resolved: don't query domain-limited DNS servers for other domains (#3621)
DNS servers which have route-only domains should only be used for the specified domains. Routing queries about other domains there is a privacy violation, prone to fail (as that DNS server was not meant to be used for other domains), and puts unnecessary load onto that server. Introduce a new helper function dns_server_limited_domains() that checks if the DNS server should only be used for some selected domains, i. e. has some route-only domains without "~.". Use that when determining whether to query it in the scope, and when writing resolv.conf. Extend the test_route_only_dns() case to ensure that the DNS server limited to ~company does not appear in resolv.conf. Add test_route_only_dns_all_domains() to ensure that a server that also has ~. does appear in resolv.conf as global name server. These reproduce #3420. Add a new test_resolved_domain_restricted_dns() test case that verifies that domain-limited DNS servers are only being used for those domains. This reproduces #3421. Clarify what a "routing domain" is in the manpage. Fixes #3420 Fixes #3421
This commit is contained in:
Martin Pitt
Zbigniew Jędrzejewski-Szmek
parent
a86b76753d
commit
b9fe94cad9
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@ -475,8 +475,8 @@
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<para>The specified domains are also used for routing of DNS queries: look-ups for host names ending in the
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domains specified here are preferably routed to the DNS servers configured for this interface. If a domain
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name is prefixed with <literal>~</literal>, the domain name becomes a pure "routing" domain, is used for
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DNS query routing purposes only and is not used in the described domain search logic. By specifying a
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name is prefixed with <literal>~</literal>, the domain name becomes a pure "routing" domain, the DNS server
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is used for the given domain names only and is not used in the described domain search logic. By specifying a
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routing domain of <literal>~.</literal> (the tilde indicating definition of a routing domain, the dot
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referring to the DNS root domain which is the implied suffix of all valid DNS names) it is possible to
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route all DNS traffic preferably to the DNS server specified for this interface. The route domain logic is
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@ -407,6 +407,7 @@ int dns_scope_socket_tcp(DnsScope *s, int family, const union in_addr_union *add
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DnsScopeMatch dns_scope_good_domain(DnsScope *s, int ifindex, uint64_t flags, const char *domain) {
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DnsSearchDomain *d;
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DnsServer *dns_server;
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assert(s);
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assert(domain);
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@ -447,6 +448,13 @@ DnsScopeMatch dns_scope_good_domain(DnsScope *s, int ifindex, uint64_t flags, co
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if (dns_name_endswith(domain, d->name) > 0)
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return DNS_SCOPE_YES;
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/* If the DNS server has route-only domains, don't send other requests
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* to it. This would be a privacy violation, will most probably fail
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* anyway, and adds unnecessary load. */
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dns_server = dns_scope_get_dns_server(s);
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if (dns_server && dns_server_limited_domains(dns_server))
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return DNS_SCOPE_NO;
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switch (s->protocol) {
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case DNS_PROTOCOL_DNS:
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@ -576,6 +576,27 @@ void dns_server_warn_downgrade(DnsServer *server) {
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server->warned_downgrade = true;
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}
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bool dns_server_limited_domains(DnsServer *server)
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{
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DnsSearchDomain *domain;
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bool domain_restricted = false;
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/* Check if the server has route-only domains without ~., i. e. whether
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* it should only be used for particular domains */
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if (!server->link)
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return false;
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LIST_FOREACH(domains, domain, server->link->search_domains)
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if (domain->route_only) {
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domain_restricted = true;
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/* ~. means "any domain", thus it is a global server */
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if (streq(DNS_SEARCH_DOMAIN_NAME(domain), "."))
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return false;
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}
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return domain_restricted;
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}
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static void dns_server_hash_func(const void *p, struct siphash *state) {
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const DnsServer *s = p;
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@ -128,6 +128,8 @@ bool dns_server_dnssec_supported(DnsServer *server);
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void dns_server_warn_downgrade(DnsServer *server);
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bool dns_server_limited_domains(DnsServer *server);
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DnsServer *dns_server_find(DnsServer *first, int family, const union in_addr_union *in_addr, int ifindex);
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void dns_server_unlink_all(DnsServer *first);
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@ -154,6 +154,16 @@ static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
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return;
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}
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/* Check if the DNS server is limited to particular domains;
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* resolv.conf does not have a syntax to express that, so it must not
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* appear as a global name server to avoid routing unrelated domains to
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* it (which is a privacy violation, will most probably fail anyway,
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* and adds unnecessary load) */
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if (dns_server_limited_domains(s)) {
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log_debug("DNS server %s has route-only domains, not using as global name server", dns_server_string(s));
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return;
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}
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if (*count == MAXNS)
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fputs("# Too many DNS servers configured, the following entries may be ignored.\n", f);
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(*count)++;
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@ -250,6 +250,38 @@ Domains= ~company''')
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self.assertNotRegex(contents, 'search.*company')
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# our global server should appear
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self.assertIn('nameserver 192.168.5.1\n', contents)
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# should not have domain-restricted server as global server
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self.assertNotIn('nameserver 192.168.42.1\n', contents)
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def test_route_only_dns_all_domains(self):
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with open('/run/systemd/network/myvpn.netdev', 'w') as f:
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f.write('''[NetDev]
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Name=dummy0
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Kind=dummy
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MACAddress=12:34:56:78:9a:bc''')
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with open('/run/systemd/network/myvpn.network', 'w') as f:
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f.write('''[Match]
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Name=dummy0
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[Network]
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Address=192.168.42.100
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DNS=192.168.42.1
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Domains= ~company ~.''')
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self.addCleanup(os.remove, '/run/systemd/network/myvpn.netdev')
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self.addCleanup(os.remove, '/run/systemd/network/myvpn.network')
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self.do_test(coldplug=True, ipv6=False,
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extra_opts='IPv6AcceptRouterAdvertisements=False')
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with open(RESOLV_CONF) as f:
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contents = f.read()
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# ~company is not a search domain, only a routing domain
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self.assertNotRegex(contents, 'search.*company')
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# our global server should appear
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self.assertIn('nameserver 192.168.5.1\n', contents)
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# should have company server as global server due to ~.
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self.assertIn('nameserver 192.168.42.1\n', contents)
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@unittest.skipUnless(have_dnsmasq, 'dnsmasq not installed')
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@ -260,7 +292,7 @@ class DnsmasqClientTest(ClientTestBase, unittest.TestCase):
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super().setUp()
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self.dnsmasq = None
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def create_iface(self, ipv6=False):
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def create_iface(self, ipv6=False, dnsmasq_opts=None):
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'''Create test interface with DHCP server behind it'''
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# add veth pair
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@ -281,6 +313,8 @@ class DnsmasqClientTest(ClientTestBase, unittest.TestCase):
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extra_opts = ['--enable-ra', '--dhcp-range=2600::10,2600::20']
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else:
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extra_opts = []
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if dnsmasq_opts:
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extra_opts += dnsmasq_opts
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self.dnsmasq = subprocess.Popen(
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['dnsmasq', '--keep-in-foreground', '--log-queries',
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'--log-facility=' + self.dnsmasq_log, '--conf-file=/dev/null',
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@ -305,6 +339,80 @@ class DnsmasqClientTest(ClientTestBase, unittest.TestCase):
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with open(self.dnsmasq_log) as f:
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sys.stdout.write('\n\n---- dnsmasq log ----\n%s\n------\n\n' % f.read())
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def test_resolved_domain_restricted_dns(self):
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'''resolved: domain-restricted DNS servers'''
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# create interface for generic connections; this will map all DNS names
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# to 192.168.42.1
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self.create_iface(dnsmasq_opts=['--address=/#/192.168.42.1'])
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self.writeConfig('/run/systemd/network/general.network', '''\
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[Match]
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Name=%s
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[Network]
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DHCP=ipv4
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IPv6AcceptRA=False''' % self.iface)
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# create second device/dnsmasq for a .company/.lab VPN interface
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# static IPs for simplicity
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subprocess.check_call(['ip', 'link', 'add', 'name', 'testvpnclient', 'type',
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'veth', 'peer', 'name', 'testvpnrouter'])
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self.addCleanup(subprocess.call, ['ip', 'link', 'del', 'dev', 'testvpnrouter'])
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subprocess.check_call(['ip', 'a', 'flush', 'dev', 'testvpnrouter'])
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subprocess.check_call(['ip', 'a', 'add', '10.241.3.1/24', 'dev', 'testvpnrouter'])
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subprocess.check_call(['ip', 'link', 'set', 'testvpnrouter', 'up'])
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vpn_dnsmasq_log = os.path.join(self.workdir, 'dnsmasq-vpn.log')
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vpn_dnsmasq = subprocess.Popen(
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['dnsmasq', '--keep-in-foreground', '--log-queries',
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'--log-facility=' + vpn_dnsmasq_log, '--conf-file=/dev/null',
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'--dhcp-leasefile=/dev/null', '--bind-interfaces',
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'--interface=testvpnrouter', '--except-interface=lo',
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'--address=/math.lab/10.241.3.3', '--address=/cantina.company/10.241.4.4'])
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self.addCleanup(vpn_dnsmasq.wait)
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self.addCleanup(vpn_dnsmasq.kill)
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self.writeConfig('/run/systemd/network/vpn.network', '''\
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[Match]
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Name=testvpnclient
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[Network]
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IPv6AcceptRA=False
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Address=10.241.3.2/24
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DNS=10.241.3.1
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Domains= ~company ~lab''')
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subprocess.check_call(['systemctl', 'start', 'systemd-networkd'])
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subprocess.check_call([self.networkd_wait_online, '--interface', self.iface,
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'--interface=testvpnclient', '--timeout=20'])
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# ensure we start fresh with every test
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subprocess.check_call(['systemctl', 'restart', 'systemd-resolved'])
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# test vpnclient specific domains; these should *not* be answered by
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# the general DNS
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out = subprocess.check_output(['systemd-resolve', 'math.lab'])
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self.assertIn(b'math.lab: 10.241.3.3', out)
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out = subprocess.check_output(['systemd-resolve', 'kettle.cantina.company'])
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self.assertIn(b'kettle.cantina.company: 10.241.4.4', out)
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# test general domains
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out = subprocess.check_output(['systemd-resolve', 'megasearch.net'])
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self.assertIn(b'megasearch.net: 192.168.42.1', out)
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with open(self.dnsmasq_log) as f:
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general_log = f.read()
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with open(vpn_dnsmasq_log) as f:
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vpn_log = f.read()
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# VPN domains should only be sent to VPN DNS
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self.assertRegex(vpn_log, 'query.*math.lab')
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self.assertRegex(vpn_log, 'query.*cantina.company')
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self.assertNotIn('lab', general_log)
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self.assertNotIn('company', general_log)
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# general domains should not be sent to the VPN DNS
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self.assertRegex(general_log, 'query.*megasearch.net')
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self.assertNotIn('megasearch.net', vpn_log)
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class NetworkdClientTest(ClientTestBase, unittest.TestCase):
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'''Test networkd client against networkd server'''
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