Revert "[client] Drop signaling-side ICE candidate filter, drop overlay STUN at mux read-side instead (#6142)"

This reverts commit b57f714350.

Restores the signaling-side ICE candidate filter and the engine/worker_ice
STUN gating that #6142 removed, re-adding the mux read-side changes in
udpmux/universal.go to their pre-#6142 form.

client/iface/bind/ice_bind.go

@@ -41,6 +41,7 @@ type ICEBind struct {
 	*wgConn.StdNetBind
 
 	transportNet transport.Net
+	filterFn     udpmux.FilterFn
 	address      wgaddr.Address
 	mtu          uint16
 
@@ -60,11 +61,12 @@ type ICEBind struct {
 	ipv6Conn *net.UDPConn
 }
 
-func NewICEBind(transportNet transport.Net, address wgaddr.Address, mtu uint16) *ICEBind {
+func NewICEBind(transportNet transport.Net, filterFn udpmux.FilterFn, address wgaddr.Address, mtu uint16) *ICEBind {
 	b, _ := wgConn.NewStdNetBind().(*wgConn.StdNetBind)
 	ib := &ICEBind{
 		StdNetBind:       b,
 		transportNet:     transportNet,
+		filterFn:         filterFn,
 		address:          address,
 		mtu:              mtu,
 		endpoints:        make(map[netip.Addr]net.Conn),
@@ -263,6 +265,7 @@ func (s *ICEBind) createOrUpdateMux() {
 		udpmux.UniversalUDPMuxParams{
 			UDPConn:   muxConn,
 			Net:       s.transportNet,
+			FilterFn:  s.filterFn,
 			WGAddress: s.address,
 			MTU:       s.mtu,
 		},

client/iface/bind/ice_bind_test.go

@@ -289,7 +289,7 @@ func setupICEBind(t *testing.T) *ICEBind {
 		IP:      netip.MustParseAddr("100.64.0.1"),
 		Network: netip.MustParsePrefix("100.64.0.0/10"),
 	}
-	return NewICEBind(transportNet, address, 1280)
+	return NewICEBind(transportNet, nil, address, 1280)
 }
 
 func createDualStackConns(t *testing.T) (*net.UDPConn, *net.UDPConn) {

client/iface/device/device_kernel_unix.go

@@ -32,6 +32,8 @@ type TunKernelDevice struct {
 	link       *wgLink
 	udpMuxConn net.PacketConn
 	udpMux     *udpmux.UniversalUDPMuxDefault
+
+	filterFn udpmux.FilterFn
 }
 
 func NewKernelDevice(name string, address wgaddr.Address, wgPort int, key string, mtu uint16, transportNet transport.Net) *TunKernelDevice {
@@ -102,6 +104,7 @@ func (t *TunKernelDevice) Up() (*udpmux.UniversalUDPMuxDefault, error) {
 	bindParams := udpmux.UniversalUDPMuxParams{
 		UDPConn:   nbnet.WrapPacketConn(rawSock),
 		Net:       t.transportNet,
+		FilterFn:  t.filterFn,
 		WGAddress: t.address,
 		MTU:       t.mtu,
 	}

client/iface/iface.go

@@ -63,6 +63,7 @@ type WGIFaceOpts struct {
 	MTU          uint16
 	MobileArgs   *device.MobileIFaceArguments
 	TransportNet transport.Net
+	FilterFn     udpmux.FilterFn
 	DisableDNS   bool
 }
 

client/iface/iface_new.go

@@ -11,7 +11,7 @@ import (
 
 // NewWGIFace Creates a new WireGuard interface instance
 func NewWGIFace(opts WGIFaceOpts) (*WGIface, error) {
-	iceBind := bind.NewICEBind(opts.TransportNet, opts.Address, opts.MTU)
+	iceBind := bind.NewICEBind(opts.TransportNet, opts.FilterFn, opts.Address, opts.MTU)
 
 	var tun WGTunDevice
 	if netstack.IsEnabled() {

client/iface/iface_new_android.go

@@ -9,7 +9,7 @@ import (
 
 // NewWGIFace Creates a new WireGuard interface instance
 func NewWGIFace(opts WGIFaceOpts) (*WGIface, error) {
-	iceBind := bind.NewICEBind(opts.TransportNet, opts.Address, opts.MTU)
+	iceBind := bind.NewICEBind(opts.TransportNet, opts.FilterFn, opts.Address, opts.MTU)
 
 	if netstack.IsEnabled() {
 		wgIFace := &WGIface{

client/iface/iface_new_ios.go

@@ -10,7 +10,7 @@ import (
 
 // NewWGIFace Creates a new WireGuard interface instance
 func NewWGIFace(opts WGIFaceOpts) (*WGIface, error) {
-	iceBind := bind.NewICEBind(opts.TransportNet, opts.Address, opts.MTU)
+	iceBind := bind.NewICEBind(opts.TransportNet, opts.FilterFn, opts.Address, opts.MTU)
 
 	wgIFace := &WGIface{
 		tun:            device.NewTunDevice(opts.IFaceName, opts.Address, opts.WGPort, opts.WGPrivKey, opts.MTU, iceBind, opts.MobileArgs.TunFd),

client/iface/iface_new_linux.go

@@ -14,7 +14,7 @@ import (
 // NewWGIFace Creates a new WireGuard interface instance
 func NewWGIFace(opts WGIFaceOpts) (*WGIface, error) {
 	if netstack.IsEnabled() {
-		iceBind := bind.NewICEBind(opts.TransportNet, opts.Address, opts.MTU)
+		iceBind := bind.NewICEBind(opts.TransportNet, opts.FilterFn, opts.Address, opts.MTU)
 		return &WGIface{
 			tun:            device.NewNetstackDevice(opts.IFaceName, opts.Address, opts.WGPort, opts.WGPrivKey, opts.MTU, iceBind, netstack.ListenAddr()),
 			userspaceBind:  true,
@@ -30,7 +30,7 @@ func NewWGIFace(opts WGIFaceOpts) (*WGIface, error) {
 	}
 
 	if device.ModuleTunIsLoaded() {
-		iceBind := bind.NewICEBind(opts.TransportNet, opts.Address, opts.MTU)
+		iceBind := bind.NewICEBind(opts.TransportNet, opts.FilterFn, opts.Address, opts.MTU)
 		return &WGIface{
 			tun:            device.NewTunDevice(opts.IFaceName, opts.Address, opts.WGPort, opts.WGPrivKey, opts.MTU, iceBind),
 			userspaceBind:  true,

client/iface/udpmux/universal.go

@@ -8,6 +8,8 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"net/netip"
+	"sync"
 	"time"
 
 	log "github.com/sirupsen/logrus"
@@ -20,6 +22,10 @@ import (
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
+// FilterFn is a function that filters out candidates based on the address.
+// If it returns true, the address is to be filtered. It also returns the prefix of matching route.
+type FilterFn func(address netip.Addr) (bool, netip.Prefix, error)
+
 // UniversalUDPMuxDefault handles STUN and TURN servers packets by wrapping the original UDPConn
 // It then passes packets to the UDPMux that does the actual connection muxing.
 type UniversalUDPMuxDefault struct {
@@ -37,6 +43,7 @@ type UniversalUDPMuxParams struct {
 	UDPConn               net.PacketConn
 	XORMappedAddrCacheTTL time.Duration
 	Net                   transport.Net
+	FilterFn              FilterFn
 	WGAddress             wgaddr.Address
 	MTU                   uint16
 }
@@ -61,6 +68,7 @@ func NewUniversalUDPMuxDefault(params UniversalUDPMuxParams) *UniversalUDPMuxDef
 		PacketConn: params.UDPConn,
 		mux:        m,
 		logger:     params.Logger,
+		filterFn:   params.FilterFn,
 		address:    params.WGAddress,
 	}
 
@@ -107,12 +115,15 @@ func (m *UniversalUDPMuxDefault) ReadFromConn(ctx context.Context) {
 	}
 }
 
-// UDPConn is a wrapper around UDPMux conn that overrides WriteTo to drop packets destined for the overlay subnet.
+// UDPConn is a wrapper around UDPMux conn that overrides ReadFrom and handles STUN/TURN packets
 type UDPConn struct {
 	net.PacketConn
-	mux     *UniversalUDPMuxDefault
+	mux      *UniversalUDPMuxDefault
-	logger  logging.LeveledLogger
+	logger   logging.LeveledLogger
-	address wgaddr.Address
+	filterFn FilterFn
+	// TODO: reset cache on route changes
+	addrCache sync.Map
+	address   wgaddr.Address
 }
 
 // GetPacketConn returns the underlying PacketConn
@@ -121,18 +132,67 @@ func (u *UDPConn) GetPacketConn() net.PacketConn {
 }
 
 func (u *UDPConn) WriteTo(b []byte, addr net.Addr) (int, error) {
-	udpAddr, ok := addr.(*net.UDPAddr)
+	if u.filterFn == nil {
-	if !ok {
 		return u.PacketConn.WriteTo(b, addr)
 	}
-	dst := udpAddr.AddrPort().Addr().Unmap()
+
-	if (u.address.Network.IsValid() && u.address.Network.Contains(dst)) || (u.address.IPv6Net.IsValid() && u.address.IPv6Net.Contains(dst)) {
+	if isRouted, found := u.addrCache.Load(addr.String()); found {
-		log.Warnf("address %s is part of the NetBird network %s, refusing to write", addr, u.address)
+		return u.handleCachedAddress(isRouted.(bool), b, addr)
-		return 0, fmt.Errorf("address %s is part of the NetBird network %s, refusing to write", addr, u.address)
+	}
+
+	return u.handleUncachedAddress(b, addr)
+}
+
+func (u *UDPConn) handleCachedAddress(isRouted bool, b []byte, addr net.Addr) (int, error) {
+	if isRouted {
+		return 0, fmt.Errorf("address %s is part of a routed network, refusing to write", addr)
 	}
 	return u.PacketConn.WriteTo(b, addr)
 }
 
+func (u *UDPConn) handleUncachedAddress(b []byte, addr net.Addr) (int, error) {
+	if err := u.performFilterCheck(addr); err != nil {
+		return 0, err
+	}
+	return u.PacketConn.WriteTo(b, addr)
+}
+
+func (u *UDPConn) performFilterCheck(addr net.Addr) error {
+	host, err := getHostFromAddr(addr)
+	if err != nil {
+		log.Errorf("Failed to get host from address %s: %v", addr, err)
+		return nil
+	}
+
+	a, err := netip.ParseAddr(host)
+	if err != nil {
+		log.Errorf("Failed to parse address %s: %v", addr, err)
+		return nil
+	}
+
+	if u.address.Network.Contains(a) {
+		log.Warnf("address %s is part of the NetBird network %s, refusing to write", addr, u.address)
+		return fmt.Errorf("address %s is part of the NetBird network %s, refusing to write", addr, u.address)
+	}
+
+	if isRouted, prefix, err := u.filterFn(a); err != nil {
+		log.Errorf("Failed to check if address %s is routed: %v", addr, err)
+	} else {
+		u.addrCache.Store(addr.String(), isRouted)
+		if isRouted {
+			// Extra log, as the error only shows up with ICE logging enabled
+			log.Infof("address %s is part of routed network %s, refusing to write", addr, prefix)
+			return fmt.Errorf("address %s is part of routed network %s, refusing to write", addr, prefix)
+		}
+	}
+	return nil
+}
+
+func getHostFromAddr(addr net.Addr) (string, error) {
+	host, _, err := net.SplitHostPort(addr.String())
+	return host, err
+}
+
 // GetSharedConn returns the shared udp conn
 func (m *UniversalUDPMuxDefault) GetSharedConn() net.PacketConn {
 	return m.params.UDPConn
@@ -165,13 +225,6 @@ func (m *UniversalUDPMuxDefault) HandleSTUNMessage(msg *stun.Message, addr net.A
 		return nil
 	}
 
-	src := udpAddr.AddrPort().Addr().Unmap()
-	wg := m.params.WGAddress
-	if (wg.Network.IsValid() && wg.Network.Contains(src)) || (wg.IPv6Net.IsValid() && wg.IPv6Net.Contains(src)) {
-		log.Debugf("dropping STUN message from overlay source %s", udpAddr)
-		return nil
-	}
-
 	if m.isXORMappedResponse(msg, udpAddr.String()) {
 		err := m.handleXORMappedResponse(udpAddr, msg)
 		if err != nil {

client/iface/wgproxy/proxy_linux_test.go

@@ -66,7 +66,7 @@ func seedProxyForProxyCloseByRemoteConn() ([]proxyInstance, error) {
 	if err != nil {
 		return nil, err
 	}
-	iceBind := bind.NewICEBind(nil, wgAddress, 1280)
+	iceBind := bind.NewICEBind(nil, nil, wgAddress, 1280)
 	endpointAddress := &net.UDPAddr{
 		IP:   net.IPv4(10, 0, 0, 1),
 		Port: 1234,

client/iface/wgproxy/proxy_seed_test.go

@@ -22,7 +22,7 @@ func seedProxyForProxyCloseByRemoteConn() ([]proxyInstance, error) {
 	if err != nil {
 		return nil, err
 	}
-	iceBind := bind.NewICEBind(nil, wgAddress, 1280)
+	iceBind := bind.NewICEBind(nil, nil, wgAddress, 1280)
 	endpointAddress := &net.UDPAddr{
 		IP:   net.IPv4(10, 0, 0, 1),
 		Port: 1234,

client/internal/engine.go

@@ -54,6 +54,7 @@ import (
 	"github.com/netbirdio/netbird/client/internal/relay"
 	"github.com/netbirdio/netbird/client/internal/rosenpass"
 	"github.com/netbirdio/netbird/client/internal/routemanager"
+	"github.com/netbirdio/netbird/client/internal/routemanager/systemops"
 	"github.com/netbirdio/netbird/client/internal/statemanager"
 	"github.com/netbirdio/netbird/client/internal/syncstore"
 	"github.com/netbirdio/netbird/client/internal/updater"
@@ -1994,6 +1995,7 @@ func (e *Engine) newWgIface() (*iface.WGIface, error) {
 		WGPrivKey:    e.config.WgPrivateKey.String(),
 		MTU:          e.config.MTU,
 		TransportNet: transportNet,
+		FilterFn:     e.addrViaRoutes,
 		DisableDNS:   e.config.DisableDNS,
 	}
 
@@ -2248,6 +2250,21 @@ func (e *Engine) startNetworkMonitor() {
 	}()
 }
 
+func (e *Engine) addrViaRoutes(addr netip.Addr) (bool, netip.Prefix, error) {
+	var vpnRoutes []netip.Prefix
+	for _, routes := range e.routeManager.GetClientRoutes() {
+		if len(routes) > 0 && routes[0] != nil {
+			vpnRoutes = append(vpnRoutes, routes[0].Network)
+		}
+	}
+
+	if isVpn, prefix := systemops.IsAddrRouted(addr, vpnRoutes); isVpn {
+		return true, prefix, nil
+	}
+
+	return false, netip.Prefix{}, nil
+}
+
 func (e *Engine) stopDNSServer() {
 	if e.dnsServer == nil {
 		return

client/internal/peer/worker_ice.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"net/netip"
 	"strconv"
 	"sync"
 	"time"
@@ -164,6 +165,10 @@ func (w *WorkerICE) OnRemoteCandidate(candidate ice.Candidate, haRoutes route.HA
 		return
 	}
 
+	if candidateViaRoutes(candidate, haRoutes) {
+		return
+	}
+
 	if err := w.agent.AddRemoteCandidate(candidate); err != nil {
 		w.log.Errorf("error while handling remote candidate")
 		return
@@ -584,6 +589,34 @@ func extraSrflxCandidate(candidate ice.Candidate) (*ice.CandidateServerReflexive
 	return ec, nil
 }
 
+func candidateViaRoutes(candidate ice.Candidate, clientRoutes route.HAMap) bool {
+	addr, err := netip.ParseAddr(candidate.Address())
+	if err != nil {
+		log.Errorf("Failed to parse IP address %s: %v", candidate.Address(), err)
+		return false
+	}
+
+	var routePrefixes []netip.Prefix
+	for _, routes := range clientRoutes {
+		if len(routes) > 0 && routes[0] != nil {
+			routePrefixes = append(routePrefixes, routes[0].Network)
+		}
+	}
+
+	for _, prefix := range routePrefixes {
+		// default route is handled by route exclusion / ip rules
+		if prefix.Bits() == 0 {
+			continue
+		}
+
+		if prefix.Contains(addr) {
+			log.Debugf("Ignoring candidate [%s], its address is part of routed network %s", candidate.String(), prefix)
+			return true
+		}
+	}
+	return false
+}
+
 func isRelayCandidate(candidate ice.Candidate) bool {
 	return candidate.Type() == ice.CandidateTypeRelay
 }

client/internal/routemanager/systemops/systemops_generic.go

@@ -121,12 +121,9 @@ func (r *SysOps) addRouteToNonVPNIntf(prefix netip.Prefix, vpnIntf wgIface, init
 		return Nexthop{}, vars.ErrRouteNotAllowed
 	}
 
-	// BSDs blackhole a /32 added inside a directly-connected subnet; Linux/Windows need it to beat the wt0 route.
+	// Check if the prefix is part of any local subnets
-	switch runtime.GOOS {
+	if isLocal, subnet := r.isPrefixInLocalSubnets(prefix); isLocal {
-	case "darwin", "freebsd", "netbsd", "openbsd", "dragonfly":
+		return Nexthop{}, fmt.Errorf("prefix %s is part of local subnet %s: %w", prefix, subnet, vars.ErrRouteNotAllowed)
-		if isLocal, subnet := r.isPrefixInLocalSubnets(prefix); isLocal {
-			return Nexthop{}, fmt.Errorf("prefix %s is part of local subnet %s: %w", prefix, subnet, vars.ErrRouteNotAllowed)
-		}
 	}
 
 	// Determine the exit interface and next hop for the prefix, so we can add a specific route