Re: Read by Group Type is denied when issued before Pairing is finsihed

On 08/24, Luiz Augusto von Dentz wrote:

Hi Konrad,

On Thu, Aug 24, 2017 at 11:24 AM, Konrad Zapalowicz
[off-list ref] wrote:

quoted

On 08/24, Luiz Augusto von Dentz wrote:

quoted

Hi Konrad,

On Wed, Aug 23, 2017 at 10:38 PM, Konrad Zapalowicz
[off-list ref] wrote:

quoted

Hey,

I have stumbled upon a problem with one of the BLE devices that I have
on my desk. BlueZ (bluetoothctl) failed to discover the primary services
and the error returned by the Read by Group type request was
"Insufficient Authentication". It did work when using gatttool though.

I have tracked it down and realized that if calling the
bt_gatt_discover_all_primary_services is delayed until after the pairing
is finished then the primary services are discovered without any issues.

The simplified bt for bt_gatt_discover_all_primary_services is:

(gdb) bt
#0  discover_services
#1  bt_gatt_discover_primary_services
#2  bt_gatt_discover_all_primary_services
#3  exchange_mtu_cb

Now, what would be the best way of approaching this. Calling it could be
delayed with a timer but would it be an optimal solution - thoughts?

Sounds to me that the device is requiring authentication for primary
services which is not following the spec:

Yes, this is true as well and it is also my concern. Yet at the same
time I would love to get this device operational. This is a Transport
Data Logger btw that I'm playing with.

quoted

4.4.1 Discover All Primary Services
...
Note: The service declaration described in Section 3.1 specifies that the
service declaration is readable and requires no authentication or authorization,
therefore insufficient authentication or read not permitted errors
shall not occur.

Is this a device already on the market? Perhaps we should contact the
manufacturer since it seems to not comply to the spec when it comes to
discovery.

Delaying is never a nice thing since it affects all devices, but we
could perhaps attempt to pair if that happens, actually, we usually do
this for regular Read/Write procedures so in case there is an
authentication error we pair and try again which might work here as
well despite not following the spec.

In the meantime I have cross-checked with the Android code and it does
things differently. So the services discovery is started in pairing_cb
that is being called when the pairing is done. I can't tell however if
this affects interoperability in any way, i.e. has a negative impact
over Linux implementation.

Not sure how Android would determine if it needs pairing before
discovering the services, in GATT the pairing is normally done on
demand when there is an authentication error. Though perhaps Android
pairs with any device capable of pairing, anyway the same could be
done with bluetoothctl> pair instead of connect command.

So I have investigated further and realized that there is an incomming
ATT connection that I have missed for the first time. As a result the
connect_cb from gatt-database.c is execued which calls the
device_attach_att that ultimately leads to gatt_client_init being
called.

The device_attach_att would be called anyway through the
new_long_term_key_callback and device_browse_gatt however since the
services are already discovered it never happens. Which is perfecly fine
btw.

I'm thinking however though if this is sane to make sure that the
services are discovered only through the new_long_term_key_callback
path. Something which would happen after the device_bonding_complete
thus would be a little bit more forgiving for devices that behave like
the described one.

Does it make sense?

Btw, even for profiles requiring pairing, like HoG, it hasn't been a
problem to pair on demand though it is probably recommended to pair
first so we don't lose a round trip while accessing the attributes
that would cause the authentication error.

quoted

Thanks,
K

quoted

quoted

Thanks,
K
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--
Luiz Augusto von Dentz

-- 
Luiz Augusto von Dentz