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)

go.mod

@@ -51,6 +51,12 @@ replace tailscale.com => github.com/coder/tailscale v1.1.1-0.20221015033036-5861
 // makes importing it directly a bit messy.
 replace github.com/gliderlabs/ssh => github.com/coder/ssh v0.0.0-20220811105153-fcea99919338
 
+// The sftp server implementation used by us does not support changing
+// the working directory, this fork adds support for it.
+//
+// Attempt to upstream: https://github.com/pkg/sftp/pull/528
+replace github.com/pkg/sftp => github.com/mafredri/sftp v1.13.6-0.20221014125459-6a7168cf46fd
+
 require (
 	cdr.dev/slog v1.4.2-0.20220525200111-18dce5c2cd5f
 	cloud.google.com/go/compute v1.10.0

go.sum

@@ -1225,6 +1225,8 @@ github.com/lucasb-eyer/go-colorful v1.2.0 h1:1nnpGOrhyZZuNyfu1QjKiUICQ74+3FNCN69
 github.com/lucasb-eyer/go-colorful v1.2.0/go.mod h1:R4dSotOR9KMtayYi1e77YzuveK+i7ruzyGqttikkLy0=
 github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0/go.mod h1:zJYVVT2jmtg6P3p1VtQj7WsuWi/y4VnjVBn7F8KPB3I=
 github.com/lyft/protoc-gen-star v0.5.3/go.mod h1:V0xaHgaf5oCCqmcxYcWiDfTiKsZsRc87/1qhoTACD8w=
+github.com/mafredri/sftp v1.13.6-0.20221014125459-6a7168cf46fd h1:X7ZK1YGbCoPkllDq/lG5PLV4k3LVddypzoH5hVgzmiw=
+github.com/mafredri/sftp v1.13.6-0.20221014125459-6a7168cf46fd/go.mod h1:wHDZ0IZX6JcBYRK1TH9bcVq8G7TLpVHYIGJRFnmPfxg=
 github.com/mafredri/udp v0.1.2-0.20220805105907-b2872e92e98d h1:E+lU8/1jcUd3guqaRvjAGCcwoPe7jcYrNv9K0OzEwdQ=
 github.com/mafredri/udp v0.1.2-0.20220805105907-b2872e92e98d/go.mod h1:GUd681aT3Tj7pdNkUtqBz5pp/GLMGIaMI9Obq6+ob48=
 github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
@@ -1505,10 +1507,6 @@ github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINE
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/profile v1.6.0/go.mod h1:qBsxPvzyUincmltOk6iyRVxHYg4adc0OFOv72ZdLa18=
-github.com/pkg/sftp v1.10.1/go.mod h1:lYOWFsE0bwd1+KfKJaKeuokY15vzFx25BLbzYYoAxZI=
-github.com/pkg/sftp v1.13.1/go.mod h1:3HaPG6Dq1ILlpPZRO0HVMrsydcdLt6HRDccSgb87qRg=
-github.com/pkg/sftp v1.13.5 h1:a3RLUqkyjYRtBTZJZ1VRrKbN3zhuPLlUc3sphVz81go=
-github.com/pkg/sftp v1.13.5/go.mod h1:wHDZ0IZX6JcBYRK1TH9bcVq8G7TLpVHYIGJRFnmPfxg=
 github.com/pmezard/go-difflib v0.0.0-20151028094244-d8ed2627bdf0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=