CHROMIUM: kernel: Initial chromiumos security module.

CHROMIUM: kernel: Initial chromiumos security module.

Initially the chromiumos security module only prevents symlinks
in mount paths. Future versions will be more restrictive and
will be configurable using a driver interface.

BUG=chromium-os:21954
TEST=Use a mount path with a symlink and observe mount failure.

Change-Id: I47ade3b7be684ab9e0533ce5ffd1e81009eaebfe
Signed-off-by: Stephan Uphoff <ups@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/10581
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
[3.4 kernel: added include linux/sched.h --grundler]