CVE-2026-74537

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

Bluetooth: ISO: hold sk properly in iso_conn_ready

sk deref in iso_conn_ready must be done either under conn->lock, or
holding a refcount, to avoid concurrent close. conn->sk is currently
accessed without either:

    [Task 1]            [Task 2]
                        iso_sock_release
    iso_conn_ready
      sk = conn->sk
                          lock_sock(sk)
                            conn->sk = NULL
      lock_sock(sk)
                          release_sock(sk)
                          iso_sock_kill(sk)
       UAF on sk deref

Fix possible UAF by holding sk refcount in iso_conn_ready().  Also
recheck after lock_sock that the socket is still valid.  Adjust locking
so conn->sk is cleared only under lock_sock.