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    SubjectRe: [patch 0/8] unprivileged mount syscall
    Quoting Miklos Szeredi (miklos@szeredi.hu):
    > > > Thinking a bit more about this, I'm quite sure most users wouldn't
    > > > even want private namespaces. It would be enough to
    > > >
    > > > chroot /share/$USER
    > > >
    > > > and be done with it.
    > > >
    > > > Private namespaces are only good for keeping a bunch of mounts
    > > > referenced by a group of processes. But my guess is, that the natural
    > > > behavior for users is to see a persistent set of mounts.
    > > >
    > > > If for example they mount something on a remote machine, then log out
    > > > from the ssh session and later log back in, they would want to see
    > > > their previous mount still there.
    > > >
    > > > Miklos
    > >
    > > Agreed on desired behavior, but not on chroot sufficing. It actually
    > > sounds like you want exactly what was outlined in the OLS paper.
    > >
    > > Users still need to be in a different mounts namespace from the admin
    > > user so long as we consider the deluser and backup problems
    >
    > I don't think it matters, because /share/$USER duplicates a part or
    > the whole of the user's namespace.
    >
    > So backup would have to be taught about /share anyway, and deluser
    > operates on /home/$USER and not on /share/*, so there shouldn't be any
    > problem.

    In what I was thinking of, /share/$USER is bind mounted to
    ~$USER/share, so it would have to be done in a private namespace in
    order for deluser to not be tricked.

    > There's actually very little difference between rbind+chroot, and
    > CLONE_NEWNS. In a private namespace:
    >
    > 1) when no more processes reference the namespace, the tree will be
    > disbanded
    >
    > 2) the mount tree won't be accessible from outside the namespace

    But it *can* be, if properly set up. That's part of the point of the
    example in the OLS paper. When a user logs in, sshd clones a new
    namespace, then bind-mounts /share/$USER into ~$USER/share. So assuming
    that /share/$USER was --make-shared'd, it and ~$USER are now in the
    same peer group, and any changes made by the user under ~$USER will
    be reflected back into /share/$USER.

    > Wanting a persistent namespace contradicts 1).

    Not necessarily, see above.

    > Wanting a per-user (as opposed to per-session) namespace contradicts
    > 2). The namespace _has_ to be accessible from outside, so that a new
    > session can access/copy it.

    Again, I *think* you are wrong that private namespace contradicts this
    requirement.

    > So both requirements point to the rbind/chroot solution.

    It all points to a combination of the two :-)

    -serge
    -
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