linux-kernel - Re: [PATCH] drm/ast: potential dereference of null pointer

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Date:   Mon, 13 Dec 2021 10:59:05 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>, airlied@...hat.com,
        airlied@...ux.ie, daniel@...ll.ch
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/ast: potential dereference of null pointer

Hi,

thanks for the patch.

Am 13.12.21 um 06:39 schrieb Jiasheng Jiang:
> he return value of kzalloc() needs to be checked.

'The'

> To avoid use of null pointer '&ast_state->base' in case of the
> failure of alloc.
> 
> Fixes: f0adbc382b8b ("drm/ast: Allocate initial CRTC state of the correct size")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>   drivers/gpu/drm/ast/ast_mode.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index 36d9575aa27b..67f8e3f90ea2 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -1120,7 +1120,8 @@ static void ast_crtc_reset(struct drm_crtc *crtc)
>   	if (crtc->state)
>   		crtc->funcs->atomic_destroy_state(crtc, crtc->state);
>   
> -	__drm_atomic_helper_crtc_reset(crtc, &ast_state->base);
> +	if (ast_state)
> +		__drm_atomic_helper_crtc_reset(crtc, &ast_state->base);

If ast_state is NULL, __drm_atomic_helper_crtc_reset() has to be called 
with a state of NULL. Otherwise the reset might leave the dangling 
pointer in the CRTC's state field.

Best regards
Thomas

>   }
>   
>   static struct drm_crtc_state *
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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