Re: nfs4_acl restricts copy_up in overlayfs

["bfields@fieldses.org" <bfields@fieldses.org>]

On Fri, Jun 01, 2018 at 07:02:20PM +0200, Miklos Szeredi wrote:
> On Fri, Jun 1, 2018 at 6:08 PM, bfields@fieldses.org
> <bfields@fieldses.org> wrote:
> > On Fri, Jun 01, 2018 at 04:43:51PM +0200, Miklos Szeredi wrote:
> >> Look at ovl_permission(), I think it pretty clearly describes this model.
> >
> > Thanks!  Uh, so generic_permission is the thing that just does the usual
> > mode/acl checks on the in-core inode, and inode_permission is the one
> > that also calls into the filesystem?
> 
> Right.
> 
> > But I'm still a little confused--if I'm reading right, "realinode" is
> > the lower inode before copyup, and the upper inode after, so can't
> > inode_permission(realinode, mask) return different results before and
> > after copyup?
> 
> Theoretically, yes.  Not in any sane setup, though.

If root squashing is enabled and you mount as root, then it will change.

That's not an unlikely case, it's pretty much the default.

--b.

> 
> The inode_permission() checks on realinode are for making sure the
> mounter cannot gain undue privileges (will be especially important
> with userns mounts).