[Bug 2028023] Re: [jammy] DNS issue triggered by command "udevadm trigger --subsystem-nomatch=input"

[Aristo Chen]

Found that the issue can be fixed by this commit in upstream

"""
commit 26591ffffd62c62796b1f65146648022d68e1279
Author: Yu Watanabe <watanabe.yu+github at gmail.com>
Date:   Sun Nov 14 15:46:47 2021 +0900

    resolve: do not clear DNS servers or friends on link which is not managed by networkd
    
    When networkd detects an unmanaged link, then the state is changed in
    the following order:
    pending -> initialized -> unmanaged
    
    The "initialized" state was added by bd08ce56156751d58584a44e766ef61340cdae2d.

diff --git a/src/resolve/resolved-link.c b/src/resolve/resolved-link.c
index 18dc3d29e9..dd219f297c 100644
--- a/src/resolve/resolved-link.c
+++ b/src/resolve/resolved-link.c
@@ -565,7 +565,7 @@ static int link_is_managed(Link *l) {
         if (r < 0)
                 return r;
 
-        return !STR_IN_SET(state, "pending", "unmanaged");
+        return !STR_IN_SET(state, "pending", "initialized", "unmanaged");
 }
 
 static void link_read_settings(Link *l) {

"""

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https://bugs.launchpad.net/bugs/2028023

Title:
  [jammy] DNS issue triggered by command "udevadm trigger --subsystem-
  nomatch=input"

Status in OEM Priority Project:
  New
Status in systemd package in Ubuntu:
  New

Bug description:
  [Summary]
  In jammy server image, when we use NetworkManager as netplan renderer, we may have DNS issue after executing command "udevadm trigger --subsystem-nomatch=input" as super user, the udevadm command may also be executed when we use "apt install XXXXXX" or "snap install XXXXXX".

  [Steps to reproduce]
  1. Login to a jammy server(jammy desktop environment works fine) image environment with Vagrant
  2. execute command "apt install network-manager"
  3. modify netplan config to use NetworkManager as renderer
  """
  # Let NetworkManager manage all devices on this system
  network:
    version: 2
    renderer: NetworkManager
  """
  4. reboot
  5. execute command "ping google.com" first to make sure DNS works fine
  6. execute command "udevadm trigger --subsystem-nomatch=input" as super user
  7. execute command "ping google.com" to check if DNS still works fine
  8. if DNS works fine, then repeat step 6-7, the fail rate is around 20-30%

  [Other info]
  I have tested the above mentioned steps for the following scenarios, which work fine without DNS issue
  1. Using focal server environment with Vagrant, there is no DNS issue
  2. Using jammy server environment with Vagrant which has DNS issue, then add the kinetic/kinetic-updates source list, install systemd(version: 251.4-1ubuntu7.3) from kinetic, and there is no DNS issue

  If using focal server environment with Vagrant, then add the
  jammy/jammy-updates source list, install systemd(version:
  249.11-0ubuntu3.9) from jammy, then I will have DNS issue as well by
  following the steps mentioned in [Steps to reproduce]

  [Other info - Vagrantfile]
  The following content is for the Vagrantfile that I used to test
  """
  Vagrant.configure("2") do |config|
    if Vagrant.has_plugin?("vagrant-timezone")
      config.timezone.value = :host
    end
    config.vm.define "test" do |test|
      test.vm.box = "ubuntu/jammy64"
      test.vm.provider "virtualbox" do |vb|
        vb.name = "test2"
        vb.memory = "4096"
        vb.cpus = 4
        config.disksize.size = "50GB"
      end
    end
  end
  """

  [Fail rate]
  20-30%

  [Test script]
  The following is the script that I used to test. Ideally it should run forever
  """
  #!/bin/bash

  set -ex

  counter=1

  while true; do
   echo "$(date): test round ${counter}"
   counter=$((counter + 1))
   sudo udevadm trigger --subsystem-nomatch=input
   ping google.com -c 2
   sleep 0.5
  done
  """

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