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List:       linux-bluetooth
Subject:    Re: [EXT] Unexpected SMP Command 0x17
From:       Marcel Holtmann <marcel () holtmann ! org>
Date:       2017-03-30 6:13:44
Message-ID: 127FD0E3-D17E-4010-B5FC-1716F9B4BCD5 () holtmann ! org
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Hi Joshua,

> > > > Yes, for secure connection the LTK is generated locally.
> > > > But issue here is observed that after Pairing is complete the key
> > > > distribution is not completed from Master.
> > > > 
> > > > i.e. After Slave sends the  "Signature key:" but Master doesn't
> > > > share any key.  Attached logs.
> > > I get that and that is clear from the logs. Something is stalling here
> > > and because of that, you run into the 30 seconds SMP timeout. We just
> > > need to know if the 4.9 kernel is doing this correctly. If so, then
> > > you can bi-sect that patch that fixes. Without proof that 4.9 is also
> > > broken, nobody will even bother to chase this down.
> > 
> > I think the problem here is race between ACL data and HCI events on USB
> > dongle...  We get initial slave keys but those get dropped due to encryption
> > changed event not being received yet. Since keys were silently dropped we later
> > on get unexpected SMP PDU and ignoring remaining keys as well which
> > eventually leads to SMP timeout.
> > 
> > If this is USB dongle (using btusd) then only (AFAIK) solution would be to have a
> > workaround for this inside chip (it would delay ACL data received right after
> > encryption change giving host time to handle encpryption change event).
> > Bluetooth specification for USB transport is unfortunatelly kinda broken.
> > 
> > --
> > pozdrawiam
> > Szymon Janc
> 
> Thank you for your reply. Your inputs are valuable to us in helping to debug the \
> issue. Yes, we are indeed using the btusb kernel module and it is using a USB \
> interface (Bluetooth over USB). 
> I noticed that when btmgmt settings are set to turn 'bredr off', the 'ssp' mode \
> also turns off. Is this behavior expected to occur? My current settings are \
> 'powered connectable discoverable bondable le secure-conn'

the SSP (Secure Simple Pairing) is a BR/EDR only feature. So when you disable BR/EDR, \
it will be disabled as well.

Regards

Marcel

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