Re: [PATCH v4 5/5] iio: as73211: copy/release available integration times to fix race

[Christian Eggers <ceggers@arri.de>]

On Friday, 18 October 2024, 12:16:44 CEST, Matteo Martelli wrote:
> While available integration times are being printed to sysfs by iio core
> (iio_read_channel_info_avail), the sampling frequency might be changed.
> This could cause the buffer shared with iio core to be corrupted. To
> prevent it, make a copy of the integration times buffer and free it in
> the read_avail_release_resource callback.
> 
> Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
> ---
>  drivers/iio/light/as73211.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/light/as73211.c b/drivers/iio/light/as73211.c
> index be0068081ebbbb37fdfb252b67a77b302ff725f6..c4c94873e6a1cc926cfb724d906b07222773c43f 100644
> --- a/drivers/iio/light/as73211.c
> +++ b/drivers/iio/light/as73211.c
> @@ -108,7 +108,8 @@ struct as73211_spec_dev_data {
>   * @creg1:  Cached Configuration Register 1.
>   * @creg2:  Cached Configuration Register 2.
>   * @creg3:  Cached Configuration Register 3.
> - * @mutex:  Keeps cached registers in sync with the device.
> + * @mutex:  Keeps cached registers in sync with the device and protects
> + *          int_time_avail concurrent access for updating and reading.
>   * @completion: Completion to wait for interrupt.
>   * @int_time_avail: Available integration times (depend on sampling frequency).
>   * @spec_dev: device-specific configuration.
> @@ -493,17 +494,32 @@ static int as73211_read_avail(struct iio_dev *indio_dev, struct iio_chan_spec co
>  		*type = IIO_VAL_INT;
>  		return IIO_AVAIL_LIST;
>  
> -	case IIO_CHAN_INFO_INT_TIME:
> +	case IIO_CHAN_INFO_INT_TIME: {
>  		*length = ARRAY_SIZE(data->int_time_avail);
> -		*vals = data->int_time_avail;
>  		*type = IIO_VAL_INT_PLUS_MICRO;
> -		return IIO_AVAIL_LIST;
>  
> +		guard(mutex)(&data->mutex);
> +
> +		*vals = kmemdup_array(data->int_time_avail, *length,
> +				      sizeof(int), GFP_KERNEL);
> +		if (!*vals)
> +			return -ENOMEM;
> +
> +		return IIO_AVAIL_LIST;
> +	}
>  	default:
>  		return -EINVAL;
>  	}
>  }
>  
> +static void as73211_read_avail_release_res(struct iio_dev *indio_dev,
> +					   struct iio_chan_spec const *chan,
> +					   const int *vals, long mask)
> +{
> +	if (mask == IIO_CHAN_INFO_INT_TIME)
> +		kfree(vals);
> +}
> +
>  static int _as73211_write_raw(struct iio_dev *indio_dev,
>  			       struct iio_chan_spec const *chan __always_unused,
>  			       int val, int val2, long mask)
> @@ -699,6 +715,7 @@ static irqreturn_t as73211_trigger_handler(int irq __always_unused, void *p)
>  static const struct iio_info as73211_info = {
>  	.read_raw = as73211_read_raw,
>  	.read_avail = as73211_read_avail,
> +	.read_avail_release_resource = as73211_read_avail_release_res,
>  	.write_raw = as73211_write_raw,
>  };
>  
> 
> 

Thanks for fixing this.

Tested-by: Christian Eggers <ceggers@arri.de>