In the Linux kernel, the following vulnerability has been resolved: Bluetooth: hci_sync: hold...

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

Bluetooth: hci_sync: hold conn in hci_connect_big_sync() callback

There is theoretical UAF if the conn is freed while the hci_sync task is running.

Hold refcount to avoid that. Handle NULL hcon, return 0 + do nothing to match the previous behavior.