ipn: program exit node into the data plane according to user pref.

Part of #1153, #1154. Fixes #1224.

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

cmd/tailscale/cli/up.go

@@ -45,6 +45,7 @@ specify any flags, options are reset to their default.
 		upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", false, "accept routes advertised by other Tailscale nodes")
 		upf.BoolVar(&upArgs.acceptDNS, "accept-dns", true, "accept DNS configuration from the admin panel")
 		upf.BoolVar(&upArgs.singleRoutes, "host-routes", true, "install host routes to other Tailscale nodes")
+		upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale IP of the exit node for internet traffic")
 		upf.BoolVar(&upArgs.shieldsUp, "shields-up", false, "don't allow incoming connections")
 		upf.BoolVar(&upArgs.forceReauth, "force-reauth", false, "force reauthentication")
 		upf.StringVar(&upArgs.advertiseTags, "advertise-tags", "", "ACL tags to request (comma-separated, e.g. eng,montreal,ssh)")
@@ -74,6 +75,7 @@ var upArgs struct {
 	acceptRoutes    bool
 	acceptDNS       bool
 	singleRoutes    bool
+	exitNodeIP      string
 	shieldsUp       bool
 	forceReauth     bool
 	advertiseRoutes string
@@ -138,6 +140,9 @@ func runUp(ctx context.Context, args []string) error {
 		if upArgs.acceptRoutes {
 			return errors.New("--accept-routes is " + notSupported)
 		}
+		if upArgs.exitNodeIP != "" {
+			return errors.New("--exit-node is " + notSupported)
+		}
 		if upArgs.netfilterMode != "off" {
 			return errors.New("--netfilter-mode values besides \"off\" " + notSupported)
 		}
@@ -170,6 +175,15 @@ func runUp(ctx context.Context, args []string) error {
 		checkIPForwarding()
 	}
 
+	var exitNodeIP netaddr.IP
+	if upArgs.exitNodeIP != "" {
+		var err error
+		exitNodeIP, err = netaddr.ParseIP(upArgs.exitNodeIP)
+		if err != nil {
+			fatalf("invalid IP address %q for --exit-node: %v", upArgs.exitNodeIP, err)
+		}
+	}
+
 	var tags []string
 	if upArgs.advertiseTags != "" {
 		tags = strings.Split(upArgs.advertiseTags, ",")
@@ -190,6 +204,7 @@ func runUp(ctx context.Context, args []string) error {
 	prefs.ControlURL = upArgs.server
 	prefs.WantRunning = true
 	prefs.RouteAll = upArgs.acceptRoutes
+	prefs.ExitNodeIP = exitNodeIP
 	prefs.CorpDNS = upArgs.acceptDNS
 	prefs.AllowSingleHosts = upArgs.singleRoutes
 	prefs.ShieldsUp = upArgs.shieldsUp

cmd/tailscale/depaware.txt

@@ -45,7 +45,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/net/packet                                     from tailscale.com/wgengine/filter
         tailscale.com/net/stun                                       from tailscale.com/net/netcheck
         tailscale.com/net/tlsdial                                    from tailscale.com/control/controlclient+
-        tailscale.com/net/tsaddr                                     from tailscale.com/net/interfaces
+        tailscale.com/net/tsaddr                                     from tailscale.com/net/interfaces+
      💣 tailscale.com/net/tshttpproxy                                from tailscale.com/control/controlclient+
         tailscale.com/paths                                          from tailscale.com/cmd/tailscale/cli
         tailscale.com/safesocket                                     from tailscale.com/cmd/tailscale/cli

control/controlclient/netmap.go

@@ -14,6 +14,7 @@ import (
 	"time"
 
 	"inet.af/netaddr"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/wgkey"
@@ -249,7 +250,6 @@ type WGConfigFlags int
 const (
 	AllowSingleHosts WGConfigFlags = 1 << iota
 	AllowSubnetRoutes
-	AllowDefaultRoute
 )
 
 // EndpointDiscoSuffix is appended to the hex representation of a peer's discovery key
@@ -271,10 +271,6 @@ func (nm *NetworkMap) WGCfg(logf logger.Logf, flags WGConfigFlags) (*wgcfg.Confi
 		if Debug.OnlyDisco && peer.DiscoKey.IsZero() {
 			continue
 		}
-		if (flags&AllowSingleHosts) == 0 && len(peer.AllowedIPs) < 2 {
-			logf("wgcfg: %v skipping a single-host peer.", peer.Key.ShortString())
-			continue
-		}
 		cfg.Peers = append(cfg.Peers, wgcfg.Peer{
 			PublicKey: wgcfg.Key(peer.Key),
 		})
@@ -298,13 +294,12 @@ func (nm *NetworkMap) WGCfg(logf logger.Logf, flags WGConfigFlags) (*wgcfg.Confi
 				}
 			}
 		}
+
 		for _, allowedIP := range peer.AllowedIPs {
-			if allowedIP.Bits == 0 {
+			if allowedIP.IsSingleIP() && tsaddr.IsTailscaleIP(allowedIP.IP) && (flags&AllowSingleHosts) == 0 {
-				if (flags & AllowDefaultRoute) == 0 {
+				logf("[v1] wgcfg: skipping node IP %v from %q (%v)",
-					logf("[v1] wgcfg: not accepting default route from %q (%v)",
+					allowedIP.IP, nodeDebugName(peer), peer.Key.ShortString())
-						nodeDebugName(peer), peer.Key.ShortString())
 				continue
-				}
 			} else if cidrIsSubnet(peer, allowedIP) {
 				if (flags & AllowSubnetRoutes) == 0 {
 					logf("[v1] wgcfg: not accepting subnet route %v from %q (%v)",

ipn/ipnlocal/local.go

@@ -306,8 +306,10 @@ func (b *LocalBackend) setClientStatus(st controlclient.Status) {
 		prefsChanged = true
 	}
 	if st.NetMap != nil {
+		if b.keepOneExitNodeLocked(st.NetMap) {
+			prefsChanged = true
+		}
 		b.setNetMapLocked(st.NetMap)
-
 	}
 	if st.URL != "" {
 		b.authURL = st.URL
@@ -365,6 +367,57 @@ func (b *LocalBackend) setClientStatus(st controlclient.Status) {
 	b.authReconfig()
 }
 
+// keepOneExitNodeLocked edits nm to retain only the default
+// routes provided by the exit node specified in b.prefs. It returns
+// whether prefs was mutated as part of the process, due to an exit
+// node IP being converted into a node ID.
+func (b *LocalBackend) keepOneExitNodeLocked(nm *controlclient.NetworkMap) (prefsChanged bool) {
+	if b.prefs.ExitNodeID == "" && b.prefs.ExitNodeIP.IsZero() {
+		return false
+	}
+
+	// If we have a desired IP on file, try to find the corresponding
+	// node.
+	if !b.prefs.ExitNodeIP.IsZero() {
+		// IP takes precedence over ID, so if both are set, clear ID.
+		if b.prefs.ExitNodeID != "" {
+			b.prefs.ExitNodeID = ""
+			prefsChanged = true
+		}
+
+	peerLoop:
+		for _, peer := range nm.Peers {
+			for _, addr := range peer.Addresses {
+				if !addr.IsSingleIP() || addr.IP != b.prefs.ExitNodeIP {
+					continue
+				}
+				// Found the node being referenced, upgrade prefs to
+				// reference it directly for next time.
+				b.prefs.ExitNodeID = peer.StableID
+				b.prefs.ExitNodeIP = netaddr.IP{}
+				prefsChanged = true
+				break peerLoop
+			}
+		}
+	}
+
+	// At this point, we have a node ID if the requested node is in
+	// the netmap. If not, the ID will be empty, and we'll strip out
+	// all default routes.
+	for _, peer := range nm.Peers {
+		out := peer.AllowedIPs[:0]
+		for _, allowedIP := range peer.AllowedIPs {
+			if allowedIP.Bits == 0 && peer.StableID != b.prefs.ExitNodeID {
+				continue
+			}
+			out = append(out, allowedIP)
+		}
+		peer.AllowedIPs = out
+	}
+
+	return prefsChanged
+}
+
 // setWgengineStatus is the callback by the wireguard engine whenever it posts a new status.
 // This updates the endpoints both in the backend and in the control client.
 func (b *LocalBackend) setWgengineStatus(s *wgengine.Status, err error) {
@@ -1203,8 +1256,6 @@ func (b *LocalBackend) authReconfig() {
 
 	var flags controlclient.WGConfigFlags
 	if uc.RouteAll {
-		flags |= controlclient.AllowDefaultRoute
-		// TODO(apenwarr): Make subnet routes a different pref?
 		flags |= controlclient.AllowSubnetRoutes
 	}
 	if uc.AllowSingleHosts {
@@ -1256,6 +1307,11 @@ func magicDNSRootDomains(nm *controlclient.NetworkMap) []string {
 	return nil
 }
 
+var (
+	ipv4Default = netaddr.MustParseIPPrefix("0.0.0.0/0")
+	ipv6Default = netaddr.MustParseIPPrefix("::/0")
+)
+
 // routerConfig produces a router.Config from a wireguard config and IPN prefs.
 func routerConfig(cfg *wgcfg.Config, prefs *ipn.Prefs) *router.Config {
 	rs := &router.Config{
@@ -1269,6 +1325,32 @@ func routerConfig(cfg *wgcfg.Config, prefs *ipn.Prefs) *router.Config {
 		rs.Routes = append(rs.Routes, unmapIPPrefixes(peer.AllowedIPs)...)
 	}
 
+	// Sanity check: we expect the control server to program both a v4
+	// and a v6 default route, if default routing is on. Fill in
+	// blackhole routes appropriately if we're missing some. This is
+	// likely to break some functionality, but if the user expressed a
+	// preference for routing remotely, we want to avoid leaking
+	// traffic at the expense of functionality.
+	if prefs.ExitNodeID != "" || !prefs.ExitNodeIP.IsZero() {
+		var default4, default6 bool
+		for _, route := range rs.Routes {
+			if route == ipv4Default {
+				default4 = true
+			} else if route == ipv6Default {
+				default6 = true
+			}
+			if default4 && default6 {
+				break
+			}
+		}
+		if !default4 {
+			rs.Routes = append(rs.Routes, ipv4Default)
+		}
+		if !default6 {
+			rs.Routes = append(rs.Routes, ipv6Default)
+		}
+	}
+
 	rs.Routes = append(rs.Routes, netaddr.IPPrefix{
 		IP:   tsaddr.TailscaleServiceIP(),
 		Bits: 32,

ipn/prefs.go

@@ -18,6 +18,7 @@ import (
 	"inet.af/netaddr"
 	"tailscale.com/atomicfile"
 	"tailscale.com/control/controlclient"
+	"tailscale.com/tailcfg"
 	"tailscale.com/types/preftype"
 )
 
@@ -28,8 +29,10 @@ type Prefs struct {
 	// ControlURL is the URL of the control server to use.
 	ControlURL string
 
-	// RouteAll specifies whether to accept subnet and default routes
+	// RouteAll specifies whether to accept subnets advertised by
-	// advertised by other nodes on the Tailscale network.
+	// other nodes on the Tailscale network. Note that this does not
+	// include default routes (0.0.0.0/0 and ::/0), those are
+	// controlled by ExitNodeID/IP below.
 	RouteAll bool
 
 	// AllowSingleHosts specifies whether to install routes for each
@@ -44,6 +47,24 @@ type Prefs struct {
 	// packets stop flowing. What's up with that?
 	AllowSingleHosts bool
 
+	// ExitNodeID and ExitNodeIP specify the node that should be used
+	// as an exit node for internet traffic. At most one of these
+	// should be non-zero.
+	//
+	// The preferred way to express the chosen node is ExitNodeID, but
+	// in some cases it's not possible to use that ID (e.g. in the
+	// linux CLI, before tailscaled has a netmap). For those
+	// situations, we allow specifying the exit node by IP, and
+	// ipnlocal.LocalBackend will translate the IP into an ID when the
+	// node is found in the netmap.
+	//
+	// If the selected exit node doesn't exist (e.g. it's not part of
+	// the current tailnet), or it doesn't offer exit node services, a
+	// blackhole route will be installed on the local system to
+	// prevent any traffic escaping to the local network.
+	ExitNodeID tailcfg.StableNodeID
+	ExitNodeIP netaddr.IP
+
 	// CorpDNS specifies whether to install the Tailscale network's
 	// DNS configuration, if it exists.
 	CorpDNS bool
@@ -191,6 +212,8 @@ func (p *Prefs) Equals(p2 *Prefs) bool {
 		p.ControlURL == p2.ControlURL &&
 		p.RouteAll == p2.RouteAll &&
 		p.AllowSingleHosts == p2.AllowSingleHosts &&
+		p.ExitNodeID == p2.ExitNodeID &&
+		p.ExitNodeIP == p2.ExitNodeIP &&
 		p.CorpDNS == p2.CorpDNS &&
 		p.WantRunning == p2.WantRunning &&
 		p.NotepadURLs == p2.NotepadURLs &&

ipn/prefs_clone.go

@@ -9,6 +9,7 @@ package ipn
 import (
 	"inet.af/netaddr"
 	"tailscale.com/control/controlclient"
+	"tailscale.com/tailcfg"
 	"tailscale.com/types/preftype"
 )
 
@@ -35,6 +36,8 @@ var _PrefsNeedsRegeneration = Prefs(struct {
 	ControlURL       string
 	RouteAll         bool
 	AllowSingleHosts bool
+	ExitNodeID       tailcfg.StableNodeID
+	ExitNodeIP       netaddr.IP
 	CorpDNS          bool
 	WantRunning      bool
 	ShieldsUp        bool

ipn/prefs_test.go

@@ -30,7 +30,7 @@ func fieldsOf(t reflect.Type) (fields []string) {
 func TestPrefsEqual(t *testing.T) {
 	tstest.PanicOnLog()
 
-	prefsHandles := []string{"ControlURL", "RouteAll", "AllowSingleHosts", "CorpDNS", "WantRunning", "ShieldsUp", "AdvertiseTags", "Hostname", "OSVersion", "DeviceModel", "NotepadURLs", "ForceDaemon", "AdvertiseRoutes", "NoSNAT", "NetfilterMode", "Persist"}
+	prefsHandles := []string{"ControlURL", "RouteAll", "AllowSingleHosts", "ExitNodeID", "ExitNodeIP", "CorpDNS", "WantRunning", "ShieldsUp", "AdvertiseTags", "Hostname", "OSVersion", "DeviceModel", "NotepadURLs", "ForceDaemon", "AdvertiseRoutes", "NoSNAT", "NetfilterMode", "Persist"}
 	if have := fieldsOf(reflect.TypeOf(Prefs{})); !reflect.DeepEqual(have, prefsHandles) {
 		t.Errorf("Prefs.Equal check might be out of sync\nfields: %q\nhandled: %q\n",
 			have, prefsHandles)
@@ -99,6 +99,28 @@ func TestPrefsEqual(t *testing.T) {
 			true,
 		},
 
+		{
+			&Prefs{ExitNodeID: "n1234"},
+			&Prefs{},
+			false,
+		},
+		{
+			&Prefs{ExitNodeID: "n1234"},
+			&Prefs{ExitNodeID: "n1234"},
+			true,
+		},
+
+		{
+			&Prefs{ExitNodeIP: netaddr.MustParseIP("1.2.3.4")},
+			&Prefs{},
+			false,
+		},
+		{
+			&Prefs{ExitNodeIP: netaddr.MustParseIP("1.2.3.4")},
+			&Prefs{ExitNodeIP: netaddr.MustParseIP("1.2.3.4")},
+			true,
+		},
+
 		{
 			&Prefs{CorpDNS: true},
 			&Prefs{CorpDNS: false},