SMACK: Add new lock for adding entry in smack master list

"smk_set_access()" function adds a new rule entry in subject label specific
list(rule_list) and in global rule list(smack_rule_list) both. Mutex lock
(rule_lock) is used to avoid simultaneous updates. But this lock is subject
label specific lock. If 2 processes tries to add different rules(i.e with
different subject labels) simultaneously, then both the processes can take
the "rule_lock" respectively. So it will cause a problem while adding
entries in master rule list.
Now a new mutex lock(smack_master_list_lock) has been taken to add entry in
smack_rule_list to avoid simultaneous updates of different rules.

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/smackfs.c

@@ -67,6 +67,7 @@ enum smk_inos {
 /*
  * List locks
  */
+static DEFINE_MUTEX(smack_master_list_lock);
 static DEFINE_MUTEX(smack_cipso_lock);
 static DEFINE_MUTEX(smack_ambient_lock);
 static DEFINE_MUTEX(smk_net4addr_lock);
@@ -262,12 +263,16 @@ static int smk_set_access(struct smack_parsed_rule *srp,
 		 * it needs to get added for reporting.
 		 */
 		if (global) {
+			mutex_unlock(rule_lock);
 			smlp = kzalloc(sizeof(*smlp), GFP_KERNEL);
 			if (smlp != NULL) {
 				smlp->smk_rule = sp;
+				mutex_lock(&smack_master_list_lock);
 				list_add_rcu(&smlp->list, &smack_rule_list);
+				mutex_unlock(&smack_master_list_lock);
 			} else
 				rc = -ENOMEM;
+			return rc;
 		}
 	}