[PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[Lee, Chun-Yi]

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]

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 the management interface")
Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [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 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_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);
+		return;
+	}
+
 	bt_dev_dbg(hdev, "");
 
 	hci_dev_lock(hdev);
-- 
2.35.3

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[Paul Menzel]

Dear Chun-Yi,


Thank you for your patch.

Am 18.07.23 um 05:43 schrieb Lee, Chun-Yi <joeyli.kernel@gmail.com>:

[…]

> Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>

As checkpatch.pl also reports, please make sure the author and 
Signed-off-by entry match.

     $ git config --global user.name "Chun-Yi  Lee"
     $ git commit --amend --author="Chun-Yi Lee <jlee@suse.com>" -s

(It’s also common to write the name in the order, so no comma is needed.)

`git format-patch` should not generate a patch with a dedicated `From:` 
at the beginning, so you can send it from a different email account. (No 
idea, why upstream Linux kernel development shouldn’t work with your 
SUSE address.)


Kind regards,

Paul

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[joeyli]

Hi Paul, 

Thanks for your review!

On Tue, Jul 18, 2023 at 07:40:37AM +0200, Paul Menzel wrote:
> Dear Chun-Yi,
> 
> 
> Thank you for your patch.
> 
> Am 18.07.23 um 05:43 schrieb Lee, Chun-Yi <joeyli.kernel@gmail.com>:
> 
> […]
> 
> > Signed-off-by: "Lee, Chun-Yi" <jlee@suse.com>
> 
> As checkpatch.pl also reports, please make sure the author and Signed-off-by
> entry match.
> 
>     $ git config --global user.name "Chun-Yi  Lee"
>     $ git commit --amend --author="Chun-Yi Lee <jlee@suse.com>" -s
> 
> (It’s also common to write the name in the order, so no comma is needed.)
> 
> `git format-patch` should not generate a patch with a dedicated `From:` at
> the beginning, so you can send it from a different email account. (No idea,
> why upstream Linux kernel development shouldn’t work with your SUSE
> address.)
>

I have set the from in .gitconfig and also tried git send-email --from "Lee, Chun-Yi <jlee@suse.com>".
But gmail always modified it to From: Lee, Chun-Yi <joeyli.kernel@gmail.com>. I have no idea why.

In next version, I will put Signed-off-by: "Lee, Chun-Yi" <joeyli.kernel@gmail.com>
to keep the From: to be sync with Signed-off-by.

Thanks a lot!
Joey Lee

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[Dan Carpenter]

You know how when people are forwarding a patch from someone else it
adds a From: as the first line in the body of the email?  You could set
your From to the @suse.com address that way.

This is sometimes done in companies where the corporate email server
mangles patches so they have to use an outside server.

regards,
dan carpenter

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[Luiz Augusto von Dentz]

Hi Chun-Yi,

On Mon, Jul 17, 2023 at 8:43 PM Lee, Chun-Yi <joeyli.kernel@gmail.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]

Btw, it is probably worth mentioning that in BR/EDR the key generation
is actually handled in the controller, below HCI.

> 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]

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 bonded
and will not persist the link key, that said the controller will still
consider it as paired, so I perhaps we should go one step forward and
disconnect if we detect such a key is being used.

> 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 the management interface")
> Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [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 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_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);
> +               return;
> +       }
> +
>         bt_dev_dbg(hdev, "");
>
>         hci_dev_lock(hdev);
> --
> 2.35.3
>


-- 
Luiz Augusto von Dentz

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[joeyli]

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 PM Lee, Chun-Yi <joeyli.kernel@gmail.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]
> 
> Btw, it is probably worth mentioning that in BR/EDR the key generation
> 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 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]
> 
> 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 bonded
> and will not persist the link key, that said the controller will still
> 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_dev *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;
+       }
+
        hci_conn_hold(conn);
        conn->disc_timeout = 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 the management interface")
> > Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [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 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_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);
> > +               return;
> > +       }
> > +
> >         bt_dev_dbg(hdev, "");
> >
> >         hci_dev_lock(hdev);
> > --
> > 2.35.3
> >

Thanks a lot!
Joey Lee

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[Luiz Augusto von Dentz]

Hi Joeyli,

On Wed, Jul 19, 2023 at 8:49 AM 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 PM Lee, Chun-Yi <joeyli.kernel@gmail.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]
> >
> > Btw, it is probably worth mentioning that in BR/EDR the key generation
> > 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 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]
> >
> > 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 bonded
> > and will not persist the link key, that said the controller will still
> > 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_dev *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.

>         hci_conn_hold(conn);
>         conn->disc_timeout = 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 the management interface")
> > > Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [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 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_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);
> > > +               return;
> > > +       }
> > > +
> > >         bt_dev_dbg(hdev, "");
> > >
> > >         hci_dev_lock(hdev);
> > > --
> > > 2.35.3
> > >
>
> Thanks a lot!
> Joey Lee



-- 
Luiz Augusto von Dentz

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[Luiz Augusto von Dentz]

Hi Joeyli,

On Wed, Jul 19, 2023 at 5:25 PM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> Hi Joeyli,
>
> On Wed, Jul 19, 2023 at 8:49 AM 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 PM Lee, Chun-Yi <joeyli.kernel@gmail.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]
> > >
> > > Btw, it is probably worth mentioning that in BR/EDR the key generation
> > > 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 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]
> > >
> > > 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 bonded
> > > and will not persist the link key, that said the controller will still
> > > 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_dev *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 = 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 the management interface")
> > > > Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [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 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_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);
> > > > +               return;
> > > > +       }
> > > > +
> > > >         bt_dev_dbg(hdev, "");
> > > >
> > > >         hci_dev_lock(hdev);
> > > > --
> > > > 2.35.3
> > > >
> >
> > Thanks a lot!
> > Joey Lee
>
>
>
> --
> Luiz Augusto von Dentz



-- 
Luiz Augusto von Dentz

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[joeyli]

Hi Luiz Augusto von Dentz,

On Thu, Jul 27, 2023 at 03:29:42PM -0700, Luiz Augusto von Dentz wrote:
> Hi Joeyli,
> 
> On Wed, Jul 19, 2023 at 5:25 PM Luiz Augusto von Dentz
> <luiz.dentz@gmail.com> wrote:
> >
> > Hi Joeyli,
> >
> > On Wed, Jul 19, 2023 at 8:49 AM 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 PM Lee, Chun-Yi <joeyli.kernel@gmail.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]
> > > >
> > > > Btw, it is probably worth mentioning that in BR/EDR the key generation
> > > > 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 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]
> > > >
> > > > 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 bonded
> > > > and will not persist the link key, that said the controller will still
> > > > 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_dev *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?
>

Sorry for my delay! I am stucking at other stuff.

I will improve the patch and send new version again.

THanks a lot!
Joey Lee
 
> > >         hci_conn_hold(conn);
> > >         conn->disc_timeout = 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 the management interface")
> > > > > Link: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-26555 [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 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_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR", &ev->bdaddr);
> > > > > +               return;
> > > > > +       }
> > > > > +
> > > > >         bt_dev_dbg(hdev, "");
> > > > >
> > > > >         hci_dev_lock(hdev);
> > > > > --
> > > > > 2.35.3
> > > > >
> > >
> > > Thanks a lot!
> > > Joey Lee
> >
> >
> >
> > --
> > Luiz Augusto von Dentz
> 
> 
> 
> -- 
> Luiz Augusto von Dentz

Re: [PATCH v2] Bluetooth: hci_event: Ignore NULL link key

[joeyli]

Hi Markus,

On Tue, Jul 18, 2023 at 07:50:13AM +0200, Markus Elfring wrote:
> >                         … Base on the paper, attacker can induce the
> > attacked target to generate …
> 
> Would you like to avoid also any wording weaknesses here?
> 
> 
> > We can ignore null link key in the handler of "Link Key Notification
> > event" to relieve the attack. …
> 
> Will corresponding imperative change descriptions become more helpful?
> 
> See also:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.5-rc2#n94
>

If possible, could you please direct change my original patch description
for your suggestion? Then I will put it in next version.

Thanks a lot!
Joey Lee