Smack: Traverse the smack_known_list using list_for_each_entry_rcu macro

In smack_from_secattr function,"smack_known_list" is being traversed
using list_for_each_entry macro, although it is a rcu protected
structure. So it should be traversed using "list_for_each_entry_rcu"
macro to fetch the rcu protected entry.
Signed-off-by: Vishal Goel <vishal.goel@samsung.com>
Signed-off-by: Himanshu Shukla <himanshu.sh@samsung.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

security/smack/smack_lsm.c

@@ -3900,7 +3900,7 @@ static struct smack_known *smack_from_secattr(struct netlbl_lsm_secattr *sap,
 		 * ambient value.
 		 */
 		rcu_read_lock();
-		list_for_each_entry(skp, &smack_known_list, list) {
+		list_for_each_entry_rcu(skp, &smack_known_list, list) {
 			if (sap->attr.mls.lvl != skp->smk_netlabel.attr.mls.lvl)
 				continue;
 			/*