Re: [RFC PATCH 3/4] usb: core: Plug the usb authentication capability

[Nicolas Bouchinet]

Hi Olivier,

Thank you for your review.

Indeed our current implementation of the usb authentication is still a bit
crude.
Currently, most, if not all of usb devices can't handle authentication. 
If we
want to have an integration that doesn't break on current hosts, we need to
have a fail safe. We are still working on the best way to handle the
combination of authentication and authorization.
See the reply to Alan [1].

[1]: 
https://lore.kernel.org/linux-usb/8cc10112-23a7-41af-b81f-7fc0c097d34d@xxxxxxxxxxxxxxxxx/

On 6/23/25 20:15, Oliver Neukum wrote:
> Hi,
>
> I am afraid someone has to address this.
>
> On 20.06.25 16:27, nicolas.bouchinet@xxxxxxxxxxxxxxxxx wrote:
>
> > +    // Set a default value for authenticated at true in order not to 
> > block devices
> > +    // that do not support the authentication
> > +    dev->authenticated = 1;
>
> So the default is authenticated. OK.
>
> > +    if (le16_to_cpu(dev->descriptor.bcdUSB) >= 0x0201) {
> > +        pr_notice("bcdUSB >= 0x0201\n");
> > +        retval = usb_get_bos_descriptor(dev);
> > +        if (!retval) {
> > +            pr_notice("found BOS\n");
> > +#ifdef CONFIG_USB_AUTHENTICATION
> > +            if (dev->bos->authent_cap) {
>
> If the device claims not to support authentication ...
>
> > +                /* If authentication cap is present, start device 
> > authent */
> > +                pr_notice("found Authent BOS\n");
> > +                retval = usb_authenticate_device(dev);
> > +                if (retval != 0) {
> > +                    pr_err("failed to authenticate the device: %d\n",
> > +                           retval);
> > +                } else if (!dev->authenticated) {
> > +                    pr_notice("device has been rejected\n");
> > +                    // return early from the configuration process
> > +                    return 0;
> > +                } else {
> > +                    pr_notice("device has been authorized\n");
> > +                }
> > +            } else {
> > +                // USB authentication unsupported
> > +                // Apply security policy on failed devices
> > +                pr_notice("no authentication capability\n");
>
> ... we do nothing about it. We enumerate.
>
> The purpose of authentication is guarding against unknown or malicious 
> devices,
> isn't it? This behavior seems to be kind of incompatible with the goal.
>
>     Regards
>         Oliver