Hello everybody,

 

We would like to propose a RFC to change the way to manage the WPS connections. Following we present our proposal and the reasons for suggesting it:


Current implementation of WPS connection requires to specify the service to which the user wants to connect, and when the connection is going to finalize, a verification is done in handle_wps_completion function to ensure that the SSID of the AP actually being connected was the one specified by the user. This violates the WiFi Alliance specification over WPS and the WPS Certification plan because:

 

  1. WiFi Alliance admits to certify devices that have no mean for the user to choose an AP to connect to, they define them as "Client devices with only a simple display or a fixed label containing a setup password" (Pag. 12 of Wi-Fi Simple Configuration Technical Specification Version 2.0.5)

 

  1. The WPS protocol includes the transition from un-configured to configured state of the AP when the first Enrollee connects, some Access Points change their SSID during this transition, that would cause the ConnMan to invalidate the connection. A tipical example of such Access Point is the Atheros used in test 5.4.2 of Wi-Fi CERTIFIED™ Wi-Fi Protected Setup™ Interoperability Test Plan – Version 2.0.15

 

After having performed a detailed study of the wpa_supplicant implementation for the WPS, we propose to implement a solution with the following general characteristics:

 

  1. The new implementation must  keep current WPS implementation for compatibility support, but as deprecated.
  2. In order to meet the specifications of Wi-Fi Alliance and based on what the WPS D-Bus Interface of wpa_supplicant offers (Documented in https://w1.fi/wpa_supplicant/devel/dbus.html#dbus_wps) we propose to add two methods to the Technology D-Bus Interface: StartWPS and CancelWPS, analogous to functions WPS.Start and WPS.Cancel provided by wpa_supplicant. In this way there is no service specified enabling simple devices to offer a very basic interface to the user for starting the WPS session. Both methods would be supported only by WiFi technology.
  3. On the other hand, some advanced WiFi modules expose more than one network interface (one for P2P, one for STA, one for AP ..) that can be active at the same time, and it is then desirable to not let connman randomly choose on which start WPS, thus we propose also to add the possibility to specify the interface over which either the start or cancel action will be performed. This would not be a mandatory parameter in order to keep the things easy for more simple systems.

Please find below the implementation proposal:

 

StartWPS:

 

Following the approach of wpa_supplicant, we propose to add the possibility to choose which role to assume (enrollee, registrar), which authentication type use (pin, pbc)  and get back the pin to be used (if required), as well as wpa_supplicant does. At this point, we can briefly define a possible prototype of the method:

 

dict StartWPS(dict parameters)

 

Where the returned dictionary could be empty or composed by at most one entry, which will be the just generated PIN by the wpa_supplicant, in case it was requested. On the other hand, the function would receive a dictionary with possible keys: “Ifname", "Role", "Type" and "Pin"; where “Ifame” is an optional parameters covering previous defined characteristic for complex systems. Whereas, parameters "Role", "Type" and "Pin" follow exactly the same behavior of the table presented in https://w1.fi/wpa_supplicant/devel/dbus.html#dbus_wps for method Start of fi.w1.wpa_supplicant1.Interface.WPS Interface.

 

When the StartWPS method gets called, it should verify if interface was specified through “Ifname” entry key. If so, WPS Session will be started in that specific interface, otherwise we suggest to look for the first available interface with the capabilities to start a WPS Session among the device_list of the Wi-Fi Technology. If it is found, then use it, if not return "[service].Error.NotSupported”.

 

Additionally, current implementation does not allow to start a WPS Session when the device is playing as Access Point (Tethering). On the contrary, wpa_supplicant does. Therefore, we propose to also add this possibility to the new implementation. It would be possible if a Service D-Bus Object is not required for starting a WPS Session, which would be true if the new methods are added to the Technology D-Bus Interface, as we propose.

 

CancelWPS:

 

This function does not require for any particular parameter. So, we propose to only continue giving the option to specify the interface. Therefore, the possible prototype of the method would be:


void CancelWPS(dict parameters)

 

Where the received dictionary could be empty or composed by at most one single entry if the user wants to specify the interface using the key “Ifname”. If so, the CancelWPS function should cancel the ongoing WPS Session running in that specific interface. Otherwise, we suggest to do it over all the Device of the Wi-Fi Technology (device_list).

 

Going into details of implementation:

 

After having studied the ConnMan architecture we think to associate the WPS concept to the Device Infrastructure because if we want to add the possibility of specify the interface (“Ifname”), the Device is the corresponding represents of a real device inside the ConnMan. Therefore, we think it is the best choice. Additionally, StartWPS and CancelWPS should be added to the device driver:

 

static struct connman_device_driver wifi_ng_driver = {

       .name         = "wifi",

       .type         = CONNMAN_DEVICE_TYPE_WIFI,

       ...

       .start_wps    = wifi_start_wps,

       .cancel_wps   = wifi_cancel_wps,

};

 

It means that WiFi plugging must implements both methods wifi_start_wps and wifi_cancel_wps. In particular, wifi_start_wps will need to receive the WPS parameters to then pass them to the ConnMan’s supplicant handler (gsuppicant/supplicant.c), which is the only one that interacts directly with the wpa_supplicant.

 

Next, the supplicant handler will call methods Start or Cancel of the fi.w1.wpa_supplicant1.Interface.WPS D-Bus Interface of the wpa_supplicant, with the required parameters. In case the method Start returns the newly generated PIN it has to be forwarded towards the Technology to then be added as an entry in the directory that would be returned by the StartWPS method. It would imply that we have to store the request message of the StartWPS method in order to reply possibly with a the PIN generated by the wpa_supplicant. To do it, we propose to store that message in the Device structure in order to be coherent with the association we previously proposed between the WPS and Device.

 

Once the WPS Session has been initiated, it could finalize successfully or fail. The current implementation does not provide further information about  such a events. Given that, we propose to notify the following events (Just the most commons):

 

We think to perform those notifications using a D-Bus Signal added to the Technology Interface, let’s call it WPSEvent. It would simply indicate when one of the described event takes place. We propose to just provide a string with the name of the event: "success", "pwd-auth-fail" or "pbc-overlap", following the wpa_supplicant notation. All this information is already provided by the wpa_supplicant in the event fi.w1.wpa_supplicant1.Interface.WPS.Event, thus it just need to be forwarded to the Technology in order to be emitted.

 

In order to forward WPS events, we propose to follow the implementation of the communication between the plug-in and the supplicant handler, it means to use the callback mechanism adding a new callback:

 

static const GSupplicantCallbacks callbacks = {

       ...

       .wps_event           = wps_event,

};

 

Thus the wifi plug-in must implement the wps_event function that will basically just call a Technology function that will emit the proposed signal.


What do you think about our proposal? Of course, everybody is welcome to give feedbacks and suggestions.

 

Best regards,

 

Jose Blanquicet