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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Thu, 27 Jul 2023 15:29:42 -0700
Message-ID: <CABBYNZJZisYm0Vgfzd8F2ge9RPJvUYBVGpj-4iySerT_wUTJNA@mail.gmail.com>
Subject: Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key
To:     joeyli <jlee@suse.com>
Cc:     "Lee, Chun-Yi" <joeyli.kernel@gmail.com>,
        Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        linux-kernel@vger.kernel.org,
        Markus Elfring <Markus.Elfring@web.de>,
        Dan Carpenter <dan.carpenter@linaro.org>,
        linux-bluetooth@vger.kernel.org
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Hi Joeyli,

On Wed, Jul 19, 2023 at 5:25=E2=80=AFPM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> Hi Joeyli,
>
> On Wed, Jul 19, 2023 at 8:49=E2=80=AFAM joeyli <jlee@suse.com> wrote:
> >
> > Hi Luiz Augusto von Dentz,
> >
> > On Tue, Jul 18, 2023 at 10:22:26AM -0700, Luiz Augusto von Dentz wrote:
> > > Hi Chun-Yi,
> > >
> > > On Mon, Jul 17, 2023 at 8:43=E2=80=AFPM Lee, Chun-Yi <joeyli.kernel@g=
mail.com> wrote:
> > > >
> > > > This change is used to relieve CVE-2020-26555. The description of t=
he
> > > > CVE:
> > > >
> > > > Bluetooth legacy BR/EDR PIN code pairing in Bluetooth Core Specific=
ation
> > > > 1.0B through 5.2 may permit an unauthenticated nearby device to spo=
of
> > > > the BD_ADDR of the peer device to complete pairing without knowledg=
e
> > > > of the PIN. [1]
> > >
> > > Btw, it is probably worth mentioning that in BR/EDR the key generatio=
n
> > > is actually handled in the controller, below HCI.
> > >
> >
> > Yes, the key generation be handled by link manager. I will mention it
> > in patch description.
> >
> > > > The detail of this attack is in IEEE paper:
> > > > BlueMirror: Reflections on Bluetooth Pairing and Provisioning Proto=
cols
> > > > [2]
> > > >
> > > > It's a reflection attack. Base on the paper, attacker can induce th=
e
> > > > attacked target to generate null link key (zero key) without PIN co=
de.
> > > >
> > > > We can ignore null link key in the handler of "Link Key Notificatio=
n
> > > > event" to relieve the attack. A similar implementation also shows i=
n
> > > > btstack project. [3]
> > >
> > > Perhaps we could clarify this statement by stating that if we ignore
> > > the link key it means the stack will not consider the device is bonde=
d
> > > and will not persist the link key, that said the controller will stil=
l
> > > consider it as paired, so I perhaps we should go one step forward and
> > > disconnect if we detect such a key is being used.
> > >
> >
> > I am new on bluetooth field. Did you mean like this patch? Sending
> > HCI_Disconnect when we found zero link key?
> >
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index ff0c331f53d6..3482031cbbb8 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -4698,6 +4700,15 @@ static void hci_link_key_notify_evt(struct hci_d=
ev *hdev, void *data,
> >         if (!conn)
> >                 goto unlock;
> >
> > +       /* Ignore NULL link key against CVE-2020-26555 */
> > +       if (!memcmp(ev->link_key, ZERO_KEY, HCI_LINK_KEY_SIZE)) {
> > +               bt_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %=
pMR", &ev->bdaddr);
> > +               hci_disconnect(conn, HCI_ERROR_AUTH_FAILURE);
> > +               hci_conn_drop(conn);
> > +               goto unlock;
> > +       }
>
> Yeah, something like that should do it, btw I hope you are testing
> these changes do actually work properly, even better if you could
> introduce a test into the likes of mgmt-tester to generate a ZERO_KEY
> so we are not caught by surprise if something doesn't quite work as
> expected, or some change cause a regression where this key is accepted
> again.

Are you still planning on updating these changes so we can apply it?

> >         hci_conn_hold(conn);
> >         conn->disc_timeout =3D HCI_DISCONN_TIMEOUT;
> >         hci_conn_drop(conn);
> >
> >
> > Is there anything I'm missing? Thanks a lot!
> >
> > > > v2:
> > > > - Used Link: tag instead of Closes:
> > > > - Used bt_dev_dbg instead of BT_DBG
> > > > - Added Fixes: tag
> > > >
> > > > Fixes: 55ed8ca10f35 ("Bluetooth: Implement link key handling for th=
e management interface")
> > > > Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=3DCVE-2020-265=
55 [1]
> > > > Link: https://ieeexplore.ieee.org/abstract/document/9474325/authors=
#authors [2]
> > > > Link: https://github.com/bluekitchen/btstack/blob/master/src/hci.c#=
L3722 [3]
> > > > Signed-off-by: "Lee, Chun-Yi" <jlee@suse.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..ff0c331f53d6 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 h=
ci_dev *hdev, void *data,
> > > >         bool persistent;
> > > >         u8 pin_len =3D 0;
> > > >
> > > > +       /* Ignore NULL link key against CVE-2020-26555 */
> > > > +       if (!memcmp(ev->link_key, ZERO_KEY, HCI_LINK_KEY_SIZE)) {
> > > > +               bt_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) f=
or %pMR", &ev->bdaddr);
> > > > +               return;
> > > > +       }
> > > > +
> > > >         bt_dev_dbg(hdev, "");
> > > >
> > > >         hci_dev_lock(hdev);
> > > > --
> > > > 2.35.3
> > > >
> >
> > Thanks a lot!
> > Joey Lee
>
>
>
> --
> Luiz Augusto von Dentz


--=20
Luiz Augusto von Dentz