Re: [PATCH 1/3] Input: atmel_mxt_ts - fix boundary check in mxt_prepare_cfg_mem

[Ricardo Ribalda]

HI Dmitry

FWIW this patch looks correct to me...

Reviewed-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>

But there are a couple of things that look weird.

1) The patch line (1503) does not seem to match your tree
https://git.kernel.org/pub/scm/linux/kernel/git/dtor/input.git/tree/drivers/input/touchscreen/atmel_mxt_ts.c#n1503

2) The sscanf just before this check has two conversions (val and
offset), but you only check for ret != 1. Should't it be ret !=2? or I
am missing something?

On Mon, 4 May 2026 at 20:54, Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> wrote:
>
> When a configuration file provides an object size that is larger than the
> driver's known mxt_obj_size(object), the driver intends to discard the
> extra bytes.
>
> The loop iterates using for (i = 0; i < size; i++). Inside the loop, the
> condition to skip processing extra bytes is:
>
>     if (i > mxt_obj_size(object))
>         continue;
>
> Since i is a 0-based index, the valid indices for the object are 0 through
> mxt_obj_size(object) - 1.
>
> When i == mxt_obj_size(object), the condition evaluates to false, and the
> code processes the byte instead of discarding it.
>
> This causes the code to calculate byte_offset = reg + i - cfg->start_ofs
> and writes the byte there, overwriting exactly one byte of the adjacent
> instance or object.
>
> Update the boundary check to skip extra bytes correctly by using >=.
>
> Fixes: 50a77c658b80 ("Input: atmel_mxt_ts - download device config using firmware loader")
> Cc: stable@xxxxxxxxxxxxxxx
> Assisted-by: Gemini:gemini-3.1-pro
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> ---
>  drivers/input/touchscreen/atmel_mxt_ts.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
> index d62bf2c95578..28b2bd889c70 100644
> --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> @@ -1503,7 +1503,7 @@ static int mxt_prepare_cfg_mem(struct mxt_data *data, struct mxt_cfg *cfg)
>                         }
>                         cfg->raw_pos += offset;
>
> -                       if (i > mxt_obj_size(object))
> +                       if (i >= mxt_obj_size(object))
>                                 continue;
>
>                         byte_offset = reg + i - cfg->start_ofs;
> --
> 2.54.0.545.g6539524ca2-goog
>


-- 
Ricardo Ribalda