Re: [PATCH] drm: fb-helper: Validate requested pixel format against bpp

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Oct 3, 2018 at 4:30 PM Eugeniy Paltsev
<eugeniy.paltsev@synopsys.com> wrote:
>
> On Wed, 2018-10-03 at 15:30 +0300, Ville Syrjälä wrote:
> > On Wed, Oct 03, 2018 at 01:36:00PM +0200, Daniel Vetter wrote:
> > > On Wed, Oct 3, 2018 at 1:05 PM Eugeniy Paltsev
> > > <Eugeniy.Paltsev@synopsys.com> wrote:
> > > >
> > > > Validate requested pixel format against bits_per_pixel to reject
> > > > invalid formats with subcomponents length sum is greater than requested
> > > > bits_per_pixel.
> > > >
> > > > weston 5.0.0 with fbdev backend tries to set up an ARGB x8r8g8b8 pixel
> > > > format without bits_per_pixel updating. So it can request
> > > > x8r8g8b8 with 16 bpp which is obviously incorrect and should be
> > > > rejected.
> > > >
> > > > Cc: stable@vger.kernel.org
> > > > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
> > >
> > > drm fbdev emulation doesn't support changing the pixel format at all.
> > > I think we should reject all such request, not just the invalid ones.
> > > Can you pls respin?
> >
> > FYI I once posted a patch to tighten up the fb-helper pixel format
> > stuff:
> > https://patchwork.freedesktop.org/patch/203189/
>
>
> Hi Daniel,
>
> will you take Ville's patch or should I create the new one which is only related
> to new pixel format validation in drm_fb_helper_check_var() ?

Ville's patch isn't the bugfix we're looking for, but a draft version
of what adding proper format support in drm's fbdev emulation could
look like. With lots&lots of open questions. Not anywhere near ready
for merging, and definitely not stable backport material.

So yes, still want the minimal bugfix.
-Daniel

>
>
> > > Thanks, Daniel
> > >
> > > > ---
> > > >  drivers/gpu/drm/drm_fb_helper.c | 7 +++++++
> > > >  1 file changed, 7 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > > > index 16ec93b75dbf..4f39da07f053 100644
> > > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > > @@ -1610,6 +1610,13 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
> > > >                 return -EINVAL;
> > > >         }
> > > >
> > > > +       if ((var->green.length + var->blue.length + var->red.length +
> > > > +           var->transp.length) > var->bits_per_pixel) {
> > > > +               DRM_DEBUG("fb requested pixel format can't fit in %d bpp\n",
> > > > +                         var->bits_per_pixel);
> > > > +               return -EINVAL;
> > > > +       }
> > > > +
> > > >         switch (var->bits_per_pixel) {
> > > >         case 16:
> > > >                 depth = (var->green.length == 6) ? 16 : 15;
> > > > --
> > > > 2.14.4
> > > >
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> > >
> > >
> > >
> > > --
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > +41 (0) 79 365 57 48 - https://urldefense.proofpoint.com/v2/url?u=http-3A__blog.ffwll.ch&d=DwIDAw&c=DPL6_X_6JkXFx7AXWqB0tg&r=ZlJN1MriPUTkBKCrPSx67
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> >
> >
> --
>  Eugeniy Paltsev



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch