Re: [PATCH] Bluetooth: Add conn type to identify addr type with SMP over BR/EDR

[Szymon Janc <szymon.janc@codecoup.pl>]

Hi Jiangbo,

On Tuesday, 18 October 2016 18:23:38 CEST Wu,Jiangbo wrote:
> Hi,
> 
> On Mon, Oct 17, 2016 at 11:05:33PM +0200, Szymon Janc wrote:
> > Hi,
> > 
> > On Saturday, 15 October 2016 00:43:13 CEST wujiangbo wrote:
> > > On Fri, Oct 14, 2016 at 05:19:38PM +0300, Johan Hedberg wrote:
> > > > Hi Jiangbo,
> > > > 
> > > > Please don't top-post on this list.
> > > > 
> > > > On Fri, Oct 14, 2016, Wu, Jiangbo wrote:
> > > > > If pair a device that unpair firstly that remove encryption key,
> > > > > encryption key event will be emitted. kernel will receive
> > > > > 'L2CAP_CID_SMP_BREDR' frame, and then it will use SMP to distribute
> > > > > key.  SMP would like to use LTK, IRK and CRSK to notify user. If it
> > > > > don't identify device by which conn type they are, only marks LE as
> > > > > the device type,
> > > > 
> > > > Why would that happen? Before SMP over BR/EDR happens pairing would
> > > > have
> > > > happened over BR/EDR, so bluetoothd should know that BR/EDR is
> > > > supported
> > > > as well (it would even be aware of an existing BR/EDR connection). Are
> > > > you perhaps trying to work around some bluetoothd bug with all this?
> > > 
> > > I use upstream bluez source code without change.
> > > 
> > > Yes, bluetoothd scan will find device type is BR/EDR or LE. As my case,
> > > device is BR/EDR. But if kernel report CRSK notify, bluetoothd will
> > > change
> > > 
> > > the device type to LE. The code you can see:
> > > 	new_csrk_callback -> btd_adapter_get_device -> 
btd_adapter_find_device
> > > 	
> > > 		if (bdaddr_type == BDADDR_BREDR)
> > > 		
> > > 			device_set_bredr_support(device);
> > > 		
> > > 		else
> > > 		
> > > 			device_set_le_support(device, bdaddr_type);
> > > 
> > > As Marcel mentioned before, LTK, IRK and CRSK are only valid for LE
> > > link.
> > > So the rootcause is why remote start to pair a BR/EDR device, the kernel
> > > will receive CRSK event.
> > > 
> > > This is the first pair, and it will pair success even if receive CRSK
> > > notify. And the second and the next all pair will be failed with remote
> > > device unpair and then pair again.
> > > 
> > > > > while Bluetoothd will use this 'addr' and 'addr type' to reply the
> > > > > comfirm to kernel.
> > > > 
> > > > What reply are you talking about? There's no user interaction involved
> > > > with SMP over BR/EDR - that would already have occurred when SSP over
> > > > BR/EDR happened.
> > > 
> > > Sorry to confuse the case, the pairing failed coming with next pair
> > > procedure. Because at the last pair with CRSK notify, device type will
> > > be
> > > changed to LE, following is the failed scenario after last success with
> > > CRSK notify. Remote unpair and pair again.
> > > 
> > > This reply is SPP, user confirm passkey reply. When pairing proceduce,
> > > User
> > > confirm the pairing request through bluetoothd, that will send mgmt op
> > > 'MGMT_OP_USER_CONFIRM_REPLY' with device address and device type in
> > > mgmt_cp_user_confirm_reply. Kernel use the device address and type to
> > > lookup hci conn. Unfortunately, it will lookup hci_conn from LE
> > > hashtable, that don't include hci conn. So spp reply couldn't send to
> > > remote, caused pair failed.
> > > 
> > > > > At the same time kernel always uses them to lookup hci_conn in LE
> > > > > hashtable firstly, because addr type always marks as LE. Obviously
> > > > > it
> > > > > will failed with SMP over BR/EDR.
> > > > 
> > > > I don't follow this either since there shouldn't have been any "reply"
> > > > from user space for SMP over BR/EDR. All there should be are events
> > > > from
> > > > the kernel for the generated LE keys.
> > > > 
> > > > > Actually, SPM is only for LE in SPEC,
> > > > 
> > > > That's not true. SMP is specified both for LE-U and ACL-U.
> > > > 
> > > > > but kernel already support and use SMP over BR/EDR. if BR/EDR
> > > > > exchanges key with SMP, it will never reply pairing response to
> > > > > remote, in other words it will be never paired, that is happened in
> > > > > our products.
> > > > 
> > > > Szymon recently implemented SMP over BR/EDR for Zephyr and used
> > > > Linux/BlueZ as a reference for testing. He didn't report any issues
> > > > like
> > > > this. It might help if you could provide some logs (particularly
> > > > HCI/btmon but also from bluetoothd) to understand what's the actual
> > > > issue you're seeing.
> > > > 
> > > > Johan
> > > 
> > > Sorry to confuse this issue, the log is not in my hand right now,
> > > so it maybe later.
> > 
> > So I was able to reproduce this issue. This is bluetoothd bug and not
> > kernel one. This bug is no specific to cross-transport pairing. It can
> > happen with any dual-mode device that is doing BR/EDR pairing while being
> > known as dual mode by bluetoothd when agent replies with passkey or
> > confirmation.
> > 
> > To fix this we probably need to hold extra information in
> > 'struct authentication_req' in device.c about type of pairing (LE or
> > BR/EDR). This is not a one-liner-fix so I don't have a patch ready yet.
> 
> Totally agree with you about dual-mode device pairing known as dual mode.
> But i want to known is that reasonable about device is to do BR/EDR pairing
> will generate CRSK notify? I'm very intersting about this fixing, this bug
> is hight priority in our product. In my opinion hold extra informatin in
> 'struct authentication_req' may not fix this bug. Because if CRSK event is
> still report, then bluetoothd will change the device type to LE even if we
> pair device that is scaned with BR/EDR. So i think the rootcase is find
> does CRSK event make sense in BR/EDR pairing, and how to handle CRSK events
> in BR/EDR pairing if it make sense. I'm confuse with those.

It doesn't change the device to LE but to dual mode device. This is
*cross-transport* pairing so keys for other transport are generated.
baddr_type specify only LE address type, not BR/EDR since there is no address 
type for BR/EDR. This is mostly true but few places in bluetoothd seem to 
asusme that for device supporting BR/EDR type is equal 0. Which is not true if 
device is dual mode.

You should be able to reproduce this bug with dual-mode devices that don't 
support cross-transport pairing: enable advertising, scan from linux, when 
device is found stop advertising and make device discoverable over BR/EDR 
(inquiry). When device is found over BR/EDR stop scanning and start pairing.

> 
> I noticed that if quikly reply the passkey confirm, this bug always be
> reproduced, but if wait for 2~3s to reply the passkey confirm, it works
> well every time. In terms of code, wait for 2~3s will cause l2cap chan
> timeout for info timer that created by HCI_EV_REMOTE_EXT_FEATURES event,
> and timeout will change l2cap chan to BT_CONNECTED. So next SMP
> resume/ready don't distribute key also CRSK events.
> 
> It can't reproduce with btmgmt, because it reply passkey confirm always only
> use BR/EDR in 'struct mgmt_cp_user_confirm_reply' not use device relation
> type.
> 
> bluetoothd.log and btmon.log are attached. It records two pair request
> sequence, one is pair success that have CRSK event, another is next pair
> reqeust don't success any, hope those maybe help you to annlyze this bug.
> 
> Thanks
> Jiangbo


-- 
pozdrawiam
Szymon Janc