netdev - Re: VRF Issue Since kernel 5

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Message-ID: <20200419203516.jrpm5jzokmswkpue@topsnens>
Date:   Sun, 19 Apr 2020 22:35:16 +0200
From:   Maximilian Bosch <maximilian@...sch.me>
To:     Mike Manning <mmanning@...tta.att-mail.com>, netdev@...r.kernel.org
Subject: Re: VRF Issue Since kernel 5

Hi!

> Can you please clarify what the issue is with using 'ip vrf exec <vrf>
> ssh' for running the ssh client in the vrf?

well, SSH was just an example to demonstrate the issue. As mentioned in
my previous emails, the `ip vrf exec`-wrapper is only needed for
processes that do TCP, UDP-traffic is still leaked through the VRF.

Thanks

  Maximilian

On Wed, Apr 08, 2020 at 11:07:31AM +0100, Mike Manning wrote:
> Hi Maximilian,
> Can you please clarify what the issue is with using 'ip vrf exec <vrf>
> ssh' for running the ssh client in the vrf? This is the recommended
> method for running an application in a VRF. As part of our VRF
> development on this a couple of years ago, we provided a changeset for
> openssh so that the vrf could be specified as an option, cf
> https://bugzilla.mindrot.org/show_bug.cgi?id=2784. That was not applied
> due to the ease of using 'ip vrf exec'.
> 
> Alternatively, to run the ssh client in the default VRF, you can bind it
> to an address on an interface (or specify the interface) in the default
> VRF using ssh -b (or -B) option, or similarly add an entry in
> /etc/ssh/ssh_config for BindAddress (or BindInterface).
> 
> Then for egress, leak a route in the default table to get to the gateway
> via the VRF (as you must already be doing), and for ingress, leak a
> route in the VRF's table for the return path to the ssh client. For
> this, get the table id for the vrf from 'ip vrf', add the route for the
> client prefix with the additional 'table <tbl-id>' option, and confirm
> the route with 'ip route show vrf <vrf-name>'.
> 
> I have started looking at the issue you have reported, but as you may
> appreciate, it is not trivial. This client-side use-case is not typical,
> as VRF config is generally applied to routers or switches, not hosts.
> 
> Thanks
> Mike
> 
> 
> On 05/04/2020 17:52, David Ahern wrote:
> > On 4/2/20 5:02 PM, Maximilian Bosch wrote:
> >> Hi!
> >>
> >>> I do not see how this worked on 4.19. My comment above is a fundamental
> >>> property of VRF and has been needed since day 1. That's why 'ip vrf
> >>> exec' exists.
> >> I'm afraid I have to disagree here: first of all, I created a
> >> regression-test in NixOS for this purpose a while ago[1]. The third test-case
> >> (lines 197-208) does basically what I demonstrated in my previous emails
> >> (opening SSH connetions through a local VRF). This worked fine until we
> >> bumped our default kernel to 5.4.x which is the reason why this testcase
> >> is temporarily commented out.
> > I do not have access to a NixOS install, nor the time to create one.
> > Please provide a set of ip commands to re-create the test that work with
> > Ubuntu, debian or fedora.
> >
> >
> >> After skimming through the VRF-related changes in 4.20 and 5.0 (which
> >> might've had some relevant changes as you suggested previously), I
> >> rebuilt the kernels 5.4.29 and 5.5.13 with
> >> 3c82a21f4320c8d54cf6456b27c8d49e5ffb722e[2] reverted on top and the
> >> commented-out testcase works fine again. In other words, my usecase
> >> seems to have worked before and the mentioned commit appears to cause
> >> the "regression".
> > The vyatta folks who made the changes will take a look.
> 
> 

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