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

[Ville Syrjälä]

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@xxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx
> > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@xxxxxxxxxxxx>
> 
> 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/

> 
> 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 - http://blog.ffwll.ch
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-- 
Ville Syrjälä
Intel