Re: [PATCH] iio: mma8452: use the correct logic to get mma8452_data

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 22 Feb 2022 10:42:21 +0800
haibo.chen@nxp.com wrote:

> From: Haibo Chen <haibo.chen@nxp.com>
> 
> The original logic to get mma8452_data is wrong, the *dev point to
> the device belong to iio_dev. we can't use this dev to find the
> correct i2c_client. The original logic happen to work because it
> finally use dev->driver_data to get iio_dev. Here use the API
> to_i2c_client() is wrong and make reader confuse. To correct the
> logic, it should be like this
> 
>   struct mma8452_data *data = iio_priv(dev_get_drvdata(dev));
> 
> But after commit 8b7651f25962 ("iio: iio_device_alloc(): Remove
> unnecessary self drvdata"), the upper logic also can't work.

I've added as second fixes tag and some explanation of why there
are two.  We should backport the fix all the way to the earlier one
but the bug isn't (by luck) exposed until the patch you mention here.

> When try to show the avialable scale in userspace, will meet kernel
> dump, kernel handle NULL pointer dereference.
> 
> So use dev_to_iio_dev() to correct the logic.
> 
> Fixes: c3cdd6e48e35 ("iio: mma8452: refactor for seperating chip specific data")
> Cc: <Stable@vger.kernel.org>
> Signed-off-by: Haibo Chen <haibo.chen@nxp.com>

Applied to the fixes-togreg branch of iio.git.

> ---
>  drivers/iio/accel/mma8452.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
> index 64b82b4503ad..0016bb947c10 100644
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
> @@ -379,8 +379,8 @@ static ssize_t mma8452_show_scale_avail(struct device *dev,
>  					struct device_attribute *attr,
>  					char *buf)
>  {
> -	struct mma8452_data *data = iio_priv(i2c_get_clientdata(
> -					     to_i2c_client(dev)));
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct mma8452_data *data = iio_priv(indio_dev);
>  
>  	return mma8452_show_int_plus_micros(buf, data->chip_info->mma_scales,
>  		ARRAY_SIZE(data->chip_info->mma_scales));