[PATCH] Bluetooth: hci_core: Don't queue tx_work while draining workqueue

[Heitor Alves de Siqueira]

Syzbot reported a warning when L2CAP calls queue_work() on the hdev
workqueue while it's being drained. This can happen during device reset or
close paths for hci_send_acl(), hci_send_sco() and hci_send_iso().

The workqueue is drained in hci_dev_do_reset() and in hci_dev_close_sync():
  - hci_dev_close_sync() clears the HCI_UP bit before draining
  - hci_dev_do_reset() sets HCI_CMD_DRAIN_WORKQUEUE before draining

Add these checks before queuing tx_work, and free the SKB if it's not
queued for transmission.

Fixes: 3eff45eaf817 ("Bluetooth: convert tx_task to workqueue")
Reported-by: syzbot+97721dd81f792e838ba0@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=97721dd81f792e838ba0
Signed-off-by: Heitor Alves de Siqueira <halves@xxxxxxxxxx>
---
 net/bluetooth/hci_core.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index c46c1236ebfa..5d5f8ad7d1a8 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -3278,6 +3278,12 @@ void hci_send_acl(struct hci_chan *chan, struct sk_buff *skb, __u16 flags)
 
 	BT_DBG("%s chan %p flags 0x%4.4x", hdev->name, chan, flags);
 
+	if (!test_bit(HCI_UP, &hdev->flags) ||
+	    hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE)) {
+		kfree_skb(skb);
+		return;
+	}
+
 	hci_queue_acl(chan, &chan->data_q, skb, flags);
 
 	queue_work(hdev->workqueue, &hdev->tx_work);
@@ -3291,6 +3297,12 @@ void hci_send_sco(struct hci_conn *conn, struct sk_buff *skb)
 
 	BT_DBG("%s len %d", hdev->name, skb->len);
 
+	if (!test_bit(HCI_UP, &hdev->flags) ||
+	    hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE)) {
+		kfree_skb(skb);
+		return;
+	}
+
 	hdr.handle = cpu_to_le16(conn->handle);
 	hdr.dlen   = skb->len;
 
@@ -3374,6 +3386,12 @@ void hci_send_iso(struct hci_conn *conn, struct sk_buff *skb)
 
 	BT_DBG("%s len %d", hdev->name, skb->len);
 
+	if (!test_bit(HCI_UP, &hdev->flags) ||
+	    hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE)) {
+		kfree_skb(skb);
+		return;
+	}
+
 	hci_queue_iso(conn, &conn->data_q, skb);
 
 	queue_work(hdev->workqueue, &hdev->tx_work);

---
base-commit: 1f63dd8ca0dc05a8272bb8155f643c691d29bb11
change-id: 20260513-hci_send-640290de7acc

Best regards,
--  
Heitor Alves de Siqueira <halves@xxxxxxxxxx>