Fix "Fix auto_redirect dropping SO_BINDTODEVICE traffic"

REDIRECT in the OUTPUT chain rewrites the destination to 127.0.0.1,
then ip_route_me_harder() reroutes with the socket's bound interface
constraint (flowi4_oif). Since 127.0.0.1 is only reachable via lo,
the routing lookup fails and the packet is silently dropped.

Add a fallback routing table with `local 127.0.0.1` entries for each
non-loopback interface. When the local table lookup fails due to OIF
mismatch, the fallback table provides a matching RTN_LOCAL route.
The kernel then overrides dev_out to loopback (route.c:2857), so the
packet is delivered locally to the redirect server as intended.

This fixes NetworkManager connectivity checks and other tools that
use SO_BINDTODEVICE (e.g. curl --interface).

go.mod

@@ -6,25 +6,25 @@ require (
 	github.com/florianl/go-nfqueue/v2 v2.0.2
 	github.com/go-ole/go-ole v1.3.0
 	github.com/google/btree v1.1.3
-	github.com/mdlayher/netlink v1.7.2
+	github.com/mdlayher/netlink v1.9.0
 	github.com/sagernet/fswatch v0.1.1
 	github.com/sagernet/gvisor v0.0.0-20250811.0-sing-box-mod.1
 	github.com/sagernet/netlink v0.0.0-20240612041022-b9a21c07ac6a
 	github.com/sagernet/nftables v0.3.0-beta.4
-	github.com/sagernet/sing v0.8.0-beta.2
+	github.com/sagernet/sing v0.8.0
 	github.com/stretchr/testify v1.11.1
 	go4.org/netipx v0.0.0-20231129151722-fdeea329fbba
 	golang.org/x/exp v0.0.0-20240613232115-7f521ea00fb8
-	golang.org/x/net v0.43.0
-	golang.org/x/sys v0.35.0
+	golang.org/x/net v0.50.0
+	golang.org/x/sys v0.41.0
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/fsnotify/fsnotify v1.7.0 // indirect
-	github.com/google/go-cmp v0.6.0 // indirect
+	github.com/google/go-cmp v0.7.0 // indirect
 	github.com/josharian/native v1.1.0 // indirect
-	github.com/mdlayher/socket v0.4.1 // indirect
+	github.com/mdlayher/socket v0.5.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/vishvananda/netns v0.0.4 // indirect
 	golang.org/x/sync v0.7.0 // indirect

go.sum

@@ -10,12 +10,18 @@ github.com/google/btree v1.1.3 h1:CVpQJjYgC4VbzxeGVHfvZrv1ctoYCAI8vbl07Fcxlyg=
 github.com/google/btree v1.1.3/go.mod h1:qOPhT0dTNdNzV6Z/lhRX0YXUafgPLFUh+gZMl761Gm4=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
 github.com/josharian/native v1.1.0 h1:uuaP0hAbW7Y4l0ZRQ6C9zfb7Mg1mbFKry/xzDAfmtLA=
 github.com/josharian/native v1.1.0/go.mod h1:7X/raswPFr05uY3HiLlYeyQntB6OO7E/d2Cu7qoaN2w=
 github.com/mdlayher/netlink v1.7.2 h1:/UtM3ofJap7Vl4QWCPDGXY8d3GIY2UGSDbK+QWmY8/g=
 github.com/mdlayher/netlink v1.7.2/go.mod h1:xraEF7uJbxLhc5fpHL4cPe221LI2bdttWlU+ZGLfQSw=
+github.com/mdlayher/netlink v1.9.0 h1:G8+GLq2x3v4D4MVIqDdNUhTUC7TKiCy/6MDkmItfKco=
+github.com/mdlayher/netlink v1.9.0/go.mod h1:YBnl5BXsCoRuwBjKKlZ+aYmEoq0r12FDA/3JC+94KDg=
 github.com/mdlayher/socket v0.4.1 h1:eM9y2/jlbs1M615oshPQOHZzj6R6wMT7bX5NPiQvn2U=
 github.com/mdlayher/socket v0.4.1/go.mod h1:cAqeGjoufqdxWkD7DkpyS+wcefOtmu5OQ8KuoJGIReA=
+github.com/mdlayher/socket v0.5.1 h1:VZaqt6RkGkt2OE9l3GcC6nZkqD3xKeQLyfleW/uBcos=
+github.com/mdlayher/socket v0.5.1/go.mod h1:TjPLHI1UgwEv5J1B5q0zTZq12A/6H7nKmtTanQE37IQ=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/sagernet/fswatch v0.1.1 h1:YqID+93B7VRfqIH3PArW/XpJv5H4OLEVWDfProGoRQs=
@@ -28,6 +34,8 @@ github.com/sagernet/nftables v0.3.0-beta.4 h1:kbULlAwAC3jvdGAC1P5Fa3GSxVwQJibNen
 github.com/sagernet/nftables v0.3.0-beta.4/go.mod h1:OQXAjvjNGGFxaTgVCSTRIhYB5/llyVDeapVoENYBDS8=
 github.com/sagernet/sing v0.8.0-beta.2 h1:3khO2eE5LMylD/v47+pnVMtFzl6lBY2v/b/V+79qpsE=
 github.com/sagernet/sing v0.8.0-beta.2/go.mod h1:ARkL0gM13/Iv5VCZmci/NuoOlePoIsW0m7BWfln/Hak=
+github.com/sagernet/sing v0.8.0 h1:OwLEwbcYfZHvu4olZVljxxC1XRicBqJ1HfiFr6F2WEE=
+github.com/sagernet/sing v0.8.0/go.mod h1:ARkL0gM13/Iv5VCZmci/NuoOlePoIsW0m7BWfln/Hak=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/vishvananda/netns v0.0.4 h1:Oeaw1EM2JMxD51g9uhtC0D7erkIjgmj8+JZc26m1YX8=
@@ -38,11 +46,15 @@ golang.org/x/exp v0.0.0-20240613232115-7f521ea00fb8 h1:yixxcjnhBmY0nkL253HFVIm0J
 golang.org/x/exp v0.0.0-20240613232115-7f521ea00fb8/go.mod h1:jj3sYF3dwk5D+ghuXyeI3r5MFf+NT2An6/9dOA95KSI=
 golang.org/x/net v0.43.0 h1:lat02VYK2j4aLzMzecihNvTlJNQUq316m2Mr9rnM6YE=
 golang.org/x/net v0.43.0/go.mod h1:vhO1fvI4dGsIjh73sWfUVjj3N7CA9WkKJNQm2svM6Jg=
+golang.org/x/net v0.50.0 h1:ucWh9eiCGyDR3vtzso0WMQinm2Dnt8cFMuQa9K33J60=
+golang.org/x/net v0.50.0/go.mod h1:UgoSli3F/pBgdJBHCTc+tp3gmrU4XswgGRgtnwWTfyM=
 golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
 golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.35.0 h1:vz1N37gP5bs89s7He8XuIYXpyY0+QlsKmzipCbUtyxI=
 golang.org/x/sys v0.35.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/sys v0.41.0 h1:Ivj+2Cp/ylzLiEU89QhWblYnOE9zerudt9Ftecq2C6k=
+golang.org/x/sys v0.41.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/time v0.7.0 h1:ntUhktv3OPE6TgYxXWv9vKvUSJyIFJlyohwbkEwPrKQ=
 golang.org/x/time v0.7.0/go.mod h1:3BpzKBy/shNhVucY/MWOyx10tF3SFh9QdLuxbVysPQM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=

redirect_linux.go

@@ -19,29 +19,31 @@ import (
 )
 
 type autoRedirect struct {
-	tunOptions             *Options
-	ctx                    context.Context
-	handler                Handler
-	logger                 logger.Logger
-	tableName              string
-	networkMonitor         NetworkUpdateMonitor
-	networkListener        *list.Element[NetworkUpdateCallback]
-	interfaceFinder        control.InterfaceFinder
-	localAddresses         []netip.Prefix
-	customRedirectPortFunc func() int
-	customRedirectPort     int
-	redirectServer         *redirectServer
-	enableIPv4             bool
-	enableIPv6             bool
-	iptablesPath           string
-	ip6tablesPath          string
-	useNFTables            bool
-	androidSu              bool
-	suPath                 string
-	routeAddressSet        *[]*netipx.IPSet
-	routeExcludeAddressSet *[]*netipx.IPSet
-	nfqueueHandler         *nfqueueHandler
-	nfqueueEnabled         bool
+	tunOptions              *Options
+	ctx                     context.Context
+	handler                 Handler
+	logger                  logger.Logger
+	tableName               string
+	networkMonitor          NetworkUpdateMonitor
+	networkListener         *list.Element[NetworkUpdateCallback]
+	interfaceFinder         control.InterfaceFinder
+	localAddresses          []netip.Prefix
+	customRedirectPortFunc  func() int
+	customRedirectPort      int
+	redirectServer          *redirectServer
+	enableIPv4              bool
+	enableIPv6              bool
+	iptablesPath            string
+	ip6tablesPath           string
+	useNFTables             bool
+	androidSu               bool
+	suPath                  string
+	routeAddressSet         *[]*netipx.IPSet
+	routeExcludeAddressSet  *[]*netipx.IPSet
+	nfqueueHandler          *nfqueueHandler
+	nfqueueEnabled          bool
+	redirectRouteTableIndex int
+	redirectInterfaces      []control.Interface
 }
 
 func NewAutoRedirect(options AutoRedirectOptions) (AutoRedirect, error) {
@@ -152,6 +154,12 @@ func (r *autoRedirect) Start() error {
 		}
 		r.cleanupNFTables()
 		err = r.setupNFTables()
+		if err == nil && r.tunOptions.AutoRedirectMarkMode {
+			err = r.setupRedirectRoutes()
+			if err != nil {
+				r.cleanupNFTables()
+			}
+		}
 	} else {
 		r.cleanupIPTables()
 		err = r.setupIPTables()
@@ -164,6 +172,7 @@ func (r *autoRedirect) Close() error {
 		r.nfqueueHandler.Close()
 	}
 	if r.useNFTables {
+		r.cleanupRedirectRoutes()
 		r.cleanupNFTables()
 	} else {
 		r.cleanupIPTables()

redirect_nftables.go

@@ -4,6 +4,7 @@ package tun
 
 import (
 	"net/netip"
+	"strings"
 
 	"github.com/sagernet/nftables"
 	"github.com/sagernet/nftables/binaryutil"
@@ -192,6 +193,25 @@ func (r *autoRedirect) setupNFTables() error {
 				},
 			},
 		})
+		nft.AddRule(&nftables.Rule{
+			Table: table,
+			Chain: chainPreRoutingUDP,
+			Exprs: []expr.Any{
+				&expr.Meta{
+					Key:      expr.MetaKeyIIFNAME,
+					Register: 1,
+				},
+				&expr.Cmp{
+					Op:       expr.CmpOpEq,
+					Register: 1,
+					Data:     nftablesIfname(r.tunOptions.Name),
+				},
+				&expr.Counter{},
+				&expr.Verdict{
+					Kind: expr.VerdictReturn,
+				},
+			},
+		})
 		nft.AddRule(&nftables.Rule{
 			Table: table,
 			Chain: chainPreRoutingUDP,
@@ -273,12 +293,22 @@ func (r *autoRedirect) setupNFTables() error {
 		if err != nil {
 			r.logger.Error("update local address set: ", err)
 		}
+		if r.tunOptions.AutoRedirectMarkMode {
+			err = r.updateRedirectRoutes()
+			if err != nil {
+				r.logger.Error("update redirect routes: ", err)
+			}
+		}
 	})
 	return nil
 }
 
 // TODO: test if this works
 func (r *autoRedirect) nftablesUpdateLocalAddressSet() error {
+	err := r.interfaceFinder.Update()
+	if err != nil {
+		return err
+	}
 	newLocalAddresses := common.FlatMap(r.interfaceFinder.Interfaces(), func(it control.Interface) []netip.Prefix {
 		return common.Filter(it.Addresses, func(prefix netip.Prefix) bool {
 			return it.Name == "lo" || prefix.Addr().IsGlobalUnicast()
@@ -287,6 +317,11 @@ func (r *autoRedirect) nftablesUpdateLocalAddressSet() error {
 	if slices.Equal(newLocalAddresses, r.localAddresses) {
 		return nil
 	}
+	if r.logger != nil {
+		r.logger.Debug("updating local address set to [", strings.Join(common.Map(newLocalAddresses, func(it netip.Prefix) string {
+			return it.String()
+		}), ", ")+"]")
+	}
 	nft, err := nftables.New()
 	if err != nil {
 		return err

redirect_nftables_rules.go

@@ -74,12 +74,11 @@ func (r *autoRedirect) nftablesCreateLocalAddressSets(
 		localAddresses4 := common.Filter(localAddresses, func(it netip.Prefix) bool {
 			return it.Addr().Is4()
 		})
-		updateAddresses4 := common.Filter(localAddresses, func(it netip.Prefix) bool {
-			return it.Addr().Is4()
-		})
 		var update bool
 		if len(lastAddresses) != 0 {
-			if !slices.Equal(localAddresses4, updateAddresses4) {
+			if !slices.Equal(localAddresses4, common.Filter(lastAddresses, func(it netip.Prefix) bool {
+				return it.Addr().Is4()
+			})) {
 				update = true
 			}
 		}
@@ -94,19 +93,14 @@ func (r *autoRedirect) nftablesCreateLocalAddressSets(
 		localAddresses6 := common.Filter(localAddresses, func(it netip.Prefix) bool {
 			return it.Addr().Is6()
 		})
-		updateAddresses6 := common.Filter(localAddresses, func(it netip.Prefix) bool {
-			return it.Addr().Is6()
-		})
 		var update bool
 		if len(lastAddresses) != 0 {
-			if !slices.Equal(localAddresses6, updateAddresses6) {
+			if !slices.Equal(localAddresses6, common.Filter(lastAddresses, func(it netip.Prefix) bool {
+				return it.Addr().Is6()
+			})) {
 				update = true
 			}
 		}
-		localAddresses6 = common.Filter(localAddresses6, func(it netip.Prefix) bool {
-			address := it.Addr()
-			return address.IsLoopback() || address.IsGlobalUnicast() && !address.IsPrivate()
-		})
 		if len(lastAddresses) == 0 || update {
 			_, err := nftablesCreateIPSet(nft, table, 6, "inet6_local_address_set", nftables.TableFamilyIPv6, nil, localAddresses6, false, update)
 			if err != nil {

redirect_route_linux.go

@@ -0,0 +1,179 @@
+//go:build linux
+
+package tun
+
+import (
+	"math/rand"
+	"net"
+	"net/netip"
+
+	"github.com/sagernet/netlink"
+	"github.com/sagernet/sing/common"
+	"github.com/sagernet/sing/common/control"
+
+	"golang.org/x/sys/unix"
+)
+
+const redirectRouteRulePriority = 1
+
+func (r *autoRedirect) setupRedirectRoutes() error {
+	for {
+		r.redirectRouteTableIndex = int(rand.Uint32())
+		if r.redirectRouteTableIndex == r.tunOptions.IPRoute2TableIndex {
+			continue
+		}
+		routeList, fErr := netlink.RouteListFiltered(netlink.FAMILY_ALL,
+			&netlink.Route{Table: r.redirectRouteTableIndex},
+			netlink.RT_FILTER_TABLE)
+		if len(routeList) == 0 || fErr != nil {
+			break
+		}
+	}
+	err := r.interfaceFinder.Update()
+	if err != nil {
+		return err
+	}
+	tunName := r.tunOptions.Name
+	r.redirectInterfaces = common.Filter(r.interfaceFinder.Interfaces(), func(it control.Interface) bool {
+		return it.Name != "lo" && it.Name != tunName && it.Flags&net.FlagUp != 0
+	})
+	r.cleanupRedirectRoutes()
+	for _, iface := range r.redirectInterfaces {
+		err = r.addRedirectRoutes(iface)
+		if err != nil {
+			return err
+		}
+	}
+	if r.enableIPv4 {
+		rule := netlink.NewRule()
+		rule.Priority = redirectRouteRulePriority
+		rule.Table = r.redirectRouteTableIndex
+		rule.Family = unix.AF_INET
+		err = netlink.RuleAdd(rule)
+		if err != nil {
+			return err
+		}
+	}
+	if r.enableIPv6 {
+		rule := netlink.NewRule()
+		rule.Priority = redirectRouteRulePriority
+		rule.Table = r.redirectRouteTableIndex
+		rule.Family = unix.AF_INET6
+		err = netlink.RuleAdd(rule)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (r *autoRedirect) addRedirectRoutes(iface control.Interface) error {
+	if r.enableIPv4 && common.Any(iface.Addresses, func(it netip.Prefix) bool {
+		return it.Addr().Is4()
+	}) {
+		err := netlink.RouteAppend(&netlink.Route{
+			LinkIndex: iface.Index,
+			Dst:       &net.IPNet{IP: net.IPv4(127, 0, 0, 1), Mask: net.CIDRMask(32, 32)},
+			Table:     r.redirectRouteTableIndex,
+			Type:      unix.RTN_LOCAL,
+			Scope:     netlink.SCOPE_HOST,
+		})
+		if err != nil {
+			return err
+		}
+	}
+	if r.enableIPv6 && common.Any(iface.Addresses, func(it netip.Prefix) bool {
+		return it.Addr().Is6() && !it.Addr().Is4In6()
+	}) {
+		err := netlink.RouteAppend(&netlink.Route{
+			LinkIndex: iface.Index,
+			Dst:       &net.IPNet{IP: net.IPv6loopback, Mask: net.CIDRMask(128, 128)},
+			Table:     r.redirectRouteTableIndex,
+			Type:      unix.RTN_LOCAL,
+			Scope:     netlink.SCOPE_HOST,
+		})
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (r *autoRedirect) removeRedirectRoutes(linkIndex int) {
+	if r.enableIPv4 {
+		_ = netlink.RouteDel(&netlink.Route{
+			LinkIndex: linkIndex,
+			Dst:       &net.IPNet{IP: net.IPv4(127, 0, 0, 1), Mask: net.CIDRMask(32, 32)},
+			Table:     r.redirectRouteTableIndex,
+			Type:      unix.RTN_LOCAL,
+		})
+	}
+	if r.enableIPv6 {
+		_ = netlink.RouteDel(&netlink.Route{
+			LinkIndex: linkIndex,
+			Dst:       &net.IPNet{IP: net.IPv6loopback, Mask: net.CIDRMask(128, 128)},
+			Table:     r.redirectRouteTableIndex,
+			Type:      unix.RTN_LOCAL,
+		})
+	}
+}
+
+func (r *autoRedirect) updateRedirectRoutes() error {
+	err := r.interfaceFinder.Update()
+	if err != nil {
+		return err
+	}
+	tunName := r.tunOptions.Name
+	newInterfaces := common.Filter(r.interfaceFinder.Interfaces(), func(it control.Interface) bool {
+		return it.Name != "lo" && it.Name != tunName && it.Flags&net.FlagUp != 0
+	})
+	oldMap := make(map[int]bool, len(r.redirectInterfaces))
+	for _, iface := range r.redirectInterfaces {
+		oldMap[iface.Index] = true
+	}
+	newMap := make(map[int]bool, len(newInterfaces))
+	for _, iface := range newInterfaces {
+		newMap[iface.Index] = true
+	}
+	for _, iface := range newInterfaces {
+		if !oldMap[iface.Index] {
+			err = r.addRedirectRoutes(iface)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	for _, iface := range r.redirectInterfaces {
+		if !newMap[iface.Index] {
+			r.removeRedirectRoutes(iface.Index)
+		}
+	}
+	r.redirectInterfaces = newInterfaces
+	return nil
+}
+
+func (r *autoRedirect) cleanupRedirectRoutes() {
+	if r.redirectRouteTableIndex == 0 {
+		return
+	}
+	routes, _ := netlink.RouteListFiltered(netlink.FAMILY_ALL,
+		&netlink.Route{Table: r.redirectRouteTableIndex},
+		netlink.RT_FILTER_TABLE)
+	for _, route := range routes {
+		_ = netlink.RouteDel(&route)
+	}
+	if r.enableIPv4 {
+		rule := netlink.NewRule()
+		rule.Priority = redirectRouteRulePriority
+		rule.Table = r.redirectRouteTableIndex
+		rule.Family = unix.AF_INET
+		_ = netlink.RuleDel(rule)
+	}
+	if r.enableIPv6 {
+		rule := netlink.NewRule()
+		rule.Priority = redirectRouteRulePriority
+		rule.Table = r.redirectRouteTableIndex
+		rule.Family = unix.AF_INET6
+		_ = netlink.RuleDel(rule)
+	}
+}

stack_mixed.go

@@ -3,6 +3,9 @@
 package tun
 
 import (
+	"errors"
+	"syscall"
+
 	"github.com/sagernet/gvisor/pkg/buffer"
 	"github.com/sagernet/gvisor/pkg/tcpip"
 	gHdr "github.com/sagernet/gvisor/pkg/tcpip/header"
@@ -169,7 +172,7 @@ func (m *Mixed) batchLoopDarwin(darwinTUN DarwinTUN) {
 	for {
 		buffers, err := darwinTUN.BatchRead()
 		if err != nil {
-			if E.IsClosed(err) {
+			if E.IsClosed(err) || errors.Is(err, syscall.EBADF) {
 				return
 			}
 			m.logger.Error(E.Cause(err, "batch read packet"))

stack_system.go

@@ -269,7 +269,7 @@ func (s *System) batchLoopDarwin(darwinTUN DarwinTUN) {
 	for {
 		buffers, err := darwinTUN.BatchRead()
 		if err != nil {
-			if E.IsClosed(err) {
+			if E.IsClosed(err) || errors.Is(err, syscall.EBADF) {
 				return
 			}
 			s.logger.Error(E.Cause(err, "batch read packet"))

tun.go

@@ -63,47 +63,49 @@ type DarwinTUN interface {
 }
 
 const (
-	DefaultIPRoute2TableIndex = 2022
-	DefaultIPRoute2RuleIndex  = 9000
+	DefaultIPRoute2TableIndex                    = 2022
+	DefaultIPRoute2RuleIndex                     = 9000
+	DefaultIPRoute2AutoRedirectFallbackRuleIndex = 32768
 )
 
 type Options struct {
-	Name                     string
-	Inet4Address             []netip.Prefix
-	Inet6Address             []netip.Prefix
-	MTU                      uint32
-	GSO                      bool
-	AutoRoute                bool
-	InterfaceScope           bool
-	Inet4Gateway             netip.Addr
-	Inet6Gateway             netip.Addr
-	DNSServers               []netip.Addr
-	IPRoute2TableIndex       int
-	IPRoute2RuleIndex        int
-	AutoRedirectMarkMode     bool
-	AutoRedirectInputMark    uint32
-	AutoRedirectOutputMark   uint32
-	AutoRedirectResetMark    uint32
-	AutoRedirectNFQueue      uint16
-	ExcludeMPTCP             bool
-	Inet4LoopbackAddress     []netip.Addr
-	Inet6LoopbackAddress     []netip.Addr
-	StrictRoute              bool
-	Inet4RouteAddress        []netip.Prefix
-	Inet6RouteAddress        []netip.Prefix
-	Inet4RouteExcludeAddress []netip.Prefix
-	Inet6RouteExcludeAddress []netip.Prefix
-	IncludeInterface         []string
-	ExcludeInterface         []string
-	IncludeUID               []ranges.Range[uint32]
-	ExcludeUID               []ranges.Range[uint32]
-	IncludeAndroidUser       []int
-	IncludePackage           []string
-	ExcludePackage           []string
-	InterfaceFinder          control.InterfaceFinder
-	InterfaceMonitor         DefaultInterfaceMonitor
-	FileDescriptor           int
-	Logger                   logger.Logger
+	Name                                  string
+	Inet4Address                          []netip.Prefix
+	Inet6Address                          []netip.Prefix
+	MTU                                   uint32
+	GSO                                   bool
+	AutoRoute                             bool
+	InterfaceScope                        bool
+	Inet4Gateway                          netip.Addr
+	Inet6Gateway                          netip.Addr
+	DNSServers                            []netip.Addr
+	IPRoute2TableIndex                    int
+	IPRoute2RuleIndex                     int
+	IPRoute2AutoRedirectFallbackRuleIndex int
+	AutoRedirectMarkMode                  bool
+	AutoRedirectInputMark                 uint32
+	AutoRedirectOutputMark                uint32
+	AutoRedirectResetMark                 uint32
+	AutoRedirectNFQueue                   uint16
+	ExcludeMPTCP                          bool
+	Inet4LoopbackAddress                  []netip.Addr
+	Inet6LoopbackAddress                  []netip.Addr
+	StrictRoute                           bool
+	Inet4RouteAddress                     []netip.Prefix
+	Inet6RouteAddress                     []netip.Prefix
+	Inet4RouteExcludeAddress              []netip.Prefix
+	Inet6RouteExcludeAddress              []netip.Prefix
+	IncludeInterface                      []string
+	ExcludeInterface                      []string
+	IncludeUID                            []ranges.Range[uint32]
+	ExcludeUID                            []ranges.Range[uint32]
+	IncludeAndroidUser                    []int
+	IncludePackage                        []string
+	ExcludePackage                        []string
+	InterfaceFinder                       control.InterfaceFinder
+	InterfaceMonitor                      DefaultInterfaceMonitor
+	FileDescriptor                        int
+	Logger                                logger.Logger
 
 	// No work for TCP, do not use.
 	_TXChecksumOffload bool

tun_linux.go

@@ -17,7 +17,6 @@ import (
 	"github.com/sagernet/sing-tun/internal/gtcpip/checksum"
 	"github.com/sagernet/sing-tun/internal/gtcpip/header"
 	"github.com/sagernet/sing/common"
-	"github.com/sagernet/sing/common/buf"
 	"github.com/sagernet/sing/common/control"
 	E "github.com/sagernet/sing/common/exceptions"
 	"github.com/sagernet/sing/common/rw"
@@ -40,6 +39,7 @@ type NativeTun struct {
 	writeAccess         sync.Mutex
 	vnetHdr             bool
 	writeBuffer         []byte
+	vnetHdrWriteBuf     []byte
 	gsoToWrite          []int
 	tcpGROTable         *tcpGROTable
 	udpGroAccess        sync.Mutex
@@ -149,7 +149,9 @@ func (t *NativeTun) configure(tunLink netlink.Link) error {
 	if t.options.GSO {
 		err = t.enableGSO()
 		if err != nil {
-			t.options.Logger.Warn(err)
+			if t.options.Logger != nil {
+				t.options.Logger.Warn(err)
+			}
 		}
 	}
 
@@ -276,7 +278,9 @@ func (t *NativeTun) Start() error {
 		if err != nil {
 			t.gro.disableTCPGRO()
 			t.gro.disableUDPGRO()
-			t.options.Logger.Warn(E.Cause(err, "disabled TUN TCP & UDP GRO due to GRO probe error"))
+			if t.options.Logger != nil {
+				t.options.Logger.Warn(E.Cause(err, "disabled TUN TCP & UDP GRO due to GRO probe error"))
+			}
 		}
 	}
 
@@ -325,6 +329,7 @@ func (t *NativeTun) Close() error {
 	if t.options.EXP_ExternalConfiguration {
 		return common.Close(common.PtrOrNil(t.tunFile))
 	}
+	t.unsetSearchDomainForSystemdResolved()
 	t.unsetAddresses()
 	return E.Errors(t.unsetRoute(), t.unsetRules(), common.Close(common.PtrOrNil(t.tunFile)))
 }
@@ -393,10 +398,7 @@ func handleVirtioRead(in []byte, bufs [][]byte, sizes []int, offset int) (int, e
 
 func (t *NativeTun) Write(p []byte) (n int, err error) {
 	if t.vnetHdr {
-		buffer := buf.Get(virtioNetHdrLen + len(p))
-		copy(buffer[virtioNetHdrLen:], p)
-		_, err = t.BatchWrite([][]byte{buffer}, virtioNetHdrLen)
-		buf.Put(buffer)
+		_, err = t.BatchWrite([][]byte{p}, virtioNetHdrLen)
 		if err != nil {
 			return
 		}
@@ -630,6 +632,22 @@ func (t *NativeTun) rules() []*netlink.Rule {
 			it.Family = unix.AF_INET6
 			rules = append(rules, it)
 		}
+		// Fallback rules after system default rules (32766: main, 32767: default)
+		// Only reached when main and default tables have no route
+		if p4 {
+			it = netlink.NewRule()
+			it.Priority = t.options.IPRoute2AutoRedirectFallbackRuleIndex
+			it.Table = t.options.IPRoute2TableIndex
+			it.Family = unix.AF_INET
+			rules = append(rules, it)
+		}
+		if p6 {
+			it = netlink.NewRule()
+			it.Priority = t.options.IPRoute2AutoRedirectFallbackRuleIndex
+			it.Table = t.options.IPRoute2TableIndex
+			it.Family = unix.AF_INET6
+			rules = append(rules, it)
+		}
 		return rules
 	}
 
@@ -1003,7 +1021,7 @@ func (t *NativeTun) unsetRules() error {
 		for _, rule := range ruleList {
 			ruleStart := t.options.IPRoute2RuleIndex
 			ruleEnd := ruleStart + 10
-			if rule.Priority >= ruleStart && rule.Priority <= ruleEnd {
+			if rule.Priority >= ruleStart && rule.Priority <= ruleEnd || (t.options.AutoRedirectMarkMode && rule.Priority == t.options.IPRoute2AutoRedirectFallbackRuleIndex) {
 				ruleToDel := netlink.NewRule()
 				ruleToDel.Family = rule.Family
 				ruleToDel.Priority = rule.Priority
@@ -1078,3 +1096,14 @@ func (t *NativeTun) setSearchDomainForSystemdResolved() {
 		_ = shell.Exec(ctlPath, append([]string{"dns", t.options.Name}, common.Map(dnsServer, netip.Addr.String)...)...).Run()
 	}()
 }
+
+func (t *NativeTun) unsetSearchDomainForSystemdResolved() {
+	if t.options.EXP_DisableDNSHijack {
+		return
+	}
+	ctlPath, err := exec.LookPath("resolvectl")
+	if err != nil {
+		return
+	}
+	_ = shell.Exec(ctlPath, "revert", t.options.Name).Run()
+}

tun_linux_gvisor.go

@@ -3,6 +3,8 @@
 package tun
 
 import (
+	"fmt"
+
 	"github.com/sagernet/gvisor/pkg/rawfile"
 	"github.com/sagernet/gvisor/pkg/tcpip/link/fdbased"
 	"github.com/sagernet/gvisor/pkg/tcpip/stack"
@@ -18,6 +20,37 @@ var _ GVisorTun = (*NativeTun)(nil)
 
 func (t *NativeTun) WritePacket(pkt *stack.PacketBuffer) (int, error) {
 	iovecs := t.iovecsOutputDefault
+	if t.vnetHdr {
+		if t.vnetHdrWriteBuf == nil {
+			t.vnetHdrWriteBuf = make([]byte, virtioNetHdrLen)
+		}
+		vnetHdr := virtioNetHdr{}
+		if pkt.GSOOptions.Type != stack.GSONone {
+			vnetHdr.hdrLen = uint16(pkt.HeaderSize())
+			if pkt.GSOOptions.NeedsCsum {
+				vnetHdr.flags = unix.VIRTIO_NET_HDR_F_NEEDS_CSUM
+				vnetHdr.csumStart = pkt.GSOOptions.L3HdrLen
+				vnetHdr.csumOffset = pkt.GSOOptions.CsumOffset
+			}
+			if uint16(pkt.Data().Size()) > pkt.GSOOptions.MSS {
+				switch pkt.GSOOptions.Type {
+				case stack.GSOTCPv4:
+					vnetHdr.gsoType = unix.VIRTIO_NET_HDR_GSO_TCPV4
+				case stack.GSOTCPv6:
+					vnetHdr.gsoType = unix.VIRTIO_NET_HDR_GSO_TCPV6
+				default:
+					panic(fmt.Sprintf("Unknown gso type: %v", pkt.GSOOptions.Type))
+				}
+				vnetHdr.gsoSize = pkt.GSOOptions.MSS
+			}
+		}
+		if err := vnetHdr.encode(t.vnetHdrWriteBuf); err != nil {
+			return 0, err
+		}
+		iovec := unix.Iovec{Base: &t.vnetHdrWriteBuf[0]}
+		iovec.SetLen(virtioNetHdrLen)
+		iovecs = append(iovecs, iovec)
+	}
 	var dataLen int
 	for _, packetSlice := range pkt.AsSlices() {
 		dataLen += len(packetSlice)

tun_windows.go

@@ -184,6 +184,13 @@ func (t *NativeTun) Start() error {
 		return err
 	}
 	if t.options.StrictRoute {
+		major, _, _ := windows.RtlGetNtVersionNumbers()
+		if major < 10 {
+			if t.options.Logger != nil {
+				t.options.Logger.Warn("strict routing is not supported on Windows versions below 10")
+			}
+			return nil
+		}
 		var engine uintptr
 		session := &winsys.FWPM_SESSION0{Flags: winsys.FWPM_SESSION_FLAG_DYNAMIC}
 		err := winsys.FwpmEngineOpen0(nil, winsys.RPC_C_AUTHN_DEFAULT, nil, session, unsafe.Pointer(&engine))