drm: udl: Properly check framebuffer mmap offsets

commit 3b82a4db8eaccce735dffd50b4d4e1578099b8e8 upstream.

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


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>