linux-kernel - Re: [PATCH] drm/msm/dpu: Add check for cstate

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Date:   Sun, 8 Jan 2023 23:56:07 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>, robdclark@...il.com,
        quic_abhinavk@...cinc.com, sean@...rly.run, airlied@...il.com,
        daniel@...ll.ch, quic_jesszhan@...cinc.com,
        ville.syrjala@...ux.intel.com, yang.lee@...ux.alibaba.com
Cc:     linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dpu: Add check for cstate

On 06/12/2022 10:05, Jiasheng Jiang wrote:
> As kzalloc may fail and return NULL pointer,
> it should be better to check cstate
> in order to avoid the NULL pointer dereference
> in __drm_atomic_helper_crtc_reset.
> 
> Fixes: 1cff7440a86e ("drm/msm: Convert to using __drm_atomic_helper_crtc_reset() for reset.")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> index 13ce321283ff..22c2787b7b38 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> @@ -968,7 +968,10 @@ static void dpu_crtc_reset(struct drm_crtc *crtc)
>   	if (crtc->state)
>   		dpu_crtc_destroy_state(crtc, crtc->state);
>   
> -	__drm_atomic_helper_crtc_reset(crtc, &cstate->base);
> +	if (cstate)
> +		__drm_atomic_helper_crtc_reset(crtc, &cstate->base);
> +	else
> +		__drm_atomic_helper_crtc_reset(crtc, NULL);

NAK.

The proper fix is to add the if() but to skip the else clause. We should 
not reset the crtc's state if memory allocation failed.

>   }
>   
>   /**

-- 
With best wishes
Dmitry