On Mon, 2017-02-20 at 17:24 +1300, Eric W. Biederman wrote: > 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. The other way to do this is with an extended attribute. I've played around with that approach and quite like it: the advantage is that it's sticky across system reboots; The down side is that it requires additional VFS code to make sure you can't execute from the non-user_ns view. James
