mirror of https://github.com/tailscale/tailscale/
ssh/tailssh: move SSH code from wgengine/netstack to this new package
Still largely incomplete, but in a better home now. Updates #3802 Change-Id: I46c5ffdeb12e306879af801b06266839157bc624 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>pull/3951/head
Brad Fitzpatrick
3 years ago
committed by
Brad Fitzpatrick
parent
6d02a48d8d
commit
1b87e025e9
@ -0,0 +1,156 @@
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// Copyright (c) 2021 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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//go:build linux
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// +build linux
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// Package tailssh is an SSH server integrated into Tailscale.
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package tailssh
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import (
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"encoding/json"
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"fmt"
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"io"
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"io/ioutil"
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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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"unsafe"
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"github.com/creack/pty"
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"github.com/gliderlabs/ssh"
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gossh "golang.org/x/crypto/ssh"
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"inet.af/netaddr"
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"tailscale.com/envknob"
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"tailscale.com/ipn/ipnlocal"
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"tailscale.com/net/tsaddr"
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"tailscale.com/types/logger"
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)
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// TODO(bradfitz): this is all very temporary as code is temporarily
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// being moved around; it will be restructured and documented in
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// following commits.
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// Handle handles an SSH connection from c.
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func Handle(logf logger.Logf, lb *ipnlocal.LocalBackend, c net.Conn) error {
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hostKey, err := ioutil.ReadFile("/etc/ssh/ssh_host_ed25519_key")
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if err != nil {
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return 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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return err
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}
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sshd := &server{lb, logf}
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srv := &ssh.Server{
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Handler: sshd.handleSSH,
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RequestHandlers: map[string]ssh.RequestHandler{},
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SubsystemHandlers: map[string]ssh.SubsystemHandler{},
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ChannelHandlers: map[string]ssh.ChannelHandler{},
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}
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for k, v := range ssh.DefaultRequestHandlers {
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srv.RequestHandlers[k] = v
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}
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for k, v := range ssh.DefaultChannelHandlers {
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srv.ChannelHandlers[k] = v
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}
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for k, v := range ssh.DefaultSubsystemHandlers {
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srv.SubsystemHandlers[k] = v
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}
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srv.AddHostKey(signer)
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srv.HandleConn(c)
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return nil
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}
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type server struct {
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lb *ipnlocal.LocalBackend
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logf logger.Logf
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}
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func (srv *server) handleSSH(s ssh.Session) {
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lb := srv.lb
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logf := srv.logf
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user := s.User()
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addr := s.RemoteAddr()
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logf("Handling SSH from %v for user %v", addr, user)
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ta, ok := addr.(*net.TCPAddr)
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if !ok {
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logf("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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logf("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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logf("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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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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srcIPP := netaddr.IPPortFrom(tanetaddr, uint16(ta.Port))
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node, uprof, ok := lb.WhoIs(srcIPP)
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if !ok {
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fmt.Fprintf(s, "Hello, %v. I don't know who you are.\n", srcIPP)
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s.Exit(0)
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return
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}
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allow := envknob.String("TS_SSH_ALLOW_LOGIN")
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if allow == "" || uprof.LoginName != allow {
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logf("ssh: access denied for %q (only allowing %q)", uprof.LoginName, allow)
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jnode, _ := json.Marshal(node)
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jprof, _ := json.Marshal(uprof)
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fmt.Fprintf(s, "Access denied.\n\nYou are node: %s\n\nYour profile: %s\n\nYou wanted %+v\n", jnode, jprof, ptyReq)
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s.Exit(1)
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return
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}
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var cmd *exec.Cmd
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sshUser := s.User()
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if os.Getuid() != 0 || sshUser == "root" {
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cmd = exec.Command("/bin/bash")
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} else {
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cmd = exec.Command("/usr/bin/env", "su", "-", sshUser)
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}
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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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logf("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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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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