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feat: add support for X11 forwarding (#7205)

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* feat: add support for X11 forwarding

* Only run X forwarding on Linux

* Fix piping

* Fix comments
This commit is contained in:
Kyle Carberry
2023-04-21 10:52:40 -05:00
committed by GitHub
parent 6f06f8dadb
commit f39e6a79de
7 changed files with 324 additions and 11 deletions
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2
agent/agent.go
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@ -161,7 +161,7 @@ type agent struct {
}
func (a *agent) init(ctx context.Context) {
sshSrv, err := agentssh.NewServer(ctx, a.logger.Named("ssh-server"), a.sshMaxTimeout)
sshSrv, err := agentssh.NewServer(ctx, a.logger.Named("ssh-server"), a.filesystem, a.sshMaxTimeout, "")
if err != nil {
panic(err)
}

20
agent/agentssh/agentssh.go
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@ -20,6 +20,7 @@ import (
"github.com/gliderlabs/ssh"
"github.com/pkg/sftp"
"github.com/spf13/afero"
"go.uber.org/atomic"
gossh "golang.org/x/crypto/ssh"
"golang.org/x/xerrors"
@ -48,6 +49,7 @@ const (
type Server struct {
mu sync.RWMutex // Protects following.
fs afero.Fs
listeners map[net.Listener]struct{}
conns map[net.Conn]struct{}
sessions map[ssh.Session]struct{}
@ -58,6 +60,7 @@ type Server struct {
logger slog.Logger
srv *ssh.Server
x11SocketDir string
Env map[string]string
AgentToken func() string
@ -68,7 +71,7 @@ type Server struct {
connCountSSHSession atomic.Int64
}
func NewServer(ctx context.Context, logger slog.Logger, maxTimeout time.Duration) (*Server, error) {
func NewServer(ctx context.Context, logger slog.Logger, fs afero.Fs, maxTimeout time.Duration, x11SocketDir string) (*Server, error) {
// Clients' should ignore the host key when connecting.
// The agent needs to authenticate with coderd to SSH,
// so SSH authentication doesn't improve security.
@ -80,15 +83,20 @@ func NewServer(ctx context.Context, logger slog.Logger, maxTimeout time.Duration
if err != nil {
return nil, err
}
if x11SocketDir == "" {
x11SocketDir = filepath.Join(os.TempDir(), ".X11-unix")
}
forwardHandler := &ssh.ForwardedTCPHandler{}
unixForwardHandler := &forwardedUnixHandler{log: logger}
s := &Server{
listeners: make(map[net.Listener]struct{}),
fs: fs,
conns: make(map[net.Conn]struct{}),
sessions: make(map[ssh.Session]struct{}),
logger: logger,
x11SocketDir: x11SocketDir,
}
s.srv = &ssh.Server{
@ -125,6 +133,7 @@ func NewServer(ctx context.Context, logger slog.Logger, maxTimeout time.Duration
"streamlocal-forward@openssh.com": unixForwardHandler.HandleSSHRequest,
"cancel-streamlocal-forward@openssh.com": unixForwardHandler.HandleSSHRequest,
},
X11Callback: s.x11Callback,
ServerConfigCallback: func(ctx ssh.Context) *gossh.ServerConfig {
return &gossh.ServerConfig{
NoClientAuth: true,
@ -163,6 +172,15 @@ func (s *Server) sessionHandler(session ssh.Session) {
ctx := session.Context()
x11, hasX11 := session.X11()
if hasX11 {
handled := s.x11Handler(session.Context(), x11)
if !handled {
_ = session.Exit(1)
return
}
}
switch ss := session.Subsystem(); ss {
case "":
case "sftp":

6
agent/agentssh/agentssh_test.go
View File

@ -10,6 +10,7 @@ import (
"sync"
"testing"
"github.com/spf13/afero"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
"go.uber.org/atomic"
@ -32,7 +33,7 @@ func TestNewServer_ServeClient(t *testing.T) {
ctx := context.Background()
logger := slogtest.Make(t, nil)
s, err := agentssh.NewServer(ctx, logger, 0)
s, err := agentssh.NewServer(ctx, logger, afero.NewMemMapFs(), 0, "")
require.NoError(t, err)
// The assumption is that these are set before serving SSH connections.
@ -50,6 +51,7 @@ func TestNewServer_ServeClient(t *testing.T) {
}()
c := sshClient(t, ln.Addr().String())
var b bytes.Buffer
sess, err := c.NewSession()
sess.Stdout = &b
@ -72,7 +74,7 @@ func TestNewServer_CloseActiveConnections(t *testing.T) {
ctx := context.Background()
logger := slogtest.Make(t, &slogtest.Options{IgnoreErrors: true})
s, err := agentssh.NewServer(ctx, logger, 0)
s, err := agentssh.NewServer(ctx, logger, afero.NewMemMapFs(), 0, "")
require.NoError(t, err)
// The assumption is that these are set before serving SSH connections.

190
agent/agentssh/x11.go Normal file
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@ -0,0 +1,190 @@
package agentssh
import (
"context"
"encoding/binary"
"encoding/hex"
"errors"
"fmt"
"net"
"os"
"path/filepath"
"strconv"
"time"
"github.com/gliderlabs/ssh"
"github.com/gofrs/flock"
"github.com/spf13/afero"
gossh "golang.org/x/crypto/ssh"
"golang.org/x/xerrors"
"cdr.dev/slog"
)
// x11Callback is called when the client requests X11 forwarding.
// It adds an Xauthority entry to the Xauthority file.
func (s *Server) x11Callback(ctx ssh.Context, x11 ssh.X11) bool {
hostname, err := os.Hostname()
if err != nil {
s.logger.Warn(ctx, "failed to get hostname", slog.Error(err))
return false
}
err = s.fs.MkdirAll(s.x11SocketDir, 0o700)
if err != nil {
s.logger.Warn(ctx, "failed to make the x11 socket dir", slog.F("dir", s.x11SocketDir), slog.Error(err))
return false
}
err = addXauthEntry(ctx, s.fs, hostname, strconv.Itoa(int(x11.ScreenNumber)), x11.AuthProtocol, x11.AuthCookie)
if err != nil {
s.logger.Warn(ctx, "failed to add Xauthority entry", slog.Error(err))
return false
}
return true
}
// x11Handler is called when a session has requested X11 forwarding.
// It listens for X11 connections and forwards them to the client.
func (s *Server) x11Handler(ctx ssh.Context, x11 ssh.X11) bool {
serverConn, valid := ctx.Value(ssh.ContextKeyConn).(*gossh.ServerConn)
if !valid {
s.logger.Warn(ctx, "failed to get server connection")
return false
}
listener, err := net.Listen("unix", filepath.Join(s.x11SocketDir, fmt.Sprintf("X%d", x11.ScreenNumber)))
if err != nil {
s.logger.Warn(ctx, "failed to listen for X11", slog.Error(err))
return false
}
s.trackListener(listener, true)
go func() {
defer listener.Close()
defer s.trackListener(listener, false)
handledFirstConnection := false
for {
conn, err := listener.Accept()
if err != nil {
if errors.Is(err, net.ErrClosed) {
return
}
s.logger.Warn(ctx, "failed to accept X11 connection", slog.Error(err))
return
}
if x11.SingleConnection && handledFirstConnection {
s.logger.Warn(ctx, "X11 connection rejected because single connection is enabled")
_ = conn.Close()
continue
}
handledFirstConnection = true
unixConn, ok := conn.(*net.UnixConn)
if !ok {
s.logger.Warn(ctx, fmt.Sprintf("failed to cast connection to UnixConn. got: %T", conn))
return
}
unixAddr, ok := unixConn.LocalAddr().(*net.UnixAddr)
if !ok {
s.logger.Warn(ctx, fmt.Sprintf("failed to cast local address to UnixAddr. got: %T", unixConn.LocalAddr()))
return
}
channel, reqs, err := serverConn.OpenChannel("x11", gossh.Marshal(struct {
OriginatorAddress string
OriginatorPort uint32
}{
OriginatorAddress: unixAddr.Name,
OriginatorPort: 0,
}))
if err != nil {
s.logger.Warn(ctx, "failed to open X11 channel", slog.Error(err))
return
}
go gossh.DiscardRequests(reqs)
go Bicopy(ctx, conn, channel)
}
}()
return true
}
// addXauthEntry adds an Xauthority entry to the Xauthority file.
// The Xauthority file is located at ~/.Xauthority.
func addXauthEntry(ctx context.Context, fs afero.Fs, host string, display string, authProtocol string, authCookie string) error {
// Get the Xauthority file path
homeDir, err := os.UserHomeDir()
if err != nil {
return xerrors.Errorf("failed to get user home directory: %w", err)
}
xauthPath := filepath.Join(homeDir, ".Xauthority")
lock := flock.New(xauthPath)
defer lock.Close()
ok, err := lock.TryLockContext(ctx, 100*time.Millisecond)
if !ok {
return xerrors.Errorf("failed to lock Xauthority file: %w", err)
}
if err != nil {
return xerrors.Errorf("failed to lock Xauthority file: %w", err)
}
// Open or create the Xauthority file
file, err := fs.OpenFile(xauthPath, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0o600)
if err != nil {
return xerrors.Errorf("failed to open Xauthority file: %w", err)
}
defer file.Close()
// Convert the authCookie from hex string to byte slice
authCookieBytes, err := hex.DecodeString(authCookie)
if err != nil {
return xerrors.Errorf("failed to decode auth cookie: %w", err)
}
// Write Xauthority entry
family := uint16(0x0100) // FamilyLocal
err = binary.Write(file, binary.BigEndian, family)
if err != nil {
return xerrors.Errorf("failed to write family: %w", err)
}
err = binary.Write(file, binary.BigEndian, uint16(len(host)))
if err != nil {
return xerrors.Errorf("failed to write host length: %w", err)
}
_, err = file.WriteString(host)
if err != nil {
return xerrors.Errorf("failed to write host: %w", err)
}
err = binary.Write(file, binary.BigEndian, uint16(len(display)))
if err != nil {
return xerrors.Errorf("failed to write display length: %w", err)
}
_, err = file.WriteString(display)
if err != nil {
return xerrors.Errorf("failed to write display: %w", err)
}
err = binary.Write(file, binary.BigEndian, uint16(len(authProtocol)))
if err != nil {
return xerrors.Errorf("failed to write auth protocol length: %w", err)
}
_, err = file.WriteString(authProtocol)
if err != nil {
return xerrors.Errorf("failed to write auth protocol: %w", err)
}
err = binary.Write(file, binary.BigEndian, uint16(len(authCookieBytes)))
if err != nil {
return xerrors.Errorf("failed to write auth cookie length: %w", err)
}
_, err = file.Write(authCookieBytes)
if err != nil {
return xerrors.Errorf("failed to write auth cookie: %w", err)
}
return nil
}

99
agent/agentssh/x11_test.go Normal file
View File

@ -0,0 +1,99 @@
package agentssh_test
import (
"context"
"encoding/hex"
"net"
"os"
"path/filepath"
"runtime"
"testing"
"github.com/gliderlabs/ssh"
"github.com/spf13/afero"
"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
"go.uber.org/atomic"
gossh "golang.org/x/crypto/ssh"
"cdr.dev/slog"
"cdr.dev/slog/sloggers/slogtest"
"github.com/coder/coder/agent/agentssh"
"github.com/coder/coder/codersdk/agentsdk"
"github.com/coder/coder/testutil"
)
func TestServer_X11(t *testing.T) {
t.Parallel()
if runtime.GOOS != "linux" {
t.Skip("X11 forwarding is only supported on Linux")
}
ctx := context.Background()
logger := slogtest.Make(t, nil).Leveled(slog.LevelDebug)
fs := afero.NewOsFs()
dir := t.TempDir()
s, err := agentssh.NewServer(ctx, logger, fs, 0, dir)
require.NoError(t, err)
defer s.Close()
// The assumption is that these are set before serving SSH connections.
s.AgentToken = func() string { return "" }
s.Manifest = atomic.NewPointer(&agentsdk.Manifest{})
ln, err := net.Listen("tcp", "127.0.0.1:0")
require.NoError(t, err)
done := make(chan struct{})
go func() {
defer close(done)
err := s.Serve(ln)
assert.Error(t, err) // Server is closed.
}()
c := sshClient(t, ln.Addr().String())
sess, err := c.NewSession()
require.NoError(t, err)
reply, err := sess.SendRequest("x11-req", true, gossh.Marshal(ssh.X11{
AuthProtocol: "MIT-MAGIC-COOKIE-1",
AuthCookie: hex.EncodeToString([]byte("cookie")),
ScreenNumber: 0,
}))
require.NoError(t, err)
assert.True(t, reply)
err = sess.Shell()
require.NoError(t, err)
x11Chans := c.HandleChannelOpen("x11")
payload := "hello world"
require.Eventually(t, func() bool {
conn, err := net.Dial("unix", filepath.Join(dir, "X0"))
if err == nil {
_, err = conn.Write([]byte(payload))
assert.NoError(t, err)
_ = conn.Close()
}
return err == nil
}, testutil.WaitShort, testutil.IntervalFast)
x11 := <-x11Chans
ch, reqs, err := x11.Accept()
require.NoError(t, err)
go gossh.DiscardRequests(reqs)
got := make([]byte, len(payload))
_, err = ch.Read(got)
require.NoError(t, err)
assert.Equal(t, payload, string(got))
_ = ch.Close()
_ = s.Close()
<-done
// Ensure the Xauthority file was written!
home, err := os.UserHomeDir()
require.NoError(t, err)
_, err = fs.Stat(filepath.Join(home, ".Xauthority"))
require.NoError(t, err)
}

2
go.mod
View File

@ -45,7 +45,7 @@ replace tailscale.com => github.com/coder/tailscale v1.1.1-0.20230418202606-ed93
// repo as tailscale.com/tempfork/gliderlabs/ssh, however, we can't replace the
// subpath and it includes changes to golang.org/x/crypto/ssh as well which
// makes importing it directly a bit messy.
replace github.com/gliderlabs/ssh => github.com/coder/ssh v0.0.0-20220811105153-fcea99919338
replace github.com/gliderlabs/ssh => github.com/coder/ssh v0.0.0-20230419180646-49c741437b53
// Waiting on https://github.com/imulab/go-scim/pull/95 to merge.
replace github.com/imulab/go-scim/pkg/v2 => github.com/coder/go-scim/pkg/v2 v2.0.0-20230221055123-1d63c1222136

4
go.sum
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@ -343,6 +343,10 @@ github.com/coder/retry v1.3.1-0.20230210155434-e90a2e1e091d h1:09JG37IgTB6n3ouX9
github.com/coder/retry v1.3.1-0.20230210155434-e90a2e1e091d/go.mod h1:r+1J5i/989wt6CUeNSuvFKKA9hHuKKPMxdzDbTuvwwk=
github.com/coder/ssh v0.0.0-20220811105153-fcea99919338 h1:tN5GKFT68YLVzJoA8AHuiMNJ0qlhoD3pGN3JY9gxSko=
github.com/coder/ssh v0.0.0-20220811105153-fcea99919338/go.mod h1:ZSS+CUoKHDrqVakTfTWUlKSr9MtMFkC4UvtQKD7O914=
github.com/coder/ssh v0.0.0-20230419175457-0612ba535202 h1:1I/Im5ZUan1Y9ypAr6VuAKQ4NbvEy/frR3cV86pKQk8=
github.com/coder/ssh v0.0.0-20230419175457-0612ba535202/go.mod h1:ZSS+CUoKHDrqVakTfTWUlKSr9MtMFkC4UvtQKD7O914=
github.com/coder/ssh v0.0.0-20230419180646-49c741437b53 h1:kaLOp3tlVnbOJIjmAvXuBTgeWWoZZlJJJ4QGeSMjOnA=
github.com/coder/ssh v0.0.0-20230419180646-49c741437b53/go.mod h1:ZSS+CUoKHDrqVakTfTWUlKSr9MtMFkC4UvtQKD7O914=
github.com/coder/tailscale v1.1.1-0.20230418202606-ed9307cf1b22 h1:bvGOqnI0ITbwOZFQ0SZ4MBw/8LLUEjxmNu57XEujrfQ=
github.com/coder/tailscale v1.1.1-0.20230418202606-ed9307cf1b22/go.mod h1:jpg+77g19FpXL43U1VoIqoSg1K/Vh5CVxycGldQ8KhA=
github.com/coder/terraform-provider-coder v0.6.23 h1:O2Rcj0umez4DfVdGnKZi63z1Xzxd0IQOn9VQDB8YU8g=