Brad Fitzpatrick
6 years ago
parent
7e5e32775a
commit
d404f1caed
@ -0,0 +1,204 @@ |
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// 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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// 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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"strings" |
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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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) |
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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; running running SSH server", 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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addr, iface, err := tailscaleInterface() |
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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 addr == nil { |
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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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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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// tailscaleInterface returns an err on a fatal problem, and all zero values
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// if no suitable inteface is found.
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func tailscaleInterface() (net.IP, *net.Interface, error) { |
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ifs, err := net.Interfaces() |
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if err != nil { |
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return nil, nil, err |
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} |
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for _, iface := range ifs { |
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if !maybeTailscaleInterfaceName(iface.Name) { |
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continue |
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} |
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addrs, err := iface.Addrs() |
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if err != nil { |
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continue |
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} |
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for _, a := range addrs { |
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if ipnet, ok := a.(*net.IPNet); ok && isTailscaleIP(ipnet.IP) { |
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return ipnet.IP, &iface, nil |
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} |
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} |
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} |
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return nil, nil, nil |
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} |
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// maybeTailscaleInterfaceName reports whether s is an interface
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// name that might be used by Tailscale.
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func maybeTailscaleInterfaceName(s string) bool { |
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return strings.HasPrefix(s, "wg") || |
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strings.HasPrefix(s, "ts") || |
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strings.HasPrefix(s, "tailscale") |
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} |
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func isTailscaleIP(ip net.IP) bool { |
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return cgNAT.Contains(ip) |
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} |
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var cgNAT = func() *net.IPNet { |
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_, ipNet, err := net.ParseCIDR("100.64.0.0/10") |
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if err != nil { |
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panic(err) |
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} |
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return ipNet |
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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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if !isTailscaleIP(ta.IP) { |
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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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return |
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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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