[client] Check for fwmark support and use fallback routing if not supported

client/iface/configurer/usp.go

@@ -362,7 +362,7 @@ func toWgUserspaceString(wgCfg wgtypes.Config) string {
 }
 
 func getFwmark() int {
-	if runtime.GOOS == "linux" && !nbnet.CustomRoutingDisabled() {
+	if nbnet.AdvancedRouting() {
 		return nbnet.NetbirdFwmark
 	}
 	return 0

client/internal/connect.go

@@ -31,6 +31,7 @@ import (
 	relayClient "github.com/netbirdio/netbird/relay/client"
 	signal "github.com/netbirdio/netbird/signal/client"
 	"github.com/netbirdio/netbird/util"
+	nbnet "github.com/netbirdio/netbird/util/net"
 	"github.com/netbirdio/netbird/version"
 )
 
@@ -114,6 +115,8 @@ func (c *ConnectClient) run(mobileDependency MobileDependency, probes *ProbeHold
 
 	log.Infof("starting NetBird client version %s on %s/%s", version.NetbirdVersion(), runtime.GOOS, runtime.GOARCH)
 
+	nbnet.Init()
+
 	backOff := &backoff.ExponentialBackOff{
 		InitialInterval:     time.Second,
 		RandomizationFactor: 1,

client/internal/routemanager/systemops/systemops_linux.go

@@ -53,20 +53,6 @@ type ruleParams struct {
 	description    string
 }
 
-// isLegacy determines whether to use the legacy routing setup
-func isLegacy() bool {
-	return os.Getenv("NB_USE_LEGACY_ROUTING") == "true" || nbnet.CustomRoutingDisabled() || nbnet.SkipSocketMark()
-}
-
-// setIsLegacy sets the legacy routing setup
-func setIsLegacy(b bool) {
-	if b {
-		os.Setenv("NB_USE_LEGACY_ROUTING", "true")
-	} else {
-		os.Unsetenv("NB_USE_LEGACY_ROUTING")
-	}
-}
-
 func getSetupRules() []ruleParams {
 	return []ruleParams{
 		{100, -1, syscall.RT_TABLE_MAIN, netlink.FAMILY_V4, false, 0, "rule with suppress prefixlen v4"},
@@ -87,7 +73,7 @@ func getSetupRules() []ruleParams {
 // This table is where a default route or other specific routes received from the management server are configured,
 // enabling VPN connectivity.
 func (r *SysOps) SetupRouting(initAddresses []net.IP, stateManager *statemanager.Manager) (_ nbnet.AddHookFunc, _ nbnet.RemoveHookFunc, err error) {
-	if isLegacy() {
+	if !nbnet.AdvancedRouting() {
 		log.Infof("Using legacy routing setup")
 		return r.setupRefCounter(initAddresses, stateManager)
 	}
@@ -103,11 +89,6 @@ func (r *SysOps) SetupRouting(initAddresses []net.IP, stateManager *statemanager
 	rules := getSetupRules()
 	for _, rule := range rules {
 		if err := addRule(rule); err != nil {
-			if errors.Is(err, syscall.EOPNOTSUPP) {
-				log.Warnf("Rule operations are not supported, falling back to the legacy routing setup")
-				setIsLegacy(true)
-				return r.setupRefCounter(initAddresses, stateManager)
-			}
 			return nil, nil, fmt.Errorf("%s: %w", rule.description, err)
 		}
 	}
@@ -130,7 +111,7 @@ func (r *SysOps) SetupRouting(initAddresses []net.IP, stateManager *statemanager
 // It systematically removes the three rules and any associated routing table entries to ensure a clean state.
 // The function uses error aggregation to report any errors encountered during the cleanup process.
 func (r *SysOps) CleanupRouting(stateManager *statemanager.Manager) error {
-	if isLegacy() {
+	if !nbnet.AdvancedRouting() {
 		return r.cleanupRefCounter(stateManager)
 	}
 
@@ -168,7 +149,7 @@ func (r *SysOps) removeFromRouteTable(prefix netip.Prefix, nexthop Nexthop) erro
 }
 
 func (r *SysOps) AddVPNRoute(prefix netip.Prefix, intf *net.Interface) error {
-	if isLegacy() {
+	if !nbnet.AdvancedRouting() {
 		return r.genericAddVPNRoute(prefix, intf)
 	}
 
@@ -191,7 +172,7 @@ func (r *SysOps) AddVPNRoute(prefix netip.Prefix, intf *net.Interface) error {
 }
 
 func (r *SysOps) RemoveVPNRoute(prefix netip.Prefix, intf *net.Interface) error {
-	if isLegacy() {
+	if !nbnet.AdvancedRouting() {
 		return r.genericRemoveVPNRoute(prefix, intf)
 	}
 
@@ -504,7 +485,7 @@ func getAddressFamily(prefix netip.Prefix) int {
 }
 
 func hasSeparateRouting() ([]netip.Prefix, error) {
-	if isLegacy() {
+	if !nbnet.AdvancedRouting() {
 		return GetRoutesFromTable()
 	}
 	return nil, ErrRoutingIsSeparate

client/internal/routemanager/systemops/systemops_unix_test.go

@@ -85,6 +85,7 @@ var testCases = []testCase{
 }
 
 func TestRouting(t *testing.T) {
+	nbnet.Init()
 	for _, tc := range testCases {
 		// todo resolve test execution on freebsd
 		if runtime.GOOS == "freebsd" {

util/grpc/dialer.go

@@ -4,13 +4,14 @@ import (
 	"context"
 	"crypto/tls"
 	"fmt"
-	"google.golang.org/grpc/codes"
-	"google.golang.org/grpc/status"
 	"net"
 	"os/user"
 	"runtime"
 	"time"
 
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
 	"github.com/cenkalti/backoff/v4"
 	log "github.com/sirupsen/logrus"
 	"google.golang.org/grpc"
@@ -37,7 +38,6 @@ func WithCustomDialer() grpc.DialOption {
 			}
 		}
 
-		log.Debug("Using nbnet.NewDialer()")
 		conn, err := nbnet.NewDialer().DialContext(ctx, "tcp", addr)
 		if err != nil {
 			log.Errorf("Failed to dial: %s", err)

util/net/env.go

@@ -2,6 +2,7 @@ package net
 
 import (
 	"os"
+	"strconv"
 
 	log "github.com/sirupsen/logrus"
 
@@ -10,20 +11,24 @@ import (
 
 const (
 	envDisableCustomRouting = "NB_DISABLE_CUSTOM_ROUTING"
-	envSkipSocketMark       = "NB_SKIP_SOCKET_MARK"
 )
 
+// CustomRoutingDisabled returns true if custom routing is disabled.
+// This will fall back to the operation mode before the exit node functionality was implemented.
+// In particular exclusion routes won't be set up and all dialers and listeners will use net.Dial and net.Listen, respectively.
 func CustomRoutingDisabled() bool {
 	if netstack.IsEnabled() {
 		return true
 	}
-	return os.Getenv(envDisableCustomRouting) == "true"
-}
 
-func SkipSocketMark() bool {
-	if skipSocketMark := os.Getenv(envSkipSocketMark); skipSocketMark == "true" {
-		log.Infof("%s is set to true, skipping SO_MARK", envSkipSocketMark)
-		return true
+	var customRoutingDisabled bool
+	if val := os.Getenv(envDisableCustomRouting); val != "" {
+		var err error
+		customRoutingDisabled, err = strconv.ParseBool(val)
+		if err != nil {
+			log.Warnf("failed to parse %s: %v", envDisableCustomRouting, err)
+		}
 	}
-	return false
+
+	return customRoutingDisabled
 }

util/net/env_generic.go

@@ -0,0 +1,12 @@
+//go:build !linux || android
+
+package net
+
+func Init() {
+	// nothing to do on non-linux
+}
+
+func AdvancedRouting() bool {
+	// non-linux currently doesn't support advanced routing
+	return false
+}

util/net/env_linux.go

@@ -0,0 +1,108 @@
+//go:build linux && !android
+
+package net
+
+import (
+	"errors"
+	"os"
+	"strconv"
+	"syscall"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/vishvananda/netlink"
+
+	"github.com/netbirdio/netbird/client/iface/netstack"
+)
+
+const (
+	// these have the same effect, skip socket env supported for backward compatibility
+	envSkipSocketMark   = "NB_SKIP_SOCKET_MARK"
+	envUseLegacyRouting = "NB_USE_LEGACY_ROUTING"
+)
+
+var advancedRoutingSupported bool
+
+func Init() {
+	advancedRoutingSupported = checkAdvancedRoutingSupport()
+}
+
+func AdvancedRouting() bool {
+	return advancedRoutingSupported
+}
+
+func checkAdvancedRoutingSupport() bool {
+	var err error
+
+	var legacyRouting bool
+	if val := os.Getenv("NB_USE_LEGACY_ROUTING"); val != "" {
+		legacyRouting, err = strconv.ParseBool(val)
+		if err != nil {
+			log.Warnf("failed to parse %s: %v", envUseLegacyRouting, err)
+		}
+	}
+
+	var skipSocketMark bool
+	if val := os.Getenv(envSkipSocketMark); val != "" {
+		skipSocketMark, err = strconv.ParseBool(val)
+		if err != nil {
+			log.Warnf("failed to parse %s: %v", envSkipSocketMark, err)
+		}
+	}
+
+	// requested to disable advanced routing
+	if legacyRouting || skipSocketMark ||
+		// envCustomRoutingDisabled disables the custom dialers.
+		// There is no point in using advanced routing without those, as they set up fwmarks on the sockets.
+		CustomRoutingDisabled() ||
+		// netstack mode doesn't need routing at all
+		netstack.IsEnabled() {
+
+		log.Info("advanced routing has been requested to be disabled")
+		return false
+	}
+
+	if !CheckFwmarkSupport() || !CheckRuleOperationsSupport() {
+		log.Warn("system doesn't support required routing features, falling back to legacy routing")
+		return false
+	}
+
+	return true
+}
+
+func CheckFwmarkSupport() bool {
+	fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, 0)
+	if err != nil {
+		log.Warnf("failed to create test socket: %v", err)
+		return false
+	}
+	defer syscall.Close(fd)
+
+	err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_MARK, 1)
+	if err != nil {
+		log.Warnf("fwmark is not supported: %v", err)
+		return false
+	}
+	return true
+}
+
+func CheckRuleOperationsSupport() bool {
+	rule := netlink.NewRule()
+	// low precedence, semi-random
+	rule.Priority = 32321
+	rule.Table = syscall.RT_TABLE_MAIN
+	rule.Family = netlink.FAMILY_V4
+
+	if err := netlink.RuleAdd(rule); err != nil {
+		if errors.Is(err, syscall.EOPNOTSUPP) {
+			log.Warn("IP rule operations are not supported")
+			return false
+		}
+		log.Warnf("failed to test rule support: %v", err)
+		return false
+	}
+
+	if err := netlink.RuleDel(rule); err != nil {
+		log.Warnf("failed to delete test rule: %v", err)
+	}
+	return true
+}

util/net/net_linux.go

@@ -5,13 +5,11 @@ package net
 import (
 	"fmt"
 	"syscall"
-
-	log "github.com/sirupsen/logrus"
 )
 
 // SetSocketMark sets the SO_MARK option on the given socket connection
 func SetSocketMark(conn syscall.Conn) error {
-	if isSocketMarkDisabled() {
+	if !AdvancedRouting() {
 		return nil
 	}
 
@@ -25,7 +23,7 @@ func SetSocketMark(conn syscall.Conn) error {
 
 // SetSocketOpt sets the SO_MARK option on the given file descriptor
 func SetSocketOpt(fd int) error {
-	if isSocketMarkDisabled() {
+	if !AdvancedRouting() {
 		return nil
 	}
 
@@ -36,7 +34,7 @@ func setRawSocketMark(conn syscall.RawConn) error {
 	var setErr error
 
 	err := conn.Control(func(fd uintptr) {
-		if isSocketMarkDisabled() {
+		if !AdvancedRouting() {
 			return
 		}
 		setErr = setSocketOptInt(int(fd))
@@ -55,15 +53,3 @@ func setRawSocketMark(conn syscall.RawConn) error {
 func setSocketOptInt(fd int) error {
 	return syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_MARK, NetbirdFwmark)
 }
-
-func isSocketMarkDisabled() bool {
-	if CustomRoutingDisabled() {
-		log.Infof("Custom routing is disabled, skipping SO_MARK")
-		return true
-	}
-
-	if SkipSocketMark() {
-		return true
-	}
-	return false
-}