LSM: Introduce LSM_FLAG_LEGACY_MAJOR

This adds a flag for the current "major" LSMs to distinguish them when
we have a universal method for ordering all LSMs. It's called "legacy"
since the distinction of "major" will go away in the blob-sharing world.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: John Johansen <john.johansen@canonical.com>

include/linux/lsm_hooks.h

@@ -2042,8 +2042,11 @@ extern char *lsm_names;
 extern void security_add_hooks(struct security_hook_list *hooks, int count,
 				char *lsm);
 
+#define LSM_FLAG_LEGACY_MAJOR	BIT(0)
+
 struct lsm_info {
 	const char *name;	/* Required. */
+	unsigned long flags;	/* Optional: flags describing LSM */
 	int (*init)(void);	/* Required. */
 };