linux-kernel - Re: [PATCH] drm/arm/malidp: fix a possible null pointer dereference

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Message-ID: <Zg1H15nvHr_zbpKo@e110455-lin.cambridge.arm.com>
Date: Wed, 3 Apr 2024 13:13:11 +0100
From: Liviu Dudau <liviu.dudau@....com>
To: Huai-Yuan Liu <qq810974084@...il.com>
Cc: maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	baijiaju1990@...look.com
Subject: Re: [PATCH] drm/arm/malidp: fix a possible null pointer dereference

Hi,

On Wed, Apr 03, 2024 at 09:43:01AM +0800, Huai-Yuan Liu wrote:
> 
> In malidp_mw_connector_reset, new memory is allocated with kzalloc, but 
> no check is performed. In order to prevent null pointer dereferencing, 
> ensure that mw_state is checked before calling 
> __drm_atomic_helper_connector_reset.

Thanks for the patch, it does look like an oversight. Can I suggest you
respin your patch and add a

	connector->state = NULL;

right after kfree(connector->state) ?

That way we can be sure we're not leaving state pointing to freed memory.

Best regards,
Liviu

> 
> Fixes: 8cbc5caf36ef ("drm: mali-dp: Add writeback connector")
> Signed-off-by: Huai-Yuan Liu <qq810974084@...il.com>
> ---
>  drivers/gpu/drm/arm/malidp_mw.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/arm/malidp_mw.c b/drivers/gpu/drm/arm/malidp_mw.c
> index 626709bec6f5..25623ef9be80 100644
> --- a/drivers/gpu/drm/arm/malidp_mw.c
> +++ b/drivers/gpu/drm/arm/malidp_mw.c
> @@ -72,7 +72,9 @@ static void malidp_mw_connector_reset(struct drm_connector *connector)
>  		__drm_atomic_helper_connector_destroy_state(connector->state);
>  
>  	kfree(connector->state);
> -	__drm_atomic_helper_connector_reset(connector, &mw_state->base);
> +
> +	if (mw_state)
> +		__drm_atomic_helper_connector_reset(connector, &mw_state->base);
>  }
>  
>  static enum drm_connector_status
> -- 
> 2.34.1
> 

-- 
====================
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