/* SPDX-License-Identifier: MIT * * Copyright (C) 2019 WireGuard LLC. All Rights Reserved. */ package router import ( "bytes" "errors" "fmt" "log" "net" "os" "sort" "time" "github.com/go-multierror/multierror" ole "github.com/go-ole/go-ole" winipcfg "github.com/tailscale/winipcfg-go" "github.com/tailscale/wireguard-go/tun" "golang.org/x/sys/windows" "tailscale.com/net/interfaces" "tailscale.com/wgengine/winnet" ) // monitorDefaultRoutes subscribes to route change events and updates // the Tailscale tunnel interface's MTU to match that of the // underlying default route. // // This is an attempt at making the MTU mostly correct, but in // practice this entire piece of code ends up just using the 1280 // value passed in at device construction time. This code might make // the MTU go lower due to very low-MTU IPv4 interfaces. // // TODO: this code is insufficient to control the MTU correctly. The // correct way to do it is per-peer PMTU discovery, and synthesizing // ICMP fragmentation-needed messages within tailscaled. This code may // address a few rare corner cases, but is unlikely to significantly // help with MTU issues compared to a static 1280B implementation. func monitorDefaultRoutes(tun *tun.NativeTun) (*winipcfg.RouteChangeCallback, error) { guid := tun.GUID() ourLuid, err := winipcfg.InterfaceGuidToLuid(&guid) lastMtu := uint32(0) if err != nil { return nil, err } doIt := func() error { mtu, err := getDefaultRouteMTU() if err != nil { return err } if mtu > 0 && (lastMtu == 0 || lastMtu != mtu) { iface, err := winipcfg.GetIpInterface(ourLuid, winipcfg.AF_INET) if err != nil { return err } iface.NlMtu = mtu - 80 // If the TUN device was created with a smaller MTU, // though, such as 1280, we don't want to go bigger than // configured. (See the comment on minimalMTU in the // wgengine package.) if min, err := tun.MTU(); err == nil && min < int(iface.NlMtu) { iface.NlMtu = uint32(min) } if iface.NlMtu < 576 { iface.NlMtu = 576 } err = iface.Set() if err != nil { return err } tun.ForceMTU(int(iface.NlMtu)) iface, err = winipcfg.GetIpInterface(ourLuid, winipcfg.AF_INET6) if err != nil { if !isMissingIPv6Err(err) { return err } } else { iface.NlMtu = mtu - 80 if iface.NlMtu < 1280 { iface.NlMtu = 1280 } err = iface.Set() if err != nil { return err } } lastMtu = mtu } return nil } err = doIt() if err != nil { return nil, err } cb, err := winipcfg.RegisterRouteChangeCallback(func(notificationType winipcfg.MibNotificationType, route *winipcfg.Route) { //fmt.Printf("MonitorDefaultRoutes: changed: %v\n", route.DestinationPrefix) if route.DestinationPrefix.PrefixLength == 0 { _ = doIt() } }) if err != nil { return nil, err } return cb, nil } func getDefaultRouteMTU() (uint32, error) { mtus, err := interfaces.NonTailscaleMTUs() if err != nil { return 0, err } routes, err := winipcfg.GetRoutes(winipcfg.AF_INET) if err != nil { return 0, err } best := ^uint32(0) mtu := uint32(0) for _, route := range routes { if route.DestinationPrefix.PrefixLength != 0 { continue } routeMTU := mtus[route.InterfaceLuid] if routeMTU == 0 { continue } if route.Metric < best { best = route.Metric mtu = routeMTU } } routes, err = winipcfg.GetRoutes(winipcfg.AF_INET6) if err != nil { return 0, err } best = ^uint32(0) for _, route := range routes { if route.DestinationPrefix.PrefixLength != 0 { continue } routeMTU := mtus[route.InterfaceLuid] if routeMTU == 0 { continue } if route.Metric < best { best = route.Metric if routeMTU < mtu { mtu = routeMTU } } } return mtu, nil } // setPrivateNetwork marks the provided network adapter's category to private. // It returns (false, nil) if the adapter was not found. func setPrivateNetwork(ifcGUID *windows.GUID) (bool, error) { // NLM_NETWORK_CATEGORY values. const ( categoryPublic = 0 categoryPrivate = 1 categoryDomain = 2 ) var c ole.Connection if err := c.Initialize(); err != nil { return false, fmt.Errorf("c.Initialize: %v", err) } defer c.Uninitialize() m, err := winnet.NewNetworkListManager(&c) if err != nil { return false, fmt.Errorf("winnet.NewNetworkListManager: %v", err) } defer m.Release() cl, err := m.GetNetworkConnections() if err != nil { return false, fmt.Errorf("m.GetNetworkConnections: %v", err) } defer cl.Release() for _, nco := range cl { aid, err := nco.GetAdapterId() if err != nil { return false, fmt.Errorf("nco.GetAdapterId: %v", err) } if aid != ifcGUID.String() { continue } n, err := nco.GetNetwork() if err != nil { return false, fmt.Errorf("GetNetwork: %v", err) } defer n.Release() cat, err := n.GetCategory() if err != nil { return false, fmt.Errorf("GetCategory: %v", err) } if cat != categoryPrivate { if err := n.SetCategory(categoryPrivate); err != nil { return false, fmt.Errorf("SetCategory: %v", err) } } return true, nil } return false, nil } func configureInterface(cfg *Config, tun *tun.NativeTun) error { const mtu = 0 guid := tun.GUID() iface, err := winipcfg.InterfaceFromGUIDEx(&guid, &winipcfg.GetAdapterAddressesFlags{ // Issue 474: on early boot, when the network is still // coming up, if the Tailscale service comes up first, // the Tailscale adapter it finds might not have the // IPv4 service available yet? Try this flag: GAA_FLAG_INCLUDE_ALL_INTERFACES: true, }) if err != nil { return err } go func() { // It takes a weirdly long time for Windows to notice the // new interface has come up. Poll periodically until it // does. const tries = 20 for i := 0; i < tries; i++ { found, err := setPrivateNetwork(&guid) if err != nil { log.Printf("setPrivateNetwork(try=%d): %v", i, err) } else { if found { return } log.Printf("setPrivateNetwork(try=%d): not found", i) } time.Sleep(1 * time.Second) } log.Printf("setPrivateNetwork: adapter %v not found after %d tries, giving up", guid, tries) }() var firstGateway4 *net.IP var firstGateway6 *net.IP addresses := make([]*net.IPNet, len(cfg.LocalAddrs)) for i, addr := range cfg.LocalAddrs { ipnet := addr.IPNet() addresses[i] = ipnet gateway := ipnet.IP if addr.IP.Is4() && firstGateway4 == nil { firstGateway4 = &gateway } else if addr.IP.Is6() && firstGateway6 == nil { firstGateway6 = &gateway } } var routes []winipcfg.RouteData foundDefault4 := false foundDefault6 := false for _, route := range cfg.Routes { if (route.IP.Is4() && firstGateway4 == nil) || (route.IP.Is6() && firstGateway6 == nil) { return errors.New("Due to a Windows limitation, one cannot have interface routes without an interface address") } ipn := route.IPNet() var gateway net.IP if route.IP.Is4() { gateway = *firstGateway4 } else if route.IP.Is6() { gateway = *firstGateway6 } r := winipcfg.RouteData{ Destination: net.IPNet{ IP: ipn.IP.Mask(ipn.Mask), Mask: ipn.Mask, }, NextHop: gateway, Metric: 0, } if bytes.Compare(r.Destination.IP, gateway) == 0 { // no need to add a route for the interface's // own IP. The kernel does that for us. // If we try to replace it, we'll fail to // add the route unless NextHop is set, but // then the interface's IP won't be pingable. continue } if route.IP.Is4() { if route.Bits == 0 { foundDefault4 = true } r.NextHop = *firstGateway4 } else if route.IP.Is6() { if route.Bits == 0 { foundDefault6 = true } r.NextHop = *firstGateway6 } routes = append(routes, r) } err = syncAddresses(iface, addresses) if err != nil { return err } sort.Slice(routes, func(i, j int) bool { return routeLess(&routes[i], &routes[j]) }) deduplicatedRoutes := []*winipcfg.RouteData{} for i := 0; i < len(routes); i++ { // There's only one way to get to a given IP+Mask, so delete // all matches after the first. if i > 0 && bytes.Equal(routes[i].Destination.IP, routes[i-1].Destination.IP) && bytes.Equal(routes[i].Destination.Mask, routes[i-1].Destination.Mask) { continue } deduplicatedRoutes = append(deduplicatedRoutes, &routes[i]) } var errAcc error err = syncRoutes(iface, deduplicatedRoutes) if err != nil && errAcc == nil { log.Printf("setroutes: %v", err) errAcc = err } ipif, err := iface.GetIpInterface(winipcfg.AF_INET) if err != nil { log.Printf("getipif: %v", err) return err } if foundDefault4 { ipif.UseAutomaticMetric = false ipif.Metric = 0 } if mtu > 0 { ipif.NlMtu = uint32(mtu) tun.ForceMTU(int(ipif.NlMtu)) } err = ipif.Set() if err != nil && errAcc == nil { errAcc = err } ipif, err = iface.GetIpInterface(winipcfg.AF_INET6) if err != nil { if !isMissingIPv6Err(err) { return err } } else { if foundDefault6 { ipif.UseAutomaticMetric = false ipif.Metric = 0 } if mtu > 0 { ipif.NlMtu = uint32(mtu) } ipif.DadTransmits = 0 ipif.RouterDiscoveryBehavior = winipcfg.RouterDiscoveryDisabled err = ipif.Set() if err != nil && errAcc == nil { errAcc = err } } return errAcc } // isMissingIPv6Err reports whether err is due to IPv6 not being enabled on the machine. // // It only currently supports the errors returned by winipcfg.Interface.GetIpInterface. func isMissingIPv6Err(err error) bool { if se, ok := err.(*os.SyscallError); ok { switch se.Syscall { case "iphlpapi.GetIpInterfaceEntry": // ERROR_NOT_FOUND from means the address family (IPv6) is not found. // (ERROR_FILE_NOT_FOUND means that the interface doesn't exist.) // https://docs.microsoft.com/en-us/windows/win32/api/netioapi/nf-netioapi-getipinterfaceentry return se.Err == windows.ERROR_NOT_FOUND } } return false } // routeLess reports whether ri should sort before rj. // The actual sort order doesn't appear to matter. The caller just // wants them sorted to be able to de-dup. func routeLess(ri, rj *winipcfg.RouteData) bool { if v := bytes.Compare(ri.Destination.IP, rj.Destination.IP); v != 0 { return v == -1 } if v := bytes.Compare(ri.Destination.Mask, rj.Destination.Mask); v != 0 { // Narrower masks first return v == 1 } if ri.Metric != rj.Metric { // Lower metrics first return ri.Metric < rj.Metric } if v := bytes.Compare(ri.NextHop, rj.NextHop); v != 0 { // No nexthop before non-empty nexthop. return v == -1 } return false } // unwrapIP returns the shortest version of ip. func unwrapIP(ip net.IP) net.IP { if ip4 := ip.To4(); ip4 != nil { return ip4 } return ip } func v4Mask(m net.IPMask) net.IPMask { if len(m) == 16 { return m[12:] } return m } func netCompare(a, b net.IPNet) int { aip, bip := unwrapIP(a.IP), unwrapIP(b.IP) v := bytes.Compare(aip, bip) if v != 0 { return v } amask, bmask := a.Mask, b.Mask if len(aip) == 4 { amask = v4Mask(a.Mask) bmask = v4Mask(b.Mask) } // narrower first return -bytes.Compare(amask, bmask) } func sortNets(a []*net.IPNet) { sort.Slice(a, func(i, j int) bool { return netCompare(*a[i], *a[j]) == -1 }) } // deltaNets returns the changes to turn a into b. func deltaNets(a, b []*net.IPNet) (add, del []*net.IPNet) { add = make([]*net.IPNet, 0, len(b)) del = make([]*net.IPNet, 0, len(a)) sortNets(a) sortNets(b) i := 0 j := 0 for i < len(a) && j < len(b) { switch netCompare(*a[i], *b[j]) { case -1: // a < b, delete del = append(del, a[i]) i++ case 0: // a == b, no diff i++ j++ case 1: // a > b, add missing entry add = append(add, b[j]) j++ default: panic("unexpected compare result") } } del = append(del, a[i:]...) add = append(add, b[j:]...) return } func excludeIPv6LinkLocal(in []*net.IPNet) (out []*net.IPNet) { out = in[:0] for _, n := range in { if len(n.IP) == 16 && n.IP.IsLinkLocalUnicast() { continue } out = append(out, n) } return out } // syncAddresses incrementally sets the interface's unicast IP addresses, // doing the minimum number of AddAddresses & DeleteAddress calls. // This avoids the full FlushAddresses. // // Any IPv6 link-local addresses are not deleted. func syncAddresses(ifc *winipcfg.Interface, want []*net.IPNet) error { var erracc error got := ifc.UnicastIPNets add, del := deltaNets(got, want) del = excludeIPv6LinkLocal(del) for _, a := range del { err := ifc.DeleteAddress(&a.IP) if err != nil { erracc = err } } err := ifc.AddAddresses(add) if err != nil { erracc = err } ifc.UnicastIPNets = make([]*net.IPNet, len(want)) copy(ifc.UnicastIPNets, want) return erracc } func routeDataCompare(a, b *winipcfg.RouteData) int { v := bytes.Compare(a.Destination.IP, b.Destination.IP) if v != 0 { return v } // Narrower masks first v = bytes.Compare(a.Destination.Mask, b.Destination.Mask) if v != 0 { return -v } // No nexthop before non-empty nexthop v = bytes.Compare(a.NextHop, b.NextHop) if v != 0 { return v } // Lower metrics first if a.Metric < b.Metric { return -1 } else if a.Metric > b.Metric { return 1 } return 0 } func sortRouteData(a []*winipcfg.RouteData) { sort.Slice(a, func(i, j int) bool { return routeDataCompare(a[i], a[j]) < 0 }) } func deltaRouteData(a, b []*winipcfg.RouteData) (add, del []*winipcfg.RouteData) { add = make([]*winipcfg.RouteData, 0, len(b)) del = make([]*winipcfg.RouteData, 0, len(a)) sortRouteData(a) sortRouteData(b) i := 0 j := 0 for i < len(a) && j < len(b) { switch routeDataCompare(a[i], b[j]) { case -1: // a < b, delete del = append(del, a[i]) i++ case 0: // a == b, no diff i++ j++ case 1: // a > b, add missing entry add = append(add, b[j]) j++ default: panic("unexpected compare result") } } del = append(del, a[i:]...) add = append(add, b[j:]...) return } // syncRoutes incrementally sets multiples routes on an interface. // This avoids a full ifc.FlushRoutes call. func syncRoutes(ifc *winipcfg.Interface, want []*winipcfg.RouteData) error { routes, err := ifc.GetRoutes(windows.AF_INET) if err != nil { return err } got := make([]*winipcfg.RouteData, 0, len(routes)) for _, r := range routes { v, err := r.ToRouteData() if err != nil { return err } got = append(got, v) } add, del := deltaRouteData(got, want) var errs []error for _, a := range del { err := ifc.DeleteRoute(&a.Destination, &a.NextHop) if err != nil { dstStr := a.Destination.String() if dstStr == "169.254.255.255/32" { // Issue 785. Ignore these routes // failing to delete. Harmless. continue } errs = append(errs, fmt.Errorf("deleting route %v: %w", dstStr, err)) } } for _, a := range add { err := ifc.AddRoute(a) if err != nil { errs = append(errs, fmt.Errorf("adding route %v: %w", &a.Destination, err)) } } return multierror.New(errs) }