LSM: Fix security_module_enable() error.

We can set default LSM module to DAC (which means "enable no LSM module").
If default LSM module was set to DAC, security_module_enable() must return 0
unless overridden via boot time parameter.
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Serge E. Hallyn <serge@hallyn.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/security.c

@@ -89,20 +89,12 @@ __setup("security=", choose_lsm);
  * Return true if:
  *	-The passed LSM is the one chosen by user at boot time,
  *	-or the passed LSM is configured as the default and the user did not
- *	 choose an alternate LSM at boot time,
- *	-or there is no default LSM set and the user didn't specify a
- *	 specific LSM and we're the first to ask for registration permission,
- *	-or the passed LSM is currently loaded.
+ *	 choose an alternate LSM at boot time.
  * Otherwise, return false.
  */
 int __init security_module_enable(struct security_operations *ops)
 {
-	if (!*chosen_lsm)
-		strncpy(chosen_lsm, ops->name, SECURITY_NAME_MAX);
-	else if (strncmp(ops->name, chosen_lsm, SECURITY_NAME_MAX))
-		return 0;
-
-	return 1;
+	return !strcmp(ops->name, chosen_lsm);
 }
 
 /**