Re: [PATCH] drm/kmb: fix dereference before NULL check in kmb_plane_atomic_update()

[Thomas Zimmermann]

Hi

Am 29.07.22 um 16:23 schrieb Thomas Zimmermann:
> Hi
>
> Am 29.07.22 um 05:07 schrieb Zeng Jingxiang:
> > From: Zeng Jingxiang <linuszeng@xxxxxxxxxxx>
> >
> > The "plane" pointer was access before checking if it was NULL.
> >
> > The drm_atomic_get_old_plane_state() function will dereference
> > the pointer "plane".
> > 345    struct drm_plane_state *old_plane_state =
> >         drm_atomic_get_old_plane_state(state, plane);
> > 346    struct drm_plane_state *new_plane_state =
> >         drm_atomic_get_new_plane_state(state, plane);
> >
> > A NULL check for "plane" indicates that it may be NULL
> > 363    if (!plane || !new_plane_state || !old_plane_state)
>
> Is this an actual bug that happens?
>
> All planes should always have a state. Therefore the tests for 
> !new_plane_state and !old_plane_state can be removed, I'd say.

Just to clarify: moving the test for !plane before using one of the 
get_plane_state functions is a correct bugfix.

Best regards
Thomas

> Best regards
> Thomas
>
> > Fixes: 977697e20b3d ("drm/atomic: Pass the full state to planes atomic 
> > disable and update")
> > Fixes: 37418bf14c13 ("drm: Use state helper instead of the plane state 
> > pointer")
> > Signed-off-by: Zeng Jingxiang <linuszeng@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/kmb/kmb_plane.c | 13 ++++++++-----
> >   1 file changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/kmb/kmb_plane.c 
> > b/drivers/gpu/drm/kmb/kmb_plane.c
> > index 2735b8eb3537..d2bc998b65ce 100644
> > --- a/drivers/gpu/drm/kmb/kmb_plane.c
> > +++ b/drivers/gpu/drm/kmb/kmb_plane.c
> > @@ -342,10 +342,7 @@ static void kmb_plane_set_alpha(struct 
> > kmb_drm_private *kmb,
> >   static void kmb_plane_atomic_update(struct drm_plane *plane,
> >                       struct drm_atomic_state *state)
> >   {
> > -    struct drm_plane_state *old_plane_state = 
> > drm_atomic_get_old_plane_state(state,
> > -                                         plane);
> > -    struct drm_plane_state *new_plane_state = 
> > drm_atomic_get_new_plane_state(state,
> > -                                         plane);
> > +    struct drm_plane_state *old_plane_state, *new_plane_state;
> >       struct drm_framebuffer *fb;
> >       struct kmb_drm_private *kmb;
> >       unsigned int width;
> > @@ -360,7 +357,13 @@ static void kmb_plane_atomic_update(struct 
> > drm_plane *plane,
> >       static dma_addr_t addr[MAX_SUB_PLANES];
> >       struct disp_cfg *init_disp_cfg;
> > -    if (!plane || !new_plane_state || !old_plane_state)
> > +    if (!plane)
> > +        return;
> > +
> > +    old_plane_state = drm_atomic_get_old_plane_state(state, plane);
> > +    new_plane_state = drm_atomic_get_new_plane_state(state, plane);
> > +
> > +    if (!new_plane_state || !old_plane_state)
> >           return;
> >       fb = new_plane_state->fb;

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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