[Bug 1988010] Re: systemd ignoring DHCP DNS servers and DNS servers set in Network Manager GUI

[Seth Arnold]

Hello Josh, which GUI are you using to change dns or dhcp settings?
Thanks

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Title:
  systemd ignoring DHCP DNS servers and DNS servers set in Network
  Manager GUI

Status in systemd package in Ubuntu:
  New

Bug description:
  Hi there!

  I'm running ubuntu 22.04.1 LTS installed via the ISO image
  ubuntu-22.04.1-desktop-amd64.iso.

  This issue affects both the Live CD and installed operating system.

  I have configured my modem's DHCP server to push my adguard home DNS
  server (cloud-hosted) as the DNS for the network. I have an access
  point that is setup to do the same.

  With the Live CD and installed operating system, there is a local DNS
  server installed that runs on 127.0.0.1:53. Somehow this bypasses the
  DNS servers I've configured for the network and suddenly websites that
  have been blocked for being malicious or harmful are now accessible.

  There is no option in the installer or GUI to disable this.

  Changing the network DNS settings via the GUI of either the live cd or
  installation do not change the behavior and do not result in the
  specified DNS server(s) being used. The 127.0.0.1:53 server still
  overrides anything set in the GUI.

  The only way I have found to override this behavior is to edit
  /etc/systemd/resolved.conf:

  1) uncomment DNSStubListener=yes
  2) change yes to no
  3) save file
  4) run the following commands in terminal:
  sudo systemctl daemon-reload
  sudo systemctl restart systemd-networkd
  sudo systemctl restart systemd-resolved

  After doing so, the DNS servers that have been provided by DHCP are
  properly used.

  This is considered a security vulnerability due to there being no way
  for a normal user to change this setting without editing system
  configuration files and no warning given to the user that the settings
  they are applying in the GUI have not been applied due to this default
  configuration.

  This is considered a hack if this is the intentional configuration as
  it overrides network configuration options set by the DHCP server.

  I've resolved it for myself for now by making a custom iso image that
  removes this configuration by default and instead installs the
  /etc/systemd/resolved.conf file attached to this bug report.

  ProblemType: Bug
  DistroRelease: Ubuntu 22.04
  Package: systemd 249.11-0ubuntu3.4
  ProcVersionSignature: Ubuntu 5.15.0-46.49-generic 5.15.39
  Uname: Linux 5.15.0-46-generic x86_64
  NonfreeKernelModules: nvidia_modeset nvidia
  ApportVersion: 2.20.11-0ubuntu82.1
  Architecture: amd64
  CasperMD5CheckResult: pass
  CurrentDesktop: ubuntu:GNOME
  Date: Sun Aug 28 21:18:35 2022
  InstallationDate: Installed on 2022-08-29 (0 days ago)
  InstallationMedia: Ubuntu 22.04.1 2022.08.28 LTS "Custom Jammy Jellyfish" (20220828)
  MachineType: Micro-Star International Co., Ltd. GS75 Stealth 9SG
  ProcEnviron:
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.15.0-46-generic root=/dev/mapper/vgubuntu-root ro quiet splash vt.handoff=7
  SourcePackage: systemd
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 03/26/2019
  dmi.bios.release: 1.12
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: E17G1IMS.10C
  dmi.board.asset.tag: Default string
  dmi.board.name: MS-17G1
  dmi.board.vendor: Micro-Star International Co., Ltd.
  dmi.board.version: REV:1.0
  dmi.chassis.asset.tag: No Asset Tag
  dmi.chassis.type: 10
  dmi.chassis.vendor: Micro-Star International Co., Ltd.
  dmi.chassis.version: N/A
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrE17G1IMS.10C:bd03/26/2019:br1.12:svnMicro-StarInternationalCo.,Ltd.:pnGS75Stealth9SG:pvrREV1.0:rvnMicro-StarInternationalCo.,Ltd.:rnMS-17G1:rvrREV1.0:cvnMicro-StarInternationalCo.,Ltd.:ct10:cvrN/A:sku17G1.1:
  dmi.product.family: GS
  dmi.product.name: GS75 Stealth 9SG
  dmi.product.sku: 17G1.1
  dmi.product.version: REV:1.0
  dmi.sys.vendor: Micro-Star International Co., Ltd.
  mtime.conffile..etc.systemd.resolved.conf: 2022-08-28T19:29:41

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