linux-kernel - Re: [PATCH] drm: bridge: it66121: Fix invalid connector dereference

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Message-ID: <d2deac24-d5ab-e1c4-81c5-4874c2f5ea07@ti.com>
Date:   Mon, 28 Aug 2023 16:34:30 +0530
From:   Aradhya Bhatia <a-bhatia1@...com>
To:     Jai Luthra <j-luthra@...com>, Phong LE <ple@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        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>,
        Nicolas Belin <nbelin@...libre.com>,
        "Andy.Hsieh" <Andy.Hsieh@...iatek.com>
CC:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <devarsht@...com>,
        <nm@...com>
Subject: Re: [PATCH] drm: bridge: it66121: Fix invalid connector dereference

Hi Jai,

Thanks for debugging the issue.

On 25-Aug-23 16:32, Jai Luthra wrote:
> Fix the NULL pointer dereference when no monitor is connected, and the
> sound card is opened from userspace.
> 
> Instead return an error as EDID information cannot be provided to
> the sound framework if there is no connector attached.
> 
> Fixes: e0fd83dbe924 ("drm: bridge: it66121: Add audio support")
> Reported-by: Nishanth Menon <nm@...com>
> Closes: https://lore.kernel.org/all/20230825105849.crhon42qndxqif4i@gondola/
> Signed-off-by: Jai Luthra <j-luthra@...com>
> ---
>  drivers/gpu/drm/bridge/ite-it66121.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
> index 466641c77fe9..d6fa00dea464 100644
> --- a/drivers/gpu/drm/bridge/ite-it66121.c
> +++ b/drivers/gpu/drm/bridge/ite-it66121.c
> @@ -1446,6 +1446,11 @@ static int it66121_audio_get_eld(struct device *dev, void *data,
>  {
>  	struct it66121_ctx *ctx = dev_get_drvdata(dev);
>  
> +	if (!ctx->connector) {
> +		dev_dbg(dev, "No connector present, cannot provide EDID data");
> +		return -EINVAL;
> +	}
> +

There are not many HDMI bridges that support codecs in the kernel, but
upon a quick look, bridge/analogix/anx7625.c and
bridge/synopsys/dw-hdmi* gracefully return a buffer of 0s when the
connector is unavailable.

I am not sure why that is done, but I also don't see the hdmi-codec
driver handle the 0s situation properly. It is business as usual for the
hdmi-codec.

Did you come across some observation when you were testing?

Regards
Aradhya

>  	mutex_lock(&ctx->lock);
>  
>  	memcpy(buf, ctx->connector->eld,
> 
> ---
> base-commit: 6269320850097903b30be8f07a5c61d9f7592393
> change-id: 20230825-it66121_edid-6ee98517808b
> 
> Best regards,