linux-kernel - Re: [PATCH] drm/msm/dpu: Fix pointer dereferenced before checking

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Message-ID: <CAF6AEGtsAH6LdE9douMMYEM2hW6_ifcqgM5mxaj43XAr=3uCTw@mail.gmail.com>
Date:   Tue, 31 May 2022 13:34:48 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Haowen Bai <baihaowen@...zu.com>
Cc:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/dpu: Fix pointer dereferenced before checking

On Mon, May 30, 2022 at 12:34 AM Haowen Bai <baihaowen@...zu.com> wrote:
>
> The ctx->hw is dereferencing before null checking, so move
> it after checking.
>
> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_hw_wb.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_wb.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_wb.c
> index bcccce292937..e59680cdd0ce 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_wb.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_wb.c
> @@ -155,11 +155,13 @@ static void dpu_hw_wb_roi(struct dpu_hw_wb *ctx, struct dpu_hw_wb_cfg *wb)
>  static void dpu_hw_wb_setup_qos_lut(struct dpu_hw_wb *ctx,
>                 struct dpu_hw_wb_qos_cfg *cfg)
>  {
> -       struct dpu_hw_blk_reg_map *c = &ctx->hw;
> +       struct dpu_hw_blk_reg_map *c;
>         u32 qos_ctrl = 0;
>
>         if (!ctx || !cfg)
>                 return;
> +
> +       c = &ctx->hw;

tbh, we should just drop both of these null checks.. there is no
codepath that can reach this with potential for either param to be
NULL

BR,
-R

>
>         DPU_REG_WRITE(c, WB_DANGER_LUT, cfg->danger_lut);
>         DPU_REG_WRITE(c, WB_SAFE_LUT, cfg->safe_lut);
> --
> 2.7.4
>