linux-kernel - Re: [PATCH v2 RESEND] drm/msm/dpu: reorder pointer operations after sanity checks to avoid NULL deref

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Message-ID: <52905653-d78c-49b3-a329-a5ed797e149b@quicinc.com>
Date: Tue, 8 Apr 2025 10:28:11 -0700
From: Jessica Zhang <quic_jesszhan@...cinc.com>
To: Qasim Ijaz <qasdev00@...il.com>, <robdclark@...il.com>,
        <quic_abhinavk@...cinc.com>, <lumag@...nel.org>, <sean@...rly.run>,
        <marijn.suijten@...ainline.org>, <airlied@...il.com>,
        <simona@...ll.ch>
CC: <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        "Dmitry
 Baryshkov" <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v2 RESEND] drm/msm/dpu: reorder pointer operations after
 sanity checks to avoid NULL deref


On 4/8/2025 10:22 AM, Qasim Ijaz wrote:
> _dpu_encoder_trigger_start dereferences "struct dpu_encoder_phys *phys"
> before the sanity checks which can lead to a NULL pointer dereference if
> phys is NULL.
>   
> Fix this by reordering the dereference after the sanity checks.
>   
> Fixes: 8144d17a81d9 ("drm/msm/dpu: Skip trigger flush and start for CWB")
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> Signed-off-by: Qasim Ijaz <qasdev00@...il.com>


Reviewed-by: Jessica Zhang <quic_jesszhan@...cinc.com>


> ---
> v2:
> - Moved Signed-off tag below Fixes tag
> - Moved dpu_enc declaration to the top and initialisation below sanity checks
>
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 0eed93a4d056..0bd1f2bfaaff 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -1667,7 +1667,7 @@ static void _dpu_encoder_trigger_flush(struct drm_encoder *drm_enc,
>    */
>   static void _dpu_encoder_trigger_start(struct dpu_encoder_phys *phys)
>   {
> -	struct dpu_encoder_virt *dpu_enc = to_dpu_encoder_virt(phys->parent);
> +	struct dpu_encoder_virt *dpu_enc;
>   
>   	if (!phys) {
>   		DPU_ERROR("invalid argument(s)\n");
> @@ -1678,6 +1678,8 @@ static void _dpu_encoder_trigger_start(struct dpu_encoder_phys *phys)
>   		DPU_ERROR("invalid pingpong hw\n");
>   		return;
>   	}
> +
> +	dpu_enc = to_dpu_encoder_virt(phys->parent);
>   
>   	if (phys->parent->encoder_type == DRM_MODE_ENCODER_VIRTUAL &&
>   	    dpu_enc->cwb_mask) {