linux-kernel - Re: [PATCH V2] Input: synaptics-rmi4

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Message-ID: <ZteAo-bklYbs29Pq@radian>
Date: Tue, 3 Sep 2024 17:33:23 -0400
From: Richard Acayan <mailingradian@...il.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Marge Yang <marge.yang@...synaptics.com>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Vincent Huang <Vincent.Huang@...synaptics.com>,
	david.chiu@...synaptics.com, derek.cheng@...synaptics.com,
	sam.tsai@...aptics.com
Subject: Re: [PATCH V2] Input: synaptics-rmi4 - Supports to query DPM value.

On Tue, Sep 03, 2024 at 11:40:38AM -0700, Dmitry Torokhov wrote:
> On Tue, Sep 03, 2024 at 02:07:23PM -0400, Richard Acayan wrote:
> > > +	/* Use the Query DPM feature when the query register exists for resolution. */
> > > +	item = rmi_get_register_desc_item(&f12->query_reg_desc, RMI_F12_QUERY_RESOLUTION);
> > > +	if (item) {
> > > +		offset = rmi_register_desc_calc_reg_offset(&f12->query_reg_desc,
> > > +			RMI_F12_QUERY_RESOLUTION);
> > > +		query_dpm_addr = fn->fd.query_base_addr	+ offset;
> > > +		ret = rmi_read(fn->rmi_dev, query_dpm_addr, buf);
> > > +		if (ret < 0) {
> > > +			dev_err(&fn->dev, "Failed to read DPM value: %d\n", ret);
> > > +			return -ENODEV;
> > > +		}
> > > +		dpm_resolution = buf[0];
> > > +
> > > +		sensor->x_mm = sensor->max_x / dpm_resolution;
> > > +		sensor->y_mm = sensor->max_y / dpm_resolution;
> > > +	} else {
> > > +		if (rmi_register_desc_has_subpacket(item, 3)) {
> > 
> > The item variable is NULL in this branch, as it was overwritten just
> > before the if statement.
> > 
> > This patch causes a NULL pointer dereference:
> 
> Ugh, indeed. I guess the simplest way of fixing this would be:
> 
> diff --git a/drivers/input/rmi4/rmi_f12.c b/drivers/input/rmi4/rmi_f12.c
> index fc2cc8e2b0ba..8246fe77114b 100644
> --- a/drivers/input/rmi4/rmi_f12.c
> +++ b/drivers/input/rmi4/rmi_f12.c
> @@ -129,9 +129,8 @@ static int rmi_f12_read_sensor_tuning(struct f12_data *f12)
>  	 * Use the Query DPM feature when the resolution query register
>  	 * exists.
>  	 */
> -	item = rmi_get_register_desc_item(&f12->query_reg_desc,
> -					  RMI_F12_QUERY_RESOLUTION);
> -	if (item) {
> +	if (rmi_get_register_desc_item(&f12->query_reg_desc,
> +				       RMI_F12_QUERY_RESOLUTION)) {
>  		offset = rmi_register_desc_calc_reg_offset(&f12->query_reg_desc,
>  						RMI_F12_QUERY_RESOLUTION);
>  		query_dpm_addr = fn->fd.query_base_addr	+ offset;
> 
> Could you please tell me if this works for you?

Yeah, it fixes the bug.