drm: udl: Properly check framebuffer mmap offsets

drm: udl: Properly check framebuffer mmap offsets

CVE-2018-8781

The memmap options sent to the udl framebuffer driver were not being
checked for all sets of possible crazy values.  Fix this up by properly
bounding the allowed values.

Reported-by: Eyal Itkin <eyalit@checkpoint.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180321154553.GA18454@kroah.com
(cherry picked from commit 3b82a4db8eaccce735dffd50b4d4e1578099b8e8)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Andy Whitcroft <andy.whitcroft@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>