linux-kernel - Re: [PATCH next] HID: hid-goodix: Fix a signedness bug in goodix_hid_get_raw

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Message-ID: <ZsjsydZtMu3RyM0P@google.com>
Date: Fri, 23 Aug 2024 13:10:49 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Charles Wang <charles.goodix@...il.com>, Jiri Kosina <jikos@...nel.org>,
	Benjamin Tissoires <bentiss@...nel.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH next] HID: hid-goodix: Fix a signedness bug in
 goodix_hid_get_raw_report()

Hi Dan,

On Fri, Aug 23, 2024 at 03:51:27PM +0300, Dan Carpenter wrote:
> GOODIX_HID_PKG_LEN_SIZE defined as sizeof(u16) (type size_t).  If the
> goodix_hid_check_ack_status() function times out and return -EINVAL then,
> because of type promotion, the negative error code is treated as a high
> positive value which is success.
> 
> Fix this by adding an explicit check for negative error codes.
> 
> Fixes: 75e16c8ce283 ("HID: hid-goodix: Add Goodix HID-over-SPI driver")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>  drivers/hid/hid-goodix-spi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/hid-goodix-spi.c b/drivers/hid/hid-goodix-spi.c
> index 5103bf0aada4..59415f95c675 100644
> --- a/drivers/hid/hid-goodix-spi.c
> +++ b/drivers/hid/hid-goodix-spi.c
> @@ -435,7 +435,8 @@ static int goodix_hid_get_raw_report(struct hid_device *hid,
>  
>  	/* Step2: check response data status */
>  	response_data_len = goodix_hid_check_ack_status(ts);
> -	if (response_data_len <= GOODIX_HID_PKG_LEN_SIZE)
> +	if (response_data_len < 0 ||
> +	    response_data_len <= GOODIX_HID_PKG_LEN_SIZE)
>  		return -EINVAL;

I think this is too subtle and we may lose your fix again in
restructuring/refactoring. Could you change goodix_hid_check_ack_status()
to take length as an argument to be filled in? And then we'd do:

	error = goodix_hid_check_ack_status(ts, &response_data_len);
	if (error)
		return error;

The check for the correct length of the response could go into
goodix_hid_check_ack_status() as well.

What do you think?

Thanks.

-- 
Dmitry