From: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Date: Wed, 1 Aug 2007 03:34:08 +0000 (-0700)
Subject: usb: document device authorization
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=732bb9ee8195053a7dc00b9eec7be48891ad8668;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

usb: document device authorization

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

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.
+