lkml.org 
[lkml]   [2020]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [Bluez PATCH v2] bluetooth: secure bluetooth stack from bluedump attack
From
Date
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

\
 
 \ /
  Last update: 2020-02-08 09:22    [W:0.050 / U:26.408 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site