[PATCH RFC] overlayfs, xattr: allow unprivileged users to whiteout

[Serge Hallyn]

Quoting Andy Whitcroft (apw at canonical.com):
> On Fri, Feb 28, 2014 at 03:15:14PM +0100, Miklos Szeredi wrote:
> > On Tue, Feb 25, 2014 at 6:31 PM, Serge Hallyn <serge.hallyn at ubuntu.com> wrote:
> > > To mark a file which exists in the lower layer as deleted,
> > > it creates a symbolic link to a file called "(overlay-whiteout)"
> > > in the writeable mount, and sets a "trusted.overlay" xattr
> > > on that link.
> > >
> > > 1. When the create the symbolic link as container root, not
> > > as the global root
> > >
> > > 2. Allow root in a container to edit "trusted.overlay*"
> > > xattrs.  Generally only global root is allowed to edit
> > > "trusted.*"
> > 
> > Shouldn't overlayfs just skip the permission checks and call
> > __vfs_setxattr_noperm() instead?
> 
> It does seem we should be avoiding the permissions here, as we have let
> the thing be mounted we have done the permissions checks for that and for
> the file access itself already.  This operation is something we definatly
> want to represent in the filesystem.

D'oh.  Yeah, that looks good.   Andy, should I send a new patch, or
can you make those changes inline?

-serge