net/dns: insert OS base config when emulating split DNS.

Part of #953.

Signed-off-by: David Anderson <danderson@tailscale.com>

net/dns/manager.go

@@ -76,7 +76,10 @@ func (m *Manager) Set(cfg Config) error {
 		forceSplitDNSForTesting(&cfg)
 	}
 
-	rcfg, ocfg := m.compileConfig(cfg)
+	rcfg, ocfg, err := m.compileConfig(cfg)
+	if err != nil {
+		return err
+	}
 
 	m.logf("Resolvercfg: %+v", rcfg)
 	m.logf("OScfg: %+v", ocfg)
@@ -93,7 +96,7 @@ func (m *Manager) Set(cfg Config) error {
 
 // compileConfig converts cfg into a quad-100 resolver configuration
 // and an OS-level configuration.
-func (m *Manager) compileConfig(cfg Config) (resolver.Config, OSConfig) {
+func (m *Manager) compileConfig(cfg Config) (resolver.Config, OSConfig, error) {
 	// Deal with trivial configs first.
 	switch {
 	case !cfg.needsOSResolver():
@@ -102,14 +105,14 @@ func (m *Manager) compileConfig(cfg Config) (resolver.Config, OSConfig) {
 		// configs clear all Tailscale DNS settings.
 		return resolver.Config{}, OSConfig{
 			SearchDomains: cfg.SearchDomains,
-		}
+		}, nil
 	case cfg.hasDefaultResolversOnly():
 		// Trivial CorpDNS configuration, just override the OS
 		// resolver.
 		return resolver.Config{}, OSConfig{
 			Nameservers:   toIPsOnly(cfg.DefaultResolvers),
 			SearchDomains: cfg.SearchDomains,
-		}
+		}, nil
 	case cfg.hasDefaultResolvers():
 		// Default resolvers plus other stuff always ends up proxying
 		// through quad-100.
@@ -127,7 +130,7 @@ func (m *Manager) compileConfig(cfg Config) (resolver.Config, OSConfig) {
 			Nameservers:   []netaddr.IP{tsaddr.TailscaleServiceIP()},
 			SearchDomains: cfg.SearchDomains,
 		}
-		return rcfg, ocfg
+		return rcfg, ocfg, nil
 	}
 
 	// From this point on, we're figuring out split DNS
@@ -144,7 +147,7 @@ func (m *Manager) compileConfig(cfg Config) (resolver.Config, OSConfig) {
 			Nameservers:   toIPsOnly(cfg.singleResolverSet()),
 			SearchDomains: cfg.SearchDomains,
 			MatchDomains:  cfg.matchDomains(),
-		}
+		}, nil
 	}
 
 	// Split DNS configuration with either multiple upstream routes,
@@ -170,10 +173,15 @@ func (m *Manager) compileConfig(cfg Config) (resolver.Config, OSConfig) {
 	if m.os.SupportsSplitDNS() {
 		ocfg.MatchDomains = cfg.matchDomains()
 	} else {
-		rcfg.Routes["."] = []netaddr.IPPort{netaddr.MustParseIPPort("8.8.8.8:53")}
+		bcfg, err := m.os.GetBaseConfig()
+		if err != nil {
+			return resolver.Config{}, OSConfig{}, err
+		}
+		rcfg.Routes["."] = toIPPorts(bcfg.Nameservers)
+		ocfg.SearchDomains = append(ocfg.SearchDomains, bcfg.SearchDomains...)
 	}
 
-	return rcfg, ocfg
+	return rcfg, ocfg, nil
 }
 
 func addFQDNDots(domains []string) []string {
@@ -196,6 +204,13 @@ func toIPsOnly(ipps []netaddr.IPPort) (ret []netaddr.IP) {
 	return ret
 }
 
+func toIPPorts(ips []netaddr.IP) (ret []netaddr.IPPort) {
+	for _, ip := range ips {
+		ret = append(ret, netaddr.IPPort{IP: ip, Port: 53})
+	}
+	return ret
+}
+
 func (m *Manager) EnqueueRequest(bs []byte, from netaddr.IPPort) error {
 	return m.resolver.EnqueueRequest(bs, from)
 }

net/dns/manager_test.go

@@ -14,7 +14,8 @@ import (
 )
 
 type fakeOSConfigurator struct {
-	SplitDNS bool
+	SplitDNS   bool
+	BaseConfig OSConfig
 
 	OSConfig       OSConfig
 	ResolverConfig resolver.Config
@@ -37,8 +38,7 @@ func (c *fakeOSConfigurator) SupportsSplitDNS() bool {
 }
 
 func (c *fakeOSConfigurator) GetBaseConfig() (OSConfig, error) {
-	// TODO
+	return c.BaseConfig, nil
-	return OSConfig{}, nil
 }
 
 func (c *fakeOSConfigurator) Close() error { return nil }
@@ -54,6 +54,7 @@ func TestManager(t *testing.T) {
 		name  string
 		in    Config
 		split bool
+		bs    OSConfig
 		os    OSConfig
 		rs    resolver.Config
 	}{
@@ -178,9 +179,13 @@ func TestManager(t *testing.T) {
 				Routes:        upstreams("corp.com", "2.2.2.2:53"),
 				SearchDomains: strs("tailscale.com", "universe.tf"),
 			},
+			bs: OSConfig{
+				Nameservers:   mustIPs("8.8.8.8"),
+				SearchDomains: strs("coffee.shop"),
+			},
 			os: OSConfig{
 				Nameservers:   mustIPs("100.100.100.100"),
-				SearchDomains: strs("tailscale.com", "universe.tf"),
+				SearchDomains: strs("tailscale.com", "universe.tf", "coffee.shop"),
 			},
 			rs: resolver.Config{
 				Routes: upstreams(
@@ -209,9 +214,13 @@ func TestManager(t *testing.T) {
 					"bigco.net", "3.3.3.3:53"),
 				SearchDomains: strs("tailscale.com", "universe.tf"),
 			},
+			bs: OSConfig{
+				Nameservers:   mustIPs("8.8.8.8"),
+				SearchDomains: strs("coffee.shop"),
+			},
 			os: OSConfig{
 				Nameservers:   mustIPs("100.100.100.100"),
-				SearchDomains: strs("tailscale.com", "universe.tf"),
+				SearchDomains: strs("tailscale.com", "universe.tf", "coffee.shop"),
 			},
 			rs: resolver.Config{
 				Routes: upstreams(
@@ -232,7 +241,7 @@ func TestManager(t *testing.T) {
 			os: OSConfig{
 				Nameservers:   mustIPs("100.100.100.100"),
 				SearchDomains: strs("tailscale.com", "universe.tf"),
-				MatchDomains:  strs("corp.com", "bigco.net"),
+				MatchDomains:  strs("bigco.net", "corp.com"),
 			},
 			rs: resolver.Config{
 				Routes: upstreams(
@@ -249,9 +258,13 @@ func TestManager(t *testing.T) {
 				AuthoritativeSuffixes: strs("ts.com"),
 				SearchDomains:         strs("tailscale.com", "universe.tf"),
 			},
+			bs: OSConfig{
+				Nameservers:   mustIPs("8.8.8.8"),
+				SearchDomains: strs("coffee.shop"),
+			},
 			os: OSConfig{
 				Nameservers:   mustIPs("100.100.100.100"),
-				SearchDomains: strs("tailscale.com", "universe.tf"),
+				SearchDomains: strs("tailscale.com", "universe.tf", "coffee.shop"),
 			},
 			rs: resolver.Config{
 				Routes: upstreams(".", "8.8.8.8:53"),
@@ -293,9 +306,13 @@ func TestManager(t *testing.T) {
 				AuthoritativeSuffixes: strs("ts.com"),
 				SearchDomains:         strs("tailscale.com", "universe.tf"),
 			},
+			bs: OSConfig{
+				Nameservers:   mustIPs("8.8.8.8"),
+				SearchDomains: strs("coffee.shop"),
+			},
 			os: OSConfig{
 				Nameservers:   mustIPs("100.100.100.100"),
-				SearchDomains: strs("tailscale.com", "universe.tf"),
+				SearchDomains: strs("tailscale.com", "universe.tf", "coffee.shop"),
 			},
 			rs: resolver.Config{
 				Routes: upstreams(
@@ -321,7 +338,7 @@ func TestManager(t *testing.T) {
 			os: OSConfig{
 				Nameservers:   mustIPs("100.100.100.100"),
 				SearchDomains: strs("tailscale.com", "universe.tf"),
-				MatchDomains:  strs("ts.com", "corp.com"),
+				MatchDomains:  strs("corp.com", "ts.com"),
 			},
 			rs: resolver.Config{
 				Routes: upstreams("corp.com.", "2.2.2.2:53"),
@@ -335,7 +352,10 @@ func TestManager(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			f := fakeOSConfigurator{SplitDNS: test.split}
+			f := fakeOSConfigurator{
+				SplitDNS:   test.split,
+				BaseConfig: test.bs,
+			}
 			m := NewManager(t.Logf, &f, nil)
 			m.resolver.TestOnlySetHook(f.SetResolver)