On Sat, Jul 06, 2013 at 09:59:39PM +0200, Thomas Karcher wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Hi lxc folks, > > the symptom my libvirt LXC container suffers from is: > > root@depot:/dev/net# ls -la > total 0 > drwxr-xr-x 2 root root 40 Jun 29 16:26 . > drwxr-xr-x 5 root root 480 Jun 29 16:26 .. > > root@depot:/dev/net# mknod tun c 10 200 > mknod: `tun': Operation not permitted > > The host is an up-to-date AMD64 Ubuntu raring on 3.8.0-25-generic that > was formerly installed from precise and then upgraded. The guest is > Ubuntu precise; however, I see the same symptom in another raring > container on the same host. > > What I tried to resolve this: > > 1) On the host, I echoed various stuff to the cgroup device files: > > cd /sys/fs/cgroup/devices/libvirt/lxc > echo "c 10:200 rwm" > devices.allow > echo "c 10:200 rwm" > depot/devices.allow > echo a > depot/devices.allow > > ... and I see the successful results in depot/devices.list, but no > success. > > 2) I inserted a line "/dev/net/tun rwk," into > /etc/apparmor.d/abstractions/lxc/container-base - no change. (I know, > it seems kind of pointless - because it's about permissions to a > device, not a path. You may deduce my desperation from this ... > > SELinux is not active. Mounts on /dev look normal to me: > > devfs on /dev type tmpfs (rw,mode=0755) > devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620) > devpts on /dev/ptmx type devpts > (rw,nosuid,relatime,gid=5,mode=620,ptmxmode=666) > cgroup on /sys/fs/cgroup/devices type cgroup (rw,relatime,devices) > > Now comes the weird part: Once I umount /dev inside the container, the > "hidden" /dev appears which contains a usable /dev/net/tun. So the > mknod problem is probably due to the dropped capabilities - but > why/how mounts the container a more restricted /dev on top of the > prepared one ...? Allowing the container direct access to the hosts' /dev would be a security flaw, so libvirt sets up a private /dev for the container. Allowing the container to use mknod would also be insecure, so we blocking mknod using both cgroups device ACL, and also droping the CAP_MKNOD capability. http://libvirt.org/drvlxc.html#devnodes Any device that the container is authorized to access per the XML configuration, will be pre-created in the container's /dev. To explicitly allow /dev/net/tun you need to tell libvirt about it. http://libvirt.org/formatdomain.html#elementsHostDevCaps Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
