On Mon, Aug 26, 2013 at 03:16:49PM +0200, David Herrmann wrote: > DRM_IOCTL_MODE_GETFB is used to retrieve information about a given > framebuffer ID. It is a read-only helper and was thus declassified for > unprivileged access in: > > commit a14b1b42477c5ef089fcda88cbaae50d979eb8f9 > Author: Mandeep Singh Baines <mandeep.baines@xxxxxxxxx> > Date: Fri Jan 20 12:11:16 2012 -0800 > > drm: remove master fd restriction on mode setting getters > > However, alongside width, height and stride information, > DRM_IOCTL_MODE_GETFB also passes back a handle to the underlying buffer of > the framebuffer. This handle allows users to mmap() it and read or write > into it. Obviously, this should be restricted to DRM-Master. > > With the current setup, *any* process with access to /dev/dri/card0 (which > means any process with access to hardware-accelerated rendering) can > access the current screen framebuffer and modify it ad libitum. > > For backwards-compatibility reasons we want to keep the > DRM_IOCTL_MODE_GETFB call unprivileged. Besides, it provides quite useful > information regarding screen setup. So we simply test whether the caller > is the current DRM-Master and if not, we return 0 as handle, which is > always invalid. A following DRM_IOCTL_GEM_CLOSE on this handle will fail > with EINVAL, but we accept this. Users shouldn't test for errors during > GEM_CLOSE, anyway. And it is still better as a failing MODE_GETFB call. > > v2: add capable(CAP_SYS_ADMIN) check for compatibility with i-g-t > > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxx> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
