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

[Dmitry Baryshkov]

On 11/04/2022 03:56, Dmitry Baryshkov wrote:
> 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>

On the other hand, this code has been removed in 5.18-rc1 in the commit 
764332bf96244cbc8baf08aa35844b29106da312.

> > ---
> >   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