Re: [PATCH 08/11] iio:health:afe4404 Fix timestamp alignment and prevent data leak.

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 17 May 2020 18:29:57 +0100
jic23@kernel.org wrote:

> From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> 
> One of a class of bugs pointed out by Lars in a recent review.
> iio_push_to_buffers_with_timestamp assumes the buffer used is aligned
> to the size of the timestamp (8 bytes).  This is not guaranteed in
> this driver which uses a 40 byte array of smaller elements on the stack.
> As Lars also noted this anti pattern can involve a leak of data to
> userspace and that indeed can happen here.  We close both issues by
> moving to a suitable structure in the iio_priv() data with alignment
> explicitly requested.  This data is allocated with kzalloc so no
> data can leak appart from previous readings.
> 
> Fixes: 87aec56e27ef ("iio: health: Add driver for the TI AFE4404 heart monitor")
> Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Andrew F. Davis <afd@ti.com>
Applied to the fixes-togreg branch of iio.git and marked for stable.

Thanks,

Jonathan

> ---
>  drivers/iio/health/afe4404.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/health/afe4404.c b/drivers/iio/health/afe4404.c
> index e728bbb21ca8..cebb1fd4d0b1 100644
> --- a/drivers/iio/health/afe4404.c
> +++ b/drivers/iio/health/afe4404.c
> @@ -83,6 +83,7 @@ static const struct reg_field afe4404_reg_fields[] = {
>   * @regulator: Pointer to the regulator for the IC
>   * @trig: IIO trigger for this device
>   * @irq: ADC_RDY line interrupt number
> + * @buffer: Used to construct a scan to push to the iio buffer.
>   */
>  struct afe4404_data {
>  	struct device *dev;
> @@ -91,6 +92,7 @@ struct afe4404_data {
>  	struct regulator *regulator;
>  	struct iio_trigger *trig;
>  	int irq;
> +	s32 buffer[10] __aligned(8);
>  };
>  
>  enum afe4404_chan_id {
> @@ -328,17 +330,17 @@ static irqreturn_t afe4404_trigger_handler(int irq, void *private)
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	struct afe4404_data *afe = iio_priv(indio_dev);
>  	int ret, bit, i = 0;
> -	s32 buffer[10];
>  
>  	for_each_set_bit(bit, indio_dev->active_scan_mask,
>  			 indio_dev->masklength) {
>  		ret = regmap_read(afe->regmap, afe4404_channel_values[bit],
> -				  &buffer[i++]);
> +				  &afe->buffer[i++]);
>  		if (ret)
>  			goto err;
>  	}
>  
> -	iio_push_to_buffers_with_timestamp(indio_dev, buffer, pf->timestamp);
> +	iio_push_to_buffers_with_timestamp(indio_dev, afe->buffer,
> +					   pf->timestamp);
>  err:
>  	iio_trigger_notify_done(indio_dev->trig);
>