linux-kernel - Re: [PATCH] drm/bridge: Add null pointer check for ITE IT6263

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Message-ID: <CALGdzurMksSELQMDxy11gHS=pfASP6x_d+Sw2uZfXguLqb=J9A@mail.gmail.com>
Date: Wed, 23 Jul 2025 09:09:14 -0700
From: Chenyuan Yang <chenyuan0y@...il.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: victor.liu@....com, andrzej.hajda@...el.com, neil.armstrong@...aro.org, 
	rfoss@...nel.org, laurent.pinchart@...asonboard.com, jonas@...boo.se, 
	jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com, 
	tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch, lumag@...nel.org, 
	biju.das.jz@...renesas.com, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: Add null pointer check for ITE IT6263

Apologies for the second email.
I am resending this message as the formatting in the previous version
was incorrect

On Tue, Jul 22, 2025 at 11:57 PM Maxime Ripard <mripard@...nel.org> wrote:
>
> On Tue, Jul 22, 2025 at 03:41:14PM -0500, Chenyuan Yang wrote:
> > drm_atomic_get_new_connector_for_encoder and
> > drm_atomic_get_new_connector_state could return Null.
>
> They can, but not in that scenario. atomic_enable will never be called
> if either would return NULL.
>
> In which situation did you trigger this bug?

This is found by our static analysis tool based on the fact that
drm_atomic_get_new_connector_state() could return NULL.
We also noticed that under the same dir, the ITE IT6505 transmitter
has such checks.
Thus, we assume it would be good to have similar checks here.

> > Thus, add the null pointer check for them with a similar format with
> > it6505_bridge_atomic_enable in ITE IT6505.
> >
> > Signed-off-by: Chenyuan Yang <chenyuan0y@...il.com>
> > Fixes: 049723628716 ("drm/bridge: Add ITE IT6263 LVDS to HDMI converter")
> > ---
> >  drivers/gpu/drm/bridge/ite-it6263.c | 15 ++++++++++++++-
> >  1 file changed, 14 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/ite-it6263.c b/drivers/gpu/drm/bridge/ite-it6263.c
> > index a3a63a977b0a..3a20b2088bf9 100644
> > --- a/drivers/gpu/drm/bridge/ite-it6263.c
> > +++ b/drivers/gpu/drm/bridge/ite-it6263.c
> > @@ -590,15 +590,28 @@ static void it6263_bridge_atomic_enable(struct drm_bridge *bridge,
> >       struct drm_connector *connector;
> >       bool is_stable = false;
> >       struct drm_crtc *crtc;
> > +     struct drm_connector_state *conn_state;
> >       unsigned int val;
> >       bool pclk_high;
> >       int i, ret;
> >
> >       connector = drm_atomic_get_new_connector_for_encoder(state,
> >                                                            bridge->encoder);
> > -     crtc = drm_atomic_get_new_connector_state(state, connector)->crtc;
> > +     if (WARN_ON(!connector))
> > +             return;
> > +
> > +     conn_state = drm_atomic_get_new_connector_state(state, connector);
> > +     if (WARN_ON(!conn_state))
> > +             return;
> > +
> > +     crtc = conn_state->crtc;
> >       crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
> > +     if (WARN_ON(!crtc_state))
> > +             return;
> > +
> >       mode = &crtc_state->adjusted_mode;
> > +     if (WARN_ON(!mode))
> > +             return;
>
> And that condition can never be true.
>
> Maxime