mirror of
https://github.com/torvalds/linux.git
synced 2024-12-11 13:41:55 +00:00
ecefae6db0
While there are a mix of things here, most of the stuff were written from Kernel developer's PoV. So, add them to the driver-api book. A follow up for this patch would be to move documents from there that are specific to sysadmins, adding them to the admin-guide. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Johan Hovold <johan@kernel.org> Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
133 lines
3.9 KiB
ReStructuredText
133 lines
3.9 KiB
ReStructuredText
==============================================================
|
|
Authorizing (or not) your USB devices to connect to the system
|
|
==============================================================
|
|
|
|
Copyright (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
|
|
its interfaces are immediately 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/bus/usb/devices/DEVICE/authorized
|
|
|
|
De-authorize a device::
|
|
|
|
$ echo 0 > /sys/bus/usb/devices/DEVICE/authorized
|
|
|
|
Set new devices connected to hostX to be deauthorized by default (ie:
|
|
lock down)::
|
|
|
|
$ echo 0 > /sys/bus/usb/devices/usbX/authorized_default
|
|
|
|
Remove the lock down::
|
|
|
|
$ echo 1 > /sys/bus/usb/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). Writing "2" to the authorized_default attribute
|
|
causes kernel to only authorize by default devices connected to internal
|
|
USB ports.
|
|
|
|
|
|
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/usb/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.
|
|
|
|
|
|
Interface authorization
|
|
-----------------------
|
|
|
|
There is a similar approach to allow or deny specific USB interfaces.
|
|
That allows to block only a subset of an USB device.
|
|
|
|
Authorize an interface::
|
|
|
|
$ echo 1 > /sys/bus/usb/devices/INTERFACE/authorized
|
|
|
|
Deauthorize an interface::
|
|
|
|
$ echo 0 > /sys/bus/usb/devices/INTERFACE/authorized
|
|
|
|
The default value for new interfaces
|
|
on a particular USB bus can be changed, too.
|
|
|
|
Allow interfaces per default::
|
|
|
|
$ echo 1 > /sys/bus/usb/devices/usbX/interface_authorized_default
|
|
|
|
Deny interfaces per default::
|
|
|
|
$ echo 0 > /sys/bus/usb/devices/usbX/interface_authorized_default
|
|
|
|
Per default the interface_authorized_default bit is 1.
|
|
So all interfaces would authorized per default.
|
|
|
|
Note:
|
|
If a deauthorized interface will be authorized so the driver probing must
|
|
be triggered manually by writing INTERFACE to /sys/bus/usb/drivers_probe
|
|
|
|
For drivers that need multiple interfaces all needed interfaces should be
|
|
authorized first. After that the drivers should be probed.
|
|
This avoids side effects.
|