netlink: access nlk groups safely in netlink bind and getname

Now there is no lock protecting nlk ngroups/groups' accessing in
netlink bind and getname. It's safe from nlk groups' setting in
netlink_release, but not from netlink_realloc_groups called by
netlink_setsockopt.

netlink_lock_table is needed in both netlink bind and getname when
accessing nlk groups.
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -955,7 +955,7 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 	struct net *net = sock_net(sk);
 	struct netlink_sock *nlk = nlk_sk(sk);
 	struct sockaddr_nl *nladdr = (struct sockaddr_nl *)addr;
-	int err;
+	int err = 0;
 	long unsigned int groups = nladdr->nl_groups;
 	bool bound;
 
@@ -983,6 +983,7 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 			return -EINVAL;
 	}
 
+	netlink_lock_table();
 	if (nlk->netlink_bind && groups) {
 		int group;
 
@@ -993,7 +994,7 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 			if (!err)
 				continue;
 			netlink_undo_bind(group, groups, sk);
-			return err;
+			goto unlock;
 		}
 	}
 
@@ -1006,12 +1007,13 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 			netlink_autobind(sock);
 		if (err) {
 			netlink_undo_bind(nlk->ngroups, groups, sk);
-			return err;
+			goto unlock;
 		}
 	}
 
 	if (!groups && (nlk->groups == NULL || !(u32)nlk->groups[0]))
-		return 0;
+		goto unlock;
+	netlink_unlock_table();
 
 	netlink_table_grab();
 	netlink_update_subscriptions(sk, nlk->subscriptions +
@@ -1022,6 +1024,10 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 	netlink_table_ungrab();
 
 	return 0;
+
+unlock:
+	netlink_unlock_table();
+	return err;
 }
 
 static int netlink_connect(struct socket *sock, struct sockaddr *addr,
@@ -1079,7 +1085,9 @@ static int netlink_getname(struct socket *sock, struct sockaddr *addr,
 		nladdr->nl_groups = netlink_group_mask(nlk->dst_group);
 	} else {
 		nladdr->nl_pid = nlk->portid;
+		netlink_lock_table();
 		nladdr->nl_groups = nlk->groups ? nlk->groups[0] : 0;
+		netlink_unlock_table();
 	}
 	return 0;
 }