linux-kernel - Re: [PATCH][next] drm/mediatek: avoid dereferencing a null hdmi

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Date:   Tue, 8 Dec 2020 09:50:02 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     Colin King <colin.king@...onical.com>
CC:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Kishon Vijay Abraham I <kishon@...com>,
        "Vinod Koul" <vkoul@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        CK Hu <ck.hu@...iatek.com>,
        chunhui dai <chunhui.dai@...iatek.com>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <kernel-janitors@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next] drm/mediatek: avoid dereferencing a null hdmi_phy
 on an error message

On Mon, 2020-12-07 at 15:09 +0000, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently there is a null pointer check for hdmi_phy that implies it
> may be null, however a dev_err messages dereferences this potential null
> pointer.  Avoid a null pointer dereference by only emitting the dev_err
> message if hdmi_phy is non-null.  It is a moot point if the error message
> needs to be printed at all, but since this is a relatively new piece of
> code it may be useful to keep the message in for the moment in case there
> are unforseen errors that need to be reported.
> 
> Addresses-Coverity: ("Dereference after null check")
> Fixes: be28b6507c46 ("drm/mediatek: separate hdmi phy to different file")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  drivers/phy/mediatek/phy-mtk-hdmi.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/phy/mediatek/phy-mtk-hdmi.c b/drivers/phy/mediatek/phy-mtk-hdmi.c
> index c5c61f5a9ea0..5184054783c7 100644
> --- a/drivers/phy/mediatek/phy-mtk-hdmi.c
> +++ b/drivers/phy/mediatek/phy-mtk-hdmi.c
> @@ -84,8 +84,9 @@ mtk_hdmi_phy_dev_get_ops(const struct mtk_hdmi_phy *hdmi_phy)
>  	    hdmi_phy->conf->hdmi_phy_disable_tmds)
>  		return &mtk_hdmi_phy_dev_ops;
>  
> -	dev_err(hdmi_phy->dev, "Failed to get dev ops of phy\n");
> -		return NULL;
> +	if (hdmi_phy)
> +		dev_err(hdmi_phy->dev, "Failed to get dev ops of phy\n");
> +			return NULL;
indentation: one tab before return

Thanks

>  }
>  
>  static void mtk_hdmi_phy_clk_get_data(struct mtk_hdmi_phy *hdmi_phy,