[PATCH] Bluetooth: hci_core: Fix queuing tx_work after workqueue is drained

[ThangNN99]

hci_send_acl(), hci_send_sco() and hci_send_iso() queue hdev->tx_work
unconditionally. They can run from the L2CAP/SCO/ISO socket send path
while hci_dev_close_sync() is draining hdev->workqueue (HCIDEVDOWN
racing with a socket write). Since that queue_work() is not chained
work from the tx_work worker itself, __queue_work() sees the queue
marked __WQ_DRAINING, warns "cannot queue %ps on wq %s", and drops
the work:

  WARNING: CPU: 1 PID: 5985 at kernel/workqueue.c:2352 __queue_work
  Call Trace:
   queue_work_on
   l2cap_chan_send
   l2cap_sock_sendmsg
   ...

hci_dev_close_sync() already sets HCI_CMD_DRAIN_WORKQUEUE before
draining, but only hci_cmd_work() and handle_cmd_cnt_and_timer()
check it before queuing. Route the tx_work producers through the
same guard via a shared hci_sched_tx() helper.

Fixes: 525daaea459f ("Bluetooth: hci_sync: Set HCI_CMD_DRAIN_WORKQUEUE during device close")
Reported-by: syzbot+b6919040d9958e2fc1ae@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=b6919040d9958e2fc1ae
Signed-off-by: ThangNN99 <ngocthang2710.1999@xxxxxxxxx>
---
 net/bluetooth/hci_core.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 35a1be57e386..09cd49b9a939 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -3236,6 +3236,17 @@ static void hci_queue_acl(struct hci_chan *chan, struct sk_buff_head *queue,
 	bt_dev_dbg(hdev, "chan %p queued %d", chan, skb_queue_len(queue));
 }
 
+/* Queue hdev->tx_work, unless hdev->workqueue is being drained by
+ * hci_dev_close_sync(), which would otherwise WARN and drop the work.
+ */
+static void hci_sched_tx(struct hci_dev *hdev)
+{
+	rcu_read_lock();
+	if (!hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
+		queue_work(hdev->workqueue, &hdev->tx_work);
+	rcu_read_unlock();
+}
+
 void hci_send_acl(struct hci_chan *chan, struct sk_buff *skb, __u16 flags)
 {
 	struct hci_dev *hdev = chan->conn->hdev;
@@ -3244,7 +3255,7 @@ void hci_send_acl(struct hci_chan *chan, struct sk_buff *skb, __u16 flags)
 
 	hci_queue_acl(chan, &chan->data_q, skb, flags);
 
-	queue_work(hdev->workqueue, &hdev->tx_work);
+	hci_sched_tx(hdev);
 }
 
 /* Send SCO data */
@@ -3269,7 +3280,7 @@ void hci_send_sco(struct hci_conn *conn, struct sk_buff *skb)
 	bt_dev_dbg(hdev, "hcon %p queued %d", conn,
 		   skb_queue_len(&conn->data_q));
 
-	queue_work(hdev->workqueue, &hdev->tx_work);
+	hci_sched_tx(hdev);
 }
 
 /* Send ISO data */
@@ -3340,7 +3351,7 @@ void hci_send_iso(struct hci_conn *conn, struct sk_buff *skb)
 
 	hci_queue_iso(conn, &conn->data_q, skb);
 
-	queue_work(hdev->workqueue, &hdev->tx_work);
+	hci_sched_tx(hdev);
 }
 
 /* ---- HCI TX task (outgoing data) ---- */
-- 
2.43.0