linux-kernel - Re: [PATCH v3 4/9] backlight: qcom-wled: Fix off-by-one maximum with default num

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Message-ID: <YcMJHmpheylD+L3l@google.com>
Date:   Wed, 22 Dec 2021 11:16:46 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     phone-devel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Pavel Dubrova <pashadubrova@...il.com>,
        Kiran Gunda <kgunda@...eaurora.org>,
        Bryan Wu <cooloney@...il.com>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Courtney Cavin <courtney.cavin@...ymobile.com>
Subject: Re: [PATCH v3 4/9] backlight: qcom-wled: Fix off-by-one maximum with
 default num_strings

On Mon, 15 Nov 2021, Marijn Suijten wrote:

> When not specifying num-strings in the DT the default is used, but +1 is
> added to it which turns WLED3 into 4 and WLED4/5 into 5 strings instead
> of 3 and 4 respectively, causing out-of-bounds reads and register
> read/writes.  This +1 exists for a deficiency in the DT parsing code,
> and is simply omitted entirely - solving this oob issue - by parsing the
> property separately much like qcom,enabled-strings.
> 
> This also enables more stringent checks on the maximum value when
> qcom,enabled-strings is provided in the DT, by parsing num-strings after
> enabled-strings to allow it to check against (and in a subsequent patch
> override) the length of enabled-strings: it is invalid to set
> num-strings higher than that.
> The DT currently utilizes it to get around an incorrect fixed read of
> four elements from that array (has been addressed in a prior patch) by
> setting a lower num-strings where desired.
> 
> Fixes: 93c64f1ea1e8 ("leds: add Qualcomm PM8941 WLED driver")
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> Reviewed-By: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> ---
>  drivers/video/backlight/qcom-wled.c | 48 ++++++++++-------------------
>  1 file changed, 16 insertions(+), 32 deletions(-)

Applied, thanks.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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