Re: [PATCH 07/11] iio:health:afe4403 Fix timestamp alignment and prevent data leak.

["Andrew F. Davis" <afd@ti.com>]

On 5/17/20 1:29 PM, 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 32 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: eec96d1e2d31 ("iio: health: Add driver for the TI AFE4403 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>
> ---
>  drivers/iio/health/afe4403.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/health/afe4403.c b/drivers/iio/health/afe4403.c
> index e9f87e42ff4f..a3507624b30f 100644
> --- a/drivers/iio/health/afe4403.c
> +++ b/drivers/iio/health/afe4403.c
> @@ -65,6 +65,7 @@ static const struct reg_field afe4403_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 data layout to push into IIO buffer.
>   */
>  struct afe4403_data {
>  	struct device *dev;
> @@ -74,6 +75,8 @@ struct afe4403_data {
>  	struct regulator *regulator;
>  	struct iio_trigger *trig;
>  	int irq;
> +	/* Ensure suitable alignment for timestamp */
> +	s32 buffer[8] __aligned(8);


One of those fancy structs with the timestamp specified would be nice
here like the other patches. IIRC we have 6 s32 channels, plus a s64 ts.

Other than that everything looks good.

Andrew


>  };
>  
>  enum afe4403_chan_id {
> @@ -309,7 +312,6 @@ static irqreturn_t afe4403_trigger_handler(int irq, void *private)
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	struct afe4403_data *afe = iio_priv(indio_dev);
>  	int ret, bit, i = 0;
> -	s32 buffer[8];
>  	u8 tx[4] = {AFE440X_CONTROL0, 0x0, 0x0, AFE440X_CONTROL0_READ};
>  	u8 rx[3];
>  
> @@ -326,7 +328,7 @@ static irqreturn_t afe4403_trigger_handler(int irq, void *private)
>  		if (ret)
>  			goto err;
>  
> -		buffer[i++] = get_unaligned_be24(&rx[0]);
> +		afe->buffer[i++] = get_unaligned_be24(&rx[0]);
>  	}
>  
>  	/* Disable reading from the device */
> @@ -335,7 +337,8 @@ static irqreturn_t afe4403_trigger_handler(int irq, void *private)
>  	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);
>  
>