ssh/tailssh: add start of real ssh tests

Updates #3802

Change-Id: I9aea4250062d3a06ca7a5e71a81d31c27a988615
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ssh/tailssh/tailssh.go

@@ -40,32 +40,39 @@ import (
 
 // Handle handles an SSH connection from c.
 func Handle(logf logger.Logf, lb *ipnlocal.LocalBackend, c net.Conn) error {
-	sshd := &server{lb, logf}
-	srv := &ssh.Server{
-		Handler:           sshd.handleSSH,
+	srv := &server{lb, logf}
+	ss, err := srv.newSSHServer()
+	if err != nil {
+		return err
+	}
+	ss.HandleConn(c)
+	return nil
+}
+
+func (srv *server) newSSHServer() (*ssh.Server, error) {
+	ss := &ssh.Server{
+		Handler:           srv.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
+		ss.RequestHandlers[k] = v
 	}
 	for k, v := range ssh.DefaultChannelHandlers {
-		srv.ChannelHandlers[k] = v
+		ss.ChannelHandlers[k] = v
 	}
 	for k, v := range ssh.DefaultSubsystemHandlers {
-		srv.SubsystemHandlers[k] = v
+		ss.SubsystemHandlers[k] = v
 	}
-	keys, err := lb.GetSSH_HostKeys()
+	keys, err := srv.lb.GetSSH_HostKeys()
 	if err != nil {
-		return err
+		return nil, err
 	}
 	for _, signer := range keys {
-		srv.AddHostKey(signer)
+		ss.AddHostKey(signer)
 	}
-
-	srv.HandleConn(c)
-	return nil
+	return ss, nil
 }
 
 type server struct {

ssh/tailssh/tailssh_test.go

@@ -8,11 +8,24 @@
 package tailssh
 
 import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"os/exec"
+	"os/user"
 	"testing"
 	"time"
 
+	"github.com/gliderlabs/ssh"
 	"inet.af/netaddr"
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnlocal"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/tailcfg"
+	"tailscale.com/tstest"
+	"tailscale.com/types/logger"
+	"tailscale.com/wgengine"
 )
 
 func TestMatchRule(t *testing.T) {
@@ -155,3 +168,75 @@ func TestMatchRule(t *testing.T) {
 }
 
 func timePtr(t time.Time) *time.Time { return &t }
+
+func TestSSH(t *testing.T) {
+	ml := new(tstest.MemLogger)
+	var logf logger.Logf = ml.Logf
+	eng, err := wgengine.NewFakeUserspaceEngine(logf, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	lb, err := ipnlocal.NewLocalBackend(logf, "",
+		new(ipn.MemoryStore),
+		new(tsdial.Dialer),
+		eng, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer lb.Shutdown()
+	dir := t.TempDir()
+	lb.SetVarRoot(dir)
+
+	srv := &server{lb, logf}
+	ss, err := srv.newSSHServer()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	u, err := user.Current()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ci := &sshConnInfo{
+		sshUser: "test",
+		srcIP:   netaddr.MustParseIP("1.2.3.4"),
+		node:    &tailcfg.Node{},
+		uprof:   &tailcfg.UserProfile{},
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	ss.Handler = func(s ssh.Session) {
+		srv.handleAcceptedSSH(ctx, s, ci, u)
+	}
+
+	ln, err := net.Listen("tcp4", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ln.Close()
+	port := ln.Addr().(*net.TCPAddr).Port
+
+	go func() {
+		for {
+			c, err := ln.Accept()
+			if err != nil {
+				if !errors.Is(err, net.ErrClosed) {
+					t.Errorf("Accept: %v", err)
+				}
+				return
+			}
+			go ss.HandleConn(c)
+		}
+	}()
+
+	got, err := exec.Command("ssh",
+		"-p", fmt.Sprint(port),
+		"-o", "StrictHostKeyChecking=no",
+		"user@127.0.0.1", "env").CombinedOutput()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("Got: %s", got)
+}