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Date:   Fri, 14 Feb 2020 15:58:36 +0100
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Howard Chung <howardchung@...gle.com>
Cc:     Bluez mailing list <linux-bluetooth@...r.kernel.org>,
        chromeos-bluetooth-upstreaming@...omium.org,
        "David S. Miller" <davem@...emloft.net>,
        Johan Hedberg <johan.hedberg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Bluez PATCH v5] bluetooth: secure bluetooth stack from bluedump
 attack

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@...gle.com>
> ---
> 
> Changes in v5:
> - Rephrase the comment
> 
> Changes in v4:
> - optimise the check in smp.c.
> 
> 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       | 19 +++++++++++++++++++
> 2 files changed, 29 insertions(+)

patch has been applied to bluetooth-next tree.

Regards

Marcel

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