linux-kernel - Re: [PATCH] drm/panel: himax-hx83102: Add NULL pointer check in hx83102_get

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Message-ID: <CAD=FV=UzEucvODyhYo=o-eroe3Q3+siKN2yWwAfOQ=L8NXBD_Q@mail.gmail.com>
Date: Tue, 3 Sep 2024 16:14:38 -0700
From: Doug Anderson <dianders@...omium.org>
To: Charles Han <hanchunchao@...pur.com>
Cc: neil.armstrong@...aro.org, yangcong5@...qin.corp-partner.google.com, 
	quic_jesszhan@...cinc.com, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, tzimmermann@...e.de, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, liuyanming@...system.com
Subject: Re: [PATCH] drm/panel: himax-hx83102: Add NULL pointer check in hx83102_get_modes

Hi,

On Fri, Aug 23, 2024 at 9:49 AM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Fri, Aug 23, 2024 at 9:35 AM Charles Han <hanchunchao@...pur.com> wrote:
> >
> > In hx83102_get_modes(), the return value of drm_mode_duplicate()
> > is assigned to mode, which will lead to a possible NULL pointer
> > dereference on failure of drm_mode_duplicate(). Even though a
> > small allocation failing is basically impossible, kernel policy
> > is still to check for NULL so add the check.
> >
> > Fixes: 0ef94554dc40 ("drm/panel: himax-hx83102: Break out as separate driver")
> > Signed-off-by: Charles Han <hanchunchao@...pur.com>
> > ---
> >  drivers/gpu/drm/panel/panel-himax-hx83102.c | 2 ++
> >  1 file changed, 2 insertions(+)
>
> FWIW, this looks to be v4 of your patch, right? The subject line
> should include a version number and you should be providing version
> history "after the cut" in your patch. Tools like "b4" and "patman"
> can help you get this correct [1]. If you plan to continue posting
> patches you'll need to start getting this right. The next version of
> your patch would be v5.
>
> [1] https://sched.co/1aBGS
>
> I see:
>
> v1: https://lore.kernel.org/r/20240821095039.15282-1-hanchunchao@inspur.com
> v2: https://lore.kernel.org/r/20240822093442.4262-1-hanchunchao@inspur.com
> v3: https://lore.kernel.org/r/20240823083657.7100-1-hanchunchao@inspur.com
>
>
> > diff --git a/drivers/gpu/drm/panel/panel-himax-hx83102.c b/drivers/gpu/drm/panel/panel-himax-hx83102.c
> > index 6e4b7e4644ce..e67555323d3b 100644
> > --- a/drivers/gpu/drm/panel/panel-himax-hx83102.c
> > +++ b/drivers/gpu/drm/panel/panel-himax-hx83102.c
> > @@ -565,6 +565,8 @@ static int hx83102_get_modes(struct drm_panel *panel,
> >         struct drm_display_mode *mode;
> >
> >         mode = drm_mode_duplicate(connector->dev, m);
> > +       if (!mode)
> > +               return -EINVAL;
>
> I would have returned -ENOMEM since drm_mode_duplicate() is defined to
> allocate memory copy the mode (like strdup does for strings) and it
> should be clear that the only failure case is failure to allocate
> memory. Other callers convert a NULL return as -ENOMEM.

FWIW: if you spin v5 of this patch and have it return -ENOMEM then I'm
happy to apply it.

-Doug