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

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Message-ID: <aPkYR_Y8XtTw-iT9@debian-BULLSEYE-live-builder-AMD64>
Date: Wed, 22 Oct 2025 14:45:43 -0300
From: Marcelo Schmitt <marcelo.schmitt1@...il.com>
To: David Lechner <dlechner@...libre.com>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] iio: adc: ad7124: fix possible OOB array access

On 10/22, David Lechner wrote:
> 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@...log.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@...aro.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@...libre.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.
> 
ah, got it. Duh, should have realized channel >= st->num_channels always true
for the invalid access case.

Thanks

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