Re: [PATCH] iio: adc: ad7124: fix possible OOB array access

[Marcelo Schmitt <marcelo.schmitt1@gmail.com>]

Hi David,

One minor question inline.
Nevertheless, the fix looks good to me.

Reviewed-by: Marcelo Schmitt <marcelo.schmitt@analog.com>

On 10/22, David Lechner wrote:
> Reorder the channel bounds check before using it to index into the
> channels array in ad7124_release_config_slot(). This prevents reading
> past the end of the array.
> 
> The value read from invalid memory was not used, so this was mostly
What is considered using the value in this context? (see other comment below)

> harmless, but we still should not be reading out of bounds in the first
> place.
> 
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/linux-iio/aPi6V-hcaKReSNWK@stanley.mountain/
> Fixes: 9065197e0d41 ("iio: adc: ad7124: change setup reg allocation strategy")
> Signed-off-by: David Lechner <dlechner@baylibre.com>
> ---
>  drivers/iio/adc/ad7124.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7124.c b/drivers/iio/adc/ad7124.c
> index 9d58ced7371d0af7004a81153888714e9795d4f4..ed828a82acb71342fb2eae27abfbbd86861cba53 100644
> --- a/drivers/iio/adc/ad7124.c
> +++ b/drivers/iio/adc/ad7124.c
> @@ -586,13 +586,18 @@ static int ad7124_request_config_slot(struct ad7124_state *st, u8 channel)
>  
>  static void ad7124_release_config_slot(struct ad7124_state *st, u8 channel)
>  {
> -	unsigned int slot = st->channels[channel].cfg.cfg_slot;
> +	unsigned int slot;
>  
>  	/*
> -	 * All of these conditions can happen at probe when all channels are
> -	 * disabled. Otherwise, they should not happen normally.
> +	 * All of these early return conditions can happen at probe when all
> +	 * channels are disabled. Otherwise, they should not happen normally.
>  	 */
> -	if (channel >= st->num_channels || slot == AD7124_CFG_SLOT_UNASSIGNED ||
> +	if (channel >= st->num_channels)
> +		return;
> +
> +	slot = st->channels[channel].cfg.cfg_slot;
> +
> +	if (slot == AD7124_CFG_SLOT_UNASSIGNED ||
>  	    st->cfg_slot_use_count[slot] == 0)
Wasn't the value potentially read from invalid memory used above?
It's fixed now, so I guess there's no point in nitpicking on that.

>  		return;

Best regards,
Marcelo