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chore: listen for dns requests on 127.0.0.53
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Turns out there is actually no black magic in systemd, they simply listen on 127.0.0.53 and forward dns requests there in resolv.conf.
Reason is the same as ours — to preserve compatibility with other applications. So we do the same in our code.

This PR also does two things:
- Adds `::1` into resolv.conf for IPv6 only resolvers.
- Drops `SO_REUSEPORT` from control options (it works without them).

Closes #8328

Signed-off-by: Dmitriy Matrenichev <dmitry.matrenichev@siderolabs.com>
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@DmitriyMV
DmitriyMV committed Feb 26, 2024
1 parent 8872a7a commit f8c556a
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Showing 7 changed files with 18 additions and 18 deletions.
4 changes: 4 additions & 0 deletions internal/app/machined/pkg/controllers/network/dns_resolve_cache.go
View file
Expand Up @@ -160,6 +160,8 @@ func (ctrl *DNSResolveCacheController) runServer(originCtx context.Context, r co
MaxTCPQueries: -1,
}
}

l.Info("dns listener created")
}

for netwk, opt := range serverOpts {
Expand Down Expand Up @@ -227,6 +229,8 @@ func closeListener(lis io.Closer, l *zap.Logger) {
if err := lis.Close(); err != nil && !errors.Is(err, net.ErrClosed) {
l.Error("error closing listener", zap.Error(err))
}

l.Info("dns listener closed")
}

func dropResolveResources(ctx context.Context, r controller.Runtime, nets ...resource.ID) error {
Expand Down
4 changes: 2 additions & 2 deletions internal/app/machined/pkg/controllers/network/dns_resolve_cache_test.go
View file
Expand Up @@ -77,7 +77,7 @@ func (suite *DNSServer) TestResolving() {
var res *dns.Msg

err := retry.Constant(2*time.Second, retry.WithUnits(100*time.Millisecond)).Retry(func() error {
r, err := dns.Exchange(msg, "127.0.0.1:10700")
r, err := dns.Exchange(msg, "127.0.0.53:10700")

res = r

Expand Down Expand Up @@ -148,7 +148,7 @@ func TestDNSServer(t *testing.T) {
AfterSetup: func(suite *ctest.DefaultSuite) {
suite.Require().NoError(suite.Runtime().RegisterController(&netctrl.DNSUpstreamController{}))
suite.Require().NoError(suite.Runtime().RegisterController(&netctrl.DNSResolveCacheController{
Addr: "127.0.0.1:10700",
Addr: "127.0.0.53:10700",
AddrV6: "[::1]:10700",
Logger: zaptest.NewLogger(t),
}))
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4 changes: 2 additions & 2 deletions internal/app/machined/pkg/controllers/network/etcfile.go
View file
Expand Up @@ -176,12 +176,12 @@ func (ctrl *EtcFileController) Run(ctx context.Context, r controller.Runtime, lo
}
}

var localDNS = netip.MustParseAddr("127.0.0.1")
var localDNS = []netip.Addr{netip.MustParseAddr("127.0.0.53"), netip.MustParseAddr("::1")}

func pickNameservers(list safe.List[*network.DNSResolveCache], resolverStatus *network.ResolverStatus) []netip.Addr {
if list.Len() > 0 {
// local dns resolve cache enabled, route host dns requests to 127.0.0.1
return []netip.Addr{localDNS}
return localDNS
}

return resolverStatus.TypedSpec().DNSServers
Expand Down
10 changes: 5 additions & 5 deletions internal/app/machined/pkg/controllers/network/etcfile_test.go
View file
Expand Up @@ -221,7 +221,7 @@ func (suite *EtcFileConfigSuite) TestComplete() {
[]resource.Resource{suite.cfg, suite.defaultAddress, suite.hostnameStatus, suite.resolverStatus, suite.dnsServer},
etcFileContents{
hosts: "127.0.0.1 localhost\n33.11.22.44 foo.example.com foo\n::1 localhost ip6-localhost ip6-loopback\nff02::1 ip6-allnodes\nff02::2 ip6-allrouters\n10.0.0.1 a b\n10.0.0.2 c d\n", //nolint:lll
resolvConf: "nameserver 127.0.0.1\n\nsearch example.com\n",
resolvConf: "nameserver 127.0.0.53\nnameserver ::1\n\nsearch example.com\n",
resolvGlobalConf: "nameserver 1.1.1.1\nnameserver 2.2.2.2\nnameserver 3.3.3.3\n\nsearch example.com\n",
},
)
Expand All @@ -232,7 +232,7 @@ func (suite *EtcFileConfigSuite) TestNoExtraHosts() {
[]resource.Resource{suite.defaultAddress, suite.hostnameStatus, suite.resolverStatus, suite.dnsServer},
etcFileContents{
hosts: "127.0.0.1 localhost\n33.11.22.44 foo.example.com foo\n::1 localhost ip6-localhost ip6-loopback\nff02::1 ip6-allnodes\nff02::2 ip6-allrouters\n",
resolvConf: "nameserver 127.0.0.1\n\nsearch example.com\n",
resolvConf: "nameserver 127.0.0.53\nnameserver ::1\n\nsearch example.com\n",
resolvGlobalConf: "nameserver 1.1.1.1\nnameserver 2.2.2.2\nnameserver 3.3.3.3\n\nsearch example.com\n",
},
)
Expand All @@ -255,7 +255,7 @@ func (suite *EtcFileConfigSuite) TestNoSearchDomain() {
[]resource.Resource{cfg, suite.defaultAddress, suite.hostnameStatus, suite.resolverStatus, suite.dnsServer},
etcFileContents{
hosts: "127.0.0.1 localhost\n33.11.22.44 foo.example.com foo\n::1 localhost ip6-localhost ip6-loopback\nff02::1 ip6-allnodes\nff02::2 ip6-allrouters\n",
resolvConf: "nameserver 127.0.0.1\n",
resolvConf: "nameserver 127.0.0.53\nnameserver ::1\n",
resolvGlobalConf: "nameserver 1.1.1.1\nnameserver 2.2.2.2\nnameserver 3.3.3.3\n",
},
)
Expand All @@ -268,7 +268,7 @@ func (suite *EtcFileConfigSuite) TestNoDomainname() {
[]resource.Resource{suite.defaultAddress, suite.hostnameStatus, suite.resolverStatus, suite.dnsServer},
etcFileContents{
hosts: "127.0.0.1 localhost\n33.11.22.44 foo\n::1 localhost ip6-localhost ip6-loopback\nff02::1 ip6-allnodes\nff02::2 ip6-allrouters\n",
resolvConf: "nameserver 127.0.0.1\n",
resolvConf: "nameserver 127.0.0.53\nnameserver ::1\n",
resolvGlobalConf: "nameserver 1.1.1.1\nnameserver 2.2.2.2\nnameserver 3.3.3.3\n",
},
)
Expand All @@ -279,7 +279,7 @@ func (suite *EtcFileConfigSuite) TestOnlyResolvers() {
[]resource.Resource{suite.resolverStatus, suite.dnsServer},
etcFileContents{
hosts: "",
resolvConf: "nameserver 127.0.0.1\n",
resolvConf: "nameserver 127.0.0.53\nnameserver ::1\n",
resolvGlobalConf: "nameserver 1.1.1.1\nnameserver 2.2.2.2\nnameserver 3.3.3.3\n",
},
)
Expand Down
2 changes: 1 addition & 1 deletion internal/app/machined/pkg/runtime/v1alpha2/v1alpha2_controller.go
View file
Expand Up @@ -189,7 +189,7 @@ func (ctrl *Controller) Run(ctx context.Context, drainer *runtime.Drainer) error
&network.AddressStatusController{},
&network.DeviceConfigController{},
&network.DNSResolveCacheController{
Addr: "127.0.0.1:53",
Addr: "127.0.0.53:53",
AddrV6: "[::1]:53",
Logger: dnsCacheLogger,
},
Expand Down
4 changes: 0 additions & 4 deletions internal/pkg/dns/dns.go
View file
Expand Up @@ -274,29 +274,25 @@ func NewUDPPacketConn(network, addr string) (net.PacketConn, error) {

var (
tcpOptions = []controlOptions{
{unix.SOL_SOCKET, unix.SO_REUSEPORT, 1, "failed to set SO_REUSEADDR"},
{unix.IPPROTO_IP, unix.IP_RECVTTL, 1, "failed to set IP_RECVTTL"},
{unix.IPPROTO_TCP, unix.TCP_FASTOPEN, 5, "failed to set TCP_FASTOPEN"}, // tcp specific stuff from systemd
{unix.IPPROTO_TCP, unix.TCP_NODELAY, 1, "failed to set TCP_NODELAY"}, // tcp specific stuff from systemd
{unix.IPPROTO_IP, unix.IP_TTL, 1, "failed to set IP_TTL"},
}

tcpOptionsV6 = []controlOptions{
{unix.SOL_SOCKET, unix.SO_REUSEPORT, 1, "failed to set SO_REUSEADDR"},
{unix.IPPROTO_IPV6, unix.IPV6_RECVHOPLIMIT, 1, "failed to set IPV6_RECVHOPLIMIT"},
{unix.IPPROTO_TCP, unix.TCP_FASTOPEN, 5, "failed to set TCP_FASTOPEN"}, // tcp specific stuff from systemd
{unix.IPPROTO_TCP, unix.TCP_NODELAY, 1, "failed to set TCP_NODELAY"}, // tcp specific stuff from systemd
{unix.IPPROTO_IPV6, unix.IPV6_UNICAST_HOPS, 1, "failed to set IPV6_UNICAST_HOPS"},
}

udpOptions = []controlOptions{
{unix.SOL_SOCKET, unix.SO_REUSEPORT, 1, "failed to set SO_REUSEADDR"},
{unix.IPPROTO_IP, unix.IP_RECVTTL, 1, "failed to set IP_RECVTTL"},
{unix.IPPROTO_IP, unix.IP_TTL, 1, "failed to set IP_TTL"},
}

udpOptionsV6 = []controlOptions{
{unix.SOL_SOCKET, unix.SO_REUSEPORT, 1, "failed to set SO_REUSEADDR"},
{unix.IPPROTO_IPV6, unix.IPV6_RECVHOPLIMIT, 1, "failed to set IPV6_RECVHOPLIMIT"},
{unix.IPPROTO_IPV6, unix.IPV6_UNICAST_HOPS, 1, "failed to set IPV6_UNICAST_HOPS"},
}
Expand Down
8 changes: 4 additions & 4 deletions internal/pkg/dns/dns_test.go
View file
Expand Up @@ -60,7 +60,7 @@ func TestDNS(t *testing.T) {

time.Sleep(10 * time.Millisecond)

r, err := dnssrv.Exchange(createQuery(), "127.0.0.1:10700")
r, err := dnssrv.Exchange(createQuery(), "127.0.0.53:10700")
test.errCheck(t, err)

if r != nil {
Expand All @@ -86,11 +86,11 @@ func TestDNSEmptyDestinations(t *testing.T) {

time.Sleep(10 * time.Millisecond)

r, err := dnssrv.Exchange(createQuery(), "127.0.0.1:10700")
r, err := dnssrv.Exchange(createQuery(), "127.0.0.53:10700")
require.NoError(t, err)
require.Equal(t, dnssrv.RcodeServerFailure, r.Rcode, r)

r, err = dnssrv.Exchange(createQuery(), "127.0.0.1:10700")
r, err = dnssrv.Exchange(createQuery(), "127.0.0.53:10700")
require.NoError(t, err)
require.Equal(t, dnssrv.RcodeServerFailure, r.Rcode, r)

Expand Down Expand Up @@ -118,7 +118,7 @@ func newServer(t *testing.T, nameservers ...string) (context.Context, func()) {

handler.SetProxy(pxs)

pc, err := dns.NewUDPPacketConn("udp", "127.0.0.1:10700")
pc, err := dns.NewUDPPacketConn("udp", "127.0.0.53:10700")
require.NoError(t, err)

runner := dns.NewRunner(dns.NewServer(dns.ServerOptins{
Expand Down

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