linux-kernel - Re: [PATCH] Bluetooth: hci_event: Ignore NULL link key

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Date:   Fri, 14 Jul 2023 11:44:28 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, linux-bluetooth@...r.kernel.org,
        "Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [PATCH] Bluetooth: hci_event: Ignore NULL link key

Hi Chun-Yi,

On Fri, Jul 14, 2023 at 9:14 AM Lee, Chun-Yi <joeyli.kernel@...il.com> wrote:
>
> This change 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. Base on the paper, attacker can induce the
> attacked target to generate null link key (zero key) without PIN code.
>
> We can ignore null link key in the handler of "Link Key Notification
> event" to relieve the attack. A similar implementation also shows in
> btstack project. [3]
>
> Closes: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [1]
> Closes: https://ieeexplore.ieee.org/abstract/document/9474325/authors#authors [2]
> Closes: https://github.com/bluekitchen/btstack/blob/master/src/hci.c#L3722 [3]

Shouldn't the last 2 be using Link: instead?

> Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>
> ---
>  net/bluetooth/hci_event.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index 95816a938cea..e81b8d6c13ba 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -4684,6 +4684,12 @@ static void hci_link_key_notify_evt(struct hci_dev *hdev, void *data,
>         bool persistent;
>         u8 pin_len = 0;
>
> +       /* Ignore NULL link key against CVE-2020-26555 */
> +       if (!memcmp(ev->link_key, ZERO_KEY, HCI_LINK_KEY_SIZE)) {
> +               BT_DBG("Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);

Please use bt_dev_dbg instead.

> +               return;
> +       }
> +
>         bt_dev_dbg(hdev, "");
>
>         hci_dev_lock(hdev);
> --
> 2.35.3
>


-- 
Luiz Augusto von Dentz