tipc: fix connection refcount error

Until now, the generic server framework maintains the connection
id's per subscriber in server's conn_idr. At tipc_close_conn, we
remove the connection id from the server list, but the connection is
valid until we call the refcount cleanup. Hence we have a window
where the server allocates the same connection to an new subscriber
leading to inconsistent reference count. We have another refcount
warning we grab the refcount in tipc_conn_lookup() for connections
with flag with CF_CONNECTED not set. This usually occurs at shutdown
when the we stop the topology server and withdraw TIPC_CFG_SRV
publication thereby triggering a withdraw message to subscribers.

In this commit, we:
1. remove the connection from the server list at recount cleanup.
2. grab the refcount for a connection only if CF_CONNECTED is set.
Tested-by: John Thompson <thompa.atl@gmail.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Parthasarathy Bhuvaragan <parthasarathy.bhuvaragan@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/server.c

@@ -91,7 +91,8 @@ static void tipc_sock_release(struct tipc_conn *con);
 static void tipc_conn_kref_release(struct kref *kref)
 {
 	struct tipc_conn *con = container_of(kref, struct tipc_conn, kref);
-	struct sockaddr_tipc *saddr = con->server->saddr;
+	struct tipc_server *s = con->server;
+	struct sockaddr_tipc *saddr = s->saddr;
 	struct socket *sock = con->sock;
 	struct sock *sk;
 
@@ -106,6 +107,11 @@ static void tipc_conn_kref_release(struct kref *kref)
 		tipc_sock_release(con);
 		sock_release(sock);
 		con->sock = NULL;
+
+		spin_lock_bh(&s->idr_lock);
+		idr_remove(&s->conn_idr, con->conid);
+		s->idr_in_use--;
+		spin_unlock_bh(&s->idr_lock);
 	}
 
 	tipc_clean_outqueues(con);
@@ -128,8 +134,10 @@ static struct tipc_conn *tipc_conn_lookup(struct tipc_server *s, int conid)
 
 	spin_lock_bh(&s->idr_lock);
 	con = idr_find(&s->conn_idr, conid);
-	if (con)
+	if (con && test_bit(CF_CONNECTED, &con->flags))
 		conn_get(con);
+	else
+		con = NULL;
 	spin_unlock_bh(&s->idr_lock);
 	return con;
 }
@@ -198,15 +206,8 @@ static void tipc_sock_release(struct tipc_conn *con)
 
 static void tipc_close_conn(struct tipc_conn *con)
 {
-	struct tipc_server *s = con->server;
-
 	if (test_and_clear_bit(CF_CONNECTED, &con->flags)) {
 
-		spin_lock_bh(&s->idr_lock);
-		idr_remove(&s->conn_idr, con->conid);
-		s->idr_in_use--;
-		spin_unlock_bh(&s->idr_lock);
-
 		/* We shouldn't flush pending works as we may be in the
 		 * thread. In fact the races with pending rx/tx work structs
 		 * are harmless for us here as we have already deleted this