// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Package portmapper is a UDP port mapping client. It currently allows for mapping over // NAT-PMP, UPnP, and PCP. package portmapper import ( "context" "encoding/binary" "errors" "fmt" "io" "net" "net/http" "sync" "time" "go4.org/mem" "inet.af/netaddr" "tailscale.com/net/interfaces" "tailscale.com/net/netns" "tailscale.com/types/logger" ) // Debug knobs for "tailscaled debug --portmap". var ( VerboseLogs bool // Disable* disables a specific service from mapping. DisableUPnP bool DisablePMP bool DisablePCP bool ) // References: // // NAT-PMP: https://tools.ietf.org/html/rfc6886 // portMapServiceTimeout is the time we wait for port mapping // services (UPnP, NAT-PMP, PCP) to respond before we give up and // decide that they're not there. Since these services are on the // same LAN as this machine and a single L3 hop away, we don't // give them much time to respond. const portMapServiceTimeout = 250 * time.Millisecond // trustServiceStillAvailableDuration is how often we re-verify a port // mapping service is available. const trustServiceStillAvailableDuration = 10 * time.Minute // Client is a port mapping client. type Client struct { logf logger.Logf ipAndGateway func() (gw, ip netaddr.IP, ok bool) onChange func() // or nil testPxPPort uint16 // if non-zero, pxpPort to use for tests testUPnPPort uint16 // if non-zero, uPnPPort to use for tests mu sync.Mutex // guards following, and all fields thereof // runningCreate is whether we're currently working on creating // a port mapping (whether GetCachedMappingOrStartCreatingOne kicked // off a createMapping goroutine). runningCreate bool lastMyIP netaddr.IP lastGW netaddr.IP closed bool lastProbe time.Time pmpPubIP netaddr.IP // non-zero if known pmpPubIPTime time.Time // time pmpPubIP last verified pmpLastEpoch uint32 pcpSawTime time.Time // time we last saw PCP was available uPnPSawTime time.Time // time we last saw UPnP was available uPnPMeta uPnPDiscoResponse // Location header from UPnP UDP discovery response uPnPHTTPClient *http.Client // netns-configured HTTP client for UPnP; nil until needed localPort uint16 mapping mapping // non-nil if we have a mapping } // mapping represents a created port-mapping over some protocol. It specifies a lease duration, // how to release the mapping, and whether the map is still valid. // // After a mapping is created, it should be immutable, and thus reads should be safe across // concurrent goroutines. type mapping interface { // Release will attempt to unmap the established port mapping. It will block until completion, // but can be called asynchronously. Release should be idempotent, and thus even if called // multiple times should not cause additional side-effects. Release(context.Context) // goodUntil will return the lease time that the mapping is valid for. GoodUntil() time.Time // renewAfter returns the earliest time that the mapping should be renewed. RenewAfter() time.Time // externalIPPort indicates what port the mapping can be reached from on the outside. External() netaddr.IPPort } // HaveMapping reports whether we have a current valid mapping. func (c *Client) HaveMapping() bool { c.mu.Lock() defer c.mu.Unlock() return c.mapping != nil && c.mapping.GoodUntil().After(time.Now()) } // pmpMapping is an already-created PMP mapping. // // All fields are immutable once created. type pmpMapping struct { c *Client gw netaddr.IPPort external netaddr.IPPort internal netaddr.IPPort renewAfter time.Time // the time at which we want to renew the mapping goodUntil time.Time // the mapping's total lifetime epoch uint32 } // externalValid reports whether m.external is valid, with both its IP and Port populated. func (m *pmpMapping) externalValid() bool { return !m.external.IP().IsZero() && m.external.Port() != 0 } func (p *pmpMapping) GoodUntil() time.Time { return p.goodUntil } func (p *pmpMapping) RenewAfter() time.Time { return p.renewAfter } func (p *pmpMapping) External() netaddr.IPPort { return p.external } // Release does a best effort fire-and-forget release of the PMP mapping m. func (m *pmpMapping) Release(ctx context.Context) { uc, err := m.c.listenPacket(ctx, "udp4", ":0") if err != nil { return } defer uc.Close() pkt := buildPMPRequestMappingPacket(m.internal.Port(), m.external.Port(), pmpMapLifetimeDelete) uc.WriteTo(pkt, m.gw.UDPAddr()) } // NewClient returns a new portmapping client. // // The optional onChange argument specifies a func to run in a new // goroutine whenever the port mapping status has changed. If nil, // it doesn't make a callback. func NewClient(logf logger.Logf, onChange func()) *Client { return &Client{ logf: logf, ipAndGateway: interfaces.LikelyHomeRouterIP, onChange: onChange, } } // SetGatewayLookupFunc set the func that returns the machine's default gateway IP, and // the primary IP address for that gateway. It must be called before the client is used. // If not called, interfaces.LikelyHomeRouterIP is used. func (c *Client) SetGatewayLookupFunc(f func() (gw, myIP netaddr.IP, ok bool)) { c.ipAndGateway = f } // NoteNetworkDown should be called when the network has transitioned to a down state. // It's too late to release port mappings at this point (the user might've just turned off // their wifi), but we can make sure we invalidate mappings for later when the network // comes back. func (c *Client) NoteNetworkDown() { c.mu.Lock() defer c.mu.Unlock() c.invalidateMappingsLocked(false) } func (c *Client) Close() error { c.mu.Lock() defer c.mu.Unlock() if c.closed { return nil } c.closed = true c.invalidateMappingsLocked(true) // TODO: close some future ever-listening UDP socket(s), // waiting for multicast announcements from router. return nil } // SetLocalPort updates the local port number to which we want to port // map UDP traffic. func (c *Client) SetLocalPort(localPort uint16) { c.mu.Lock() defer c.mu.Unlock() if c.localPort == localPort { return } c.localPort = localPort c.invalidateMappingsLocked(true) } func (c *Client) gatewayAndSelfIP() (gw, myIP netaddr.IP, ok bool) { gw, myIP, ok = c.ipAndGateway() if !ok { gw = netaddr.IP{} myIP = netaddr.IP{} } c.mu.Lock() defer c.mu.Unlock() if gw != c.lastGW || myIP != c.lastMyIP || !ok { c.lastMyIP = myIP c.lastGW = gw c.invalidateMappingsLocked(true) } return } // pxpPort returns the NAT-PMP and PCP port number. // It returns 5351, except for in tests where it varies by run. func (c *Client) pxpPort() uint16 { if c.testPxPPort != 0 { return c.testPxPPort } return pmpDefaultPort } // upnpPort returns the UPnP discovery port number. // It returns 1900, except for in tests where it varies by run. func (c *Client) upnpPort() uint16 { if c.testUPnPPort != 0 { return c.testUPnPPort } return upnpDefaultPort } func (c *Client) listenPacket(ctx context.Context, network, addr string) (net.PacketConn, error) { // When running under testing conditions, we bind the IGD server // to localhost, and may be running in an environment where our // netns code would decide that binding the portmapper client // socket to the default route interface is the correct way to // ensure connectivity. This can result in us trying to send // packets for 127.0.0.1 out the machine's LAN interface, which // obviously gets dropped on the floor. // // So, under those testing conditions, do _not_ use netns to // create listening sockets. Such sockets are vulnerable to // routing loops, but it's tests that don't set up routing loops, // so we don't care. if c.testPxPPort != 0 || c.testUPnPPort != 0 { var lc net.ListenConfig return lc.ListenPacket(ctx, network, addr) } return netns.Listener().ListenPacket(ctx, network, addr) } func (c *Client) invalidateMappingsLocked(releaseOld bool) { if c.mapping != nil { if releaseOld { c.mapping.Release(context.Background()) } c.mapping = nil } c.pmpPubIP = netaddr.IP{} c.pmpPubIPTime = time.Time{} c.pcpSawTime = time.Time{} c.uPnPSawTime = time.Time{} c.uPnPMeta = uPnPDiscoResponse{} } func (c *Client) sawPMPRecently() bool { c.mu.Lock() defer c.mu.Unlock() return c.sawPMPRecentlyLocked() } func (c *Client) sawPMPRecentlyLocked() bool { return !c.pmpPubIP.IsZero() && c.pmpPubIPTime.After(time.Now().Add(-trustServiceStillAvailableDuration)) } func (c *Client) sawPCPRecently() bool { c.mu.Lock() defer c.mu.Unlock() return c.sawPCPRecentlyLocked() } func (c *Client) sawPCPRecentlyLocked() bool { return c.pcpSawTime.After(time.Now().Add(-trustServiceStillAvailableDuration)) } func (c *Client) sawUPnPRecently() bool { c.mu.Lock() defer c.mu.Unlock() return c.uPnPSawTime.After(time.Now().Add(-trustServiceStillAvailableDuration)) } // closeCloserOnContextDone starts a new goroutine to call c.Close // if/when ctx becomes done. // To stop the goroutine, call the returned stop func. func closeCloserOnContextDone(ctx context.Context, c io.Closer) (stop func()) { // Close uc on ctx being done. ctxDone := ctx.Done() if ctxDone == nil { return func() {} } stopWaitDone := make(chan struct{}) go func() { select { case <-stopWaitDone: case <-ctxDone: c.Close() } }() return func() { close(stopWaitDone) } } // NoMappingError is returned when no NAT mapping could be done. type NoMappingError struct { err error } func (nme NoMappingError) Unwrap() error { return nme.err } func (nme NoMappingError) Error() string { return fmt.Sprintf("no NAT mapping available: %v", nme.err) } // IsNoMappingError reports whether err is of type NoMappingError. func IsNoMappingError(err error) bool { _, ok := err.(NoMappingError) return ok } var ( ErrNoPortMappingServices = errors.New("no port mapping services were found") ErrGatewayRange = errors.New("skipping portmap; gateway range likely lacks support") ) // GetCachedMappingOrStartCreatingOne quickly returns with our current cached portmapping, if any. // If there's not one, it starts up a background goroutine to create one. // If the background goroutine ends up creating one, the onChange hook registered with the // NewClient constructor (if any) will fire. func (c *Client) GetCachedMappingOrStartCreatingOne() (external netaddr.IPPort, ok bool) { c.mu.Lock() defer c.mu.Unlock() // Do we have an existing mapping that's valid? now := time.Now() if m := c.mapping; m != nil { if now.Before(m.GoodUntil()) { if now.After(m.RenewAfter()) { c.maybeStartMappingLocked() } return m.External(), true } } c.maybeStartMappingLocked() return netaddr.IPPort{}, false } // maybeStartMappingLocked starts a createMapping goroutine up, if one isn't already running. // // c.mu must be held. func (c *Client) maybeStartMappingLocked() { if !c.runningCreate { c.runningCreate = true go c.createMapping() } } func (c *Client) createMapping() { ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second) defer cancel() defer func() { c.mu.Lock() defer c.mu.Unlock() c.runningCreate = false }() if _, err := c.createOrGetMapping(ctx); err == nil && c.onChange != nil { go c.onChange() } else if err != nil && !IsNoMappingError(err) { c.logf("createOrGetMapping: %v", err) } } // wildcardIP is used when the previous external IP is not known for PCP port mapping. var wildcardIP = netaddr.MustParseIP("0.0.0.0") // createOrGetMapping either creates a new mapping or returns a cached // valid one. // // If no mapping is available, the error will be of type // NoMappingError; see IsNoMappingError. func (c *Client) createOrGetMapping(ctx context.Context) (external netaddr.IPPort, err error) { if DisableUPnP && DisablePCP && DisablePMP { return netaddr.IPPort{}, NoMappingError{ErrNoPortMappingServices} } gw, myIP, ok := c.gatewayAndSelfIP() if !ok { return netaddr.IPPort{}, NoMappingError{ErrGatewayRange} } c.mu.Lock() localPort := c.localPort internalAddr := netaddr.IPPortFrom(myIP, localPort) // prevPort is the port we had most previously, if any. We try // to ask for the same port. 0 means to give us any port. var prevPort uint16 // Do we have an existing mapping that's valid? now := time.Now() if m := c.mapping; m != nil { if now.Before(m.RenewAfter()) { defer c.mu.Unlock() return m.External(), nil } // The mapping might still be valid, so just try to renew it. prevPort = m.External().Port() } if DisablePCP && DisablePMP { c.mu.Unlock() if external, ok := c.getUPnPPortMapping(ctx, gw, internalAddr, prevPort); ok { return external, nil } return netaddr.IPPort{}, NoMappingError{ErrNoPortMappingServices} } // If we just did a Probe (e.g. via netchecker) but didn't // find a PMP service, bail out early rather than probing // again. Cuts down latency for most clients. haveRecentPMP := c.sawPMPRecentlyLocked() haveRecentPCP := c.sawPCPRecentlyLocked() // Since PMP mapping may require multiple calls, and it's not clear from the outset // whether we're doing a PCP or PMP call, initialize the PMP mapping here, // and only return it once completed. // // PCP returns all the information necessary for a mapping in a single packet, so we can // construct it upon receiving that packet. m := &pmpMapping{ c: c, gw: netaddr.IPPortFrom(gw, c.pxpPort()), internal: internalAddr, } if haveRecentPMP { m.external = m.external.WithIP(c.pmpPubIP) } if c.lastProbe.After(now.Add(-5*time.Second)) && !haveRecentPMP && !haveRecentPCP { c.mu.Unlock() // fallback to UPnP portmapping if external, ok := c.getUPnPPortMapping(ctx, gw, internalAddr, prevPort); ok { return external, nil } return netaddr.IPPort{}, NoMappingError{ErrNoPortMappingServices} } c.mu.Unlock() uc, err := c.listenPacket(ctx, "udp4", ":0") if err != nil { return netaddr.IPPort{}, err } defer uc.Close() uc.SetReadDeadline(time.Now().Add(portMapServiceTimeout)) defer closeCloserOnContextDone(ctx, uc)() pxpAddr := netaddr.IPPortFrom(gw, c.pxpPort()) pxpAddru := pxpAddr.UDPAddr() preferPCP := !DisablePCP && (DisablePMP || (!haveRecentPMP && haveRecentPCP)) // Create a mapping, defaulting to PMP unless only PCP was seen recently. if preferPCP { // TODO replace wildcardIP here with previous external if known. // Only do PCP mapping in the case when PMP did not appear to be available recently. pkt := buildPCPRequestMappingPacket(myIP, localPort, prevPort, pcpMapLifetimeSec, wildcardIP) if _, err := uc.WriteTo(pkt, pxpAddru); err != nil { return netaddr.IPPort{}, err } } else { // Ask for our external address if needed. if m.external.IP().IsZero() { if _, err := uc.WriteTo(pmpReqExternalAddrPacket, pxpAddru); err != nil { return netaddr.IPPort{}, err } } pkt := buildPMPRequestMappingPacket(localPort, prevPort, pmpMapLifetimeSec) if _, err := uc.WriteTo(pkt, pxpAddru); err != nil { return netaddr.IPPort{}, err } } res := make([]byte, 1500) for { n, srci, err := uc.ReadFrom(res) if err != nil { if ctx.Err() == context.Canceled { return netaddr.IPPort{}, err } // fallback to UPnP portmapping if mapping, ok := c.getUPnPPortMapping(ctx, gw, internalAddr, prevPort); ok { return mapping, nil } return netaddr.IPPort{}, NoMappingError{ErrNoPortMappingServices} } srcu := srci.(*net.UDPAddr) src, ok := netaddr.FromStdAddr(srcu.IP, srcu.Port, srcu.Zone) if !ok { continue } if src == pxpAddr { version := res[0] switch version { case pmpVersion: pres, ok := parsePMPResponse(res[:n]) if !ok { c.logf("unexpected PMP response: % 02x", res[:n]) continue } if pres.ResultCode != 0 { return netaddr.IPPort{}, NoMappingError{fmt.Errorf("PMP response Op=0x%x,Res=0x%x", pres.OpCode, pres.ResultCode)} } if pres.OpCode == pmpOpReply|pmpOpMapPublicAddr { m.external = m.external.WithIP(pres.PublicAddr) } if pres.OpCode == pmpOpReply|pmpOpMapUDP { m.external = m.external.WithPort(pres.ExternalPort) d := time.Duration(pres.MappingValidSeconds) * time.Second now := time.Now() m.goodUntil = now.Add(d) m.renewAfter = now.Add(d / 2) // renew in half the time m.epoch = pres.SecondsSinceEpoch } case pcpVersion: pcpMapping, err := parsePCPMapResponse(res[:n]) if err != nil { c.logf("failed to get PCP mapping: %v", err) // PCP should only have a single packet response return netaddr.IPPort{}, NoMappingError{ErrNoPortMappingServices} } pcpMapping.c = c pcpMapping.internal = m.internal pcpMapping.gw = netaddr.IPPortFrom(gw, c.pxpPort()) c.mu.Lock() defer c.mu.Unlock() c.mapping = pcpMapping return pcpMapping.external, nil default: c.logf("unknown PMP/PCP version number: %d %v", version, res[:n]) return netaddr.IPPort{}, NoMappingError{ErrNoPortMappingServices} } } if m.externalValid() { c.mu.Lock() defer c.mu.Unlock() c.mapping = m return m.external, nil } } } type pmpResultCode uint16 // NAT-PMP constants. const ( pmpDefaultPort = 5351 pmpMapLifetimeSec = 7200 // RFC recommended 2 hour map duration pmpMapLifetimeDelete = 0 // 0 second lifetime deletes pmpVersion = 0 pmpOpMapPublicAddr = 0 pmpOpMapUDP = 1 pmpOpReply = 0x80 // OR'd into request's op code on response pmpCodeOK pmpResultCode = 0 pmpCodeUnsupportedVersion pmpResultCode = 1 pmpCodeNotAuthorized pmpResultCode = 2 // "e.g., box supports mapping, but user has turned feature off" pmpCodeNetworkFailure pmpResultCode = 3 // "e.g., NAT box itself has not obtained a DHCP lease" pmpCodeOutOfResources pmpResultCode = 4 pmpCodeUnsupportedOpcode pmpResultCode = 5 ) func buildPMPRequestMappingPacket(localPort, prevPort uint16, lifetimeSec uint32) (pkt []byte) { pkt = make([]byte, 12) pkt[1] = pmpOpMapUDP binary.BigEndian.PutUint16(pkt[4:], localPort) binary.BigEndian.PutUint16(pkt[6:], prevPort) binary.BigEndian.PutUint32(pkt[8:], lifetimeSec) return pkt } type pmpResponse struct { OpCode uint8 ResultCode pmpResultCode SecondsSinceEpoch uint32 // For Map ops: MappingValidSeconds uint32 InternalPort uint16 ExternalPort uint16 // For public addr ops: PublicAddr netaddr.IP } func parsePMPResponse(pkt []byte) (res pmpResponse, ok bool) { if len(pkt) < 12 { return } ver := pkt[0] if ver != 0 { return } res.OpCode = pkt[1] res.ResultCode = pmpResultCode(binary.BigEndian.Uint16(pkt[2:])) res.SecondsSinceEpoch = binary.BigEndian.Uint32(pkt[4:]) if res.OpCode == pmpOpReply|pmpOpMapUDP { if len(pkt) != 16 { return res, false } res.InternalPort = binary.BigEndian.Uint16(pkt[8:]) res.ExternalPort = binary.BigEndian.Uint16(pkt[10:]) res.MappingValidSeconds = binary.BigEndian.Uint32(pkt[12:]) } if res.OpCode == pmpOpReply|pmpOpMapPublicAddr { if len(pkt) != 12 { return res, false } res.PublicAddr = netaddr.IPv4(pkt[8], pkt[9], pkt[10], pkt[11]) } return res, true } type ProbeResult struct { PCP bool PMP bool UPnP bool } // Probe returns a summary of which port mapping services are // available on the network. // // If a probe has run recently and there haven't been any network changes since, // the returned result might be server from the Client's cache, without // sending any network traffic. func (c *Client) Probe(ctx context.Context) (res ProbeResult, err error) { gw, myIP, ok := c.gatewayAndSelfIP() if !ok { return res, ErrGatewayRange } defer func() { if err == nil { c.mu.Lock() defer c.mu.Unlock() c.lastProbe = time.Now() } }() uc, err := c.listenPacket(context.Background(), "udp4", ":0") if err != nil { c.logf("ProbePCP: %v", err) return res, err } defer uc.Close() ctx, cancel := context.WithTimeout(ctx, 250*time.Millisecond) defer cancel() defer closeCloserOnContextDone(ctx, uc)() pxpAddr := netaddr.IPPortFrom(gw, c.pxpPort()).UDPAddr() upnpAddr := netaddr.IPPortFrom(gw, c.upnpPort()).UDPAddr() // Don't send probes to services that we recently learned (for // the same gw/myIP) are available. See // https://github.com/tailscale/tailscale/issues/1001 if c.sawPMPRecently() { res.PMP = true } else if !DisablePMP { uc.WriteTo(pmpReqExternalAddrPacket, pxpAddr) } if c.sawPCPRecently() { res.PCP = true } else if !DisablePCP { uc.WriteTo(pcpAnnounceRequest(myIP), pxpAddr) } if c.sawUPnPRecently() { res.UPnP = true } else if !DisableUPnP { uc.WriteTo(uPnPPacket, upnpAddr) } buf := make([]byte, 1500) pcpHeard := false // true when we get any PCP response for { if pcpHeard && res.PMP && res.UPnP { // Nothing more to discover. return res, nil } n, addr, err := uc.ReadFrom(buf) if err != nil { if ctx.Err() == context.DeadlineExceeded { err = nil } return res, err } port := uint16(addr.(*net.UDPAddr).Port) switch port { case c.upnpPort(): if mem.Contains(mem.B(buf[:n]), mem.S(":InternetGatewayDevice:")) { meta, err := parseUPnPDiscoResponse(buf[:n]) if err != nil { c.logf("unrecognized UPnP discovery response; ignoring") } if VerboseLogs { c.logf("UPnP reply %+v, %q", meta, buf[:n]) } res.UPnP = true c.mu.Lock() c.uPnPSawTime = time.Now() if c.uPnPMeta != meta { c.logf("UPnP meta changed: %+v", meta) c.uPnPMeta = meta } c.mu.Unlock() } case c.pxpPort(): // same value for PMP and PCP if pres, ok := parsePCPResponse(buf[:n]); ok { if pres.OpCode == pcpOpReply|pcpOpAnnounce { pcpHeard = true c.mu.Lock() c.pcpSawTime = time.Now() c.mu.Unlock() switch pres.ResultCode { case pcpCodeOK: c.logf("Got PCP response: epoch: %v", pres.Epoch) res.PCP = true continue case pcpCodeNotAuthorized: // A PCP service is running, but refuses to // provide port mapping services. res.PCP = false continue default: // Fall through to unexpected log line. } } c.logf("unexpected PCP probe response: %+v", pres) } if pres, ok := parsePMPResponse(buf[:n]); ok { if pres.OpCode == pmpOpReply|pmpOpMapPublicAddr && pres.ResultCode == pmpCodeOK { c.logf("Got PMP response; IP: %v, epoch: %v", pres.PublicAddr, pres.SecondsSinceEpoch) res.PMP = true c.mu.Lock() c.pmpPubIP = pres.PublicAddr c.pmpPubIPTime = time.Now() c.pmpLastEpoch = pres.SecondsSinceEpoch c.mu.Unlock() continue } c.logf("unexpected PMP probe response: %+v", pres) } } } } var pmpReqExternalAddrPacket = []byte{pmpVersion, pmpOpMapPublicAddr} // 0, 0 const ( upnpDefaultPort = 1900 // for UDP discovery only; TCP port discovered later ) // uPnPPacket is the UPnP UDP discovery packet's request body. var uPnPPacket = []byte("M-SEARCH * HTTP/1.1\r\n" + "HOST: 239.255.255.250:1900\r\n" + "ST: ssdp:all\r\n" + "MAN: \"ssdp:discover\"\r\n" + "MX: 2\r\n\r\n")