Re: [PATCH] dpu1: dpu_encoder: fix a missing check on list iterator

[Dmitry Baryshkov]

On 27/03/2022 10:32, Xiaomeng Tong wrote:
> The bug is here:
> 	 cstate = to_dpu_crtc_state(drm_crtc->state);
>
> For the drm_for_each_crtc(), just like list_for_each_entry(),
> the list iterator 'drm_crtc' will point to a bogus position
> containing HEAD if the list is empty or no element is found.
> This case must be checked before any use of the iterator,
> otherwise it will lead to a invalid memory access.
>
> To fix this bug, use a new variable 'iter' as the list iterator,
> while use the origin variable 'drm_crtc' as a dedicated pointer
> to point to the found element.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: b107603b4ad0f ("drm/msm/dpu: map mixer/ctl hw blocks in encoder modeset")
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 1e648db439f9..d3fdb18e96f9 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -965,7 +965,7 @@ static void dpu_encoder_virt_mode_set(struct drm_encoder *drm_enc,
>   	struct dpu_kms *dpu_kms;
>   	struct list_head *connector_list;
>   	struct drm_connector *conn = NULL, *conn_iter;
> -	struct drm_crtc *drm_crtc;
> +	struct drm_crtc *drm_crtc = NULL, *iter;
>   	struct dpu_crtc_state *cstate;
>   	struct dpu_global_state *global_state;
>   	struct dpu_hw_blk *hw_pp[MAX_CHANNELS_PER_ENC];
> @@ -1007,9 +1007,14 @@ static void dpu_encoder_virt_mode_set(struct drm_encoder *drm_enc,
>   		return;
>   	}
>   
> -	drm_for_each_crtc(drm_crtc, drm_enc->dev)
> -		if (drm_crtc->state->encoder_mask & drm_encoder_mask(drm_enc))
> +	drm_for_each_crtc(iter, drm_enc->dev)
> +		if (iter->state->encoder_mask & drm_encoder_mask(drm_enc)) {
> +			drm_crtc = iter;
>   			break;
> +		}
> +
> +	if (!drm_crtc)
> +		return;
>   
>   	/* Query resource that have been reserved in atomic check step. */
>   	num_pp = dpu_rm_get_assigned_resources(&dpu_kms->rm, global_state,


--
With best wishes
Dmitry