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Merge master.kernel.org:/pub/scm/linux/kernel/git/gregkh/usb-2.6
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* master.kernel.org:/pub/scm/linux/kernel/git/gregkh/usb-2.6: (142 commits)
  USB: fix race in autosuspend reschedule
  atmel_usba_udc: Keep track of the device status
  USB: Nikon D40X unusual_devs entry
  USB: serial core should respect driver requirements
  USB: documentation for USB power management
  USB: skip autosuspended devices during system resume
  USB: mutual exclusion for EHCI init and port resets
  USB: allow usbstorage to have LUNS greater than 2Tb
  USB: Adding support for SHARP WS011SH to ipaq.c
  USB: add atmel_usba_udc driver
  USB: ohci SSB bus glue
  USB: ehci build fixes on au1xxx, ppc-soc
  USB: add runtime frame_no quirk for big-endian OHCI
  USB: funsoft: Fix termios
  USB: visor: termios bits
  USB: unusual_devs entry for Nikon DSC D2Xs
  USB: re-remove <linux/usb_sl811.h>
  USB: move <linux/usb_gadget.h> to <linux/usb/gadget.h>
  USB: Export URB statistics for powertop
  USB: serial gadget: Disable endpoints on unload
  ...
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Linus Torvalds committed Oct 12, 2007
2 parents 4d5709a + d1aa3e6 commit 117494a
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92 changes: 92 additions & 0 deletions Documentation/usb/authorization.txt
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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.

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