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| -rw-r--r-- | Documentation/usb/authorization.txt | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/Documentation/usb/authorization.txt b/Documentation/usb/authorization.txt new file mode 100644 index 000000000000..2af400609498 --- /dev/null +++ b/Documentation/usb/authorization.txt @@ -0,0 +1,92 @@ + +Authorizing (or not) your USB devices to connect to the system + +(C) 2007 Inaky Perez-Gonzalez <inaky@linux.intel.com> Intel Corporation + +This feature allows you to control if a USB device can be used (or +not) in a system. This feature will allow you to implement a lock-down +of USB devices, fully controlled by user space. + +As of now, when a USB device is connected it is configured and +it's interfaces inmediately made available to the users. With this +modification, only if root authorizes the device to be configured will +then it be possible to use it. + +Usage: + +Authorize a device to connect: + +$ echo 1 > /sys/usb/devices/DEVICE/authorized + +Deauthorize a device: + +$ echo 0 > /sys/usb/devices/DEVICE/authorized + +Set new devices connected to hostX to be deauthorized by default (ie: +lock down): + +$ echo 0 > /sys/bus/devices/usbX/authorized_default + +Remove the lock down: + +$ echo 1 > /sys/bus/devices/usbX/authorized_default + +By default, Wired USB devices are authorized by default to +connect. Wireless USB hosts deauthorize by default all new connected +devices (this is so because we need to do an authentication phase +before authorizing). + + +Example system lockdown (lame) +----------------------- + +Imagine you want to implement a lockdown so only devices of type XYZ +can be connected (for example, it is a kiosk machine with a visible +USB port): + +boot up +rc.local -> + + for host in /sys/bus/devices/usb* + do + echo 0 > $host/authorized_default + done + +Hookup an script to udev, for new USB devices + + if device_is_my_type $DEV + then + echo 1 > $device_path/authorized + done + + +Now, device_is_my_type() is where the juice for a lockdown is. Just +checking if the class, type and protocol match something is the worse +security verification you can make (or the best, for someone willing +to break it). If you need something secure, use crypto and Certificate +Authentication or stuff like that. Something simple for an storage key +could be: + +function device_is_my_type() +{ + echo 1 > authorized # temporarily authorize it + # FIXME: make sure none can mount it + mount DEVICENODE /mntpoint + sum=$(md5sum /mntpoint/.signature) + if [ $sum = $(cat /etc/lockdown/keysum) ] + then + echo "We are good, connected" + umount /mntpoint + # Other stuff so others can use it + else + echo 0 > authorized + fi +} + + +Of course, this is lame, you'd want to do a real certificate +verification stuff with PKI, so you don't depend on a shared secret, +etc, but you get the idea. Anybody with access to a device gadget kit +can fake descriptors and device info. Don't trust that. You are +welcome. + |