mirror of
https://github.com/tailscale/tailscale.git
synced 2024-12-05 07:55:36 +00:00
72b6d98298
Signed-off-by: David Anderson <danderson@tailscale.com>
177 lines
3.8 KiB
Go
177 lines
3.8 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build !windows
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// The tsshd binary is an SSH server that accepts connections
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// from anybody on the same Tailscale network.
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//
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// It does not use passwords or SSH public key.
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//
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// Any user name is accepted; users are logged in as whoever is
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// running this daemon.
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//
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// Warning: use at your own risk. This code has had very few eyeballs
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// on it.
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package main
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import (
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"flag"
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"fmt"
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"io"
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"io/ioutil"
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"log"
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"net"
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"os"
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"os/exec"
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"syscall"
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"time"
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"unsafe"
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"github.com/gliderlabs/ssh"
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"github.com/kr/pty"
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gossh "golang.org/x/crypto/ssh"
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"inet.af/netaddr"
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"tailscale.com/net/interfaces"
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"tailscale.com/net/tsaddr"
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)
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var (
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port = flag.Int("port", 2200, "port to listen on")
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hostKey = flag.String("hostkey", "", "SSH host key")
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)
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func main() {
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flag.Parse()
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if *hostKey == "" {
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log.Fatalf("missing required --hostkey")
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}
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hostKey, err := ioutil.ReadFile(*hostKey)
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if err != nil {
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log.Fatal(err)
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}
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signer, err := gossh.ParsePrivateKey(hostKey)
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if err != nil {
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log.Printf("failed to parse SSH host key: %v", err)
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return
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}
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warned := false
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for {
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addrs, iface, err := interfaces.Tailscale()
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if err != nil {
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log.Fatalf("listing interfaces: %v", err)
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}
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if len(addrs) == 0 {
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if !warned {
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log.Printf("no tailscale interface found; polling until one is available")
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warned = true
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}
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// TODO: use netlink or other OS-specific mechanism to efficiently
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// wait for change in interfaces. Polling every N seconds is good enough
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// for now.
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time.Sleep(5 * time.Second)
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continue
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}
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warned = false
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var addr netaddr.IP
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for _, a := range addrs {
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if a.Is4() {
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addr = a
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break
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}
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}
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listen := net.JoinHostPort(addr.String(), fmt.Sprint(*port))
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log.Printf("tailscale ssh server listening on %v, %v", iface.Name, listen)
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s := &ssh.Server{
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Addr: listen,
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Handler: handleSSH,
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}
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s.AddHostKey(signer)
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err = s.ListenAndServe()
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log.Fatalf("tailscale sshd failed: %v", err)
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}
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}
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func handleSSH(s ssh.Session) {
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user := s.User()
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addr := s.RemoteAddr()
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ta, ok := addr.(*net.TCPAddr)
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if !ok {
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log.Printf("tsshd: rejecting non-TCP addr %T %v", addr, addr)
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s.Exit(1)
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return
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}
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tanetaddr, ok := netaddr.FromStdIP(ta.IP)
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if !ok {
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log.Printf("tsshd: rejecting unparseable addr %v", ta.IP)
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s.Exit(1)
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return
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}
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if !tsaddr.IsTailscaleIP(tanetaddr) {
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log.Printf("tsshd: rejecting non-Tailscale addr %v", ta.IP)
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s.Exit(1)
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return
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}
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log.Printf("new session for %q from %v", user, ta)
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defer log.Printf("closing session for %q from %v", user, ta)
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ptyReq, winCh, isPty := s.Pty()
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if !isPty {
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fmt.Fprintf(s, "TODO scp etc")
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s.Exit(1)
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return
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}
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userWantsShell := len(s.Command()) == 0
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if userWantsShell {
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shell, err := shellOfUser(s.User())
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if err != nil {
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fmt.Fprintf(s, "failed to find shell: %v\n", err)
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s.Exit(1)
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return
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}
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cmd := exec.Command(shell)
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cmd.Env = append(cmd.Env, fmt.Sprintf("TERM=%s", ptyReq.Term))
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f, err := pty.Start(cmd)
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if err != nil {
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log.Printf("running shell: %v", err)
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s.Exit(1)
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return
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}
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defer f.Close()
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go func() {
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for win := range winCh {
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setWinsize(f, win.Width, win.Height)
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}
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}()
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go func() {
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io.Copy(f, s) // stdin
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}()
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io.Copy(s, f) // stdout
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cmd.Process.Kill()
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if err := cmd.Wait(); err != nil {
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s.Exit(1)
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}
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s.Exit(0)
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return
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}
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fmt.Fprintf(s, "TODO: args\n")
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s.Exit(1)
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}
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func shellOfUser(user string) (string, error) {
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// TODO
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return "/bin/bash", nil
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}
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func setWinsize(f *os.File, w, h int) {
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syscall.Syscall(syscall.SYS_IOCTL, f.Fd(), uintptr(syscall.TIOCSWINSZ),
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uintptr(unsafe.Pointer(&struct{ h, w, x, y uint16 }{uint16(h), uint16(w), 0, 0})))
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}
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