Bluetooth: ignore NULL link key and reject connection with the device which has same BD_ADDR

This patch set is used to relieve CVE-2020-26555. The description of the CVE:

Bluetooth legacy BR/EDR PIN code pairing in Bluetooth Core Specification 1.0B through 5.2 may permit an unauthenticated nearby device to spoof the BD_ADDR of the peer device to complete pairing without knowledge of the PIN. [1]

The detail of this attack is in IEEE paper:
BlueMirror: Reflections on Bluetooth Pairing and Provisioning Protocols
[2]

It's a reflection attack. The paper mentioned that attacker can induce the attacked target to generate null link key (zero key) without PIN code. In BR/EDR, the key generation is actually handled in the controller which is below HCI.

Thus, we can ignore null link key in the handler of "Link Key Notification event" to relieve the attack. And, a condition of this attack is that attacker should change the BR_ADDR of his hacking device (Host B) to equal to the BR_ADDR with the target device being attacked (Host A). So we reject the connection with device which has same BD_ADDR both on HCI_Create_Connection and HCI_Connection_Request to prevent the attack.

Similar implementations also show in btstack project. [3][4][5]

Lee, Chun-Yi (2):
Bluetooth: hci_event: Ignore NULL link key
Bluetooth: Reject connection with the device which has same BD_ADDR

 net/bluetooth/hci_conn.c  |  7 +++++++
 net/bluetooth/hci_event.c | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)

2.35.3