[Bug 1726124] Re: DNS domain search paths not updated when VPN started

Thu Nov 16 12:39:23 UTC 2017

Paul Smith, what you describe is information leakage and shouldn't IMHO
work as you say by default.

Consider that I'm connected to a corporate network and have an
(untrusted) VPN active which I only want to use to access resources on
its network (never-default: yes). Then by having the resolver adding the
domain of the VPN network to short name lookups could leak those local
names to the remote VPN (depending on the order the lookups are
performed in) and potentially allow the untrusted network to take over
internal services that are accessed using short names. This could happen
by mistake also (such as setting "mail" as your smtp server if the
remote network uses the same name).

I don't think the order of the lookups can be controlled to prevent
this, for example what should determine the order when you have to VPN
active?

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Title:
  DNS domain search paths not updated when VPN started

Status in network-manager package in Ubuntu:
  New
Status in network-manager-openvpn package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  New

Bug description:
  I connect to work with openvpn through network-manager-openvpn.  I'm
  selecting automatic (DHCP) to get an IP address, and "Use this
  connection only for resources on its network" to support split
  tunneling.

  In the last few versions of Ubuntu I used, this all worked fine.  In
  Ubuntu 17.10 (fresh install, not upgrade) I can access hosts on both
  my VPN network and the internet, BUT I have to use FQDN for my VPN
  network hosts: the updates to the DNS search path provided by my VPN
  DHCP server are never being applied.

  Investigating the system I see that /etc/resolv.conf is pointing to
  /run/systemd/resolve/stub-resolv.conf and that resolv.conf does not
  have any of the VPN's search path settings in it:

    # This file is managed by man:systemd-resolved(8). Do not edit.
    #
    # 127.0.0.53 is the systemd-resolved stub resolver.
    # run "systemd-resolve --status" to see details about the actual nameservers.
    nameserver 127.0.0.53

    search home

  In previous versions of Ubuntu, where NetworkManager controlled the
  resolver not systemd, /etc/resolv.conf pointed to
  /run/NetworkManager/resolv.conf and there was a local dnsmasq instance
  that managed all the complexity.  In Ubuntu 17.10 when I look in
  /run/NetworkManager/resolv.conf file, I see that the search paths ARE
  properly updated there:

    $ cat /run/NetworkManager/resolv.conf 
    # Generated by NetworkManager
    search internal.mycorp.com other.mycorp.com home
    nameserver 127.0.1.1

  However this file isn't being used, and also there's no dnsmasq
  running on the system so if I switch my /etc/resolv.conf to point to
  this file instead, then all lookups fail.

  Strangely, if I look at the systemd-resolv status I see that in theory
  systemd-resolve does seem to know about the proper search paths:

    $ systemd-resolve --status
       ...
    Link 3 (tun0)
          Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
           LLMNR setting: yes
    MulticastDNS setting: no
          DNSSEC setting: no
        DNSSEC supported: no
             DNS Servers: 10.3.0.10
                          10.8.42.2
              DNS Domain: ~internal.mycorp.com
                          ~other.mycorp.com

  but for whatever reason the search domains are not getting put into
  the resolv.conf file:

    $ host mydesk
    ;; connection timed out; no servers could be reached

    $ host mydesk.internal.mycorp.com
    mydesk.internal.mycorp.com has address 10.8.37.74

  (BTW, the timeout in the failed attempt above takes 10s: it is SUPER
  frustrating when all your host lookups are taking that long just to
  fail).

  ProblemType: Bug
  DistroRelease: Ubuntu 17.10
  Package: systemd 234-2ubuntu12
  ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
  Uname: Linux 4.13.0-16-generic x86_64
  ApportVersion: 2.20.7-0ubuntu3
  Architecture: amd64
  CurrentDesktop: GNOME
  Date: Sun Oct 22 15:08:57 2017
  InstallationDate: Installed on 2017-10-21 (1 days ago)
  InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Release amd64 (20171018)
  MachineType: System manufacturer System Product Name
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.13.0-16-generic root=UUID=4384306c-5fed-4b48-97a6-a6d594c4f72b ro quiet splash vt.handoff=7
  SourcePackage: systemd
  SystemdDelta:
   [EXTENDED]   /lib/systemd/system/rc-local.service → /lib/systemd/system/rc-local.service.d/debian.conf
   [EXTENDED]   /lib/systemd/system/user at .service → /lib/systemd/system/user at .service.d/timeout.conf

   2 overridden configuration files found.
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 12/02/2014
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: 2101
  dmi.board.asset.tag: To Be Filled By O.E.M.
  dmi.board.name: M5A78L-M/USB3
  dmi.board.vendor: ASUSTeK Computer INC.
  dmi.board.version: Rev X.0x
  dmi.chassis.asset.tag: Asset-1234567890
  dmi.chassis.type: 3
  dmi.chassis.vendor: Chassis Manufacture
  dmi.chassis.version: Chassis Version
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2101:bd12/02/2014:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnM5A78L-M/USB3:rvrRevX.0x:cvnChassisManufacture:ct3:cvrChassisVersion:
  dmi.product.family: To Be Filled By O.E.M.
  dmi.product.name: System Product Name
  dmi.product.version: System Version
  dmi.sys.vendor: System manufacturer

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