Re: [PATCH v2] tty: Allow stealing of controlling ttys within user namespaces

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Jan 24, 2014 at 03:31:15PM -0800, Eric W. Biederman wrote:
> Seth Forshee <seth.forshee@canonical.com> writes:
> 
> > root is allowed to steal ttys from other sessions, but it
> > requires system-wide CAP_SYS_ADMIN and therefore is not possible
> > for root within a user namespace. This should be allowed so long
> > as the process doing the stealing is privileged towards the
> > session which currently owns the tty.
> >
> > Update this code to only require CAP_SYS_ADMIN in the user
> > namespaces of the target session's tasks, allowing the tty to be
> > stolen from sessions whose tasks are in the same or lesser
> > privileged user namespaces.
> 
> This code looks essentially correct.  I would like to look at it a bit
> more before we merge it, just to ensure something silly hasn't been
> missed, but the only thing that concerns me at this point is are we
> checking the proper per task bits.
> 
> The case I am currently worrying about is a task that does something
> privileged drops perms sets dumpable and then calls setns() on the
> userns.
> 
> So I think we may have to solve the dumpable problem at the same time as
> we solve this issue.
> 
> Now I don't know if it makes sense to take this through the tty tree or
> my userns tree.  I am inclined to take it through the userns tree simply
> because I am reviewing it and I have seen the several failed attempts at
> this but if Greg wants it in the tty tree I won't object.

No objection from me.

thanks,

greg k-h