| Message ID | 20200207180348.Bluez.v2.1.Ia71869d2f3e19a76a6a352c61088a085a1d41ba6@changeid (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Marcel Holtmann |
| Headers | show |
| Series | [Bluez,v2] bluetooth: secure bluetooth stack from bluedump attack | expand |
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 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 6ddc4a74a5e4..334d7ccd8d6e 100644 > --- a/net/bluetooth/hci_event.c > +++ b/net/bluetooth/hci_event.c > @@ -4557,6 +4557,16 @@ 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 = 2; > + goto confirm; > + } > + we need to document the meaning and handling of confirm_hint 2 in doc/mgmt-api.txt. Maybe it is better to introduce a new mgmt event for this. Otherwise this looks like a nice and simple approach to put the actual policy into the daemon. > 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 83449a88a182..f58426dea4de 100644 > --- a/net/bluetooth/smp.c > +++ b/net/bluetooth/smp.c > @@ -2118,6 +2118,7 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb) > u8 *pkax, *pkbx, *na, *nb; > u32 passkey; > int err; > + struct smp_ltk *key; This is tiny style thing, but generally, we put the structs earlier and let the int err be the last. > > BT_DBG("conn %p", conn); > > @@ -2168,6 +2169,23 @@ 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, > + 2); > + if (err) > + return SMP_UNSPECIFIED; > + set_bit(SMP_FLAG_WAIT_USER, &smp->flags); > + } > } This limits this to outgoing connections. Is this intentional? Regards Marcel
diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c index 6ddc4a74a5e4..334d7ccd8d6e 100644 --- a/net/bluetooth/hci_event.c +++ b/net/bluetooth/hci_event.c @@ -4557,6 +4557,16 @@ 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 = 2; + 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 83449a88a182..f58426dea4de 100644 --- a/net/bluetooth/smp.c +++ b/net/bluetooth/smp.c @@ -2118,6 +2118,7 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb) u8 *pkax, *pkbx, *na, *nb; u32 passkey; int err; + struct smp_ltk *key; BT_DBG("conn %p", conn); @@ -2168,6 +2169,23 @@ 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, + 2); + if (err) + return SMP_UNSPECIFIED; + set_bit(SMP_FLAG_WAIT_USER, &smp->flags); + } } mackey_and_ltk:
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 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(+)