UPSTREAM: selinux: check sidtab limit before adding a new entry

We need to error out when trying to add an entry above SIDTAB_MAX in
sidtab_reverse_lookup() to avoid overflow on the odd chance that this
happens.

Cc: stable@vger.kernel.org
Fixes: ee1a84fdfeed ("selinux: overhaul sidtab to fix bug and improve performance")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Paul Moore <paul@paul-moore.com>

(cherry picked from commit acbc372e6109c803cbee4733769d02008381740f)
Change-Id: I88e6b5b1626c901e41ecbf1dfdded6f4e7301332
Bug: 140252993
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>