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

[David Lechner <dlechner@baylibre.com>]

On 10/22/25 11:54 AM, Marcelo Schmitt wrote:
> 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.

This code was unreachable with an undefined slot even before
this change because of the check to channel >= st->num_channels
before it.

> 
>>  		return;
> 
> Best regards,
> Marcelo