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portmap, cmd/gomodfs: make the static portmapper importable #30

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Merged
bradfitz merged 1 commit into from
Oct 5, 2026
Merged

portmap, cmd/gomodfs: make the static portmapper importable #30

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256 changes: 16 additions & 240 deletions cmd/gomodfs/portmapper.go
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Original file line number Diff line number Diff line change
@@ -1,258 +1,34 @@
package main

import (
"bufio"
"bytes"
"encoding/binary"
"fmt"
"io"
"log"
"net"

"github.com/tailscale/gomodfs/temp-dev-fork/willscott/go-nfs"
"github.com/tailscale/gomodfs/portmap"
)

func startPortmapper() error {
tcpLn, err := net.Listen("tcp", rpcBindAddr)
if err != nil {
return err
}
go runPortMapperTCP(tcpLn)

udpAddr := mustResolveUDP(rpcBindAddr)
udpConn, err := net.ListenUDP("udp", udpAddr)
if err != nil {
return err
}
go runPortMapperUDP(udpConn)
return nil
}

func runPortMapperTCP(ln net.Listener) {
defer ln.Close()

log.Printf("portmap-static: listening on TCP %s", ln.Addr())

for {
conn, err := ln.Accept()
if err != nil {
log.Printf("runPortMapperTCP.Accept: %v", err)
return
}
handleRPCBindConn(conn)
}
}

func runPortMapperUDP(conn *net.UDPConn) {
defer conn.Close()
log.Printf("portmap-static: listening on UDP %s", conn.LocalAddr())

buf := make([]byte, 64*1024)
for {
n, addr, err := conn.ReadFromUDP(buf)
if err != nil {
log.Printf("runPortMapperUDP: %v", err)
return
}
handleUDPPacket(conn, addr, buf[:n])
}
}

const (
rpcBindAddr = ":111"
staticPort = 2049

rpcCall = 0
rpcReply = 1

replyMsgAccepted = 0
authNull = 0
acceptSuccess = 0

portmapProg = 100000
portmapVers = 2

pmapProcNull = 0
pmapprocGetport = 3

protTCP = 6
protUDP = 17

nfsProg = 100003
mountProg = 100005
nlmProg = 100021
)

func mustResolveUDP(addr string) *net.UDPAddr {
ua, err := net.ResolveUDPAddr("udp", addr)
func startPortmapper() error {
tcpLn, err := net.Listen("tcp", rpcBindAddr)
if err != nil {
log.Fatal(err)
}
return ua
}

func handleRPCBindConn(c net.Conn) {
log.Printf("rpcbind: accepted TCP connection from %s", c.RemoteAddr())
defer c.Close()
br := bufio.NewReader(c)
for {
rec, err := nfs.ReadRPCRecord(br)
log.Printf("rpcbind: TCP conn %s sent rec % 02x", c.RemoteAddr(), rec)
if err != nil {
if err != io.EOF {
log.Printf("rpcbind: readRPCRecord: %v", err)
}
return
}
handleTCPPacket(c, rec)
}
}

func handleTCPPacket(c net.Conn, data []byte) {
log.Printf("rpcbind: received %d bytes from TCP %s: % 02x", len(data), c.RemoteAddr(), data)
handlePacket(data, func(resp []byte) error {
var buf [4]byte
const lastFragMask = 1 << 31
binary.BigEndian.PutUint32(buf[:], uint32(len(resp))|lastFragMask)
_, err := fmt.Fprintf(c, "%s%s", buf[:], resp)
return err
})
}

func handleUDPPacket(conn *net.UDPConn, addr *net.UDPAddr, data []byte) {
log.Printf("rpcbind: received %d bytes from UDP %s: % 02x", len(data), addr, data)
handlePacket(data, func(resp []byte) error {
_, err := conn.WriteToUDP(resp, addr)
return err
})
}

func handlePacket(data []byte, sendResp func([]byte) error) {
r := bytes.NewReader(data)

var xid, mtype, rpcvers, prog, vers, proc uint32
if err := binary.Read(r, binary.BigEndian, &xid); err != nil {
return
}
if err := binary.Read(r, binary.BigEndian, &mtype); err != nil || mtype != rpcCall {
return
}
if err := binary.Read(r, binary.BigEndian, &rpcvers); err != nil || rpcvers != 2 {
return
}
if err := binary.Read(r, binary.BigEndian, &prog); err != nil || prog != portmapProg {
log.Printf("portmap-static: unknown program %02x; want %02x", prog, portmapProg)
return
}
if err := binary.Read(r, binary.BigEndian, &vers); err != nil || vers != portmapVers {
return
}
if err := binary.Read(r, binary.BigEndian, &proc); err != nil {
return
}

log.Printf("portmap-static: RPC call rpcver=%v xid=%d prog=%d vers=%d proc=%d", rpcvers, xid, prog, vers, proc)

if !skipOpaqueAuth(r) { // cred
log.Printf("portmap-static: failed to skip cred")
return
}
if !skipOpaqueAuth(r) { // verf
log.Printf("portmap-static: failed to skip cred")
return
}

if proc == pmapProcNull {
// Reply with empty response
var buf bytes.Buffer
writeReplySuccess(&buf, xid)
resp := buf.Bytes()
log.Printf("rpcbind: replying to null ping")
if err := sendResp(resp); err != nil {
log.Printf("rpcbind: sendResp: %v", err)
}
return
}

if proc != pmapprocGetport {
log.Printf("portmap-static: unknown procedure %08x; want %08x", proc, pmapprocGetport)
return
}

// Portmap v2 pmap args: prog, vers, prot, port
var argProg, argVers, argProt, argPort uint32
if err := binary.Read(r, binary.BigEndian, &argProg); err != nil {
return
}
if err := binary.Read(r, binary.BigEndian, &argVers); err != nil {
return
}
if err := binary.Read(r, binary.BigEndian, &argProt); err != nil {
return
}
if err := binary.Read(r, binary.BigEndian, &argPort); err != nil {
return
}
_ = argVers
_ = argProt
_ = argPort

log.Printf("rpcbind: GetPort prog=%d vers=%d prot=%d port=%d", argProg, argVers, argProt, argPort)

var port uint32
switch argProt {
case protUDP:
port = 0 // don't advertise UDP support
case protTCP:
switch argProg {
case nfsProg, mountProg, nlmProg:
port = staticPort
}
}

resp := buildPortReply(xid, port)
log.Printf("rpcbind: replying with port %d: % 02x", port, resp)
if err := sendResp(resp); err != nil {
log.Printf("rpcbind: sendResp: %v", err)
}
}

func skipOpaqueAuth(r *bytes.Reader) bool {
var flavor, length uint32
if err := binary.Read(r, binary.BigEndian, &flavor); err != nil {
return false
}
if err := binary.Read(r, binary.BigEndian, &length); err != nil {
return false
}
_ = flavor
pad := (length + 3) &^ 3
if pad == 0 {
return true
udpConn, err := net.ListenPacket("udp", rpcBindAddr)
if err != nil {
tcpLn.Close()
return err
}
_, err := r.Seek(int64(pad), 1)
return err == nil
}

func writeReplySuccess(buf *bytes.Buffer, xid uint32) {
// rpc_msg
_ = binary.Write(buf, binary.BigEndian, xid) // xid
_ = binary.Write(buf, binary.BigEndian, uint32(rpcReply)) // mtype = REPLY
_ = binary.Write(buf, binary.BigEndian, uint32(replyMsgAccepted)) // reply_stat = MSG_ACCEPTED

// verf: AUTH_NULL, length 0
_ = binary.Write(buf, binary.BigEndian, uint32(authNull))
_ = binary.Write(buf, binary.BigEndian, uint32(0))

_ = binary.Write(buf, binary.BigEndian, uint32(acceptSuccess))
}

func buildPortReply(xid, port uint32) []byte {
var buf bytes.Buffer
writeReplySuccess(&buf, xid)

// result: uint32 port
_ = binary.Write(&buf, binary.BigEndian, port)

return buf.Bytes()
pm := &portmap.Server{Port: staticPort, Logf: log.Printf}
log.Printf("portmap-static: listening on TCP and UDP %s", rpcBindAddr)
go func() {
log.Printf("portmap-static: TCP: %v", pm.ServeTCP(tcpLn))
}()
go func() {
log.Printf("portmap-static: UDP: %v", pm.ServeUDP(udpConn))
}()
return nil
}
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