tailcfg, ipn/ipnlocal, wgengine/magicsock: add only-tcp-443 node attr

Updates tailscale/corp#17879

Change-Id: I0dc305d147b76c409cf729b599a94fa723aef0e0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -1230,6 +1230,7 @@ func (b *LocalBackend) SetControlClientStatus(c controlclient.Client, st control
 
 		b.e.SetNetworkMap(st.NetMap)
 		b.MagicConn().SetDERPMap(st.NetMap.DERPMap)
+		b.MagicConn().SetOnlyTCP443(st.NetMap.HasCap(tailcfg.NodeAttrOnlyTCP443))
 
 		// Update our cached DERP map
 		dnsfallback.UpdateCache(st.NetMap.DERPMap, b.logf)

net/portmapper/portmapper.go

@@ -49,6 +49,17 @@ type DebugKnobs struct {
 	DisableUPnP bool
 	DisablePMP  bool
 	DisablePCP  bool
+
+	// DisableAll, if non-nil, is a func that reports whether all port
+	// mapping attempts should be disabled.
+	DisableAll func() bool
+}
+
+func (k *DebugKnobs) disableAll() bool {
+	if k.DisableAll != nil {
+		return k.DisableAll()
+	}
+	return false
 }
 
 // References:
@@ -403,6 +414,7 @@ func IsNoMappingError(err error) bool {
 	ErrNoPortMappingServices = errors.New("no port mapping services were found")
 	ErrGatewayRange          = errors.New("skipping portmap; gateway range likely lacks support")
 	ErrGatewayIPv6           = errors.New("skipping portmap; no IPv6 support for portmapping")
+	ErrPortMappingDisabled   = errors.New("port mapping is disabled")
 )
 
 // GetCachedMappingOrStartCreatingOne quickly returns with our current cached portmapping, if any.
@@ -464,6 +476,9 @@ func (c *Client) createMapping() {
 // If no mapping is available, the error will be of type
 // NoMappingError; see IsNoMappingError.
 func (c *Client) createOrGetMapping(ctx context.Context) (external netip.AddrPort, err error) {
+	if c.debug.disableAll() {
+		return netip.AddrPort{}, NoMappingError{ErrPortMappingDisabled}
+	}
 	if c.debug.DisableUPnP && c.debug.DisablePCP && c.debug.DisablePMP {
 		return netip.AddrPort{}, NoMappingError{ErrNoPortMappingServices}
 	}
@@ -777,6 +792,9 @@ type ProbeResult struct {
 // 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) {
+	if c.debug.disableAll() {
+		return res, ErrPortMappingDisabled
+	}
 	gw, myIP, ok := c.gatewayAndSelfIP()
 	if !ok {
 		return res, ErrGatewayRange

tailcfg/tailcfg.go

@@ -2133,6 +2133,13 @@ type Oauth2Token struct {
 	// e.g. https://tailscale.com/cap/funnel-ports?ports=80,443,8080-8090
 	CapabilityFunnelPorts NodeCapability = "https://tailscale.com/cap/funnel-ports"
 
+	// NodeAttrOnlyTCP443 specifies that the client should not attempt to generate
+	// any outbound traffic that isn't TCP on port 443 (HTTPS). This is used for
+	// clients in restricted environments where only HTTPS traffic is allowed
+	// other types of traffic trips outbound firewall alarms. This thus implies
+	// all traffic is over DERP.
+	NodeAttrOnlyTCP443 NodeCapability = "only-tcp-443"
+
 	// NodeAttrFunnel grants the ability for a node to host ingress traffic.
 	NodeAttrFunnel NodeCapability = "funnel"
 	// NodeAttrSSHAggregator grants the ability for a node to collect SSH sessions.

wgengine/magicsock/derp.go

@@ -729,6 +729,13 @@ func (c *Conn) processDERPReadResult(dm derpReadResult, b []byte) (n int, ep *en
 	return n, ep
 }
 
+// SetOnlyTCP443 set whether the magicsock connection is restricted
+// to only using TCP port 443 outbound. If true, no UDP is allowed,
+// no STUN checks are performend, etc.
+func (c *Conn) SetOnlyTCP443(v bool) {
+	c.onlyTCP443.Store(v)
+}
+
 // SetDERPMap controls which (if any) DERP servers are used.
 // A nil value means to disable DERP; it's disabled by default.
 func (c *Conn) SetDERPMap(dm *tailcfg.DERPMap) {

wgengine/magicsock/magicsock.go

@@ -198,6 +198,8 @@ type Conn struct {
 	mu     sync.Mutex
 	muCond *sync.Cond
 
+	onlyTCP443 atomic.Bool
+
 	closed  bool        // Close was called
 	closing atomic.Bool // Close is in progress (or done)
 
@@ -444,7 +446,10 @@ func NewConn(opts Options) (*Conn, error) {
 	c.idleFunc = opts.IdleFunc
 	c.testOnlyPacketListener = opts.TestOnlyPacketListener
 	c.noteRecvActivity = opts.NoteRecvActivity
-	c.portMapper = portmapper.NewClient(logger.WithPrefix(c.logf, "portmapper: "), opts.NetMon, nil, opts.ControlKnobs, c.onPortMapChanged)
+	portMapOpts := &portmapper.DebugKnobs{
+		DisableAll: func() bool { return c.onlyTCP443.Load() },
+	}
+	c.portMapper = portmapper.NewClient(logger.WithPrefix(c.logf, "portmapper: "), opts.NetMon, portMapOpts, opts.ControlKnobs, c.onPortMapChanged)
 	if opts.NetMon != nil {
 		c.portMapper.SetGatewayLookupFunc(opts.NetMon.GatewayAndSelfIP)
 	}
@@ -1067,6 +1072,9 @@ func (c *Conn) sendUDP(ipp netip.AddrPort, b []byte) (sent bool, err error) {
 // sendUDP sends UDP packet b to addr.
 // See sendAddr's docs on the return value meanings.
 func (c *Conn) sendUDPStd(addr netip.AddrPort, b []byte) (sent bool, err error) {
+	if c.onlyTCP443.Load() {
+		return false, nil
+	}
 	switch {
 	case addr.Addr().Is4():
 		_, err = c.pconn4.WriteToUDPAddrPort(b, addr)