Re: [PATCH -mm 1/2] user namespace : add unshare

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 08 Jun 2007 17:14:07 +0200
Cedric Le Goater <clg@fr.ibm.com> wrote:

> Basically, it will allow a process to unshare its user_struct table, resetting
> at the same time its own user_struct and all the associated accounting.
> 
> A new root user (uid == 0) is added to the user namespace upon creation.  Such
> root users have full privileges and it seems that theses privileges should be
> controlled through some means (process capabilities ?)

This second paragraph is distressingly indecisive.  How much thought has
gone into this??

For a start, it seems wrong for the kernel to hardwire knowledge about UID
0 in this fashion.

I'd have thought that a better model for user-namespace unsharing would be
to do a copy-by-value of the entire namespace, then permit a
suitably-privileged application to go through and kill off any unwanted
users from the now-unshared user namespace.

Or maybe just remove that "Insert new root user" altogether?  What would
then go wrong?