Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

From: Eric W. Biederman
Date: Sun Feb 19 2017 - 23:38:47 EST

James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> writes:

> On Fri, 2017-02-17 at 14:57 +1300, Eric W. Biederman wrote:
>> I think I am missing something but I completely do not understand
>> that subthread that says use file marks and perform the work in the
>> vfs. The problem is that fundamentally we need multiple mappings and
>> I don't see a mark on a file (even an inherited mark) providing the
>> mapping so I don't see the point.
> The point of the mark is that it's a statement by the system
> administrator that the underlying subtree is safe to be mounted by an
> unprivileged container in the containers user view (i.e. with
> current_user_ns() == s_user_ns). For the unprivileged container
> there's no real arbitrary s_user_ns use case because the unprivileged
> container must prove it can set up the mapping, so it would likely
> always be mounting from within a user_ns with the mapping it wanted.

As a statement that it is ok for the unprivileged mapping code to
operate that seems reasonable. I don't currently the need for such an
ok from the system adminstrator, but if you need it a flag that
propagates to children and child directories seems reasonable.