syzbot reports a slab use-after-free in hci_conn_hash_flush [1].
After releasing an object using hci_conn_del_sysfs in the
hci_conn_cleanup function, releasing the same object again
using the hci_dev_put and hci_conn_put functions causes a double free.
Here's a simplified flow:

hci_conn_del_sysfs:
  hci_dev_put
    put_device
      kobject_put
        kref_put
          kobject_release
            kobject_cleanup
              kfree_const
                kfree(name)

hci_dev_put:
  ...
    kfree(name)

hci_conn_put:
  put_device
    ...
      kfree(name)

This patch drop the hci_dev_put and hci_conn_put function
call in hci_conn_cleanup function, because the object is
freed in hci_conn_del_sysfs function.

This patch also fixes the refcounting in hci_conn_add_sysfs() and
hci_conn_del_sysfs() to take into account device_add() failures.

This fixes CVE-2023-28464.

Link: https://syzkaller.appspot.com/bug?id=1bb51491ca5df96a5f724899d1dbb87afda61419 [1]
Signed-off-by: ZhengHan Wang <wzhmmmmm@gmail.com>
Co-developed-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>