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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build linux
// +build linux
package netstack
import (
"encoding/json"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"os"
"os/exec"
"syscall"
"unsafe"
"github.com/creack/pty"
"github.com/gliderlabs/ssh"
gossh "golang.org/x/crypto/ssh"
"inet.af/netaddr"
"tailscale.com/envknob"
"tailscale.com/net/tsaddr"
)
func init() {
sshDemo = sshDemoImpl
}
func sshDemoImpl(ns *Impl, c net.Conn) error {
hostKey, err := ioutil.ReadFile("/etc/ssh/ssh_host_ed25519_key")
if err != nil {
return err
}
signer, err := gossh.ParsePrivateKey(hostKey)
if err != nil {
return err
}
srv := &ssh.Server{
Handler: ns.handleSSH,
RequestHandlers: map[string]ssh.RequestHandler{},
SubsystemHandlers: map[string]ssh.SubsystemHandler{},
ChannelHandlers: map[string]ssh.ChannelHandler{},
}
for k, v := range ssh.DefaultRequestHandlers {
srv.RequestHandlers[k] = v
}
for k, v := range ssh.DefaultChannelHandlers {
srv.ChannelHandlers[k] = v
}
for k, v := range ssh.DefaultSubsystemHandlers {
srv.SubsystemHandlers[k] = v
}
srv.AddHostKey(signer)
srv.HandleConn(c)
return nil
}
func (ns *Impl) handleSSH(s ssh.Session) {
lb := ns.lb
user := s.User()
addr := s.RemoteAddr()
log.Printf("Handling SSH from %v for user %v", addr, user)
ta, ok := addr.(*net.TCPAddr)
if !ok {
log.Printf("tsshd: rejecting non-TCP addr %T %v", addr, addr)
s.Exit(1)
return
}
tanetaddr, ok := netaddr.FromStdIP(ta.IP)
if !ok {
log.Printf("tsshd: rejecting unparseable addr %v", ta.IP)
s.Exit(1)
return
}
if !tsaddr.IsTailscaleIP(tanetaddr) {
log.Printf("tsshd: rejecting non-Tailscale addr %v", ta.IP)
s.Exit(1)
return
}
ptyReq, winCh, isPty := s.Pty()
if !isPty {
fmt.Fprintf(s, "TODO scp etc")
s.Exit(1)
return
}
srcIPP := netaddr.IPPortFrom(tanetaddr, uint16(ta.Port))
node, uprof, ok := lb.WhoIs(srcIPP)
if !ok {
fmt.Fprintf(s, "Hello, %v. I don't know who you are.\n", srcIPP)
s.Exit(0)
return
}
allow := envknob.String("TS_SSH_ALLOW_LOGIN")
if allow == "" || uprof.LoginName != allow {
log.Printf("ssh: access denied for %q (only allowing %q)", uprof.LoginName, allow)
jnode, _ := json.Marshal(node)
jprof, _ := json.Marshal(uprof)
fmt.Fprintf(s, "Access denied.\n\nYou are node: %s\n\nYour profile: %s\n\nYou wanted %+v\n", jnode, jprof, ptyReq)
s.Exit(1)
return
}
cmd := exec.Command("/bin/bash")
cmd.Env = append(cmd.Env, fmt.Sprintf("TERM=%s", ptyReq.Term))
f, err := pty.Start(cmd)
if err != nil {
log.Printf("running shell: %v", err)
s.Exit(1)
return
}
defer f.Close()
go func() {
for win := range winCh {
setWinsize(f, win.Width, win.Height)
}
}()
go func() {
io.Copy(f, s) // stdin
}()
io.Copy(s, f) // stdout
cmd.Process.Kill()
if err := cmd.Wait(); err != nil {
s.Exit(1)
}
s.Exit(0)
return
}
func setWinsize(f *os.File, w, h int) {
syscall.Syscall(syscall.SYS_IOCTL, f.Fd(), uintptr(syscall.TIOCSWINSZ),
uintptr(unsafe.Pointer(&struct{ h, w, x, y uint16 }{uint16(h), uint16(w), 0, 0})))
}
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