[lxc-devel] Systemd creates btrfs subvolume under /var/lib/machines and makes lxc-destroy fail

[Serge Hallyn]

Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > On Sun, Feb 15, 2015 at 05:21:19PM +0100, Christian Brauner wrote:
> > > Hello,
> > > 
> > > I test the newest systemd from git on a regular basis by compiling it
> > > and installing it into a container and booting it. I did that with the
> > > several current systemd versions from git for the last couple of
> > > weeks.
> > > It seems that in the next version when booting a container with
> > > lxc-start, systemd creates a btrfs subvolume under
> > > 
> > >     rootfs/var/lib/machines
> > > 
> > > in every container. This will cause lxc-destroy for unprivileged
> > > containers to
> > > fail. (Because subvolumes can currently be created but not destroyed
> > > by
> > > unprivileged users.) There either needs to be a way to destroy btrfs
> > > subvolumes
> > > for unprivileged user with lxc-destroy or the creation of btrfs
> > > subvolumes
> > > during container boot needs to be prevented. Is the second option
> > > already
> > > available?
> > > 
> > > Best,
> > > Christian
> > 
> > Add user_subvol_rm_allowed to your fstab and unprivileged users will be
> > able to remove subvolumes.
> 
> I have user_subvol_rm_allowed set. But it will fail nonetheless.
> lxc-destroy seems to expect that the rootfs is a btrfs subvolume.
> However, if it sees that rootfs itself is simply a folder and not a
> subvolume it will try to recursively delete it and then fail when it
> encounters a subvolume within the rootfs.
> (Systemd seems to create a btrfs subvolume only when the rootfs is a
> simple folder.) I think there should be some way of making lxc-destroy
> destroy all btrfs subvolumes within rootfs no matter if it is itself a
> subvolume or a simple folder. Sorry, this wasn't clear in my first mail.

Ugh.  I guess patch for that would be welcome, though the safety of
that in case of a misconfigured privileged container worries me.  But
we can only protect that user from himself so much...