linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
* [Bluez PATCH v3] bluetooth: secure bluetooth stack from bluedump attack
@ 2020-02-12 13:23 Howard Chung
  2020-02-12 15:19 ` Marcel Holtmann
  0 siblings, 1 reply; 4+ messages in thread
From: Howard Chung @ 2020-02-12 13:23 UTC (permalink / raw)
  To: linux-bluetooth, marcel
  Cc: chromeos-bluetooth-upstreaming, Howard Chung, David S. Miller,
	Johan Hedberg, netdev, linux-kernel

Attack scenario:
1. A Chromebook (let's call this device A) is paired to a legitimate
   Bluetooth classic device (e.g. a speaker) (let's call this device
   B).
2. A malicious device (let's call this device C) pretends to be the
   Bluetooth speaker by using the same BT address.
3. If device A is not currently connected to device B, device A will
   be ready to accept connection from device B in the background
   (technically, doing Page Scan).
4. Therefore, device C can initiate connection to device A
   (because device A is doing Page Scan) and device A will accept the
   connection because device A trusts device C's address which is the
   same as device B's address.
5. Device C won't be able to communicate at any high level Bluetooth
   profile with device A because device A enforces that device C is
   encrypted with their common Link Key, which device C doesn't have.
   But device C can initiate pairing with device A with just-works
   model without requiring user interaction (there is only pairing
   notification). After pairing, device A now trusts device C with a
   new different link key, common between device A and C.
6. From now on, device A trusts device C, so device C can at anytime
   connect to device A to do any kind of high-level hijacking, e.g.
   speaker hijack or mouse/keyboard hijack.

Since we don't know whether the repairing is legitimate or not,
leave the decision to user space if all the conditions below are met.
- the pairing is initialized by peer
- the authorization method is just-work
- host already had the link key to the peer

Signed-off-by: Howard Chung <howardchung@google.com>
---

Changes in v3:
- Change confirm_hint from 2 to 1
- Fix coding style (declaration order)

Changes in v2:
- Remove the HCI_PERMIT_JUST_WORK_REPAIR debugfs option
- Fix the added code in classic
- Add a similar fix for LE

 net/bluetooth/hci_event.c | 10 ++++++++++
 net/bluetooth/smp.c       | 18 ++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 2c833dae9366..e6982f4f51ea 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4571,6 +4571,16 @@ static void hci_user_confirm_request_evt(struct hci_dev *hdev,
 			goto confirm;
 		}
 
+		/* If there already exists link key in local host, leave the
+		 * decision to user space since the remote device could be
+		 * legitimate or malicious.
+		 */
+		if (hci_find_link_key(hdev, &ev->bdaddr)) {
+			bt_dev_warn(hdev, "Local host already has link key");
+			confirm_hint = 1;
+			goto confirm;
+		}
+
 		BT_DBG("Auto-accept of user confirmation with %ums delay",
 		       hdev->auto_accept_delay);
 
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 2cba6e07c02b..1483ceea3bab 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -2139,6 +2139,7 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
 	struct l2cap_chan *chan = conn->smp;
 	struct smp_chan *smp = chan->data;
 	struct hci_conn *hcon = conn->hcon;
+	struct smp_ltk *key;
 	u8 *pkax, *pkbx, *na, *nb;
 	u32 passkey;
 	int err;
@@ -2192,6 +2193,23 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
 		smp_send_cmd(conn, SMP_CMD_PAIRING_RANDOM, sizeof(smp->prnd),
 			     smp->prnd);
 		SMP_ALLOW_CMD(smp, SMP_CMD_DHKEY_CHECK);
+
+		key = hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
+				   hcon->role);
+
+		/* If there already exists link key in local host, leave the
+		 * decision to user space since the remote device could be
+		 * legitimate or malicious.
+		 */
+		if (smp->method == JUST_WORKS && key) {
+			err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
+							hcon->type,
+							hcon->dst_type, passkey,
+							1);
+			if (err)
+				return SMP_UNSPECIFIED;
+			set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
+		}
 	}
 
 mackey_and_ltk:
-- 
2.25.0.225.g125e21ebc7-goog


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [Bluez PATCH v3] bluetooth: secure bluetooth stack from bluedump attack
  2020-02-12 13:23 [Bluez PATCH v3] bluetooth: secure bluetooth stack from bluedump attack Howard Chung
@ 2020-02-12 15:19 ` Marcel Holtmann
  2020-02-12 15:37   ` Johan Hedberg
  0 siblings, 1 reply; 4+ messages in thread
From: Marcel Holtmann @ 2020-02-12 15:19 UTC (permalink / raw)
  To: Howard Chung
  Cc: Bluez mailing list, ChromeOS Bluetooth Upstreaming,
	David S. Miller, Johan Hedberg, netdev, linux-kernel

Hi Howard,

> Attack scenario:
> 1. A Chromebook (let's call this device A) is paired to a legitimate
>   Bluetooth classic device (e.g. a speaker) (let's call this device
>   B).
> 2. A malicious device (let's call this device C) pretends to be the
>   Bluetooth speaker by using the same BT address.
> 3. If device A is not currently connected to device B, device A will
>   be ready to accept connection from device B in the background
>   (technically, doing Page Scan).
> 4. Therefore, device C can initiate connection to device A
>   (because device A is doing Page Scan) and device A will accept the
>   connection because device A trusts device C's address which is the
>   same as device B's address.
> 5. Device C won't be able to communicate at any high level Bluetooth
>   profile with device A because device A enforces that device C is
>   encrypted with their common Link Key, which device C doesn't have.
>   But device C can initiate pairing with device A with just-works
>   model without requiring user interaction (there is only pairing
>   notification). After pairing, device A now trusts device C with a
>   new different link key, common between device A and C.
> 6. From now on, device A trusts device C, so device C can at anytime
>   connect to device A to do any kind of high-level hijacking, e.g.
>   speaker hijack or mouse/keyboard hijack.
> 
> Since we don't know whether the repairing is legitimate or not,
> leave the decision to user space if all the conditions below are met.
> - the pairing is initialized by peer
> - the authorization method is just-work
> - host already had the link key to the peer
> 
> Signed-off-by: Howard Chung <howardchung@google.com>
> ---
> 
> Changes in v3:
> - Change confirm_hint from 2 to 1
> - Fix coding style (declaration order)
> 
> Changes in v2:
> - Remove the HCI_PERMIT_JUST_WORK_REPAIR debugfs option
> - Fix the added code in classic
> - Add a similar fix for LE
> 
> net/bluetooth/hci_event.c | 10 ++++++++++
> net/bluetooth/smp.c       | 18 ++++++++++++++++++
> 2 files changed, 28 insertions(+)
> 
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index 2c833dae9366..e6982f4f51ea 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -4571,6 +4571,16 @@ static void hci_user_confirm_request_evt(struct hci_dev *hdev,
> 			goto confirm;
> 		}
> 
> +		/* If there already exists link key in local host, leave the
> +		 * decision to user space since the remote device could be
> +		 * legitimate or malicious.
> +		 */
> +		if (hci_find_link_key(hdev, &ev->bdaddr)) {
> +			bt_dev_warn(hdev, "Local host already has link key");
> +			confirm_hint = 1;
> +			goto confirm;
> +		}
> +
> 		BT_DBG("Auto-accept of user confirmation with %ums delay",
> 		       hdev->auto_accept_delay);
> 
> diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
> index 2cba6e07c02b..1483ceea3bab 100644
> --- a/net/bluetooth/smp.c
> +++ b/net/bluetooth/smp.c
> @@ -2139,6 +2139,7 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
> 	struct l2cap_chan *chan = conn->smp;
> 	struct smp_chan *smp = chan->data;
> 	struct hci_conn *hcon = conn->hcon;
> +	struct smp_ltk *key;
> 	u8 *pkax, *pkbx, *na, *nb;
> 	u32 passkey;
> 	int err;
> @@ -2192,6 +2193,23 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
> 		smp_send_cmd(conn, SMP_CMD_PAIRING_RANDOM, sizeof(smp->prnd),
> 			     smp->prnd);
> 		SMP_ALLOW_CMD(smp, SMP_CMD_DHKEY_CHECK);
> +
> +		key = hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
> +				   hcon->role);
> +
> +		/* If there already exists link key in local host, leave the
> +		 * decision to user space since the remote device could be
> +		 * legitimate or malicious.
> +		 */
> +		if (smp->method == JUST_WORKS && key) {
> +			err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
> +							hcon->type,
> +							hcon->dst_type, passkey,
> +							1);
> +			if (err)
> +				return SMP_UNSPECIFIED;
> +			set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
> +		}
> 	}

while this looks good, I like to optimize this to only look up the LTK when needed.

	/* comment here */
	if (smp->method != JUST_WORKS)
		goto mackey_and_ltk;


	/* and command here */
	if (hci_find_ltk()) {
		mgmt_user_confirm_request()
		..
	}

And my preference that we also get an Ack from Johan or Luiz that double checked that this is fine.

Regards

Marcel


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [Bluez PATCH v3] bluetooth: secure bluetooth stack from bluedump attack
  2020-02-12 15:19 ` Marcel Holtmann
@ 2020-02-12 15:37   ` Johan Hedberg
  2020-02-12 21:29     ` Luiz Augusto von Dentz
  0 siblings, 1 reply; 4+ messages in thread
From: Johan Hedberg @ 2020-02-12 15:37 UTC (permalink / raw)
  To: Marcel Holtmann
  Cc: Howard Chung, Bluez mailing list, ChromeOS Bluetooth Upstreaming,
	David S. Miller, netdev, linux-kernel

Hi Marcel,

On 12. Feb 2020, at 17.19, Marcel Holtmann <marcel@holtmann.org> wrote:
>> +		key = hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
>> +				   hcon->role);
>> +
>> +		/* If there already exists link key in local host, leave the
>> +		 * decision to user space since the remote device could be
>> +		 * legitimate or malicious.
>> +		 */
>> +		if (smp->method == JUST_WORKS && key) {
>> +			err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
>> +							hcon->type,
>> +							hcon->dst_type, passkey,
>> +							1);
>> +			if (err)
>> +				return SMP_UNSPECIFIED;
>> +			set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
>> +		}
>> 	}
> 
> while this looks good, I like to optimize this to only look up the LTK when needed.
> 
> 	/* comment here */
> 	if (smp->method != JUST_WORKS)
> 		goto mackey_and_ltk;
> 
> 
> 	/* and command here */
> 	if (hci_find_ltk()) {
> 		mgmt_user_confirm_request()
> 		..
> 	}
> 
> And my preference that we also get an Ack from Johan or Luiz that double checked that this is fine.

Acked-by: Johan Hedberg <johan.hedberg@intel.com>

Johan

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [Bluez PATCH v3] bluetooth: secure bluetooth stack from bluedump attack
  2020-02-12 15:37   ` Johan Hedberg
@ 2020-02-12 21:29     ` Luiz Augusto von Dentz
  0 siblings, 0 replies; 4+ messages in thread
From: Luiz Augusto von Dentz @ 2020-02-12 21:29 UTC (permalink / raw)
  To: Johan Hedberg
  Cc: Marcel Holtmann, Howard Chung, Bluez mailing list,
	ChromeOS Bluetooth Upstreaming, David S. Miller,
	open list:NETWORKING [GENERAL],
	Linux Kernel Mailing List

Hi Howard,

On Wed, Feb 12, 2020 at 7:39 AM Johan Hedberg <johan.hedberg@gmail.com> wrote:
>
> Hi Marcel,
>
> On 12. Feb 2020, at 17.19, Marcel Holtmann <marcel@holtmann.org> wrote:
> >> +            key = hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
> >> +                               hcon->role);
> >> +
> >> +            /* If there already exists link key in local host, leave the
> >> +             * decision to user space since the remote device could be
> >> +             * legitimate or malicious.
> >> +             */
> >> +            if (smp->method == JUST_WORKS && key) {
> >> +                    err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
> >> +                                                    hcon->type,
> >> +                                                    hcon->dst_type, passkey,
> >> +                                                    1);
> >> +                    if (err)
> >> +                            return SMP_UNSPECIFIED;
> >> +                    set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
> >> +            }
> >>      }
> >
> > while this looks good, I like to optimize this to only look up the LTK when needed.

I wonder why we don't just call user confirm everytime? That way the
new policy preference applies to both a new pair or when already
paired, and we don't have to really do the key lookup here since the
userspace can do the check if really needed.

> >
> >       /* comment here */
> >       if (smp->method != JUST_WORKS)
> >               goto mackey_and_ltk;
> >
> >
> >       /* and command here */
> >       if (hci_find_ltk()) {
> >               mgmt_user_confirm_request()
> >               ..
> >       }
> >
> > And my preference that we also get an Ack from Johan or Luiz that double checked that this is fine.
>
> Acked-by: Johan Hedberg <johan.hedberg@intel.com>
>
> Johan



-- 
Luiz Augusto von Dentz

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2020-02-12 21:30 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-12 13:23 [Bluez PATCH v3] bluetooth: secure bluetooth stack from bluedump attack Howard Chung
2020-02-12 15:19 ` Marcel Holtmann
2020-02-12 15:37   ` Johan Hedberg
2020-02-12 21:29     ` Luiz Augusto von Dentz

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).