[PATCH] fbdev: potential information leak in do_fb_ioctl()

[Arnd Bergmann]

On Wed, Jan 15, 2020 at 2:09 PM Bartlomiej Zolnierkiewicz
<b.zolnierkie at samsung.com> wrote:

> > $ git grep -wl register_framebuffer | xargs grep -L framebuffer_alloc
> > Documentation/fb/framebuffer.rst
> > drivers/media/pci/ivtv/ivtvfb.c
> > drivers/media/platform/vivid/vivid-osd.c
> > drivers/video/fbdev/68328fb.c
> > drivers/video/fbdev/acornfb.c
> > drivers/video/fbdev/amba-clcd.c
> > drivers/video/fbdev/atafb.c
> > drivers/video/fbdev/au1100fb.c
> > drivers/video/fbdev/controlfb.c
> > drivers/video/fbdev/core/fbmem.c
> > drivers/video/fbdev/cyber2000fb.c
> > drivers/video/fbdev/fsl-diu-fb.c
> > drivers/video/fbdev/g364fb.c
> > drivers/video/fbdev/goldfishfb.c
> > drivers/video/fbdev/hpfb.c
> > drivers/video/fbdev/macfb.c
> > drivers/video/fbdev/matrox/matroxfb_base.c
> > drivers/video/fbdev/matrox/matroxfb_crtc2.c
> > drivers/video/fbdev/maxinefb.c
> > drivers/video/fbdev/ocfb.c
> > drivers/video/fbdev/pxafb.c
> > drivers/video/fbdev/sa1100fb.c
> > drivers/video/fbdev/stifb.c
> > drivers/video/fbdev/valkyriefb.c
> > drivers/video/fbdev/vermilion/vermilion.c
> > drivers/video/fbdev/vt8500lcdfb.c
> > drivers/video/fbdev/wm8505fb.c
> > drivers/video/fbdev/xilinxfb.c
> >
> > It's possible (even likely, the ones I looked at are fine) that they
> > all correctly
> > zero out the fb_info structure first, but it seems hard to guarantee, so
> > Eric's suggestion would possibly still be the safer choice.
>
> I've audited all above instances and they are all fine. They either
> use the fb_info structure embedded in a driver specific structure
> (which is zeroed out) or (in case of some m68k specific drivers) use
> a static fb_info instance.
>
> Since fbdev is closed for new drivers it should be now fine to use
> the simpler approach (just use memcpy()).

Yes, let's do that then. The complex approach seems more likely
to introduce a bug than one of the existing drivers to stop initializing
the structure correctly.

      Arnd