Re: [PATCH 02/11] iio:accel:mma8452: Fix timestamp alignment and prevent data leak.

[Lars-Peter Clausen <lars@metafoo.de>]

On 5/17/20 7:29 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 16 byte u8 array 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
> ensured by use of an explicit c structure.  This data is allocated
> with kzalloc so no data can leak appart from previous readings.
>
> Fixes: c7eeea93ac60 ("iio: Add Freescale MMA8452Q 3-axis accelerometer driver")
> Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Peter Meerwald <pmeerw@pmeerw.net>
> ---
>   drivers/iio/accel/mma8452.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/accel/mma8452.c b/drivers/iio/accel/mma8452.c
> index 00e100fc845a..704867ffda7a 100644
> --- a/drivers/iio/accel/mma8452.c
> +++ b/drivers/iio/accel/mma8452.c
> @@ -110,6 +110,12 @@ struct mma8452_data {
>   	int sleep_val;
>   	struct regulator *vdd_reg;
>   	struct regulator *vddio_reg;
> +
> +	/* Ensure correct alignment of time stamp when present */
> +	struct {
> +		__be16 channels[3];
> +		s64 ts;
> +	} buffer;


I feel we should have a macro for this.

DECLARE_IIO_BUFFER_WITH_TIMESTAMP(buffer, __be16, 3);

The name is maybe a bit too long.

And potentially also DECLARE_IIO_BUFFER_WITH_TIMESTAMP_ON_STACK() which 
initializes it to zero.

>   };
>   
>    /**
> @@ -1091,14 +1097,13 @@ static irqreturn_t mma8452_trigger_handler(int irq, void *p)
>   	struct iio_poll_func *pf = p;
>   	struct iio_dev *indio_dev = pf->indio_dev;
>   	struct mma8452_data *data = iio_priv(indio_dev);
> -	u8 buffer[16]; /* 3 16-bit channels + padding + ts */
>   	int ret;
>   
> -	ret = mma8452_read(data, (__be16 *)buffer);
> +	ret = mma8452_read(data, data->buffer.channels);
>   	if (ret < 0)
>   		goto done;
>   
> -	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
> +	iio_push_to_buffers_with_timestamp(indio_dev, &data->buffer,
>   					   iio_get_time_ns(indio_dev));
>   
>   done: