CVE-2026-74533

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: ISO: fix race of kfree vs kref_get_unless_zero

hci_conn::iso_data is accessed and modified without lock or RCU.
This leads to a race

    [Task hdev->workqueue]                 	[Task 2]
    iso_recv                                    iso_conn_put(conn)
      conn = LOAD hcon->iso_data                  iso_conn_free(conn)
      iso_conn_hold_unless_zero(conn)               hcon->iso_data = NULL
                                                    kfree(conn)
        kref_get_unless_zero(&conn->ref) /* UAF */

and also to races in iso_conn_add() vs. iso_conn_free().

Fix by adding spinlock hci_conn::proto_lock and using it to guard
hci_conn::iso_data.