On Tue, Jan 28, 2020 at 03:47:57PM +0000, Tim Jaacks wrote: > >On Tue, Jan 28, 2020 at 08:24:30AM +0000, Tim Jaacks wrote: > >> 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@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@myhost:~$ sudo lxc-create -q -t debian -n mylxc -- -r stretch > >> myuser@myhost:~$ sudo lxc-start -n mylxc > >> > >> Then I add the device node to the LXC: > >> > >> myuser@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@myhost:~$ sudo lxc-attach -n mylxc > >> root@mylxc:/# ls -la /dev/usb/hiddev0 > >> crw-r--r-- 1 root root 180, 0 Aug 27 11:26 /dev/usb/hiddev0 > >> root@mylxc:/# cat /dev/usb/hiddev0 > >> ??????????^C > >> root@mylxc:/# > >> > >> I then enable root access via SSH without a password: > >> > >> myuser@myhost:~$ sudo lxc-attach -n mylxc > >> root@mylxc:/# sed -i 's/#\?PermitRootLogin.*/PermitRootLogin yes/g' > >> /etc/ssh/sshd_config > >> root@mylxc:/# sed -i 's/#\?PermitEmptyPasswords.*/PermitEmptyPasswords > >> yes/g' /etc/ssh/sshd_config > >> root@mylxc:/# sed -i 's/#\?UsePAM.*/UsePAM no/g' /etc/ssh/sshd_config > >> root@mylxc:/# passwd -d root > >> passwd: password expiry information changed. > >> root@mylxc:/# /etc/init.d/ssh restart > >> Restarting ssh (via systemctl): ssh.service. > >> root@mylxc:/# exit > >> > >> When I connect via SSH now, the device node is there, but I cannot access > >> it: > >> > >> myuser@myhost:~$ ssh root@<lxc-ip-address> > >> root@mylxc:~# ls -la /dev/usb/hiddev0 > >> crw-r--r-- 1 root root 180, 0 Aug 27 11:26 /dev/usb/hiddev0 > >> root@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? > > > > Can you look at your cgroup membership in both cases? > > > > I am not sure what this means exactly. I have tried reading > /proc/<pid>/cgroups of both the SSH process (upper) and the lxc-attach > process (lower): > > tim.jaacks@a048:~$ cat /proc/26732/cgroup > 11:pids:/lxc/mylxc/system.slice/ssh.service > 10:net_cls,net_prio:/lxc/mylxc > 9:perf_event:/lxc/mylxc > 8:freezer:/lxc/mylxc > 7:cpuset:/lxc/mylxc > 6:rdma:/lxc/mylxc > 5:memory:/lxc/mylxc > 4:cpu,cpuacct:/lxc/mylxc > 3:devices:/lxc/mylxc/system.slice/ssh.service > 2:blkio:/lxc/mylxc > 1:name=systemd:/lxc/mylxc/system.slice/ssh.service > 0::/lxc/mylxc > > tim.jaacks@a048:~$ cat /proc/26600/cgroup > 11:pids:/user.slice/user-1001.slice/session-1528.scope > 10:net_cls,net_prio:/ > 9:perf_event:/ > 8:freezer:/user/root/0 > 7:cpuset:/ > 6:rdma:/ > 5:memory:/user/root/0 > 4:cpu,cpuacct:/user.slice > 3:devices:/user.slice > 2:blkio:/user.slice > 1:name=systemd:/user/root/0 > 0::/user.slice/user-1001.slice/session-1528.scope > > Does this help? I have no idea what all these fields mean.
Yes it does, thanks :) You want to look at the devices: lines in each. The ssh session placed you in the container's devices cgroup, /lxc/mylxc/system.slice/ssh.service . You could now cat /sys/fs/cgroup/devices/lxc/mylxc/system.slice/ssh.service/devices.list to see what devices you have access to that way. If you look at /proc/26600/cgroup , it is in /user.slice . Now, unless you actually did "lxc-attach -e -n mylxc", that should not be right. You should be placed in the container's cgroup, but you weren't. This may be a bug. Ah, I see that result when I start unprivileged containers. Perhaps it also happens when you start a root-owned container with subuid mappings? Does your container have subuid mappings? Anyway, i suspect the answer will be to give your container lxc.devices lines to your container config. -serge _______________________________________________ lxc-users mailing list lxc-users@lists.linuxcontainers.org http://lists.linuxcontainers.org/listinfo/lxc-users
