* [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 related [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
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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
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