Good news, the network-manager SRU is not broken or wrong, but an additional SRU, on systemd, is needed to actually fix this bug.
I got a hint from Iain Lane (Laney, thank you very much) to the following fix in systemd upstream: https://github.com/systemd/systemd/commit/a97a3b256 and backported it to Bionic's systemd package (debdiff attached). With the network-manager SRU from -proposed attached plus the patched systemd package installed the problem goes away. If I repeat the test of [Test Case] (after a reboot) the DNS requests to any of the VPN's domains go actually only to the VPN's DNS. ** Patch added: "systemd_237-3ubuntu10.21_237-3ubuntu10.22.debdiff" https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1754671/+attachment/5262723/+files/systemd_237-3ubuntu10.21_237-3ubuntu10.22.debdiff ** Also affects: systemd (Ubuntu) Importance: Undecided Status: New ** Changed in: systemd (Ubuntu) Status: New => Fix Released ** Changed in: systemd (Ubuntu Bionic) Status: New => Triaged ** Changed in: systemd (Ubuntu) Importance: Undecided => High ** Changed in: systemd (Ubuntu Bionic) Importance: Undecided => High -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to network-manager in Ubuntu. https://bugs.launchpad.net/bugs/1754671 Title: Full-tunnel VPN DNS leakage regression Status in NetworkManager: Fix Released Status in network-manager package in Ubuntu: Fix Released Status in systemd package in Ubuntu: Fix Released Status in network-manager source package in Bionic: Fix Committed Status in systemd source package in Bionic: Triaged Bug description: [Impact] When using a VPN the DNS requests might still be sent to a DNS server outside the VPN when they should not [Test case] 1) Set up a VPN with split tunneling: a) Configure VPN normally (set up remote host, any ports and options needed for the VPN to work) b) Under the IPv4 tab: enable "Use this connection only for the resources on its network". c) Under the IPv6 tab: enable "Use this connection only for the resources on its network". 2) Connect to the VPN. 3) Run 'systemd-resolve --status'; note the DNS servers configured: a) For the VPN; under a separate link (probably tun0), note down the IP of the DNS server(s). Also note the name of the interface (link). b) For the "main" connection; under the link for your ethernet or wireless devices (wl*, en*, whatever it may be), note down the IP of the DNS server(s). Also note the name of the interface (link). 4) In a separate terminal, run 'sudo tcpdump -ni <the main interface> port 53'; let it run. 5) In a separate terminal, run 'sudo tcpdump -ni <the VPN interface> port 53'; let it run. 6) In yet another terminal, issue name resolution requests using dig: a) For a name known to be reachable via the public network: 'dig www.yahoo.com' b) For a name known to be reachable only via the VPN: 'dig <some DNS behind the VPN>' 7) Check the output of each terminal running tcpdump. When requesting the public name, traffic can go through either. When requesting the "private" name (behind the VPN), traffic should only be going through the interface for the VPN. Additionally, ensure the IP receiving the requests for the VPN name is indeed the IP address noted above for the VPN's DNS server. If you see no traffic showing in tcpdump output when requesting a name, it may be because it is cached by systemd-resolved. Use a different name you have not tried before. [Regression potential] The code change the handling of DNS servers when using a VPN, we should check that name resolution still work whne using a VPN in different configurations ----------------- In 16.04 the NetworkManager package used to carry this patch: http://bazaar.launchpad.net/~network-manager/network-manager/ubuntu/view/head:/debian/patches/Filter-DNS-servers-to-add-to-dnsmasq-based-on-availa.patch It fixed the DNS setup so that when I'm on the VPN, I am not sending unencrypted DNS queries to the (potentially hostile) local nameservers. This patch disappeared in an update. I think it was present in 1.2.2-0ubuntu0.16.04.4 but was dropped some time later. This security bug exists upstream too: https://bugzilla.gnome.org/show_bug.cgi?id=746422 It's not a *regression* there though, as they didn't fix it yet (unfortunately!) To manage notifications about this bug go to: https://bugs.launchpad.net/network-manager/+bug/1754671/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
