Add support for multicast (#243)

core/nic.go

@@ -2,8 +2,11 @@ package core
 
 import (
  "fmt"
+ "net"
 
  "gvisor.dev/gvisor/pkg/tcpip"
+ "gvisor.dev/gvisor/pkg/tcpip/network/ipv4"
+ "gvisor.dev/gvisor/pkg/tcpip/network/ipv6"
  "gvisor.dev/gvisor/pkg/tcpip/stack"
 
  "github.com/xjasonlyu/tun2socks/v2/core/option"
@@ -56,3 +59,61 @@ func withSpoofing(nicID tcpip.NICID, v bool) option.Option {
  return nil
  }
 }
+
+// withMulticastGroups adds a NIC to the given multicast groups.
+func withMulticastGroups(nicID tcpip.NICID, multicastGroups []net.IP) option.Option {
+ return func(s *stack.Stack) error {
+ if multicastGroups == nil {
+ return nil
+ }
+ // The default NIC of tun2 is working on Spoofing mode. When the UDP Endpoint
+ // tries to use a non-local address to connect, the network stack will
+ // generate a temporary addressState to build the route, which can be primary
+ // but is ephemeral. Nevertheless, when the UDP Endpoint tries to use a
+ // multicast address to connect, the network stack will select an available
+ // primary addressState to build the route. However, when tun2socks is in the
+ // just-initialized or idle state, there will be no available primary addressState,
+ // and the connect operation will fail. Therefore, we need to add permanent addresses,
+ // e.g. 10.0.0.1/8 and fd00:1/8, to the default NIC, which are only used to build
+ // routes for multicast response and do not affect other connections.
+ //
+ // In fact, for multicast, the sender normally does not expect a response.
+ // So, the ep.net.Connect is unnecessary. If we implement a custom UDP Forwarder
+ // and ForwarderRequest in the future, we can remove these code.
+ s.AddProtocolAddress(
+ nicID,
+ tcpip.ProtocolAddress{
+ Protocol: ipv4.ProtocolNumber,
+ AddressWithPrefix: tcpip.AddressWithPrefix{
+ Address: "\x0A\x00\x00\x01",
+ PrefixLen: 8,
+ },
+ },
+ stack.AddressProperties{PEB: stack.CanBePrimaryEndpoint},
+ )
+ s.AddProtocolAddress(
+ nicID,
+ tcpip.ProtocolAddress{
+ Protocol: ipv6.ProtocolNumber,
+ AddressWithPrefix: tcpip.AddressWithPrefix{
+ Address: "\xfd\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01",
+ PrefixLen: 8,
+ },
+ },
+ stack.AddressProperties{PEB: stack.CanBePrimaryEndpoint},
+ )
+ for _, multicastGroup := range multicastGroups {
+ if tcpIpAddr := multicastGroup.To4(); tcpIpAddr != nil {
+ if err := s.JoinGroup(ipv4.ProtocolNumber, nicID, tcpip.Address(tcpIpAddr)); err != nil {
+ return fmt.Errorf("join multicast groups: %s", err)
+ }
+ } else {
+ tcpIpAddr := multicastGroup.To16()
+ if err := s.JoinGroup(ipv6.ProtocolNumber, nicID, tcpip.Address(tcpIpAddr)); err != nil {
+ return fmt.Errorf("join multicast groups: %s", err)
+ }
+ }
+ }
+ return nil
+ }
+}

core/stack.go

@@ -1,6 +1,8 @@
 package core
 
 import (
+ "net"
+
  "gvisor.dev/gvisor/pkg/tcpip"
  "gvisor.dev/gvisor/pkg/tcpip/network/ipv4"
  "gvisor.dev/gvisor/pkg/tcpip/network/ipv6"
@@ -23,6 +25,10 @@ type Config struct {
  // stack to set transport handlers.
  TransportHandler adapter.TransportHandler
 
+ // MulticastGroups is used by internal stack to add
+ // nic to given groups
+ MulticastGroups []net.IP
+
  // Options are supplement options to apply settings
  // for the internal stack.
  Options []option.Option
@@ -88,6 +94,9 @@ func CreateStack(cfg *Config) (*stack.Stack, error) {
  // Add default route table for IPv4 and IPv6. This will handle
  // all incoming ICMP packets.
  withRouteTable(nicID),
+
+ // Adds default NIC to the given multicast groups.
+ withMulticastGroups(nicID, cfg.MulticastGroups),
  )
 
  for _, opt := range opts {

engine/engine.go

@@ -214,9 +214,15 @@ func netstack(k *Key) (err error) {
  opts = append(opts, option.WithTCPReceiveBufferSize(int(size)))
  }
 
+ var multicastGroups []net.IP = nil
+ if multicastGroups, err = parseMulticastGroups(k.MulticastGroups); err != nil {
+ return err
+ }
+
  if _defaultStack, err = core.CreateStack(&core.Config{
  LinkEndpoint: _defaultDevice,
  TransportHandler: &mirror.Tunnel{},
+ MulticastGroups: multicastGroups,
  Options: opts,
  }); err != nil {
  return

engine/key.go

@@ -13,6 +13,7 @@ type Key struct {
  TCPModerateReceiveBuffer bool `yaml:"tcp-moderate-receive-buffer"`
  TCPSendBufferSize string `yaml:"tcp-send-buffer-size"`
  TCPReceiveBufferSize string `yaml:"tcp-receive-buffer-size"`
+ MulticastGroups string `yaml:"multicast-groups"`
  TUNPreUp string `yaml:"tun-pre-up"`
  TUNPostUp string `yaml:"tun-post-up"`
  UDPTimeout time.Duration `yaml:"udp-timeout"`

engine/parse.go

@@ -150,3 +150,22 @@ func parseShadowsocks(u *url.URL) (address, method, password, obfsMode, obfsHost
 
  return
 }
+
+func parseMulticastGroups(multicastGroupsString string) ([]net.IP, error) {
+ if multicastGroupsString == "" {
+ return nil, nil
+ }
+ ipStrings := strings.Split(multicastGroupsString, ",")
+ multicastGroups := []net.IP{}
+ for _, ipString := range ipStrings {
+ ip := net.ParseIP(ipString)
+ if ip == nil {
+ return nil, fmt.Errorf("unsupported ip format: %s", ipString)
+ }
+ if !ip.IsMulticast() {
+ return nil, fmt.Errorf("invalid multicast address: %s", ipString)
+ }
+ multicastGroups = append(multicastGroups, ip)
+ }
+ return multicastGroups, nil
+}

main.go

@@ -36,6 +36,7 @@ func init() {
  flag.StringVar(&key.TCPSendBufferSize, "tcp-sndbuf", "", "Set TCP send buffer size for netstack")
  flag.StringVar(&key.TCPReceiveBufferSize, "tcp-rcvbuf", "", "Set TCP receive buffer size for netstack")
  flag.BoolVar(&key.TCPModerateReceiveBuffer, "tcp-auto-tuning", false, "Enable TCP receive buffer auto-tuning")
+ flag.StringVar(&key.MulticastGroups, "multicast-groups", "", "Join these multicast groups ip1,ip2,...")
  flag.StringVar(&key.TUNPreUp, "tun-pre-up", "", "Execute a command before TUN device setup")
  flag.StringVar(&key.TUNPostUp, "tun-post-up", "", "Execute a command after TUN device setup")
  flag.BoolVar(&versionFlag, "version", false, "Show version and then quit")