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listener_linux.go
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/
listener_linux.go
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package udp
import (
"bytes"
"context"
"encoding/binary"
"fmt"
"net"
"os"
"strconv"
"syscall"
"unsafe"
"github.com/go-gost/core/common/bufpool"
"golang.org/x/sys/unix"
)
func (l *redirectListener) listenUDP(addr string) (*net.UDPConn, error) {
lc := net.ListenConfig{
Control: func(network, address string, c syscall.RawConn) error {
return c.Control(func(fd uintptr) {
if err := unix.SetsockoptInt(int(fd), unix.SOL_IP, unix.IP_TRANSPARENT, 1); err != nil {
l.logger.Errorf("SetsockoptInt(SOL_IP, IP_TRANSPARENT, 1): %v", err)
}
if err := unix.SetsockoptInt(int(fd), unix.SOL_IP, unix.IP_RECVORIGDSTADDR, 1); err != nil {
l.logger.Errorf("SetsockoptInt(SOL_IP, IP_RECVORIGDSTADDR, 1): %v", err)
}
})
},
}
pc, err := lc.ListenPacket(context.Background(), "udp", addr)
if err != nil {
return nil, err
}
return pc.(*net.UDPConn), nil
}
func (l *redirectListener) accept() (conn net.Conn, err error) {
b := bufpool.Get(l.md.readBufferSize)
n, raddr, dstAddr, err := readFromUDP(l.ln, *b)
if err != nil {
l.logger.Error(err)
return
}
l.logger.Infof("%s >> %s", raddr.String(), dstAddr.String())
c, err := dialUDP("udp", dstAddr, raddr)
if err != nil {
l.logger.Error(err)
return
}
conn = &redirConn{
Conn: c,
buf: (*b)[:n],
ttl: l.md.ttl,
}
return
}
// ReadFromUDP reads a UDP packet from c, copying the payload into b.
// It returns the number of bytes copied into b and the return address
// that was on the packet.
//
// Out-of-band data is also read in so that the original destination
// address can be identified and parsed.
func readFromUDP(conn *net.UDPConn, b []byte) (n int, remoteAddr *net.UDPAddr, dstAddr *net.UDPAddr, err error) {
oob := bufpool.Get(1024)
defer bufpool.Put(oob)
n, oobn, _, remoteAddr, err := conn.ReadMsgUDP(b, *oob)
if err != nil {
return 0, nil, nil, err
}
msgs, err := unix.ParseSocketControlMessage((*oob)[:oobn])
if err != nil {
return 0, nil, nil, fmt.Errorf("parsing socket control message: %s", err)
}
for _, msg := range msgs {
if msg.Header.Level == unix.SOL_IP && msg.Header.Type == unix.IP_RECVORIGDSTADDR {
originalDstRaw := &unix.RawSockaddrInet4{}
if err = binary.Read(bytes.NewReader(msg.Data), binary.LittleEndian, originalDstRaw); err != nil {
return 0, nil, nil, fmt.Errorf("reading original destination address: %s", err)
}
switch originalDstRaw.Family {
case unix.AF_INET:
pp := (*unix.RawSockaddrInet4)(unsafe.Pointer(originalDstRaw))
p := (*[2]byte)(unsafe.Pointer(&pp.Port))
dstAddr = &net.UDPAddr{
IP: net.IPv4(pp.Addr[0], pp.Addr[1], pp.Addr[2], pp.Addr[3]),
Port: int(p[0])<<8 + int(p[1]),
}
case unix.AF_INET6:
pp := (*unix.RawSockaddrInet6)(unsafe.Pointer(originalDstRaw))
p := (*[2]byte)(unsafe.Pointer(&pp.Port))
dstAddr = &net.UDPAddr{
IP: net.IP(pp.Addr[:]),
Port: int(p[0])<<8 + int(p[1]),
Zone: strconv.Itoa(int(pp.Scope_id)),
}
default:
return 0, nil, nil, fmt.Errorf("original destination is an unsupported network family")
}
break
}
}
if dstAddr == nil {
return 0, nil, nil, fmt.Errorf("unable to obtain original destination: %s", err)
}
return
}
// DialUDP connects to the remote address raddr on the network net,
// which must be "udp", "udp4", or "udp6". If laddr is not nil, it is
// used as the local address for the connection.
func dialUDP(network string, laddr *net.UDPAddr, raddr *net.UDPAddr) (net.Conn, error) {
remoteSocketAddress, err := udpAddrToSocketAddr(raddr)
if err != nil {
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("build destination socket address: %s", err)}
}
localSocketAddress, err := udpAddrToSocketAddr(laddr)
if err != nil {
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("build local socket address: %s", err)}
}
fileDescriptor, err := unix.Socket(udpAddrFamily(network, laddr, raddr), unix.SOCK_DGRAM, 0)
if err != nil {
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("socket open: %s", err)}
}
if err = unix.SetsockoptInt(fileDescriptor, unix.SOL_IP, unix.IP_TRANSPARENT, 1); err != nil {
unix.Close(fileDescriptor)
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("set socket option: IP_TRANSPARENT: %s", err)}
}
if err = unix.SetsockoptInt(fileDescriptor, unix.SOL_SOCKET, unix.SO_REUSEADDR, 1); err != nil {
unix.Close(fileDescriptor)
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("set socket option: SO_REUSEADDR: %s", err)}
}
if err = unix.SetsockoptInt(fileDescriptor, unix.SOL_SOCKET, unix.SO_REUSEPORT, 1); err != nil {
unix.Close(fileDescriptor)
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("set socket option: SO_REUSEPORT: %s", err)}
}
if err = unix.Bind(fileDescriptor, localSocketAddress); err != nil {
unix.Close(fileDescriptor)
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("socket bind %v: %s", laddr, err)}
}
if err = unix.Connect(fileDescriptor, remoteSocketAddress); err != nil {
unix.Close(fileDescriptor)
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("socket connect: %s", err)}
}
fdFile := os.NewFile(uintptr(fileDescriptor), fmt.Sprintf("net-udp-dial-%s", raddr.String()))
defer fdFile.Close()
remoteConn, err := net.FileConn(fdFile)
if err != nil {
unix.Close(fileDescriptor)
return nil, &net.OpError{Op: "dial", Err: fmt.Errorf("convert file descriptor to connection: %s", err)}
}
return remoteConn, nil
}
// udpAddToSockerAddr will convert a UDPAddr
// into a Sockaddr that may be used when
// connecting and binding sockets
func udpAddrToSocketAddr(addr *net.UDPAddr) (unix.Sockaddr, error) {
switch {
case addr.IP.To4() != nil:
ip := [4]byte{}
copy(ip[:], addr.IP.To4())
return &unix.SockaddrInet4{Addr: ip, Port: addr.Port}, nil
default:
ip := [16]byte{}
copy(ip[:], addr.IP.To16())
zoneID, err := strconv.ParseUint(addr.Zone, 10, 32)
if err != nil {
return nil, err
}
return &unix.SockaddrInet6{Addr: ip, Port: addr.Port, ZoneId: uint32(zoneID)}, nil
}
}
// udpAddrFamily will attempt to work
// out the address family based on the
// network and UDP addresses
func udpAddrFamily(net string, laddr, raddr *net.UDPAddr) int {
switch net[len(net)-1] {
case '4':
return unix.AF_INET
case '6':
return unix.AF_INET6
}
if (laddr == nil || laddr.IP.To4() != nil) &&
(raddr == nil || laddr.IP.To4() != nil) {
return unix.AF_INET
}
return unix.AF_INET6
}