Add ability to respect the system route table for unsafe route on linux (#839)

cidr/tree4.go

@@ -13,8 +13,14 @@ type Node struct {
 	value  interface{}
 }
 
+type entry struct {
+	CIDR  *net.IPNet
+	Value *interface{}
+}
+
 type Tree4 struct {
 	root *Node
+	list []entry
 }
 
 const (
@@ -24,6 +30,7 @@ const (
 func NewTree4() *Tree4 {
 	tree := new(Tree4)
 	tree.root = &Node{}
+	tree.list = []entry{}
 	return tree
 }
 
@@ -53,6 +60,15 @@ func (tree *Tree4) AddCIDR(cidr *net.IPNet, val interface{}) {
 
 	// We already have this range so update the value
 	if next != nil {
+		addCIDR := cidr.String()
+		for i, v := range tree.list {
+			if addCIDR == v.CIDR.String() {
+				tree.list = append(tree.list[:i], tree.list[i+1:]...)
+				break
+			}
+		}
+
+		tree.list = append(tree.list, entry{CIDR: cidr, Value: &val})
 		node.value = val
 		return
 	}
@@ -74,9 +90,10 @@ func (tree *Tree4) AddCIDR(cidr *net.IPNet, val interface{}) {
 
 	// Final node marks our cidr, set the value
 	node.value = val
+	tree.list = append(tree.list, entry{CIDR: cidr, Value: &val})
 }
 
-// Finds the first match, which may be the least specific
+// Contains finds the first match, which may be the least specific
 func (tree *Tree4) Contains(ip iputil.VpnIp) (value interface{}) {
 	bit := startbit
 	node := tree.root
@@ -99,7 +116,7 @@ func (tree *Tree4) Contains(ip iputil.VpnIp) (value interface{}) {
 	return value
 }
 
-// Finds the most specific match
+// MostSpecificContains finds the most specific match
 func (tree *Tree4) MostSpecificContains(ip iputil.VpnIp) (value interface{}) {
 	bit := startbit
 	node := tree.root
@@ -121,7 +138,7 @@ func (tree *Tree4) MostSpecificContains(ip iputil.VpnIp) (value interface{}) {
 	return value
 }
 
-// Finds the most specific match
+// Match finds the most specific match
 func (tree *Tree4) Match(ip iputil.VpnIp) (value interface{}) {
 	bit := startbit
 	node := tree.root
@@ -143,3 +160,8 @@ func (tree *Tree4) Match(ip iputil.VpnIp) (value interface{}) {
 	}
 	return value
 }
+
+// List will return all CIDRs and their current values. Do not modify the contents!
+func (tree *Tree4) List() []entry {
+	return tree.list
+}

cidr/tree4_test.go

@@ -8,6 +8,20 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestCIDRTree_List(t *testing.T) {
+	tree := NewTree4()
+	tree.AddCIDR(Parse("1.0.0.0/16"), "1")
+	tree.AddCIDR(Parse("1.0.0.0/8"), "2")
+	tree.AddCIDR(Parse("1.0.0.0/16"), "3")
+	tree.AddCIDR(Parse("1.0.0.0/16"), "4")
+	list := tree.List()
+	assert.Len(t, list, 2)
+	assert.Equal(t, "1.0.0.0/8", list[0].CIDR.String())
+	assert.Equal(t, "2", *list[0].Value)
+	assert.Equal(t, "1.0.0.0/16", list[1].CIDR.String())
+	assert.Equal(t, "4", *list[1].Value)
+}
+
 func TestCIDRTree_Contains(t *testing.T) {
 	tree := NewTree4()
 	tree.AddCIDR(Parse("1.0.0.0/8"), "1")

examples/config.yml

@@ -223,6 +223,10 @@ tun:
     #  metric: 100
     #  install: true
 
+  # On linux only, set to true to manage unsafe routes directly on the system route table with gateway routes instead of
+  # in nebula configuration files. Default false, not reloadable.
+  #use_system_route_table: false
+
 # TODO
 # Configure logging level
 logging:

overlay/tun.go

@@ -35,6 +35,7 @@ func NewDeviceFromConfig(c *config.C, l *logrus.Logger, tunCidr *net.IPNet, fd *
 			c.GetInt("tun.mtu", DefaultMTU),
 			routes,
 			c.GetInt("tun.tx_queue", 500),
+			c.GetBool("tun.use_system_route_table", false),
 		)
 
 	default:
@@ -46,6 +47,7 @@ func NewDeviceFromConfig(c *config.C, l *logrus.Logger, tunCidr *net.IPNet, fd *
 			routes,
 			c.GetInt("tun.tx_queue", 500),
 			routines > 1,
+			c.GetBool("tun.use_system_route_table", false),
 		)
 	}
 }

overlay/tun_android.go

@@ -22,7 +22,7 @@ type tun struct {
 	l         *logrus.Logger
 }
 
-func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, _ int, routes []Route, _ int) (*tun, error) {
+func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, _ int, routes []Route, _ int, _ bool) (*tun, error) {
 	routeTree, err := makeRouteTree(l, routes, false)
 	if err != nil {
 		return nil, err
@@ -41,7 +41,7 @@ func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, _ int, routes
 	}, nil
 }
 
-func newTun(_ *logrus.Logger, _ string, _ *net.IPNet, _ int, _ []Route, _ int, _ bool) (*tun, error) {
+func newTun(_ *logrus.Logger, _ string, _ *net.IPNet, _ int, _ []Route, _ int, _ bool, _ bool) (*tun, error) {
 	return nil, fmt.Errorf("newTun not supported in Android")
 }
 

overlay/tun_darwin.go

@@ -77,7 +77,7 @@ type ifreqMTU struct {
 	pad  [8]byte
 }
 
-func newTun(l *logrus.Logger, name string, cidr *net.IPNet, defaultMTU int, routes []Route, _ int, _ bool) (*tun, error) {
+func newTun(l *logrus.Logger, name string, cidr *net.IPNet, defaultMTU int, routes []Route, _ int, _ bool, _ bool) (*tun, error) {
 	routeTree, err := makeRouteTree(l, routes, false)
 	if err != nil {
 		return nil, err
@@ -170,7 +170,7 @@ func (t *tun) deviceBytes() (o [16]byte) {
 	return
 }
 
-func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int) (*tun, error) {
+func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int, _ bool) (*tun, error) {
 	return nil, fmt.Errorf("newTunFromFd not supported in Darwin")
 }
 

overlay/tun_freebsd.go

@@ -38,11 +38,11 @@ func (t *tun) Close() error {
 	return nil
 }
 
-func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int) (*tun, error) {
+func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int, _ bool) (*tun, error) {
 	return nil, fmt.Errorf("newTunFromFd not supported in FreeBSD")
 }
 
-func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int, routes []Route, _ int, _ bool) (*tun, error) {
+func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int, routes []Route, _ int, _ bool, _ bool) (*tun, error) {
 	routeTree, err := makeRouteTree(l, routes, false)
 	if err != nil {
 		return nil, err

overlay/tun_ios.go

@@ -23,11 +23,11 @@ type tun struct {
 	routeTree *cidr.Tree4
 }
 
-func newTun(_ *logrus.Logger, _ string, _ *net.IPNet, _ int, _ []Route, _ int, _ bool) (*tun, error) {
+func newTun(_ *logrus.Logger, _ string, _ *net.IPNet, _ int, _ []Route, _ int, _ bool, _ bool) (*tun, error) {
 	return nil, fmt.Errorf("newTun not supported in iOS")
 }
 
-func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, _ int, routes []Route, _ int) (*tun, error) {
+func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, _ int, routes []Route, _ int, _ bool) (*tun, error) {
 	routeTree, err := makeRouteTree(l, routes, false)
 	if err != nil {
 		return nil, err

overlay/tun_linux.go

@@ -4,11 +4,13 @@
 package overlay
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"net"
 	"os"
 	"strings"
+	"sync/atomic"
 	"unsafe"
 
 	"github.com/sirupsen/logrus"
@@ -26,8 +28,12 @@ type tun struct {
 	MaxMTU     int
 	DefaultMTU int
 	TXQueueLen int
+
 	Routes          []Route
-	routeTree  *cidr.Tree4
+	routeTree       atomic.Pointer[cidr.Tree4]
+	routeChan       chan struct{}
+	useSystemRoutes bool
+
 	l *logrus.Logger
 }
 
@@ -63,7 +69,7 @@ type ifreqQLEN struct {
 	pad   [8]byte
 }
 
-func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, defaultMTU int, routes []Route, txQueueLen int) (*tun, error) {
+func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, defaultMTU int, routes []Route, txQueueLen int, useSystemRoutes bool) (*tun, error) {
 	routeTree, err := makeRouteTree(l, routes, true)
 	if err != nil {
 		return nil, err
@@ -71,7 +77,7 @@ func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, defaultMTU in
 
 	file := os.NewFile(uintptr(deviceFd), "/dev/net/tun")
 
-	return &tun{
+	t := &tun{
 		ReadWriteCloser: file,
 		fd:              int(file.Fd()),
 		Device:          "tun0",
@@ -79,12 +85,14 @@ func newTunFromFd(l *logrus.Logger, deviceFd int, cidr *net.IPNet, defaultMTU in
 		DefaultMTU:      defaultMTU,
 		TXQueueLen:      txQueueLen,
 		Routes:          routes,
-		routeTree:       routeTree,
+		useSystemRoutes: useSystemRoutes,
 		l:               l,
-	}, nil
+	}
+	t.routeTree.Store(routeTree)
+	return t, nil
 }
 
-func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int, routes []Route, txQueueLen int, multiqueue bool) (*tun, error) {
+func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int, routes []Route, txQueueLen int, multiqueue bool, useSystemRoutes bool) (*tun, error) {
 	fd, err := unix.Open("/dev/net/tun", os.O_RDWR, 0)
 	if err != nil {
 		return nil, err
@@ -119,7 +127,7 @@ func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int
 		return nil, err
 	}
 
-	return &tun{
+	t := &tun{
 		ReadWriteCloser: file,
 		fd:              int(file.Fd()),
 		Device:          name,
@@ -128,9 +136,11 @@ func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int
 		DefaultMTU:      defaultMTU,
 		TXQueueLen:      txQueueLen,
 		Routes:          routes,
-		routeTree:       routeTree,
+		useSystemRoutes: useSystemRoutes,
 		l:               l,
-	}, nil
+	}
+	t.routeTree.Store(routeTree)
+	return t, nil
 }
 
 func (t *tun) NewMultiQueueReader() (io.ReadWriteCloser, error) {
@@ -152,7 +162,7 @@ func (t *tun) NewMultiQueueReader() (io.ReadWriteCloser, error) {
 }
 
 func (t *tun) RouteFor(ip iputil.VpnIp) iputil.VpnIp {
-	r := t.routeTree.MostSpecificContains(ip)
+	r := t.routeTree.Load().MostSpecificContains(ip)
 	if r != nil {
 		return r.(iputil.VpnIp)
 	}
@@ -183,16 +193,20 @@ func (t *tun) Write(b []byte) (int, error) {
 	}
 }
 
-func (t tun) deviceBytes() (o [16]byte) {
+func (t *tun) deviceBytes() (o [16]byte) {
 	for i, c := range t.Device {
 		o[i] = byte(c)
 	}
 	return
 }
 
-func (t tun) Activate() error {
+func (t *tun) Activate() error {
 	devName := t.deviceBytes()
 
+	if t.useSystemRoutes {
+		t.watchRoutes()
+	}
+
 	var addr, mask [4]byte
 
 	copy(addr[:], t.cidr.IP.To4())
@@ -318,7 +332,7 @@ func (t *tun) Name() string {
 	return t.Device
 }
 
-func (t tun) advMSS(r Route) int {
+func (t *tun) advMSS(r Route) int {
 	mtu := r.MTU
 	if r.MTU == 0 {
 		mtu = t.DefaultMTU
@@ -330,3 +344,83 @@ func (t tun) advMSS(r Route) int {
 	}
 	return 0
 }
+
+func (t *tun) watchRoutes() {
+	rch := make(chan netlink.RouteUpdate)
+	doneChan := make(chan struct{})
+
+	if err := netlink.RouteSubscribe(rch, doneChan); err != nil {
+		t.l.WithError(err).Errorf("failed to subscribe to system route changes")
+		return
+	}
+
+	t.routeChan = doneChan
+
+	go func() {
+		for {
+			select {
+			case r := <-rch:
+				t.updateRoutes(r)
+			case <-doneChan:
+				// netlink.RouteSubscriber will close the rch for us
+				return
+			}
+		}
+	}()
+}
+
+func (t *tun) updateRoutes(r netlink.RouteUpdate) {
+	if r.Gw == nil {
+		// Not a gateway route, ignore
+		t.l.WithField("route", r).Debug("Ignoring route update, not a gateway route")
+		return
+	}
+
+	if !t.cidr.Contains(r.Gw) {
+		// Gateway isn't in our overlay network, ignore
+		t.l.WithField("route", r).Debug("Ignoring route update, not in our network")
+		return
+	}
+
+	if x := r.Dst.IP.To4(); x == nil {
+		// Nebula only handles ipv4 on the overlay currently
+		t.l.WithField("route", r).Debug("Ignoring route update, destination is not ipv4")
+		return
+	}
+
+	newTree := cidr.NewTree4()
+	if r.Type == unix.RTM_NEWROUTE {
+		for _, oldR := range t.routeTree.Load().List() {
+			newTree.AddCIDR(oldR.CIDR, oldR.Value)
+		}
+
+		t.l.WithField("destination", r.Dst).WithField("via", r.Gw).Info("Adding route")
+		newTree.AddCIDR(r.Dst, iputil.Ip2VpnIp(r.Gw))
+
+	} else {
+		gw := iputil.Ip2VpnIp(r.Gw)
+		for _, oldR := range t.routeTree.Load().List() {
+			if bytes.Equal(oldR.CIDR.IP, r.Dst.IP) && bytes.Equal(oldR.CIDR.Mask, r.Dst.Mask) && *oldR.Value != nil && (*oldR.Value).(iputil.VpnIp) == gw {
+				// This is the record to delete
+				t.l.WithField("destination", r.Dst).WithField("via", r.Gw).Info("Removing route")
+				continue
+			}
+
+			newTree.AddCIDR(oldR.CIDR, oldR.Value)
+		}
+	}
+
+	t.routeTree.Store(newTree)
+}
+
+func (t *tun) Close() error {
+	if t.routeChan != nil {
+		close(t.routeChan)
+	}
+
+	if t.ReadWriteCloser != nil {
+		t.ReadWriteCloser.Close()
+	}
+
+	return nil
+}

overlay/tun_linux_test.go

@@ -7,19 +7,19 @@ import "testing"
 
 var runAdvMSSTests = []struct {
 	name     string
-	tun      tun
+	tun      *tun
 	r        Route
 	expected int
 }{
 	// Standard case, default MTU is the device max MTU
-	{"default", tun{DefaultMTU: 1440, MaxMTU: 1440}, Route{}, 0},
+	{"default", &tun{DefaultMTU: 1440, MaxMTU: 1440}, Route{}, 0},
-	{"default-min", tun{DefaultMTU: 1440, MaxMTU: 1440}, Route{MTU: 1440}, 0},
+	{"default-min", &tun{DefaultMTU: 1440, MaxMTU: 1440}, Route{MTU: 1440}, 0},
-	{"default-low", tun{DefaultMTU: 1440, MaxMTU: 1440}, Route{MTU: 1200}, 1160},
+	{"default-low", &tun{DefaultMTU: 1440, MaxMTU: 1440}, Route{MTU: 1200}, 1160},
 
 	// Case where we have a route MTU set higher than the default
-	{"route", tun{DefaultMTU: 1440, MaxMTU: 8941}, Route{}, 1400},
+	{"route", &tun{DefaultMTU: 1440, MaxMTU: 8941}, Route{}, 1400},
-	{"route-min", tun{DefaultMTU: 1440, MaxMTU: 8941}, Route{MTU: 1440}, 1400},
+	{"route-min", &tun{DefaultMTU: 1440, MaxMTU: 8941}, Route{MTU: 1440}, 1400},
-	{"route-high", tun{DefaultMTU: 1440, MaxMTU: 8941}, Route{MTU: 8941}, 0},
+	{"route-high", &tun{DefaultMTU: 1440, MaxMTU: 8941}, Route{MTU: 8941}, 0},
 }
 
 func TestTunAdvMSS(t *testing.T) {

overlay/tun_tester.go

@@ -25,7 +25,7 @@ type TestTun struct {
 	TxPackets chan []byte // Packets transmitted outside by nebula
 }
 
-func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, _ int, routes []Route, _ int, _ bool) (*TestTun, error) {
+func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, _ int, routes []Route, _ int, _ bool, _ bool) (*TestTun, error) {
 	routeTree, err := makeRouteTree(l, routes, false)
 	if err != nil {
 		return nil, err
@@ -42,7 +42,7 @@ func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, _ int, routes
 	}, nil
 }
 
-func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int) (*TestTun, error) {
+func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int, _ bool) (*TestTun, error) {
 	return nil, fmt.Errorf("newTunFromFd not supported")
 }
 

overlay/tun_windows.go

@@ -14,11 +14,11 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
-func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int) (Device, error) {
+func newTunFromFd(_ *logrus.Logger, _ int, _ *net.IPNet, _ int, _ []Route, _ int, _ bool) (Device, error) {
 	return nil, fmt.Errorf("newTunFromFd not supported in Windows")
 }
 
-func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int, routes []Route, _ int, _ bool) (Device, error) {
+func newTun(l *logrus.Logger, deviceName string, cidr *net.IPNet, defaultMTU int, routes []Route, _ int, _ bool, _ bool) (Device, error) {
 	useWintun := true
 	if err := checkWinTunExists(); err != nil {
 		l.WithError(err).Warn("Check Wintun driver failed, fallback to wintap driver")