[systemd-devel] Writing a udev rule for U2F security tokens?

[Greg KH]

On Mon, Oct 27, 2014 at 04:37:14PM -0700, Andy Lutomirski wrote:
> On Mon, Oct 27, 2014 at 4:32 PM, Greg KH <gregkh at linuxfoundation.org> wrote:
> > On Mon, Oct 27, 2014 at 04:12:30PM -0700, Andy Lutomirski wrote:
> >> Hi-
> >>
> >> I'd like to write a generic udev rule for U2F security tokens and to
> >> possibly get it integrated into systemd / udev, but I'm not sure how
> >> to write it in the first place.
> >>
> >> U2F tokens are USB HID devices that have a usage page 0xF1D0 that
> >> contains usage 0x01.  The rule should match any hidraw device with
> >> that property.  Can this be done without a user helper?  Is there an
> >> existing helper in which it would make sense to add such a check?
> >>
> >> Here's the draft USB forum allocation:
> >>
> >> http://www.usb.org/developers/hidpage/HUTRR48.pdf
> >>
> >> Here's the draft spec from the FIDO Alliance:
> >>
> >> https://fidoalliance.org/specs/fido-u2f-HID-protocol-v1.0-rd-20141008.pdf
> >>
> >> In practice, I expect little change between the draft and final specs,
> >> since these devices are already for sale and Chromium supports them.
> >
> > I don't understand, what would a udev rule do with these devices?
> > Shouldn't they be exported automatically using the hid "raw" interface
> > so that userspace can talk to them?  What else needs to be done?
> 
> Wow, I clearly failed to transfer my thoughts into email...
> 
> I want to set ID_SECURITY_TOKEN=1 or, more generally, cause the
> uaccess tag to be set so that users have permission to use the token.
> 
> This rule works in Fedora for the existing tokens by Yubico:
> 
> KERNEL=="hidraw*", SUBSYSTEM=="hidraw", ATTRS{idVendor}=="1050",
> ATTRS{idProduct}=="0113|0114|0115|0116|0120",
> ENV{ID_SECURITY_TOKEN}="1"
> 
> but it won't work for other brands of U2F token.

If there's no sysfs attribute that you can read directly to determine
that it is a a U2F token, then it's not easy to write a udev rule.

You can write a "simple" program to read the hid pages from the hidraw
interface, and then set an environment variable from there if the "FIDO
Alliance Page" is present.  You can use a udev rule for that, but it
will have to be an external tool.

hope this helps,

greg k-h