Hi Jan,
On 2020-07-02 12:06, Jan Behrens wrote:
On Thu, 2 Jul 2020 11:23:32 +0200
Hans Petter Selasky <[email protected]> wrote:
On 2020-07-02 11:15, Jan Behrens wrote:
On Thu, 2 Jul 2020 10:54:27 +0200
Hans Petter Selasky <[email protected]> wrote:
On 2020-07-02 10:47, Jan Behrens wrote:
But wouldn't both drivers require access to the entries in /dev ?
Yes, user-space drivers would require access to /dev, yes, but kernel
drivers not, like mouse, keyboard, storage, network.
Thus not every user could mess with any USB device, or do I get it
wrong?
A so-called composite USB device may appear like a USB storage device
(kernel driver) and a security token (firefox). Firefox can only grab
the device if you set the proper permissions for /dev of course, but the
reset device IOCTL then also becomes possible, which is why we currently
block it for non-root.
--HPS
Okay, so if I understand it right, the problem is due to devices that
shall be partly accessible by root, and partly by users. Some device
nodes (e.g. /dev/usb/2.2.1 ) while others (e.g. /dev/usr/2.2.2 ) are
limited to root access only. An USB reset always affects all devices
(e.g. also /dev/usb/2.2.2, 2.2.3, etc.), right?
Yes, correct.
Does /dev/usb/2.2.0 (in the given example) represent the device as a
whole, or is it just another subdevice? (What's the correct term for
"subdevice" in this context by the way? I assume "interface"?)
I experienced that /dev/usb/2.2.0 and /dev/usb/2.2.1, 2.2.2, 2.2.3,
etc. get treated differently when I reset the LimeSDR Mini with
"usbconfig -u 2 -a 2 reset". The devices 2.2.1 and up are supposingly
re-created (and have their access rights reset), while the device 2.2.0
maintains any manually changed access rights.
Let me explain, now you are getting me into dirty details :-)
This device is used for all of LibUSB interfaces and gives access to all
endpoints:
/dev/usb/X.Y.0
These devices are legacy devices, which allow direct access to the
endpoint via the shell. They are there to support the old user-space
model FreeBSD had. And they are re-created when you reset/reconfigure a
USB device. Actually you can "echo > /dev/usb/X.Y.N" to write directly
to an endpoint from user-space. But don't do that unless it is a modem
endpoint which support AT commands for example.
/dev/usb/X.Y.[1..15]
Is it correct that 2.2.0 identifies the device as a whole?
Yes, this is correct.
What do you think?
I'm not sure if this is (from a semantic point of view) the best thing
to do. I would say you should only be able to reset a device if you
have been granted access to the device as a whole (including all
interfaces/subdevices/whatever), as the reset seems to affect all of
those.
In FreeBSD and LibUSB there is no such concept. Everything is oriented
around interfaces. There is a function to claim an interface, but not
the device itself. (man libusb_claim_interface)
That sounds better than adding a sysctl option to me. But I assume that
would require a lot of changes in the code?
If a simple rule can be formulated, I could implement it in the generic
USB kernel code.
--HPS
Regards,
Jan
--HPS
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