1 files changed, 61 insertions, 0 deletions
diff --git a/nixpkgs/nixos/tests/systemd-timesyncd-nscd-dnssec.nix b/nixpkgs/nixos/tests/systemd-timesyncd-nscd-dnssec.nix
new file mode 100644
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+++ b/nixpkgs/nixos/tests/systemd-timesyncd-nscd-dnssec.nix
@@ -0,0 +1,61 @@
+# This test verifies that systemd-timesyncd can resolve the NTP server hostname when DNSSEC validation
+# fails even though it is enforced in the systemd-resolved settings. It is required in order to solve
+# the chicken-and-egg problem when DNSSEC validation needs the correct time to work, but to set the
+# correct time, we need to connect to an NTP server, which usually requires resolving its hostname.
+#
+# This test does the following:
+# - Sets up a DNS server (tinydns) listening on the eth1 ip addess, serving .ntp and fake.ntp records.
+# - Configures that DNS server as a resolver and enables DNSSEC in systemd-resolved settings.
+# - Configures systemd-timesyncd to use fake.ntp hostname as an NTP server.
+# - Performs a regular DNS lookup, to ensure it fails due to broken DNSSEC.
+# - Waits until systemd-timesyncd resolves fake.ntp by checking its debug output.
+#   Here, we don't expect systemd-timesyncd to connect and synchronize time because there is no NTP
+#   server running. For this test to succeed, we only need to ensure that systemd-timesyncd
+#   resolves the IP address of the fake.ntp host.
+
+import ./make-test-python.nix ({ pkgs, ... }:
+
+let
+  ntpHostname = "fake.ntp";
+  ntpIP = "192.0.2.1";
+in
+{
+  name = "systemd-timesyncd";
+  nodes.machine = { pkgs, lib, config, ... }:
+    let
+      eth1IP = (lib.head config.networking.interfaces.eth1.ipv4.addresses).address;
+    in
+    {
+      # Setup a local DNS server for the NTP domain on the eth1 IP address
+      services.tinydns = {
+        enable = true;
+        ip = eth1IP;
+        data = ''
+          .ntp:${eth1IP}
+          +.${ntpHostname}:${ntpIP}
+        '';
+      };
+
+      # Enable systemd-resolved with DNSSEC and use the local DNS as a name server
+      services.resolved.enable = true;
+      services.resolved.dnssec = "true";
+      networking.nameservers = [ eth1IP ];
+
+      # Configure systemd-timesyncd to use our NTP hostname
+      services.timesyncd.enable = lib.mkForce true;
+      services.timesyncd.servers = [ ntpHostname ];
+      services.timesyncd.extraConfig = ''
+        FallbackNTP=${ntpHostname}
+      '';
+
+      # The debug output is necessary to determine whether systemd-timesyncd successfully resolves our NTP hostname or not
+      systemd.services.systemd-timesyncd.environment.SYSTEMD_LOG_LEVEL = "debug";
+    };
+
+  testScript = ''
+    machine.wait_for_unit("tinydns.service")
+    machine.wait_for_unit("systemd-timesyncd.service")
+    machine.fail("resolvectl query ${ntpHostname}")
+    machine.wait_until_succeeds("journalctl -u systemd-timesyncd.service --grep='Resolved address ${ntpIP}:123 for ${ntpHostname}'")
+  '';
+})