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

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Message-ID: <CAD=FV=UxzUoAPbKtX3Xvq=g8DNcatQ8-s-8rcGEeE+G40a9RhQ@mail.gmail.com>
Date:   Wed, 7 Jun 2023 07:03:50 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Su Hui <suhui@...china.com>
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

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.


-Doug

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];
>  }
>
>  static void ti_sn65dsi86_enable_comms(struct ti_sn65dsi86 *pdata)
> --
> 2.30.2
>