In the Linux kernel, the following vulnerability has been resolved: Bluetooth: SCO: hold sk properly in sco_conn_ready sk deref in sco_con

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

Bluetooth: SCO: hold sk properly in sco_conn_ready

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

 1[Task 1]            [Task 2]
 2                    sco_sock_release
 3sco_conn_ready
 4  sk = conn->sk
 5                      lock_sock(sk)
 6                        conn->sk = NULL
 7  lock_sock(sk)
 8                      release_sock(sk)
 9                      sco_sock_kill(sk)
10   UAF on sk deref

and similarly for access to sco_get_sock_listen() return value.

Fix possible UAF by holding sk refcount in sco_conn_ready() and making
sco_get_sock_listen() increase refcount. Also recheck after lock_sock
that the socket is still valid. Adjust conn->sk locking so it's
protected also by lock_sock() of the associated socket if any.