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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 15 Jan 2020 14:16:57 +0100
Message-ID: <CAK8P3a3SJZ+j0jzYGtETaLGUXwwn0WqjN+wojUrYngOui9+h7A@mail.gmail.com>
Subject: Re: [PATCH] fbdev: potential information leak in do_fb_ioctl()
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Joe Perches <joe@perches.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Andrea Righi <righi.andrea@gmail.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Sam Ravnborg <sam@ravnborg.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Peter Rosin <peda@axentia.se>,
        Gerd Hoffmann <kraxel@redhat.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        kernel-janitors@vger.kernel.org, security@kernel.org,
        Kees Cook <keescook@chromium.org>,
        Julia Lawall <Julia.Lawall@lip6.fr>
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On Wed, Jan 15, 2020 at 2:09 PM Bartlomiej Zolnierkiewicz
<b.zolnierkie@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