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Re: Remote Debian installation assistance for newbies using WireGuard VPN

On Wed, 2018-04-25 at 18:17 +0200, Philip Hands wrote:
> ST <smntov@gmail.com> writes:
> > On Wed, 2018-04-25 at 14:50 +0200, Philip Hands wrote:
> >> ST <smntov@gmail.com> writes:
> >> 
> >> > Hello Debian Install System Team,
> >> >
> >> > there used to be Linux install parties - a very cool event in itself and
> >> > a way to bring new users into community. However it is not so easy to
> >> > organize and it is somewhat limiting in time and space.
> >> >
> >> > Several weeks ago I learned about the kernel-space VPN - WireGuard [1]
> >> > and was so positively shocked by the ease of it's configuration/use [2]
> >> > so that I don't stop to think how it can be effectively utilized.
> >> >
> >> > Today I was thinking whether it would be possible to use this technology
> >> > to enable an experienced Linux user to help a fellow newbie to install
> >> > Debian on his Windows box?...
> >> >
> >> > The idea is to add an "Remote assistance mode" into win32-loader. Once
> >> > toggled - it will preseed and run Debian Installer (after reboot)
> >> > without any interaction until it:
> >> > 1. creates a WG interface,
> >> > 2. obtains an IP from a (not yet extent) Debian WireGuard VPN server [3]
> >> > (the assisting Linux profi also should be part of this VPN so he can SSH
> >> > to the newbie through NAT).
> >> > 3. runs SSH server listening on that IP.
> >> > 4. generates a short random password for the root user and displays it
> >> > together with its IP from step #2 on the monitor of the newbie. This
> >> > information (IP and root's password) are communicated by newbie to his
> >> > Linux profi friend by phone/sms/etc..
> >> >
> >> >>From this point on the Linux profi can SSH to the box and continue the
> >> > installation process in text mode.
> >> >
> >> > Is something like this possible?
> >> 
> >> I've not yet used WireGuard, but from what I can see one needs a unique
> >> key per client to be known to the server (perhaps there's a way of
> >> telling it not to care).  Also, the examples around the place also seem
> >> to suggest that one needs a UDP port per connection.
> >> 
> >> Also, the wireguard.com front page does currently say:
> >> 
> >>   WireGuard is not yet complete. _You should not rely on this code._
> >> 
> >> Anyway, I don't see that one actually needs WireGuard to implement it.
> >> 
> >> A similar result could be achieved by configuring the new system to ssh
> >> to a server somewhere, and either have that connection used for the
> >> remote control, or have ssh also do port-forwarding back to the new
> >> installation.
> >
> > Indeed?!... I'm positively shocked once again... Never knew it could be
> > possible. Let's say we have a newbie (with a private IP - N which is
> > behind NAT) and the same for a profie with IP P. And a publicly visible
> > server with the IP S. Let's say both can SSH to S:22 and know each
> > others' passwords/keys.
> >
> >  Could you, please, describe in details how one can implement both
> > approaches, namely:
> >
> > 1. "to ssh to a server somewhere, and either have that connection used",
> > i.e. `ssh newbie@S:22`... so what now? How profi can get through to N?
> Many years ago I used to plumb things like this together with expect,
> but there's bound to be a better way to do it these days -- tmate.io
> (mentioned elsewhere in the thread) seems like it might be part of such
> a solution.  I doesn't trike me as the optimal approach though.
> > 2. "or have ssh also do port-forwarding back to the new installation"
> > could you, please show the sequence of commands to achieve this?
> One would use something like this on the target system:
>   ssh -R 0:localhost:22 newbie@S
> which leaves you with the challenge of telling the "profi" the port
> that's been allocated, which is probably scriptable on the server
> somehow,

It sounds like a great approach. The port should be allocated randomly
from available ports instead of the VPN IP form step #2 above. This
random port together with the random root password will be displayed on
newbie's monitor. Both credentials he will pass by phone to the profi.

>  at which point they can do what boils down to:
>   ssh -J profie@S:22 -p $DYN_PORT root@localhost
> which should jump via the server, up the reverse port forward, and then
> onto the target.
> Making that so that nobody gets to do anything nasty on the server

This should be no problem: there will be two accounts (with known
private/public keys) - newbie and profi. On the newbie account you'll
block absolutely every possible command (with *) via `visudo`. For the
profi you'll block via `visudo` almost everything except for `ssh`
command with very strict possible arguments which enable only utilizing
the reverse tunnel established by newbies.

>  or to
> connect to the wrong newbie

There is nothing to implement here - if a profi tries to connect to some
other newbie - he will fail, since he doesn't know his local root

I think something like this could be made a part of Debian
infrastructure not just for Installation purpose, but also at any point
of time. One might implement some sort of "SOS! Need help!" button in
Gnome, or elsewhere which will allow profis to help newbies in the same

This design is also easily scalable/made failure proof by providing
several SSH servers for reverse tunnels within one DNS A entry. Newbie
will establish connections to _all_ known SSH servers, while profi will
pick up any random one.

While digging into this I found that `autossh` might be useful here for
keeping the tunnel alive for long periods of time.

So what do you think about this idea? Should I file a feature request
for this? If yes - where?

Thank you!

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