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<title>Re: GSoC Port Forwarding</title>
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<table border=0 cellspacing=0 cellpadding=0 width="100%" class="header-part1"><tr><td><div class="headerdisplayname" style="display:inline;">Oggetto: </div>Re: GSoC Port Forwarding</td></tr><tr><td><div class="headerdisplayname" style="display:inline;">Mittente: </div>Giulio <giulio@gmx.com></td></tr><tr><td><div class="headerdisplayname" style="display:inline;">Data: </div>22/06/2021, 14:28</td></tr></table><table border=0 cellspacing=0 cellpadding=0 width="100%" class="header-part2"><tr><td><div class="headerdisplayname" style="display:inline;">A: </div>Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com></td></tr><tr><td><div class="headerdisplayname" style="display:inline;">CC: </div>Frédéric Pierret <frederic.pierret@qubes-os.org></td></tr></table><br>
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<div class="moz-text-flowed" style="font-family: -moz-fixed; font-size: 14px;" lang="x-unicode">Hello,
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<br>thank you for the detailed response.
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<br>
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<br>Il 22/06/2021 04:43, Marek Marczykowski-Górecki ha scritto:
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<br><blockquote type=cite style="color: #007cff;">Hi, I'm replying to both emails at once:
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<br>
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<br>On Sun, Jun 20, 2021 at 10:50:04PM +0200, Giulio wrote:
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<br><blockquote type=cite style="color: #007cff;">Questions:
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<br>
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<br>1) Should we both support internal port forwarding and external port
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<br>forwarding? Such as exposing a port for another domain or exposing a
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<br>port through the public network interface? I would say yes.
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<br></blockquote>
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<br>Yes, I think so. Technically, those two cases should be quite similar.
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<br>See also the case of sys-vpn much lower in the email.
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<br>
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<br></blockquote>
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<br>I think that I'm actually failing to picture all the possible internal
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scenarios.
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<br>
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<br>1) In the case of external port forwarding <sys-net> should forward to
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<sys-firewall> and <sys-firewall> then to the <appvm>.
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<br>In this case the port gets forwarded on the external interface ie: a LAN
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or a public ip address depending on the network environment.
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<br>2) In the case of internal port forwarding, the port is forwarded only
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from <sys-firewall> to <appvm>. In that case, another <appvm2> can visit
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the <appvm> service using <sys-firewall> ip address and the chosen port.
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<br>In this case, the ports get exposed on <sys-firewall> and thus depending
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on how the rules are implemented, may be available to all the AppVMs
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that share the same <sys-firewall>.
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<br>
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<br>In both cases may be important to allow to specify access rules for the
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forwarded port, such as the lan/public ip addresses ranges allowed for
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case 1 and the appvm name for case 2.
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<br>
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<br><blockquote type=cite style="color: #007cff;"><blockquote type=cite style="color: #007cff;">3) Since the expire= feature seems to be already implemented (and
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<br>limited for the expiring full outgoing access) would it be useful to be
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<br>implemented in gui and cli for every rule? I would say yes since the
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<br>admin and agent code seems to be already there. The same goes for the
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<br>"comment=" field.
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<br></blockquote>
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<br>Per-rule expire may be tricky to handle at the GUI level, I have no idea
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<br>how to make the UI for this not very confusing...
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<br>But the comment field is definitely useful to use.
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<br>
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<br></blockquote>
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<br>How do you see the same checkbox that actually allows full internet
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access with the 5 minutes expiration time, displayed also on the window
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for adding a rule?
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<br>However I think there is time to think more through this as the UI will
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be the last component.
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<br>
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<br><blockquote type=cite style="color: #007cff;"><blockquote type=cite style="color: #007cff;">4) How would you implement the management of forwarding rules in the
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<br>network providing domain (sys-net)? Shall the user add a rule both in
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<br>the target domain (ie the one with webserver and another one in sys-net)
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<br>or should it be fully automatic from the first?
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<br></blockquote>
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<br>From the user point of view, I think it should be automated as much as
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<br>possible. Like, let the user choose which port in which VM redirect to
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<br>where. There may be cases when such redirection won't be possible - if
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<br>there is no network path between the two points.
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<br>
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<br></blockquote>
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<br>I agree with you. We might just check when the user adds an internal
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forwarding rule if both the source and the destination shares the same
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<firewallvm>, don't we?
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<br>
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<br>
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<br><blockquote type=cite style="color: #007cff;"><blockquote type=cite style="color: #007cff;">5) Users should be able to set forward rules using domain names and not
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<br>static ip addresses. In this case, the actual ip addresses of the dst
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<br>domains should be collected in a similr way as currently DNS are
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<br>resolved in `/core-agent-linux/qubesagent/firewall.py`, would this be good?
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<br></blockquote>
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<br>But here we are mostly talking about IP addresses of different VMs,
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<br>right? Those can (and should) be resolved at core-admin side, so the VM
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<br>applying the rules will have all the IP given. In fact VM may not be
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<br>able to resolve IP of another VM at all.
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<br>
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<br></blockquote>
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<br>Thanks for the insight, it totally makes sense.
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<br>
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<br><blockquote type=cite style="color: #007cff;"><blockquote type=cite style="color: #007cff;">Proposed XML Syntax:
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<br><rule>
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<br> <properties>
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<br> <property name="action">forward</property>
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<br> <property name="proto">udp</property>
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<br> <property name="dstports">443-8080-5555</property>
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<br> </properties>
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<br><rule>
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<br></blockquote>
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<br>I don't see an important information here: forward to <span class="moz-txt-underscore"><span class="moz-txt-tag">_</span>where<span class="moz-txt-tag">_</span></span>.
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<br>
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<br><blockquote type=cite style="color: #007cff;">Proposed Admin API Syntax:
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<br>action=forward proto=udp dstports=443-8080-5555 [expire=<unix
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<br>timestamp>] [comment=random text]
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<br></blockquote>
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<br>Similar here, there needs to be a forward target (IP, and possibly a
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<br>port)
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<br>
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<br>On Tue, Jun 22, 2021 at 01:49:15AM +0200, Giulio wrote:
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<br><blockquote type=cite style="color: #007cff;">Since in the case of port forwarding the target ip address would always be the <vmname> IP address,
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<br></blockquote>
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<br>This is very true. But there needs to be an information where to forward
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<br>the traffic to (as noted earlier). Plus, possibly a second set of ports
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<br>(if you want to redirect to a different port).
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<br>
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<br></blockquote>
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<br>I am still failing to understand something here, could you give me a an
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example on when the dsthosts would different rather than the <appvm> or
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<firewallvm> ip?
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<br>
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<br>
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<br><blockquote type=cite style="color: #007cff;"><blockquote type=cite style="color: #007cff;">I think my main concern now is the question 4 from the aforementioned
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<br>email. Shall the rules be automatically implemented in all 3 involved
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<br>vms? (<netvm,firewallvm,appvm>). I think yes, because otherwise it would
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<br>be counterintuitive to be a partially manual and partially automatic
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<br>operation. But since it actually 'automatically' exposes more attack
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<br>surface, by loosening up all 3 vms network rules, I guess that maybe
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<br>more reasoning on it would be helpful.
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<br></blockquote>
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<br>Yes, but you need to pass the traffic somehow. The direct connection can
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<br>be achieved with qvm-connnect-tcp (connecting to the target directly
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<br>using qrexec, bypassing intermediate VMs), but it has its limits (low
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<br>performance, TCP only). To keep it as actual IP traffic, you need to
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<br>change firewall rules at all intermediate VMs too.
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<br>
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<br>Lets have a specific example: in default setup, redirect TCP port 80
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<br>from the outside, to 'work' VM port 8080.
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<br>
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<br>The setup looks like this:
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<br>
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sys-net -> sys-firewall -> work
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<br>
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<br>For this, you will need those rules:
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<br>
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<br>1. In sys-net: forward TCP port 80 to sys-firewall
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<br>2. In sys-firewall: forward TCP port 80 to work, port 8080
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<br>3. In work: allow TCP port 8080
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<br>
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<br>Now is the important design question: how to store those rules? If you
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<br>store them at all three places separately, it
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<br>will be easier to apply them at runtime, but it will be harder to
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<br>correlate them in UI. Plus, if any of them get modified/removed, it may
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<br>be non-trivial to troubleshoot the issue.
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<br>The other approach is to store the forward rules only in one place (the
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<br>target, 'work' in this example? or the source, 'sys-net' here?). This
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<br>way, it's harder to mess thing up. But when applying the rules (building
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<br>rule sets for qubes-firewall service in all the involved VMs), you need
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<br>to check several places.
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<br>Plus, the UI should clearly show such redirected ports at all involved
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<br>places, because it does affect system security - it must be easy to spot
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<br>if any redirects are enabled.
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<br>
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<br>
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<br>To make things more complex (sorry...), there may be a VPN or other
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<br>proxy service (Tor?) involved. For example:
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<br>
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<br>sys-net -> sys-firewall -> sys-vpn -> work
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<br>
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<br>In such a case, the "external" VM for 'work' is not really sys-net, but
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<br>rather sys-vpn. And actually you need to be careful to not accidentally
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<br>bypass VPN either by allowing 'work' to communicate outside of the VPN,
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<br>or (maybe even worse) systems on the LAN (via sys-net) reach inside VPN.
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<br>
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<br>This case is not easy to solve, because currently core-admin has no idea
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<br>whether sys-vpn (or other such VM) do any of such tunnelling. Maybe we
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<br>need to (finally) introduce some flag to mark such VMs?
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<br>
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<br>
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<br>And another question: what should happen if you change netvm of 'work'.
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<br>For example switch to something like:
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<br>
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<br> sys-net -> sys-firewall -> (other VMs, but not 'work')
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<br>
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<br> sys-wifi -> work
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<br>
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<br>Should the redirection stay active via sys-wifi? I think it should not,
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<br>at least not automatically (maybe have an option for that?).
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<br>
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<br></blockquote>
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<br>I understand all of your points and consequently it is hard to figure
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out a catch-all solution.
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<br>
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<br>I tried charting the flow of the possible solution.
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<br><a class="moz-txt-link-freetext" href="https://git.lsd.cat/Qubes/gsoc/src/master/assets/implementation.png">https://git.lsd.cat/Qubes/gsoc/src/master/assets/implementation.png</a>
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<br>
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<br>As a sum up:
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<br>1) Rules are stored only in <appvm>/firewall.xml
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<br>2) Rules can either be internal or exteranl (ie: they are applied only
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to <firewallvm> or both to <firewallvm> and its <netvm>)
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<br>3) Forwarding rules should be purged if <appvm> changes <firewall>
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(maybe also if <firewallvm> changes <netvm>? But that would be harde to
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detect I guess)
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<br>4) Users should be able to specify both the forwarded port and
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destination port as you were saying
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<br>5) Users should be able to eventually restrict forwarding to designated
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networks (with 0.0.0.0/0 being the wildcard instead of being a wildcard
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by default)
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<br>
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<br>However, in this case it will surely be harder to display the rules in
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all the affected vms.
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<br>The other approach, as you were suggesting, of adding each specific rule
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in each vm conf does make sense, but I think then it would necessary
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something to keep track of the rule dependencies (such as a unique
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identifier). Furthermore there is a higher risk of having orphaned rules
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or a inconsistent state.
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<br>
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<br>Furthermore, in the "internal" vpn case that I have in mind, the idea is
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to forward the local port via the VPN interface or Tor (but in the Tor
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case users should just stick to Whonix). Some providers, such as
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Mullvad, AirVPN, PIA etc allows port forwarding this way and I think
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that's the most relevant case since it allows exposing a service on the
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internet while maintaining a bit of privacy/anonimity and whithout
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needing to bypass the local network NAT. Is this the same case you are
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referring to?
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<br>
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<br><blockquote type=cite style="color: #007cff;">And finally, don't forget IPv6 exists. Which means you can have the same
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<br>port on IPv4 and IPv6. And theoretically they could be redirected to
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<br>different places (but I'm not sure if that's a good idea...).
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<br>
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<br></blockquote>
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<br>I think that once we have figured out the overall logic to implement, it
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should not be hard to duplicate it for ipv4/ipv6. I think the main
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problem to think about is to insert proper checks to prevent users from
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adding mixed rules.
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<br>
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<br>Cheers
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<br>Giulio
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<br></div></body>
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</html>
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</table></div> |