Date:   Tue, 16 Nov 2021 11:58:53 +0000
From:   Daniel Thompson <daniel.thompson@linaro.org>
To:     Marijn Suijten <marijn.suijten@somainline.org>
Cc:     phone-devel@vger.kernel.org, Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Lee Jones <lee.jones@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        ~postmarketos/upstreaming@lists.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@somainline.org>,
        Konrad Dybcio <konrad.dybcio@somainline.org>,
        Martin Botka <martin.botka@somainline.org>,
        Jami Kettunen <jami.kettunen@somainline.org>,
        Pavel Dubrova <pashadubrova@gmail.com>,
        Kiran Gunda <kgunda@codeaurora.org>,
        Bryan Wu <cooloney@gmail.com>, linux-arm-msm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
        Courtney Cavin <courtney.cavin@sonymobile.com>
Subject: Re: [PATCH v3 4/9] backlight: qcom-wled: Fix off-by-one maximum with
 default num_strings
Message-ID: <20211116115853.mujwmb3v4r5s6c5v@maple.lan>
References: <20211115203459.1634079-1-marijn.suijten@somainline.org>
 <20211115203459.1634079-5-marijn.suijten@somainline.org>
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On Mon, Nov 15, 2021 at 09:34:54PM +0100, 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@somainline.org>
> Reviewed-By: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.