[SRU] cannot execute 'netplan generate' from within a snap

there is no direct access to the command, only the dbus service is allowed for security reasons, you can call:

  dbus-send --system \
    --type=method_call \
    --print-reply \
    --dest=io.netplan.Netplan \
    /io/netplan/Netplan io.netplan.Netplan.Apply

when the network-setup-control interface is connected ...

https://github.com/ogra1/config-snap/blob/master/snap/hooks/connect-plug-network-setup-control

is a working example ...

Thanks for your reply.
Unfortunately, I need to run 'netplan generate' not 'netplan apply', which is a subset of the Apply() call (i.e. only validating the YAML configs and generating the corresponding NetworkManager / networkd / OVS / ... configs), but not restarting the systemd-networkd and/or NetworkManager services.

I saw that the Netplan.Apply() command contains some SNAP special handling, forwarding the command through multiple layers of DBus / busctl commands, finally ending up to call 'netplan apply' on the host/base system (which doesn't seem optimal – but works).
The same is not true for 'netplan generate', as there is no Netplan.Generate() DBus method and no special handling for running 'netplan generate' inside snaps.

We should consider whitelisting the relevant netplan binary, as it is executed anyways after calling several layers of DBus commands in between, but without all the special handling needed. I've prepared a PR for that:

https://github.com/snapcore/snapd/pull/10212

well, there is a clear reluctance from the security team to allowing direct calling of the netplan binary as it needs a lot of additional paths opened in the interface for all the different backend bits the apply call needs to execute ... there have been many discussions around this topic over the years and the permitting of the d-bus call was the outcome ...

https://forum.snapcraft.io/t/network-related-interfaces-dont-permit-to-execute-netplan/1079

https://forum.snapcraft.io/t/netplan-apply-inside-snaps/12411

What is the use case for running netplan generate from a strict snap? Probably if you need this and as commented in the PR you need access to /run/systemd/system, the way forward is to add a Generate D-Bus call to netplan and make netplan generate do the same trick that apply does, so that netplan generate in snapd policy is just allowed as a d-bus call to Generate() which just executes the real `netplan generate` outside of confinement

The new io.netplan.Netplan.Generate() DBus API has been implemented in netplan upstream:
https://github.com/canonical/netplan/pull/208
https://github.com/canonical/netplan/pull/209

It needs to be released and SRUed down to Bionic for the snapd change to be accepted (https://github.com/snapcore/snapd/pull/10212)

Hello Lukas, or anyone else affected,

Accepted netplan.io into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/netplan.io/0.99-0ubuntu3~18.04.5 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

All autopkgtests for the newly accepted netplan.io (0.99-0ubuntu3~18.04.5) for bionic have finished running.
The following regressions have been reported in tests triggered by the package:

netplan.io/0.99-0ubuntu3~18.04.5 (ppc64el, i386)

Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-migration/bionic/update_excuses.html#netplan.io

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

Hello Brian, thanks for accepting this SRU into bionic-proposed.

I've tested netplan.io 0.99-0ubuntu3~18.04.5
root@bb:~# dpkg -l | grep netplan
ii libnetplan0:amd64 0.99-0ubuntu3~18.04.5 amd64
ii netplan.io 0.99-0ubuntu3~18.04.5 amd64

The autopkgtests at https://autopkgtest.ubuntu.com/packages/netplan.io ran successfully (after a retry for i386 and ppc64el) and the logs are attached to the bug description.
Additionally, I tested the new io.netplan.Netplan.Generate() DBus API to be working as well:

root@bb:~# cat /run/systemd/network/10-netplan-eth0.network
[Match]
Name=eth0

[Network]
DHCP=ipv4
LinkLocalAddressing=ipv6

[DHCP]
RouteMetric=100
UseMTU=true

root@bb:~# vim /etc/netplan/50-cloud-init.yaml # adding "dhcp6: true"
root@bb:~# busctl call io.netplan.Netplan /io/netplan/Netplan io.netplan.Netplan Generate
b true
root@bb:~# cat /run/systemd/network/10-netplan-eth0.network
[Match]
Name=eth0

[Network]
DHCP=yes
LinkLocalAddressing=ipv6

[DHCP]
RouteMetric=100
UseMTU=true

=> DHCP=ipv4 changed to DHCP=yes (i.e. IPv4 & IPv6)

This bug was fixed in the package netplan.io - 0.99-0ubuntu3~18.04.5

---------------
netplan.io (0.99-0ubuntu3~18.04.5) bionic; urgency=medium

  * d/p/0006-dbus-cli-implement-io.netplan.Netplan.Generate-208.patch:
    Implement the io.netplan.Netplan.Generate() DBus API, to allow calling
    'generate' from within a snap (LP: #1926442)
  * Update debian/gbp.conf

 -- Lukas Märdian <email address hidden> Tue, 07 Sep 2021 17:19:37 +0200

The verification of the Stable Release Update for netplan.io has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.