[lxc-users] Device node in LXC is not accessible when connected via SSH

[Tim Jaacks]

Hello everyone,

I have a problem where a physical hardware device passed through to an LXC container cannot be read from or written to when I am connected via SSH.

The device node of my physical hardware device looks like this:

	myuser at myhost:~$ ls -la /dev/usb/hiddev0
	crw-rw-rw- 1 root root 180, 0 Jul 30 10:27 /dev/usb/hiddev0

This is how I create and start my container:

	myuser at myhost:~$ sudo lxc-create -q -t debian -n mylxc -- -r stretch
	myuser at myhost:~$ sudo lxc-start -n mylxc

Then I add the device node to the LXC:

	myuser at myhost:~$ sudo lxc-device -n mylxc add /dev/usb/hiddev0

Afterwards the device is available in the LXC and I can read from it after having attached to the LXC:

	myuser at myhost:~$ sudo lxc-attach -n mylxc
	root at mylxc:/# ls -la /dev/usb/hiddev0
	crw-r--r-- 1 root root 180, 0 Aug 27 11:26 /dev/usb/hiddev0
	root at mylxc:/# cat /dev/usb/hiddev0
	����������^C
	root at mylxc:/#

I then enable root access via SSH without a password:

	myuser at myhost:~$ sudo lxc-attach -n mylxc
	root at mylxc:/# sed -i 's/#\?PermitRootLogin.*/PermitRootLogin yes/g' /etc/ssh/sshd_config
	root at mylxc:/# sed -i 's/#\?PermitEmptyPasswords.*/PermitEmptyPasswords yes/g' /etc/ssh/sshd_config
	root at mylxc:/# sed -i 's/#\?UsePAM.*/UsePAM no/g' /etc/ssh/sshd_config
	root at mylxc:/# passwd -d root
	passwd: password expiry information changed.
	root at mylxc:/# /etc/init.d/ssh restart
	Restarting ssh (via systemctl): ssh.service.
	root at mylxc:/# exit

When I connect via SSH now, the device node is there, but I cannot access it:

	myuser at myhost:~$ ssh root@<lxc-ip-address>
	root at mylxc:~# ls -la /dev/usb/hiddev0
	crw-r--r-- 1 root root 180, 0 Aug 27 11:26 /dev/usb/hiddev0
	root at mylxc:~# cat /dev/usb/hiddev0
	cat: /dev/usb/hiddev0: Operation not permitted

In both cases (lxc-attach and ssh) I am the root user (verified via whoami), so this cannot be the problem.

Why am I not allowed to access the device when I am connected via SSH?

Mit freundlichen Grüßen / Best regards
Tim Jaacks
DEVELOPMENT ENGINEER
Garz & Fricke GmbH
Schlachthofstrasse 20
21079 Hamburg
Direct: +49 40 791 899 - 183
Fax: +49 40 791899 - 39
tim.jaacks at garz-fricke.com
www.garz-fricke.com
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