[systemd-devel] Supporting U2F over HID on Linux?

[Andy Lutomirski]

On Sun, Nov 2, 2014 at 3:01 PM, Benjamin Tissoires
<benjamin.tissoires at gmail.com> wrote:
> On Sun, Nov 2, 2014 at 5:49 PM, Andy Lutomirski <luto at amacapital.net> wrote:
>> On Sun, Nov 2, 2014 at 2:45 PM, Benjamin Tissoires
>> <benjamin.tissoires at gmail.com> wrote:
>>> On Sun, Nov 2, 2014 at 4:40 PM, Jiri Kosina <jkosina at suse.cz> wrote:
>>>> On Sun, 2 Nov 2014, Jiri Kosina wrote:
>>>>
>>>>> Alternatively, you can just write udev rule which triggers on HID devices,
>>>>> issues HIDIOCGRDESC ioctl() on the just-created hidraw node, and decides
>>>>> afterwards whether node permissions need to be altered ... right?
>>>>
>>>> Just to make myself clear here -- this is basically alternative to your
>>>> 1st option, but for cases where you want to make yourself independent on
>>>> sysfs existence (I don't what is the craziness level of setups you are
>>>> considering).
>>>>
>>>
>>> I am a little bit concerned with the user space retrieving the
>>> descriptor, parsing it and then deciding how to set the permissions.
>>> It's not that it is super complex, but it will duplicate the parsing
>>> we already do in the kernel. Wacom tried to do that in their usb
>>> driver, and they never managed to fully implement one.
>>>
>>> I think the HID_GROUP solution is super trivial:
>>> - add a match on the U2F input report and set the group to
>>> HID_GROUP_U2F (2 lines in hid_scan_input_usage() in hid-core.c)
>>> - allow hid-generic to also match HID_GROUP_U2F (1 line in hid-generic.c).
>>>
>>> Then, the udev rule would be super trivial.
>>
>> I'm confused.  What would the user-visible effect of this be?  Would
>> the hidraw node still show up?  What is user code supposed to match to
>> detect a U2F device or to otherwise set permissions?
>>
>
> The only change with what we currently have is that the modalias of
> the device will be something like
> MODALIAS=hid:b0003gHID_GROUP_U2Fv0000XXXXp0000XXXX. (replace
> HID_GROUP_U2F with the proper hex value). So matching against this
> modalias is trivial, and you can just put the hidraw node rw for
> users.

Do we really want udev matching against MODALIAS, and do we really
want udev rules to hardcode hid group constants?

I'd like this idea better if we added a HID_GROUP uevent property with
a textual description, or perhaps something a little more specific.
The hid group field seems to be used for different types of things.

--Andy