tipc: destroy topsrv workqueues before closing connections

tipc_topsrv_stop() closed subscriber connections while the topology
server's send and receive workqueues were still running. Socket
callbacks and subscription events could then queue more work, and
in-flight send/recv work could drop the last connection reference
during the conn_idr walk.

That race produced several teardown failures: refcount_t addition on
0 from conn_get() on a connection whose release was blocked on
idr_lock, a subsequent use-after-free in tipc_conn_close(),
queue_work() on an already destroyed workqueue from the listener
data-ready callback, and an RCU stall in tipc_topsrv_exit_net()
while the walk spun under idr_lock.

Clear srv->listener under idr_lock so it acts as a shutdown flag,
skip queue_work() once it is NULL, destroy the workqueues to flush
in-flight work, and only then close the remaining connections.
Refuse tipc_conn_lookup() after that flag is cleared, and drop
idr_lock when the teardown walk finds no connection, so an
in-flight subscription event cannot pin idr_in_use while the
walk holds the lock.

v3 supersedes the narrower in-thread diff Tung Quang Nguyen
posted on 2026-09-23. It keeps his teardown order and adds the
lookup refusal and the empty-idr unlock.

Fixes: c5fa7b3cf3 ("tipc: introduce new TIPC server infrastructure")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: LLM
Signed-off-by: Yuqi Xu <xuyuqiabc@gmail.com>
Reviewed-by: Ren Wei <weir@nebusec.ai>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/topsrv.c

@@ -55,7 +55,7 @@
 /**
  * struct tipc_topsrv - TIPC server structure
  * @conn_idr: identifier set of connection
- * @idr_lock: protect the connection identifier set
+ * @idr_lock: protect the connection identifier set and listener
  * @idr_in_use: amount of allocated identifier entry
  * @net: network namespace instance
  * @awork: accept work item
@@ -218,6 +218,10 @@ static struct tipc_conn *tipc_conn_lookup(struct tipc_topsrv *s, int conid)
 	struct tipc_conn *con;
 
 	spin_lock_bh(&s->idr_lock);
+	if (!s->listener) {
+		spin_unlock_bh(&s->idr_lock);
+		return NULL;
+	}
 	con = idr_find(&s->conn_idr, conid);
 	if (!connected(con) || !kref_get_unless_zero(&con->kref))
 		con = NULL;
@@ -301,10 +305,20 @@ static void tipc_conn_send_to_sock(struct tipc_conn *con)
 static void tipc_conn_send_work(struct work_struct *work)
 {
 	struct tipc_conn *con = container_of(work, struct tipc_conn, swork);
+	struct tipc_topsrv *srv;
+
+	srv = con->server;
+	spin_lock_bh(&srv->idr_lock);
+	if (!srv->listener) {
+		spin_unlock_bh(&srv->idr_lock);
+		goto out;
+	}
+	spin_unlock_bh(&srv->idr_lock);
 
 	if (connected(con))
 		tipc_conn_send_to_sock(con);
 
+out:
 	conn_put(con);
 }
 
@@ -334,8 +348,14 @@ void tipc_topsrv_queue_evt(struct net *net, int conid,
 	list_add_tail(&e->list, &con->outqueue);
 	spin_unlock_bh(&con->outqueue_lock);
 
-	if (queue_work(srv->send_wq, &con->swork))
-		return;
+	spin_lock_bh(&srv->idr_lock);
+	if (srv->listener) {
+		if (queue_work(srv->send_wq, &con->swork)) {
+			spin_unlock_bh(&srv->idr_lock);
+			return;
+		}
+	}
+	spin_unlock_bh(&srv->idr_lock);
 err:
 	conn_put(con);
 }
@@ -346,14 +366,20 @@ void tipc_topsrv_queue_evt(struct net *net, int conid,
  */
 static void tipc_conn_write_space(struct sock *sk)
 {
+	struct tipc_topsrv *srv;
 	struct tipc_conn *con;
 
 	read_lock_bh(&sk->sk_callback_lock);
 	con = sk->sk_user_data;
 	if (connected(con)) {
-		conn_get(con);
-		if (!queue_work(con->server->send_wq, &con->swork))
-			conn_put(con);
+		srv = con->server;
+		spin_lock_bh(&srv->idr_lock);
+		if (srv->listener) {
+			conn_get(con);
+			if (!queue_work(srv->send_wq, &con->swork))
+				conn_put(con);
+		}
+		spin_unlock_bh(&srv->idr_lock);
 	}
 	read_unlock_bh(&sk->sk_callback_lock);
 }
@@ -418,8 +444,17 @@ static int tipc_conn_rcv_from_sock(struct tipc_conn *con)
 static void tipc_conn_recv_work(struct work_struct *work)
 {
 	struct tipc_conn *con = container_of(work, struct tipc_conn, rwork);
+	struct tipc_topsrv *srv;
 	int count = 0;
 
+	srv = con->server;
+	spin_lock_bh(&srv->idr_lock);
+	if (!srv->listener) {
+		spin_unlock_bh(&srv->idr_lock);
+		goto out;
+	}
+	spin_unlock_bh(&srv->idr_lock);
+
 	while (connected(con)) {
 		if (tipc_conn_rcv_from_sock(con))
 			break;
@@ -430,6 +465,7 @@ static void tipc_conn_recv_work(struct work_struct *work)
 			count = 0;
 		}
 	}
+out:
 	conn_put(con);
 }
 
@@ -438,6 +474,7 @@ static void tipc_conn_recv_work(struct work_struct *work)
  */
 static void tipc_conn_data_ready(struct sock *sk)
 {
+	struct tipc_topsrv *srv;
 	struct tipc_conn *con;
 
 	trace_sk_data_ready(sk);
@@ -445,9 +482,14 @@ static void tipc_conn_data_ready(struct sock *sk)
 	read_lock_bh(&sk->sk_callback_lock);
 	con = sk->sk_user_data;
 	if (connected(con)) {
-		conn_get(con);
-		if (!queue_work(con->server->rcv_wq, &con->rwork))
-			conn_put(con);
+		srv = con->server;
+		spin_lock_bh(&srv->idr_lock);
+		if (srv->listener) {
+			conn_get(con);
+			if (!queue_work(srv->rcv_wq, &con->rwork))
+				conn_put(con);
+		}
+		spin_unlock_bh(&srv->idr_lock);
 	}
 	read_unlock_bh(&sk->sk_callback_lock);
 }
@@ -503,8 +545,12 @@ static void tipc_topsrv_listener_data_ready(struct sock *sk)
 
 	read_lock_bh(&sk->sk_callback_lock);
 	srv = sk->sk_user_data;
-	if (srv)
-		queue_work(srv->rcv_wq, &srv->awork);
+	if (srv) {
+		spin_lock_bh(&srv->idr_lock);
+		if (srv->listener)
+			queue_work(srv->rcv_wq, &srv->awork);
+		spin_unlock_bh(&srv->idr_lock);
+	}
 	read_unlock_bh(&sk->sk_callback_lock);
 }
 
@@ -700,23 +746,27 @@ static void tipc_topsrv_stop(struct net *net)
 	struct tipc_conn *con;
 	int id;
 
+	spin_lock_bh(&srv->idr_lock);
+	srv->listener = NULL;
+	spin_unlock_bh(&srv->idr_lock);
+	tipc_topsrv_work_stop(srv);
+
 	spin_lock_bh(&srv->idr_lock);
 	for (id = 0; srv->idr_in_use; id++) {
 		con = idr_find(&srv->conn_idr, id);
 		if (con) {
-			conn_get(con);
 			spin_unlock_bh(&srv->idr_lock);
 			tipc_conn_close(con);
-			conn_put(con);
 			spin_lock_bh(&srv->idr_lock);
+			continue;
 		}
+		spin_unlock_bh(&srv->idr_lock);
+		spin_lock_bh(&srv->idr_lock);
 	}
 	__module_get(lsock->ops->owner);
 	__module_get(lsock->sk->sk_prot_creator->owner);
-	srv->listener = NULL;
 	spin_unlock_bh(&srv->idr_lock);
 
-	tipc_topsrv_work_stop(srv);
 	sock_release(lsock);
 	idr_destroy(&srv->conn_idr);
 	kfree(srv);