Bluetooth: hci_sync: fix race in hci_cmd_sync_dequeue_once

hci_cmd_sync_dequeue_once() does lookup and then cancel
the entry under two separate lock sections. Meanwhile,
hci_cmd_sync_work() can also delete the same entry,
leading to double list_del() and "UAF".

Fix this by holding cmd_sync_work_lock across both
lookup and cancel, so that the entry cannot be removed
concurrently.

Fixes: 505ea2b ("Bluetooth: hci_sync: Add helper functions to manipulate cmd_sync queue")
Reported-by: Cen Zhang <zzzccc427@163.com>
Signed-off-by: Cen Zhang <zzzccc427@163.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Author: Cen Zhang

net/bluetooth/hci_sync.c

@@ -863,11 +863,17 @@ bool hci_cmd_sync_dequeue_once(struct hci_dev *hdev,
 {
 	struct hci_cmd_sync_work_entry *entry;
 
-	entry = hci_cmd_sync_lookup_entry(hdev, func, data, destroy);
-	if (!entry)
+	mutex_lock(&hdev->cmd_sync_work_lock);
+
+	entry = _hci_cmd_sync_lookup_entry(hdev, func, data, destroy);
+	if (!entry) {
+		mutex_unlock(&hdev->cmd_sync_work_lock);
 		return false;
+	}
 
-	hci_cmd_sync_cancel_entry(hdev, entry);
+	_hci_cmd_sync_cancel_entry(hdev, entry, -ECANCELED);
+
+	mutex_unlock(&hdev->cmd_sync_work_lock);
 
 	return true;
 }