linux-kernel - Re: [PATCH] drm/vc4: hdmi: Fix pointer dereference before check

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Date:   Wed, 2 Nov 2022 10:01:53 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     José Expósito <jose.exposito89@...il.com>
Cc:     emma@...olt.net, airlied@...il.com, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/vc4: hdmi: Fix pointer dereference before check

Hi,

On Sat, Oct 29, 2022 at 11:34:13AM +0200, José Expósito wrote:
> Commit 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug") introduced
> the vc4_hdmi_reset_link() function. This function dereferences the
> "connector" pointer before checking whether it is NULL or not.
> 
> Rework variable assignment to avoid this issue.
> 
> Fixes: 6bed2ea3cb38 ("drm/vc4: hdmi: Reset link on hotplug")
> Signed-off-by: José Expósito <jose.exposito89@...il.com>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index 4a73fafca51b..07d058b6afb7 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -319,9 +319,9 @@ static int reset_pipe(struct drm_crtc *crtc,
>  static int vc4_hdmi_reset_link(struct drm_connector *connector,
>  			       struct drm_modeset_acquire_ctx *ctx)
>  {
> -	struct drm_device *drm = connector->dev;
> -	struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
> -	struct drm_encoder *encoder = &vc4_hdmi->encoder.base;
> +	struct drm_device *drm;
> +	struct vc4_hdmi *vc4_hdmi;
> +	struct drm_encoder *encoder;
>  	struct drm_connector_state *conn_state;
>  	struct drm_crtc_state *crtc_state;
>  	struct drm_crtc *crtc;
> @@ -332,6 +332,10 @@ static int vc4_hdmi_reset_link(struct drm_connector *connector,
>  	if (!connector)
>  		return 0;
>  
> +	drm = connector->dev;
> +	vc4_hdmi = connector_to_vc4_hdmi(connector);
> +	encoder = &vc4_hdmi->encoder.base;
> +

I don't think that's right. Connector shouldn't be NULL to begin with,
how did you notice this?

Maxime

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