Creds: creds->security can be NULL is selinux is disabled

__validate_process_creds should check if selinux is actually enabled before
running tests on the selinux portion of the credentials struct.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/selinux/exports.c

@@ -63,3 +63,9 @@ void selinux_secmark_refcount_dec(void)
 	atomic_dec(&selinux_secmark_refcount);
 }
 EXPORT_SYMBOL_GPL(selinux_secmark_refcount_dec);
+
+bool selinux_is_enabled(void)
+{
+	return selinux_enabled;
+}
+EXPORT_SYMBOL_GPL(selinux_is_enabled);