Merge pull request #239201 from nesteroff/fix-timesync

systemd: disable NSCD when DNSSEC validation is disabled in timesyncd

+7
nixos/modules/system/boot/timesyncd.nix
···
wantedBy = [ "sysinit.target" ];
aliases = [ "dbus-org.freedesktop.timesync1.service" ];
restartTriggers = [ config.environment.etc."systemd/timesyncd.conf".source ];
+
# systemd-timesyncd disables DNSSEC validation in the nss-resolve module by setting SYSTEMD_NSS_RESOLVE_VALIDATE to 0 in the unit file.
+
# This 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.
+
# In order for nss-resolve to be able to read this environment variable we patch systemd-timesyncd to disable NSCD and use NSS modules directly.
+
# This means that systemd-timesyncd needs to have NSS modules path in LD_LIBRARY_PATH. When systemd-resolved is disabled we still need to set
+
# NSS module path so that systemd-timesyncd keeps using other NSS modules that are configured in the system.
+
environment.LD_LIBRARY_PATH = config.system.nssModules.path;
preStart = (
# Ensure that we have some stored time to prevent
+1
nixos/tests/all-tests.nix
···
systemd-shutdown = handleTest ./systemd-shutdown.nix {};
systemd-sysupdate = runTest ./systemd-sysupdate.nix;
systemd-timesyncd = handleTest ./systemd-timesyncd.nix {};
+
systemd-timesyncd-nscd-dnssec = handleTest ./systemd-timesyncd-nscd-dnssec.nix {};
systemd-user-tmpfiles-rules = handleTest ./systemd-user-tmpfiles-rules.nix {};
systemd-misc = handleTest ./systemd-misc.nix {};
systemd-userdbd = handleTest ./systemd-userdbd.nix {};
+61
nixos/tests/systemd-timesyncd-nscd-dnssec.nix
···
+
# 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}'")
+
'';
+
})
+46
pkgs/os-specific/linux/systemd/0020-timesyncd-disable-NSCD-when-DNSSEC-validation-is-dis.patch
···
+
From 7a27556920fe1feefd17096841c8f3ca1294a1b3 Mon Sep 17 00:00:00 2001
+
From: Yuri Nesterov <yuriy.nesterov@unikie.com>
+
Date: Wed, 21 Jun 2023 17:17:38 +0300
+
Subject: [PATCH] timesyncd: disable NSCD when DNSSEC validation is disabled
+
+
Systemd-timesyncd sets SYSTEMD_NSS_RESOLVE_VALIDATE=0 in the unit file
+
to disable DNSSEC validation but it doesn't work when NSCD is used in
+
the system. This patch disabes NSCD in systemd-timesyncd when
+
SYSTEMD_NSS_RESOLVE_VALIDATE is set to 0 so that it uses NSS libraries
+
directly.
+
---
+
src/timesync/timesyncd.c | 11 +++++++++++
+
1 file changed, 11 insertions(+)
+
+
diff --git a/src/timesync/timesyncd.c b/src/timesync/timesyncd.c
+
index 1d8ebecc91..2b0ae361ff 100644
+
--- a/src/timesync/timesyncd.c
+
+++ b/src/timesync/timesyncd.c
+
@@ -21,6 +21,11 @@
+
#include "timesyncd-conf.h"
+
#include "timesyncd-manager.h"
+
#include "user-util.h"
+
+#include "env-util.h"
+
+
+
+struct traced_file;
+
+extern void __nss_disable_nscd(void (*)(size_t, struct traced_file *));
+
+static void register_traced_file(size_t dbidx, struct traced_file *finfo) {}
+
+
static int advance_tstamp(int fd, const struct stat *st) {
+
assert_se(fd >= 0);
+
@@ -198,6 +203,12 @@ static int run(int argc, char *argv[]) {
+
if (r < 0)
+
return log_error_errno(r, "Failed to parse fallback server strings: %m");
+
+
+ r = getenv_bool_secure("SYSTEMD_NSS_RESOLVE_VALIDATE");
+
+ if (r == 0) {
+
+ log_info("Disabling NSCD because DNSSEC validation is turned off");
+
+ __nss_disable_nscd(register_traced_file);
+
+ }
+
+
+
log_debug("systemd-timesyncd running as pid " PID_FMT, getpid_cached());
+
+
notify_message = notify_start("READY=1\n"
+
--
+
2.34.1
+
+1
pkgs/os-specific/linux/systemd/default.nix
···
./0017-core-don-t-taint-on-unmerged-usr.patch
./0018-tpm2_context_init-fix-driver-name-checking.patch
./0019-systemctl-edit-suggest-systemdctl-edit-runtime-on-sy.patch
+
./0020-timesyncd-disable-NSCD-when-DNSSEC-validation-is-dis.patch
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