ssh/test/session_test.go - crypto - Git at Google

 // Copyright 2012 The Go 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 !windows && !js && !wasip1

 package test

 // Session functional tests.

 import (
 	"bytes"
 	"errors"
 	"fmt"
 	"io"
 	"path/filepath"
 	"regexp"
 	"runtime"
 	"strings"
 	"testing"

 	"golang.org/x/crypto/ssh"
 )

 func skipIfIssue64959(t *testing.T, err error) {
 	if err != nil && runtime.GOOS == "darwin" && strings.Contains(err.Error(), "ssh: unexpected packet in response to channel open: <nil>") {
 		t.Helper()
 		t.Skipf("skipping test broken on some versions of macOS; see https://go.dev/issue/64959")
 	}
 }

 func TestRunCommandSuccess(t *testing.T) {
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("session failed: %v", err)
 	}
 	defer session.Close()
 	err = session.Run("true")
 	if err != nil {
 		t.Fatalf("session failed: %v", err)
 	}
 }

 func TestHostKeyCheck(t *testing.T) {
 	server := newServer(t)

 	conf := clientConfig()
 	hostDB := hostKeyDB()
 	conf.HostKeyCallback = hostDB.Check

 	// change the keys.
 	hostDB.keys[ssh.KeyAlgoRSA][25]++
 	hostDB.keys[ssh.KeyAlgoDSA][25]++
 	hostDB.keys[ssh.KeyAlgoECDSA256][25]++

 	conn, err := server.TryDial(conf)
 	if err == nil {
 		conn.Close()
 		t.Fatalf("dial should have failed.")
 	} else if !strings.Contains(err.Error(), "host key mismatch") {
 		t.Fatalf("'host key mismatch' not found in %v", err)
 	}
 }

 func TestRunCommandStdin(t *testing.T) {
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("session failed: %v", err)
 	}
 	defer session.Close()

 	r, w := io.Pipe()
 	defer r.Close()
 	defer w.Close()
 	session.Stdin = r

 	err = session.Run("true")
 	if err != nil {
 		t.Fatalf("session failed: %v", err)
 	}
 }

 func TestRunCommandStdinError(t *testing.T) {
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("session failed: %v", err)
 	}
 	defer session.Close()

 	r, w := io.Pipe()
 	defer r.Close()
 	session.Stdin = r
 	pipeErr := errors.New("closing write end of pipe")
 	w.CloseWithError(pipeErr)

 	err = session.Run("true")
 	if err != pipeErr {
 		t.Fatalf("expected %v, found %v", pipeErr, err)
 	}
 }

 func TestRunCommandFailed(t *testing.T) {
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("session failed: %v", err)
 	}
 	defer session.Close()
 	err = session.Run(`bash -c "kill -9 $$"`)
 	if err == nil {
 		t.Fatalf("session succeeded: %v", err)
 	}
 }

 func TestRunCommandWeClosed(t *testing.T) {
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("session failed: %v", err)
 	}
 	err = session.Shell()
 	if err != nil {
 		t.Fatalf("shell failed: %v", err)
 	}
 	err = session.Close()
 	if err != nil {
 		t.Fatalf("shell failed: %v", err)
 	}
 }

 func TestFuncLargeRead(t *testing.T) {
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("unable to create new session: %s", err)
 	}

 	stdout, err := session.StdoutPipe()
 	if err != nil {
 		t.Fatalf("unable to acquire stdout pipe: %s", err)
 	}

 	err = session.Start("dd if=/dev/urandom bs=2048 count=1024")
 	if err != nil {
 		t.Fatalf("unable to execute remote command: %s", err)
 	}

 	buf := new(bytes.Buffer)
 	n, err := io.Copy(buf, stdout)
 	if err != nil {
 		t.Fatalf("error reading from remote stdout: %s", err)
 	}

 	if n != 2048*1024 {
 		t.Fatalf("Expected %d bytes but read only %d from remote command", 2048, n)
 	}
 }

 func TestKeyChange(t *testing.T) {
 	server := newServer(t)
 	conf := clientConfig()
 	hostDB := hostKeyDB()
 	conf.HostKeyCallback = hostDB.Check
 	conf.RekeyThreshold = 1024
 	conn := server.Dial(conf)
 	defer conn.Close()

 	for i := 0; i < 4; i++ {
 		session, err := conn.NewSession()
 		if err != nil {
 			skipIfIssue64959(t, err)
 			t.Fatalf("unable to create new session: %s", err)
 		}

 		stdout, err := session.StdoutPipe()
 		if err != nil {
 			t.Fatalf("unable to acquire stdout pipe: %s", err)
 		}

 		err = session.Start("dd if=/dev/urandom bs=1024 count=1")
 		if err != nil {
 			t.Fatalf("unable to execute remote command: %s", err)
 		}
 		buf := new(bytes.Buffer)
 		n, err := io.Copy(buf, stdout)
 		if err != nil {
 			t.Fatalf("error reading from remote stdout: %s", err)
 		}

 		want := int64(1024)
 		if n != want {
 			t.Fatalf("Expected %d bytes but read only %d from remote command", want, n)
 		}
 	}

 	if changes := hostDB.checkCount; changes < 4 {
 		t.Errorf("got %d key changes, want 4", changes)
 	}
 }

 func TestValidTerminalMode(t *testing.T) {
 	if runtime.GOOS == "aix" {
 		// On AIX, sshd cannot acquire /dev/pts/* if launched as
 		// a non-root user.
 		t.Skipf("skipping on %s", runtime.GOOS)
 	}
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("session failed: %v", err)
 	}
 	defer session.Close()

 	stdout, err := session.StdoutPipe()
 	if err != nil {
 		t.Fatalf("unable to acquire stdout pipe: %s", err)
 	}

 	stdin, err := session.StdinPipe()
 	if err != nil {
 		t.Fatalf("unable to acquire stdin pipe: %s", err)
 	}

 	tm := ssh.TerminalModes{ssh.ECHO: 0}
 	if err = session.RequestPty("xterm", 80, 40, tm); err != nil {
 		t.Fatalf("req-pty failed: %s", err)
 	}

 	err = session.Shell()
 	if err != nil {
 		t.Fatalf("session failed: %s", err)
 	}

 	if _, err := io.WriteString(stdin, "echo && echo SHELL $SHELL && stty -a && exit\n"); err != nil {
 		t.Fatal(err)
 	}

 	buf := new(strings.Builder)
 	if _, err := io.Copy(buf, stdout); err != nil {
 		t.Fatalf("reading failed: %s", err)
 	}

 	if testing.Verbose() {
 		t.Logf("echo && echo SHELL $SHELL && stty -a && exit:\n%s", buf)
 	}

 	shellLine := regexp.MustCompile("(?m)^SHELL (.*)$").FindStringSubmatch(buf.String())
 	if len(shellLine) != 2 {
 		t.Fatalf("missing output from echo SHELL $SHELL")
 	}
 	switch shell := filepath.Base(strings.TrimSpace(shellLine[1])); shell {
 	case "sh", "bash":
 	default:
 		t.Skipf("skipping test on non-Bourne shell %q", shell)
 	}

 	if sttyOutput := buf.String(); !strings.Contains(sttyOutput, "-echo ") {
 		t.Fatal("terminal mode failure: expected -echo in stty output")
 	}
 }

 func TestWindowChange(t *testing.T) {
 	if runtime.GOOS == "aix" {
 		// On AIX, sshd cannot acquire /dev/pts/* if launched as
 		// a non-root user.
 		t.Skipf("skipping on %s", runtime.GOOS)
 	}
 	server := newServer(t)
 	conn := server.Dial(clientConfig())
 	defer conn.Close()

 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("session failed: %v", err)
 	}
 	defer session.Close()

 	stdout, err := session.StdoutPipe()
 	if err != nil {
 		t.Fatalf("unable to acquire stdout pipe: %s", err)
 	}

 	stdin, err := session.StdinPipe()
 	if err != nil {
 		t.Fatalf("unable to acquire stdin pipe: %s", err)
 	}

 	tm := ssh.TerminalModes{ssh.ECHO: 0}
 	if err = session.RequestPty("xterm", 80, 40, tm); err != nil {
 		t.Fatalf("req-pty failed: %s", err)
 	}

 	if err := session.WindowChange(100, 100); err != nil {
 		t.Fatalf("window-change failed: %s", err)
 	}

 	err = session.Shell()
 	if err != nil {
 		t.Fatalf("session failed: %s", err)
 	}

 	stdin.Write([]byte("stty size && exit\n"))

 	var buf bytes.Buffer
 	if _, err := io.Copy(&buf, stdout); err != nil {
 		t.Fatalf("reading failed: %s", err)
 	}

 	if sttyOutput := buf.String(); !strings.Contains(sttyOutput, "100 100") {
 		t.Fatalf("terminal WindowChange failure: expected \"100 100\" stty output, got %s", sttyOutput)
 	}
 }

 func testOneCipher(t *testing.T, cipher string, cipherOrder []string) {
 	server := newServer(t)
 	conf := clientConfig()
 	conf.Ciphers = []string{cipher}
 	// Don't fail if sshd doesn't have the cipher.
 	conf.Ciphers = append(conf.Ciphers, cipherOrder...)
 	conn, err := server.TryDial(conf)
 	if err != nil {
 		t.Fatalf("TryDial: %v", err)
 	}
 	defer conn.Close()

 	numBytes := 4096

 	// Exercise receiving data from the server
 	session, err := conn.NewSession()
 	if err != nil {
 		skipIfIssue64959(t, err)
 		t.Fatalf("NewSession: %v", err)
 	}

 	out, err := session.Output(fmt.Sprintf("dd if=/dev/zero bs=%d count=1", numBytes))
 	if err != nil {
 		t.Fatalf("Output: %v", err)
 	}

 	if len(out) != numBytes {
 		t.Fatalf("got %d bytes, want %d bytes", len(out), numBytes)
 	}

 	// Exercise sending data to the server
 	if _, _, err := conn.Conn.SendRequest("drop-me", false, make([]byte, numBytes)); err != nil {
 		t.Fatalf("SendRequest: %v", err)
 	}
 }

 var deprecatedCiphers = []string{
 	"aes128-cbc", "3des-cbc",
 	"arcfour128", "arcfour256",
 }

 func TestCiphers(t *testing.T) {
 	var config ssh.Config
 	config.SetDefaults()
 	cipherOrder := append(config.Ciphers, deprecatedCiphers...)

 	for _, ciph := range cipherOrder {
 		t.Run(ciph, func(t *testing.T) {
 			testOneCipher(t, ciph, cipherOrder)
 		})
 	}
 }

 func TestMACs(t *testing.T) {
 	var config ssh.Config
 	config.SetDefaults()
 	macOrder := config.MACs

 	for _, mac := range macOrder {
 		t.Run(mac, func(t *testing.T) {
 			server := newServer(t)
 			conf := clientConfig()
 			conf.MACs = []string{mac}
 			// Don't fail if sshd doesn't have the MAC.
 			conf.MACs = append(conf.MACs, macOrder...)
 			if conn, err := server.TryDial(conf); err == nil {
 				conn.Close()
 			} else {
 				t.Fatalf("failed for MAC %q", mac)
 			}
 		})
 	}
 }

 func TestKeyExchanges(t *testing.T) {
 	var config ssh.Config
 	config.SetDefaults()
 	kexOrder := config.KeyExchanges
 	// Based on the discussion in #17230, the key exchange algorithms
 	// diffie-hellman-group-exchange-sha1 and diffie-hellman-group-exchange-sha256
 	// are not included in the default list of supported kex so we have to add them
 	// here manually.
 	kexOrder = append(kexOrder, "diffie-hellman-group-exchange-sha1", "diffie-hellman-group-exchange-sha256")
 	// The key exchange algorithms diffie-hellman-group16-sha512 is disabled by
 	// default so we add it here manually.
 	kexOrder = append(kexOrder, "diffie-hellman-group16-sha512")
 	for _, kex := range kexOrder {
 		t.Run(kex, func(t *testing.T) {
 			server := newServer(t)
 			conf := clientConfig()
 			// Don't fail if sshd doesn't have the kex.
 			conf.KeyExchanges = append([]string{kex}, kexOrder...)
 			conn, err := server.TryDial(conf)
 			if err == nil {
 				conn.Close()
 			} else {
 				t.Errorf("failed for kex %q", kex)
 			}
 		})
 	}
 }

 func TestClientAuthAlgorithms(t *testing.T) {
 	for _, key := range []string{
 		"rsa",
 		"ecdsa",
 		"ed25519",
 	} {
 		t.Run(key, func(t *testing.T) {
 			server := newServer(t)
 			conf := clientConfig()
 			conf.SetDefaults()
 			conf.Auth = []ssh.AuthMethod{
 				ssh.PublicKeys(testSigners[key]),
 			}

 			conn, err := server.TryDial(conf)
 			if err == nil {
 				conn.Close()
 			} else {
 				t.Errorf("failed for key %q", key)
 			}
 		})
 	}
 }
	// Copyright 2012 The Go 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 !windows && !js && !wasip1

	package test

	// Session functional tests.

	import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"path/filepath"
	"regexp"
	"runtime"
	"strings"
	"testing"

	"golang.org/x/crypto/ssh"
	)

	func skipIfIssue64959(t *testing.T, err error) {
	if err != nil && runtime.GOOS == "darwin" && strings.Contains(err.Error(), "ssh: unexpected packet in response to channel open: <nil>") {
	t.Helper()
	t.Skipf("skipping test broken on some versions of macOS; see https://go.dev/issue/64959")
	}
	}

	func TestRunCommandSuccess(t *testing.T) {
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("session failed: %v", err)
	}
	defer session.Close()
	err = session.Run("true")
	if err != nil {
	t.Fatalf("session failed: %v", err)
	}
	}

	func TestHostKeyCheck(t *testing.T) {
	server := newServer(t)

	conf := clientConfig()
	hostDB := hostKeyDB()
	conf.HostKeyCallback = hostDB.Check

	// change the keys.
	hostDB.keys[ssh.KeyAlgoRSA][25]++
	hostDB.keys[ssh.KeyAlgoDSA][25]++
	hostDB.keys[ssh.KeyAlgoECDSA256][25]++

	conn, err := server.TryDial(conf)
	if err == nil {
	conn.Close()
	t.Fatalf("dial should have failed.")
	} else if !strings.Contains(err.Error(), "host key mismatch") {
	t.Fatalf("'host key mismatch' not found in %v", err)
	}
	}

	func TestRunCommandStdin(t *testing.T) {
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("session failed: %v", err)
	}
	defer session.Close()

	r, w := io.Pipe()
	defer r.Close()
	defer w.Close()
	session.Stdin = r

	err = session.Run("true")
	if err != nil {
	t.Fatalf("session failed: %v", err)
	}
	}

	func TestRunCommandStdinError(t *testing.T) {
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("session failed: %v", err)
	}
	defer session.Close()

	r, w := io.Pipe()
	defer r.Close()
	session.Stdin = r
	pipeErr := errors.New("closing write end of pipe")
	w.CloseWithError(pipeErr)

	err = session.Run("true")
	if err != pipeErr {
	t.Fatalf("expected %v, found %v", pipeErr, err)
	}
	}

	func TestRunCommandFailed(t *testing.T) {
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("session failed: %v", err)
	}
	defer session.Close()
	err = session.Run(`bash -c "kill -9 $$"`)
	if err == nil {
	t.Fatalf("session succeeded: %v", err)
	}
	}

	func TestRunCommandWeClosed(t *testing.T) {
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("session failed: %v", err)
	}
	err = session.Shell()
	if err != nil {
	t.Fatalf("shell failed: %v", err)
	}
	err = session.Close()
	if err != nil {
	t.Fatalf("shell failed: %v", err)
	}
	}

	func TestFuncLargeRead(t *testing.T) {
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("unable to create new session: %s", err)
	}

	stdout, err := session.StdoutPipe()
	if err != nil {
	t.Fatalf("unable to acquire stdout pipe: %s", err)
	}

	err = session.Start("dd if=/dev/urandom bs=2048 count=1024")
	if err != nil {
	t.Fatalf("unable to execute remote command: %s", err)
	}

	buf := new(bytes.Buffer)
	n, err := io.Copy(buf, stdout)
	if err != nil {
	t.Fatalf("error reading from remote stdout: %s", err)
	}

	if n != 2048*1024 {
	t.Fatalf("Expected %d bytes but read only %d from remote command", 2048, n)
	}
	}

	func TestKeyChange(t *testing.T) {
	server := newServer(t)
	conf := clientConfig()
	hostDB := hostKeyDB()
	conf.HostKeyCallback = hostDB.Check
	conf.RekeyThreshold = 1024
	conn := server.Dial(conf)
	defer conn.Close()

	for i := 0; i < 4; i++ {
	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("unable to create new session: %s", err)
	}

	stdout, err := session.StdoutPipe()
	if err != nil {
	t.Fatalf("unable to acquire stdout pipe: %s", err)
	}

	err = session.Start("dd if=/dev/urandom bs=1024 count=1")
	if err != nil {
	t.Fatalf("unable to execute remote command: %s", err)
	}
	buf := new(bytes.Buffer)
	n, err := io.Copy(buf, stdout)
	if err != nil {
	t.Fatalf("error reading from remote stdout: %s", err)
	}

	want := int64(1024)
	if n != want {
	t.Fatalf("Expected %d bytes but read only %d from remote command", want, n)
	}
	}

	if changes := hostDB.checkCount; changes < 4 {
	t.Errorf("got %d key changes, want 4", changes)
	}
	}

	func TestValidTerminalMode(t *testing.T) {
	if runtime.GOOS == "aix" {
	// On AIX, sshd cannot acquire /dev/pts/* if launched as
	// a non-root user.
	t.Skipf("skipping on %s", runtime.GOOS)
	}
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("session failed: %v", err)
	}
	defer session.Close()

	stdout, err := session.StdoutPipe()
	if err != nil {
	t.Fatalf("unable to acquire stdout pipe: %s", err)
	}

	stdin, err := session.StdinPipe()
	if err != nil {
	t.Fatalf("unable to acquire stdin pipe: %s", err)
	}

	tm := ssh.TerminalModes{ssh.ECHO: 0}
	if err = session.RequestPty("xterm", 80, 40, tm); err != nil {
	t.Fatalf("req-pty failed: %s", err)
	}

	err = session.Shell()
	if err != nil {
	t.Fatalf("session failed: %s", err)
	}

	if _, err := io.WriteString(stdin, "echo && echo SHELL $SHELL && stty -a && exit\n"); err != nil {
	t.Fatal(err)
	}

	buf := new(strings.Builder)
	if _, err := io.Copy(buf, stdout); err != nil {
	t.Fatalf("reading failed: %s", err)
	}

	if testing.Verbose() {
	t.Logf("echo && echo SHELL $SHELL && stty -a && exit:\n%s", buf)
	}

	shellLine := regexp.MustCompile("(?m)^SHELL (.*)$").FindStringSubmatch(buf.String())
	if len(shellLine) != 2 {
	t.Fatalf("missing output from echo SHELL $SHELL")
	}
	switch shell := filepath.Base(strings.TrimSpace(shellLine[1])); shell {
	case "sh", "bash":
	default:
	t.Skipf("skipping test on non-Bourne shell %q", shell)
	}

	if sttyOutput := buf.String(); !strings.Contains(sttyOutput, "-echo ") {
	t.Fatal("terminal mode failure: expected -echo in stty output")
	}
	}

	func TestWindowChange(t *testing.T) {
	if runtime.GOOS == "aix" {
	// On AIX, sshd cannot acquire /dev/pts/* if launched as
	// a non-root user.
	t.Skipf("skipping on %s", runtime.GOOS)
	}
	server := newServer(t)
	conn := server.Dial(clientConfig())
	defer conn.Close()

	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("session failed: %v", err)
	}
	defer session.Close()

	stdout, err := session.StdoutPipe()
	if err != nil {
	t.Fatalf("unable to acquire stdout pipe: %s", err)
	}

	stdin, err := session.StdinPipe()
	if err != nil {
	t.Fatalf("unable to acquire stdin pipe: %s", err)
	}

	tm := ssh.TerminalModes{ssh.ECHO: 0}
	if err = session.RequestPty("xterm", 80, 40, tm); err != nil {
	t.Fatalf("req-pty failed: %s", err)
	}

	if err := session.WindowChange(100, 100); err != nil {
	t.Fatalf("window-change failed: %s", err)
	}

	err = session.Shell()
	if err != nil {
	t.Fatalf("session failed: %s", err)
	}

	stdin.Write([]byte("stty size && exit\n"))

	var buf bytes.Buffer
	if _, err := io.Copy(&buf, stdout); err != nil {
	t.Fatalf("reading failed: %s", err)
	}

	if sttyOutput := buf.String(); !strings.Contains(sttyOutput, "100 100") {
	t.Fatalf("terminal WindowChange failure: expected \"100 100\" stty output, got %s", sttyOutput)
	}
	}

	func testOneCipher(t *testing.T, cipher string, cipherOrder []string) {
	server := newServer(t)
	conf := clientConfig()
	conf.Ciphers = []string{cipher}
	// Don't fail if sshd doesn't have the cipher.
	conf.Ciphers = append(conf.Ciphers, cipherOrder...)
	conn, err := server.TryDial(conf)
	if err != nil {
	t.Fatalf("TryDial: %v", err)
	}
	defer conn.Close()

	numBytes := 4096

	// Exercise receiving data from the server
	session, err := conn.NewSession()
	if err != nil {
	skipIfIssue64959(t, err)
	t.Fatalf("NewSession: %v", err)
	}

	out, err := session.Output(fmt.Sprintf("dd if=/dev/zero bs=%d count=1", numBytes))
	if err != nil {
	t.Fatalf("Output: %v", err)
	}

	if len(out) != numBytes {
	t.Fatalf("got %d bytes, want %d bytes", len(out), numBytes)
	}

	// Exercise sending data to the server
	if _, _, err := conn.Conn.SendRequest("drop-me", false, make([]byte, numBytes)); err != nil {
	t.Fatalf("SendRequest: %v", err)
	}
	}

	var deprecatedCiphers = []string{
	"aes128-cbc", "3des-cbc",
	"arcfour128", "arcfour256",
	}

	func TestCiphers(t *testing.T) {
	var config ssh.Config
	config.SetDefaults()
	cipherOrder := append(config.Ciphers, deprecatedCiphers...)

	for _, ciph := range cipherOrder {
	t.Run(ciph, func(t *testing.T) {
	testOneCipher(t, ciph, cipherOrder)
	})
	}
	}

	func TestMACs(t *testing.T) {
	var config ssh.Config
	config.SetDefaults()
	macOrder := config.MACs

	for _, mac := range macOrder {
	t.Run(mac, func(t *testing.T) {
	server := newServer(t)
	conf := clientConfig()
	conf.MACs = []string{mac}
	// Don't fail if sshd doesn't have the MAC.
	conf.MACs = append(conf.MACs, macOrder...)
	if conn, err := server.TryDial(conf); err == nil {
	conn.Close()
	} else {
	t.Fatalf("failed for MAC %q", mac)
	}
	})
	}
	}

	func TestKeyExchanges(t *testing.T) {
	var config ssh.Config
	config.SetDefaults()
	kexOrder := config.KeyExchanges
	// Based on the discussion in #17230, the key exchange algorithms
	// diffie-hellman-group-exchange-sha1 and diffie-hellman-group-exchange-sha256
	// are not included in the default list of supported kex so we have to add them
	// here manually.
	kexOrder = append(kexOrder, "diffie-hellman-group-exchange-sha1", "diffie-hellman-group-exchange-sha256")
	// The key exchange algorithms diffie-hellman-group16-sha512 is disabled by
	// default so we add it here manually.
	kexOrder = append(kexOrder, "diffie-hellman-group16-sha512")
	for _, kex := range kexOrder {
	t.Run(kex, func(t *testing.T) {
	server := newServer(t)
	conf := clientConfig()
	// Don't fail if sshd doesn't have the kex.
	conf.KeyExchanges = append([]string{kex}, kexOrder...)
	conn, err := server.TryDial(conf)
	if err == nil {
	conn.Close()
	} else {
	t.Errorf("failed for kex %q", kex)
	}
	})
	}
	}

	func TestClientAuthAlgorithms(t *testing.T) {
	for _, key := range []string{
	"rsa",
	"ecdsa",
	"ed25519",
	} {
	t.Run(key, func(t *testing.T) {
	server := newServer(t)
	conf := clientConfig()
	conf.SetDefaults()
	conf.Auth = []ssh.AuthMethod{
	ssh.PublicKeys(testSigners[key]),
	}

	conn, err := server.TryDial(conf)
	if err == nil {
	conn.Close()
	} else {
	t.Errorf("failed for key %q", key)
	}
	})
	}
	}