linux-kernel - Re: [PATCH v2] drm/bridge: ti-sn65dsi86: Avoid possible buffer overflow

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Date:   Thu, 8 Jun 2023 09:18:12 +0800
From:   Su Hui <suhui@...china.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, andersson@...nel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2] drm/bridge: ti-sn65dsi86: Avoid possible buffer
 overflow

On 2023/6/7 22:03, Doug Anderson wrote:
> Hi,
>
> On Tue, Jun 6, 2023 at 6:25 PM Su Hui <suhui@...china.com> wrote:
>> Smatch error:buffer overflow 'ti_sn_bridge_refclk_lut' 5 <= 5.
>>
>> Fixes: cea86c5bb442 ("drm/bridge: ti-sn65dsi86: Implement the pwm_chip")
>> Signed-off-by: Su Hui <suhui@...china.com>
>> ---
>>   drivers/gpu/drm/bridge/ti-sn65dsi86.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
>> index 7a748785c545..bb88406495e9 100644
>> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
>> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
>> @@ -305,7 +305,7 @@ static void ti_sn_bridge_set_refclk_freq(struct ti_sn65dsi86 *pdata)
>>           * The PWM refclk is based on the value written to SN_DPPLL_SRC_REG,
>>           * regardless of its actual sourcing.
>>           */
>> -       pdata->pwm_refclk_freq = ti_sn_bridge_refclk_lut[i];
>> +       pdata->pwm_refclk_freq = ti_sn_bridge_refclk_lut[i < refclk_lut_size ? i : 1];
> This looks more correct, but it really needs a comment since it's
> totally not obviously what you're doing here. IMO the best solution
> here is to update "i" right after the for loop and have a comment
> about the datasheet saying that "1" is the default rate so we'll fall
> back to that if we couldn't find a match. Moving it to right after the
> for loop will change the value written into the registers, but that's
> fine and makes it clearer what's happening.
Got it. Add some comment and move the code up.
I will send patch v3 soon.
Thanks for your suggestion again :) .

Su Hui

>
> -Doug