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server_complex.go
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249 lines (218 loc) · 5.89 KB
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// Based on https://gist.github.com/jpillora/b480fde82bff51a06238
// A simple SSH server providing bash sessions
//
// Server:
// cd my/new/dir/
// ssh-keygen -t rsa #generate server keypair
// go get -v .
// go run sshd.go
//
// Client:
// ssh foo@localhost -p 2022
package main
import (
"encoding/binary"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"os"
"os/exec"
"sync"
"syscall"
"unsafe"
"github.com/kr/pty"
"golang.org/x/crypto/ssh"
)
var (
DEFAULT_SHELL string = "sh"
)
func main() {
// An SSH server is represented by a ServerConfig, which holds
// certificate details and handles authentication of ServerConns.
sshConfig := &ssh.ServerConfig{
NoClientAuth: true,
}
// You can generate a keypair with 'ssh-keygen -t rsa -C "test@example.com"'
privateBytes, err := ioutil.ReadFile("./id_rsa")
if err != nil {
log.Fatal("Failed to load private key (./id_rsa)")
}
private, err := ssh.ParsePrivateKey(privateBytes)
if err != nil {
log.Fatal("Failed to parse private key")
}
sshConfig.AddHostKey(private)
// Once a ServerConfig has been configured, connections can be accepted.
listener, err := net.Listen("tcp4", ":2022")
if err != nil {
log.Fatalf("failed to listen on *:2022")
}
// Accept all connections
log.Printf("listening on %s", ":2022")
for {
tcpConn, err := listener.Accept()
if err != nil {
log.Printf("failed to accept incoming connection (%s)", err)
continue
}
// Before use, a handshake must be performed on the incoming net.Conn.
sshConn, chans, reqs, err := ssh.NewServerConn(tcpConn, sshConfig)
if err != nil {
log.Printf("failed to handshake (%s)", err)
continue
}
// Check remote address
log.Printf("new ssh connection from %s (%s)", sshConn.RemoteAddr(), sshConn.ClientVersion())
// Print incoming out-of-band Requests
go handleRequests(reqs)
// Accept all channels
go handleChannels(chans)
}
}
func handleRequests(reqs <-chan *ssh.Request) {
for req := range reqs {
log.Printf("recieved out-of-band request: %+v", req)
}
}
// Start assigns a pseudo-terminal tty os.File to c.Stdin, c.Stdout,
// and c.Stderr, calls c.Start, and returns the File of the tty's
// corresponding pty.
func PtyRun(c *exec.Cmd, tty *os.File) (err error) {
defer tty.Close()
c.Stdout = tty
c.Stdin = tty
c.Stderr = tty
c.SysProcAttr = &syscall.SysProcAttr{
Setctty: true,
Setsid: true,
}
return c.Start()
}
func handleChannels(chans <-chan ssh.NewChannel) {
// Service the incoming Channel channel.
for newChannel := range chans {
// Channels have a type, depending on the application level
// protocol intended. In the case of a shell, the type is
// "session" and ServerShell may be used to present a simple
// terminal interface.
if t := newChannel.ChannelType(); t != "session" {
newChannel.Reject(ssh.UnknownChannelType, fmt.Sprintf("unknown channel type: %s", t))
continue
}
channel, requests, err := newChannel.Accept()
if err != nil {
log.Printf("could not accept channel (%s)", err)
continue
}
// allocate a terminal for this channel
log.Print("creating pty...")
// Create new pty
f, tty, err := pty.Open()
if err != nil {
log.Printf("could not start pty (%s)", err)
continue
}
var shell string
shell = os.Getenv("SHELL")
if shell == "" {
shell = DEFAULT_SHELL
}
// Sessions have out-of-band requests such as "shell", "pty-req" and "env"
go func(in <-chan *ssh.Request) {
for req := range in {
log.Printf("%v %s", req.Payload, req.Payload)
ok := false
switch req.Type {
case "exec":
ok = true
command := string(req.Payload[4 : req.Payload[3]+4])
cmd := exec.Command(shell, []string{"-c", command}...)
cmd.Stdout = channel
cmd.Stderr = channel
cmd.Stdin = channel
err := cmd.Start()
if err != nil {
log.Printf("could not start command (%s)", err)
continue
}
// teardown session
go func() {
_, err := cmd.Process.Wait()
if err != nil {
log.Printf("failed to exit bash (%s)", err)
}
channel.Close()
log.Printf("session closed")
}()
case "shell":
cmd := exec.Command(shell)
cmd.Env = []string{"TERM=xterm"}
err := PtyRun(cmd, tty)
if err != nil {
log.Printf("%s", err)
}
// Teardown session
var once sync.Once
close := func() {
channel.Close()
log.Printf("session closed")
}
// Pipe session to bash and visa-versa
go func() {
io.Copy(channel, f)
once.Do(close)
}()
go func() {
io.Copy(f, channel)
once.Do(close)
}()
// We don't accept any commands (Payload),
// only the default shell.
if len(req.Payload) == 0 {
ok = true
}
case "pty-req":
// Responding 'ok' here will let the client
// know we have a pty ready for input
ok = true
// Parse body...
termLen := req.Payload[3]
termEnv := string(req.Payload[4 : termLen+4])
w, h := parseDims(req.Payload[termLen+4:])
SetWinsize(f.Fd(), w, h)
log.Printf("pty-req '%s'", termEnv)
case "window-change":
w, h := parseDims(req.Payload)
SetWinsize(f.Fd(), w, h)
continue //no response
}
if !ok {
log.Printf("declining %s request...", req.Type)
}
req.Reply(ok, nil)
}
}(requests)
}
}
// =======================
// parseDims extracts two uint32s from the provided buffer.
func parseDims(b []byte) (uint32, uint32) {
w := binary.BigEndian.Uint32(b)
h := binary.BigEndian.Uint32(b[4:])
return w, h
}
// Winsize stores the Height and Width of a terminal.
type Winsize struct {
Height uint16
Width uint16
x uint16 // unused
y uint16 // unused
}
// SetWinsize sets the size of the given pty.
func SetWinsize(fd uintptr, w, h uint32) {
log.Printf("window resize %dx%d", w, h)
ws := &Winsize{Width: uint16(w), Height: uint16(h)}
syscall.Syscall(syscall.SYS_IOCTL, fd, uintptr(syscall.TIOCSWINSZ), uintptr(unsafe.Pointer(ws)))
}