Re: [PATCH v3 27/27] iio:adc:max1118 Fix alignment of timestamp and data leak issues

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 22 Jul 2020 16:51:03 +0100
Jonathan Cameron <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 an 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.
> 
> This data is allocated with kzalloc so no data can leak apart
> from previous readings.
> 
> The explicit alignment of ts is necessary to ensure correct padding
> on architectures where s64 is only 4 bytes aligned such as x86_32.
> 
> Fixes: a9e9c7153e96 ("iio: adc: add max1117/max1118/max1119 ADC driver")
> Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> Cc: Akinobu Mita <akinobu.mita@gmail.com>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Applied and marked for stable.

Thanks,

Jonathan

> ---
>  drivers/iio/adc/max1118.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/max1118.c b/drivers/iio/adc/max1118.c
> index 01b20e420ac4..6efb0b43d938 100644
> --- a/drivers/iio/adc/max1118.c
> +++ b/drivers/iio/adc/max1118.c
> @@ -36,6 +36,11 @@ struct max1118 {
>  	struct spi_device *spi;
>  	struct mutex lock;
>  	struct regulator *reg;
> +	/* Ensure natural alignment of buffer elements */
> +	struct {
> +		u8 channels[2];
> +		s64 ts __aligned(8);
> +	} scan;
>  
>  	u8 data ____cacheline_aligned;
>  };
> @@ -166,7 +171,6 @@ static irqreturn_t max1118_trigger_handler(int irq, void *p)
>  	struct iio_poll_func *pf = p;
>  	struct iio_dev *indio_dev = pf->indio_dev;
>  	struct max1118 *adc = iio_priv(indio_dev);
> -	u8 data[16] = { }; /* 2x 8-bit ADC data + padding + 8 bytes timestamp */
>  	int scan_index;
>  	int i = 0;
>  
> @@ -184,10 +188,10 @@ static irqreturn_t max1118_trigger_handler(int irq, void *p)
>  			goto out;
>  		}
>  
> -		data[i] = ret;
> +		adc->scan.channels[i] = ret;
>  		i++;
>  	}
> -	iio_push_to_buffers_with_timestamp(indio_dev, data,
> +	iio_push_to_buffers_with_timestamp(indio_dev, &adc->scan,
>  					   iio_get_time_ns(indio_dev));
>  out:
>  	mutex_unlock(&adc->lock);