linux-kernel - Re: [PATCH V2] iio: gp2ap020a00f: Fix signedness bug

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Message-ID: <20220415185205.26a3d352@jic23-huawei>
Date:   Fri, 15 Apr 2022 18:52:05 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Haowen Bai <baihaowen@...zu.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>, <linux-iio@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] iio: gp2ap020a00f: Fix signedness bug

On Fri, 15 Apr 2022 09:20:37 +0800
Haowen Bai <baihaowen@...zu.com> wrote:

> function gp2ap020a00f_get_thresh_reg() is unsigned but returning -EINVAL 
> errcode, and thresh_reg_l is unsigned but receiving -EINVAL errcode. so 
> we have to change u8 -> int.
> 
> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
Hi,

The return value is not checked in *read_event_val(), so if we actually got
-EINVAL (in reality we can't because the switch in *_get_thresh_reg*) always
matches) then we'd use it to index an array (after performing some maths on
the value).  So please also add a check that the return value is not
negative in read_event_val()

Same is true or write_event_val.


Note that the bug here is probably the fact we return -EINVAL in the
first place. We could just stop doing that but it would be non obvious
when looking at the code that we couldn't get a failure to match in
the switch statement - so fixing as you have done (plus the extra
check I'm requesting) is probably the neatest solution.

Thanks,

Jonathan


> ---
> V1->V2: s8 is not enough to hold an (arbitrary) error code. To be on the safe
> side we need to use int
> 
>  drivers/iio/light/gp2ap020a00f.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/light/gp2ap020a00f.c b/drivers/iio/light/gp2ap020a00f.c
> index b820041159f7..b0e62d3c6fa0 100644
> --- a/drivers/iio/light/gp2ap020a00f.c
> +++ b/drivers/iio/light/gp2ap020a00f.c
> @@ -994,7 +994,7 @@ static irqreturn_t gp2ap020a00f_trigger_handler(int irq, void *data)
>  	return IRQ_HANDLED;
>  }
>  
> -static u8 gp2ap020a00f_get_thresh_reg(const struct iio_chan_spec *chan,
> +static int gp2ap020a00f_get_thresh_reg(const struct iio_chan_spec *chan,
>  					     enum iio_event_direction event_dir)
>  {
>  	switch (chan->type) {
> @@ -1025,7 +1025,7 @@ static int gp2ap020a00f_write_event_val(struct iio_dev *indio_dev,
>  	struct gp2ap020a00f_data *data = iio_priv(indio_dev);
>  	bool event_en = false;
>  	u8 thresh_val_id;
> -	u8 thresh_reg_l;
> +	int thresh_reg_l;
>  	int err = 0;
>  
>  	mutex_lock(&data->lock);
> @@ -1082,7 +1082,7 @@ static int gp2ap020a00f_read_event_val(struct iio_dev *indio_dev,
>  				       int *val, int *val2)
>  {
>  	struct gp2ap020a00f_data *data = iio_priv(indio_dev);
> -	u8 thresh_reg_l;
> +	int thresh_reg_l;
>  	int err = IIO_VAL_INT;
>  
>  	mutex_lock(&data->lock);