fix: Start SFTP sessions in user home (working directory) (#4549)

* fix: Start SFTP sessions in user home (working directory)

This commit switches to our fork of `pkg/sftp` which includes a Server
option for changing the current working directory.

Attempt to upstream: https://github.com/pkg/sftp/pull/528

Supercedes and closes #4420

Fixes #3620

* Update fork

agent/agent.go

@@ -448,7 +448,18 @@ func (a *agent) init(ctx context.Context) {
 			"sftp": func(session ssh.Session) {
 				session.DisablePTYEmulation()
 
-				server, err := sftp.NewServer(session)
+				var opts []sftp.ServerOption
+				// Change current working directory to the users home
+				// directory so that SFTP connections land there.
+				// https://github.com/coder/coder/issues/3620
+				u, err := user.Current()
+				if err != nil {
+					a.logger.Warn(ctx, "get sftp working directory failed, unable to get current user", slog.Error(err))
+				} else {
+					opts = append(opts, sftp.WithServerWorkingDirectory(u.HomeDir))
+				}
+
+				server, err := sftp.NewServer(session, opts...)
 				if err != nil {
 					a.logger.Debug(session.Context(), "initialize sftp server", slog.Error(err))
 					return

agent/agent_test.go

@@ -10,6 +10,7 @@ import (
 	"net/netip"
 	"os"
 	"os/exec"
+	"os/user"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -212,12 +213,21 @@ func TestAgent(t *testing.T) {
 
 	t.Run("SFTP", func(t *testing.T) {
 		t.Parallel()
+		u, err := user.Current()
+		require.NoError(t, err, "get current user")
+		home := u.HomeDir
+		if runtime.GOOS == "windows" {
+			home = "/" + strings.ReplaceAll(home, "\\", "/")
+		}
 		conn, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)
 		sshClient, err := conn.SSHClient()
 		require.NoError(t, err)
 		defer sshClient.Close()
 		client, err := sftp.NewClient(sshClient)
 		require.NoError(t, err)
+		wd, err := client.Getwd()
+		require.NoError(t, err, "get working directory")
+		require.Equal(t, home, wd, "working directory should be home user home")
 		tempFile := filepath.Join(t.TempDir(), "sftp")
 		file, err := client.Create(tempFile)
 		require.NoError(t, err)