Re: [PATCH] Input: goodix - clamp the device-reported contact count

[Hans de Goede]

Hi,

On 13-Jun-26 04:10, Bryam Vargas via B4 Relay wrote:
> From: Bryam Vargas <hexlabsecurity@xxxxxxxxx>
> 
> goodix_ts_read_input_report() copies the number of touch points reported
> by the device into an on-stack buffer
> 
> 	u8 point_data[2 + GOODIX_MAX_CONTACT_SIZE * GOODIX_MAX_CONTACTS];
> 
> which is sized for at most GOODIX_MAX_CONTACTS (10) contacts. The only
> runtime check bounds the per-interrupt count against ts->max_touch_num,
> but that value is taken verbatim from a 4-bit field of the device
> configuration block and is never clamped:
> 
> 	ts->max_touch_num = ts->config[MAX_CONTACTS_LOC] & 0x0f;
> 
> The nibble can be 0..15, so a malfunctioning, malicious or counterfeit
> controller (or an attacker tampering with the I2C bus) can advertise up
> to 15 contacts. goodix_ts_read_input_report() then accepts a touch_num
> of up to 15 and the second goodix_i2c_read() writes
> ts->contact_size * (touch_num - 1) bytes past the one-contact header into
> point_data - up to 30 bytes (45 with the 9-byte report format) beyond the
> 92-byte buffer: a stack out-of-bounds write.
> 
> Clamp max_touch_num to GOODIX_MAX_CONTACTS, the number of contacts
> point_data[] is sized for, when reading it from the configuration.
> 
> Fixes: a7ac7c95d468 ("Input: goodix - use max touch number from device config")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Bryam Vargas <hexlabsecurity@xxxxxxxxx>

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <johannes.goede@xxxxxxxxxxxxxxxx>

Regards,

Hans


> ---
>  drivers/input/touchscreen/goodix.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/input/touchscreen/goodix.c b/drivers/input/touchscreen/goodix.c
> index f8798d11ec03..17fcfe45988c 100644
> --- a/drivers/input/touchscreen/goodix.c
> +++ b/drivers/input/touchscreen/goodix.c
> @@ -1057,7 +1057,8 @@ static void goodix_read_config(struct goodix_ts_data *ts)
>  	}
>  
>  	ts->int_trigger_type = ts->config[TRIGGER_LOC] & 0x03;
> -	ts->max_touch_num = ts->config[MAX_CONTACTS_LOC] & 0x0f;
> +	ts->max_touch_num = min(ts->config[MAX_CONTACTS_LOC] & 0x0f,
> +				GOODIX_MAX_CONTACTS);
>  
>  	x_max = get_unaligned_le16(&ts->config[RESOLUTION_LOC]);
>  	y_max = get_unaligned_le16(&ts->config[RESOLUTION_LOC + 2]);
> 
> ---
> base-commit: 8e65320d91cdc3b241d4b94855c88459b91abf66
> change-id: 20260612-b4-disp-6844625d-463f81173dc6
> 
> Best regards,