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108 lines
2.0 KiB
Go
108 lines
2.0 KiB
Go
// +build linux
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package obfssh
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import (
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"encoding/binary"
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"fmt"
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"net"
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"syscall"
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"unsafe"
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)
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const (
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// SO_ORIGINAL_DST in linux/netfilter_ipv4.h
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soOriginalDst = 80
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)
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func getOriginDst(c net.Conn) (net.Addr, error) {
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var sockaddr syscall.RawSockaddrAny
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var len = unsafe.Sizeof(sockaddr)
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cc, ok := c.(*net.TCPConn)
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if !ok {
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return nil, fmt.Errorf("only tcp socket supported")
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}
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f, err := cc.File()
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if err != nil {
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return nil, err
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}
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defer f.Close()
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// ipv4
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level := syscall.SOL_IP
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remoteIP := c.RemoteAddr().(*net.TCPAddr).IP
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if remoteIP.To4() == nil {
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// ipv6
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level = syscall.SOL_IPV6
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}
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// get original ip destination, in C like this
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//
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// struct sockaddr addr;
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// memset(&addr, 0, sizeof(addr);
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// int len = sizeof(addr);
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// getsocketopt(fd, SOL_IP, SO_ORIGINAL_DST, &addr, &len);
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//
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_, _, errno := syscall.Syscall6(sysGetSockOpt, f.Fd(),
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uintptr(level), uintptr(soOriginalDst),
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uintptr(unsafe.Pointer(&sockaddr)),
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uintptr(unsafe.Pointer(&len)), 0)
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if errno != 0 {
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return nil, fmt.Errorf("syscall error %d", errno)
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}
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var port uint16
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var ip net.IP
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switch sockaddr.Addr.Family {
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case syscall.AF_INET:
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a := (*syscall.RawSockaddrInet4)(unsafe.Pointer(&sockaddr))
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ip = net.IP(a.Addr[0:])
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port = ntohs(a.Port)
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case syscall.AF_INET6:
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a := (*syscall.RawSockaddrInet6)(unsafe.Pointer(&sockaddr))
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ip = net.IP(a.Addr[0:])
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port = ntohs(a.Port)
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default:
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return nil, fmt.Errorf("unknown socket family: %d",
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sockaddr.Addr.Family)
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}
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addr := &net.TCPAddr{IP: ip, Port: int(port)}
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return addr, nil
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}
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func ntohs(a uint16) uint16 {
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if isLittleEndian {
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b := make([]byte, 2)
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binary.BigEndian.PutUint16(b, a)
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c := binary.LittleEndian.Uint16(b)
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return c
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}
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return a
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}
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var isLittleEndian = isHostLittleEndian()
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func isHostLittleEndian() bool {
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// determine the byte order
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var num uint16 = 0x1234
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buf := make([]byte, 2)
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binary.BigEndian.PutUint16(buf, num)
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p := (*[2]byte)(unsafe.Pointer(&num))
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if p[0] != buf[0] {
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// little endian
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return true
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}
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// big endian
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return false
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}
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