linux-kernel - Re: [PATCH] iio: adc: qcom-pm8xxx-xoadc: Remove useless condition in pm8xxx_xoadc_parse

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Date:   Tue, 14 Mar 2023 22:12:08 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Kasumov Ruslan <xhxgldhlpfy@...il.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-arm-msm@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org,
        Kasumov Ruslan <s02210418@....cs.msu.ru>
Subject: Re: [PATCH] iio: adc: qcom-pm8xxx-xoadc: Remove useless condition in pm8xxx_xoadc_parse_channel()

On Tue, Mar 14, 2023 at 8:37 PM Kasumov Ruslan <xhxgldhlpfy@...il.com> wrote:

> The left side of the loop condition never becomes false.
> hwchan cannot be NULL, because it points to elements of the
> hw_channels array that takes one of 4 predefined values:
> pm8018_xoadc_channels, pm8038_xoadc_channels,
> pm8058_xoadc_channels, pm8921_xoadc_channels.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.

I am not impressed with that tool. See below:

> Fixes: 63c3ecd946d4 ("iio: adc: add a driver for Qualcomm PM8xxx HK/XOADC")
> Signed-off-by: Kasumov Ruslan <s02210418@....cs.msu.ru>

(...)
>         hwchan = &hw_channels[0];
> -       while (hwchan && hwchan->datasheet_name) {
> +       while (hwchan->datasheet_name) {
>                 if (hwchan->pre_scale_mux == pre_scale_mux &&
>                     hwchan->amux_channel == amux_channel)
>                         break;

NAK have you tested this on a real system?

Here is the complete loop:

        hwchan = &hw_channels[0];
        while (hwchan && hwchan->datasheet_name) {
                if (hwchan->pre_scale_mux == pre_scale_mux &&
                    hwchan->amux_channel == amux_channel)
                        break;
                hwchan++;
                chid++;
        }

Notice how hwchan is used as iterator in hwchan++.

What you are doing will cause a zero-pointer dereference.

Whoever is developing "SVACE" needs to fix the tool to understand
this kind of usage.

Yours,
Linus Walleij