_cfg {
>  	off_t raw_pos;
>  
>  	u8 *mem;
> -	size_t mem_size;
> -	int start_ofs;
> +	u16 mem_size;
> +	u16 start_ofs;
>  
>  	struct mxt_info info;
>  };
> @@ -1657,6 +1657,13 @@ static int mxt_update_cfg(struct mxt_data *data, const struct firmware *fw)
>  	cfg.start_ofs = MXT_OBJECT_START +
>  			data->info->object_num * sizeof(struct mxt_object) +
>  			MXT_INFO_CHECKSUM_SIZE;
> +
> +	if (data->mem_size < cfg.start_ofs) {

This is supposed to be "<=", like the commit message says.

> +		dev_err(dev, "Memory size too small: %u < %u\n",
> +			data->mem_size, cfg.start_ofs);
> +		return -EINVAL;
> +	}
> +
>  	cfg.mem_size = data->mem_size - cfg.start_ofs;
>  
>  	u8 *mem_buf __free(kfree) = cfg.mem = kzalloc(cfg.mem_size, GFP_KERNEL);

-- 
Dmitry