Re: [PATCH] KEYS: allow changing key ownership with CAP_SYS_ADMIN in a NS

["Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org>]

On Mon, Oct 02, 2017 at 10:30:43PM -0500, Eric W. Biederman wrote:
> Dimitri John Ledkov <xnox-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org> writes:
> 
> > Currently, changing key ownership from one namespaced uid/gid to
> > another namespaced uid/gid is only allowed by processes that have
> > CAP_SYS_ADMIN in the intial namespace. Fix the capability check to
> > also check the capability in the current capability.
> 
> Nacked-by: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
> 
> I won't deny the issue, but unless I am misreading something this
> will allow me to change the the uid of any key simply by unsharing
> a user namespace.  At which point there is no point in having a
> permission check at all.

Right so without having looked closely, at the very least you need to
verify that the ucrrent user is privileged over key->{uid,gid} and
over @user and @group.  Now the latter is I *think* being done
implicitly by the make_kuid(current_user_ns, user) at the top.  So
you need to further verify that key->uid and key->gid are mapped into
current_user_ns.

That *may* be sufficient.

-serge