Bluetooth: ISO: Fix a use-after-free of the hci_conn pointer

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

Bluetooth: ISO: Fix a use-after-free of the hci_conn pointer

In iso_sock_rebind_bc(), the bis pointer is cached, then the socket lock is

dropped:

bis = iso_pi(sk)->conn->hcon;

/* Release the socket before lookups since that requires hci_dev_lock

* which shall not be acquired while holding sock_lock for proper

* ordering.

*/

release_sock(sk);

hci_dev_lock(bis->hdev);

During the unlocked window, could a concurrent close() destroy the connection

and free the bis structure, causing hci_dev_lock(bis->hdev) to access memory

after it is freed, fix this by using the hdev reference which was safely

acquired via iso_conn_get_hdev().