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

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Date:   Mon, 10 Jan 2022 08:19:45 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     devicetree@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio@...r.kernel.org,
        Robin van der Gracht <robin@...tonic.nl>,
        linux-kernel@...r.kernel.org,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        David Jander <david@...tonic.nl>
Subject: Re: [PATCH v1 1/1] iio: adc: tsc2046: fix memory corruption by
 preventing array overflow

Hi Jonathan,

On Sun, Jan 09, 2022 at 03:25:57PM +0000, Jonathan Cameron wrote:
> On Fri,  7 Jan 2022 09:14:01 +0100
> Oleksij Rempel <o.rempel@...gutronix.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@...gutronix.de>
> Hi Olesij,
> 
> Have you managed to make this occur, or is it inspection only?

Yes, this bug has eaten my rx_one and tx_one pointers on probe. I wonted
to use this buffers for read_raw and noticed that they do not exist.

> 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.

I didn't tested if active_scan_mask will trigger this issue as well, but
It it looked safer to me, to avoid this issue in both places. Even if on
of it is only theoretical.

> 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.

I was thinking about this as well, because big part of this code was
inspired by other drivers. But i didn't reviewed other places so far.

Regards,
Oleksij
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