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+
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+Authorizing (or not) your USB devices to connect to the system
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+
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+(C) 2007 Inaky Perez-Gonzalez <inaky@linux.intel.com> Intel Corporation
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+
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+This feature allows you to control if a USB device can be used (or
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+not) in a system. This feature will allow you to implement a lock-down
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+of USB devices, fully controlled by user space.
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+
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+As of now, when a USB device is connected it is configured and
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+it's interfaces inmediately made available to the users. With this
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+modification, only if root authorizes the device to be configured will
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+then it be possible to use it.
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+
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+Usage:
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+
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+Authorize a device to connect:
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+
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+$ echo 1 > /sys/usb/devices/DEVICE/authorized
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+
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+Deauthorize a device:
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+
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+$ echo 0 > /sys/usb/devices/DEVICE/authorized
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+
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+Set new devices connected to hostX to be deauthorized by default (ie:
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+lock down):
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+
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+$ echo 0 > /sys/bus/devices/usbX/authorized_default
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+
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+Remove the lock down:
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+
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+$ echo 1 > /sys/bus/devices/usbX/authorized_default
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+
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+By default, Wired USB devices are authorized by default to
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+connect. Wireless USB hosts deauthorize by default all new connected
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+devices (this is so because we need to do an authentication phase
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+before authorizing).
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+
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+
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+Example system lockdown (lame)
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+-----------------------
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+
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+Imagine you want to implement a lockdown so only devices of type XYZ
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+can be connected (for example, it is a kiosk machine with a visible
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+USB port):
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+
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+boot up
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+rc.local ->
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+
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+ for host in /sys/bus/devices/usb*
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+ do
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+ echo 0 > $host/authorized_default
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+ done
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+
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+Hookup an script to udev, for new USB devices
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+
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+ if device_is_my_type $DEV
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+ then
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+ echo 1 > $device_path/authorized
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+ done
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+
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+
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+Now, device_is_my_type() is where the juice for a lockdown is. Just
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+checking if the class, type and protocol match something is the worse
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+security verification you can make (or the best, for someone willing
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+to break it). If you need something secure, use crypto and Certificate
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+Authentication or stuff like that. Something simple for an storage key
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+could be:
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+
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+function device_is_my_type()
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+{
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+ echo 1 > authorized # temporarily authorize it
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+ # FIXME: make sure none can mount it
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+ mount DEVICENODE /mntpoint
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+ sum=$(md5sum /mntpoint/.signature)
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+ if [ $sum = $(cat /etc/lockdown/keysum) ]
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+ then
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+ echo "We are good, connected"
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+ umount /mntpoint
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+ # Other stuff so others can use it
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+ else
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+ echo 0 > authorized
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+ fi
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+}
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+
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+
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+Of course, this is lame, you'd want to do a real certificate
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+verification stuff with PKI, so you don't depend on a shared secret,
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+etc, but you get the idea. Anybody with access to a device gadget kit
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+can fake descriptors and device info. Don't trust that. You are
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+welcome.
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+
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Inaky Perez-Gonzalez