Merge branch 'tipc-fix-two-race-issues-in-tipc_conn_alloc'

Xin Long says:

====================
tipc: fix two race issues in tipc_conn_alloc

The race exists beteen tipc_topsrv_accept() and tipc_conn_close(),
one is allocating the con while the other is freeing it and there
is no proper lock protecting it. Therefore, a null-pointer-defer
and a use-after-free may be triggered, see details on each patch.
====================

Link: https://lore.kernel.org/r/cover.1668807842.git.lucien.xin@gmail.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>

net/tipc/topsrv.c

@@ -176,7 +176,7 @@ static void tipc_conn_close(struct tipc_conn *con)
 	conn_put(con);
 }
 
-static struct tipc_conn *tipc_conn_alloc(struct tipc_topsrv *s)
+static struct tipc_conn *tipc_conn_alloc(struct tipc_topsrv *s, struct socket *sock)
 {
 	struct tipc_conn *con;
 	int ret;
@@ -202,10 +202,12 @@ static struct tipc_conn *tipc_conn_alloc(struct tipc_topsrv *s)
 	}
 	con->conid = ret;
 	s->idr_in_use++;
-	spin_unlock_bh(&s->idr_lock);
 
 	set_bit(CF_CONNECTED, &con->flags);
 	con->server = s;
+	con->sock = sock;
+	conn_get(con);
+	spin_unlock_bh(&s->idr_lock);
 
 	return con;
 }
@@ -467,7 +469,7 @@ static void tipc_topsrv_accept(struct work_struct *work)
 		ret = kernel_accept(lsock, &newsock, O_NONBLOCK);
 		if (ret < 0)
 			return;
-		con = tipc_conn_alloc(srv);
+		con = tipc_conn_alloc(srv, newsock);
 		if (IS_ERR(con)) {
 			ret = PTR_ERR(con);
 			sock_release(newsock);
@@ -479,11 +481,11 @@ static void tipc_topsrv_accept(struct work_struct *work)
 		newsk->sk_data_ready = tipc_conn_data_ready;
 		newsk->sk_write_space = tipc_conn_write_space;
 		newsk->sk_user_data = con;
-		con->sock = newsock;
 		write_unlock_bh(&newsk->sk_callback_lock);
 
 		/* Wake up receive process in case of 'SYN+' message */
 		newsk->sk_data_ready(newsk);
+		conn_put(con);
 	}
 }
 
@@ -577,17 +579,17 @@ bool tipc_topsrv_kern_subscr(struct net *net, u32 port, u32 type, u32 lower,
 	sub.filter = filter;
 	*(u64 *)&sub.usr_handle = (u64)port;
 
-	con = tipc_conn_alloc(tipc_topsrv(net));
+	con = tipc_conn_alloc(tipc_topsrv(net), NULL);
 	if (IS_ERR(con))
 		return false;
 
 	*conid = con->conid;
-	con->sock = NULL;
 	rc = tipc_conn_rcv_sub(tipc_topsrv(net), con, &sub);
-	if (rc >= 0)
-		return true;
+	if (rc)
+		conn_put(con);
+
 	conn_put(con);
-	return false;
+	return !rc;
 }
 
 void tipc_topsrv_kern_unsubscr(struct net *net, int conid)