Re: [PATCH v1 1/1] iio: adc: tsc2046: fix memory corruption by preventing array overflow

[Jonathan Cameron <jic23@kernel.org>]

On Fri,  7 Jan 2022 09:14:01 +0100
Oleksij Rempel <o.rempel@pengutronix.de> wrote:

> On one side we have indio_dev->num_channels includes all physical channels +
> timestamp channel. On other side we have an array allocated only for
> physical channels. So, fix memory corruption by ARRAY_SIZE() instead of
> num_channels variable.
> 
> Fixes: 9374e8f5a38d ("iio: adc: add ADC driver for the TI TSC2046 controller")
> Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Hi Olesij,

Have you managed to make this occur, or is it inspection only?

I 'think' (it's been a while since I looked at the particular code) that the timestamp
bit in active_scan_mask will never actually be set because we handle that as a
separate flag.

So it is indeed an efficiency improvement to not check that bit but I don't think
it's a bug to do so.  More than possible I'm missing something though!

This one had me quite worried when I first read it because this is a very common
pattern to see in IIO drivers.

Jonathan

> ---
>  drivers/iio/adc/ti-tsc2046.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-tsc2046.c b/drivers/iio/adc/ti-tsc2046.c
> index 91f6bd5effe7..8126084616e6 100644
> --- a/drivers/iio/adc/ti-tsc2046.c
> +++ b/drivers/iio/adc/ti-tsc2046.c
> @@ -395,7 +395,7 @@ static int tsc2046_adc_update_scan_mode(struct iio_dev *indio_dev,
>  	mutex_lock(&priv->slock);
>  
>  	size = 0;
> -	for_each_set_bit(ch_idx, active_scan_mask, indio_dev->num_channels) {
> +	for_each_set_bit(ch_idx, active_scan_mask, ARRAY_SIZE(priv->l)) {
>  		size += tsc2046_adc_group_set_layout(priv, group, ch_idx);
>  		tsc2046_adc_group_set_cmd(priv, group, ch_idx);
>  		group++;
> @@ -561,7 +561,7 @@ static int tsc2046_adc_setup_spi_msg(struct tsc2046_adc_priv *priv)
>  	 * enabled.
>  	 */
>  	size = 0;
> -	for (ch_idx = 0; ch_idx < priv->dcfg->num_channels; ch_idx++)
> +	for (ch_idx = 0; ch_idx < ARRAY_SIZE(priv->l); ch_idx++)
>  		size += tsc2046_adc_group_set_layout(priv, ch_idx, ch_idx);
>  
>  	priv->tx = devm_kzalloc(&priv->spi->dev, size, GFP_KERNEL);