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scp.go
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scp.go
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/*
* Teleport
* Copyright (C) 2023 Gravitational, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
// Package scp handles file uploads and downloads via SCP command.
// See https://web.archive.org/web/20170215184048/https://blogs.oracle.com/janp/entry/how_the_scp_protocol_works
// for the high-level protocol overview.
//
// Authoritative source for the protocol is the source code for OpenSSH scp:
// https://github.com/openssh/openssh-portable/blob/add926dd1bbe3c4db06e27cab8ab0f9a3d00a0c2/scp.c
package scp
import (
"bufio"
"errors"
"fmt"
"io"
"os"
"path/filepath"
"strconv"
"strings"
"time"
"github.com/gravitational/trace"
log "github.com/sirupsen/logrus"
"github.com/gravitational/teleport"
"github.com/gravitational/teleport/lib/events"
"github.com/gravitational/teleport/lib/utils"
)
const (
// OKByte is SCP OK message bytes
OKByte = 0x0
// WarnByte tells that next goes a warning string
WarnByte = 0x1
// ErrByte tells that next goes an error string
ErrByte = 0x2
)
// Flags describes SCP command line flags
type Flags struct {
// Source indicates upload mode
Source bool
// Sink indicates receive mode
Sink bool
// Verbose sets a logging mode
Verbose bool
// Target sets targeted files to be transferred
Target []string
// Recursive indicates recursive file transfer
Recursive bool
// RemoteAddr is a remote host address
RemoteAddr string
// LocalAddr is a local host address
LocalAddr string
// DirectoryMode indicates that a directory is being sent.
DirectoryMode bool
// PreserveAttrs preserves access and modification times
// from the original file
PreserveAttrs bool
}
// Config describes Command configuration settings
type Config struct {
// Flags is a set of SCP command line flags
Flags Flags
// User is a user who runs SCP command
User string
// AuditLog is AuditLog log
AuditLog events.AuditLogSessionStreamer
// ProgressWriter is a writer for printing the progress
// (used only on the client)
ProgressWriter io.Writer
// FileSystem is a source file system abstraction for the SCP command
FileSystem FileSystem
// RemoteLocation is a destination location of the file
RemoteLocation string
// RunOnServer is low level API flag that indicates that
// this command will be run on the server
RunOnServer bool
// Log optionally specifies the logger
Log log.FieldLogger
}
// Command is an API that describes command operations
type Command interface {
// Execute processes SCP traffic
Execute(ch io.ReadWriter) error
// GetRemoteShellCmd returns a remote shell command that
// has to be executed on the remove server (handled by Teleport)
GetRemoteShellCmd() (string, error)
}
// FileSystem is an interface that abstracts file system methods used in SCP command functions
type FileSystem interface {
// IsDir returns true if a given file path is a directory
IsDir(path string) bool
// GetFileInfo returns FileInfo for a given file path
GetFileInfo(filePath string) (FileInfo, error)
// MkDir creates a directory
MkDir(path string, mode int) error
// OpenFile opens a file and returns its Reader
OpenFile(filePath string) (io.ReadCloser, error)
// CreateFile creates a new file
CreateFile(filePath string, length uint64) (io.WriteCloser, error)
// Chmod sets file permissions
Chmod(path string, mode int) error
// Chtimes sets file access and modification time
Chtimes(path string, atime, mtime time.Time) error
}
// FileInfo provides access to file metadata
type FileInfo interface {
// IsDir returns true if a file is a directory
IsDir() bool
// ReadDir returns information of directory files
ReadDir() ([]FileInfo, error)
// GetName returns a file name
GetName() string
// GetPath returns a file path
GetPath() string
// GetModePerm returns file permissions
GetModePerm() os.FileMode
// GetSize returns file size
GetSize() int64
// GetModTime returns file modification time
GetModTime() time.Time
// GetAccessTime returns file last access time
GetAccessTime() time.Time
}
// CreateDownloadCommand configures and returns a command used
// to download a file
func CreateDownloadCommand(cfg Config) (Command, error) {
cfg.Flags.Sink = true
cfg.Flags.Source = false
cmd, err := CreateCommand(cfg)
if err != nil {
return nil, trace.Wrap(err)
}
return cmd, nil
}
// CreateUploadCommand configures and returns a command used
// to upload a file
func CreateUploadCommand(cfg Config) (Command, error) {
cfg.Flags.Sink = false
cfg.Flags.Source = true
cmd, err := CreateCommand(cfg)
if err != nil {
return nil, trace.Wrap(err)
}
return cmd, nil
}
// CheckAndSetDefaults checks and sets default values
func (c *Config) CheckAndSetDefaults() error {
logger := c.Log
if logger == nil {
logger = log.StandardLogger()
}
c.Log = logger.WithFields(log.Fields{
teleport.ComponentKey: "SCP",
teleport.ComponentFields: log.Fields{
"LocalAddr": c.Flags.LocalAddr,
"RemoteAddr": c.Flags.RemoteAddr,
"Target": c.Flags.Target,
"PreserveAttrs": c.Flags.PreserveAttrs,
"User": c.User,
"RunOnServer": c.RunOnServer,
"RemoteLocation": c.RemoteLocation,
},
})
if c.FileSystem == nil {
c.FileSystem = &localFileSystem{}
}
if c.User == "" {
return trace.BadParameter("missing User parameter")
}
return nil
}
// CreateCommand creates and returns a new SCP command with
// specified configuration.
func CreateCommand(cfg Config) (Command, error) {
err := cfg.CheckAndSetDefaults()
if err != nil {
return nil, trace.Wrap(err)
}
return &command{
Config: cfg,
log: cfg.Log,
}, nil
}
// Command mimics behavior of SCP command line tool
// to teleport can pretend it launches real SCP behind the scenes
type command struct {
Config
log log.FieldLogger
}
// Execute implements SSH file copy (SCP). It is called on both tsh (client)
// and teleport (server) side.
func (cmd *command) Execute(ch io.ReadWriter) (err error) {
if cmd.Flags.Source {
return trace.Wrap(cmd.serveSource(ch))
}
return trace.Wrap(cmd.serveSink(ch))
}
// GetRemoteShellCmd returns a command line to copy
// file(s) or a directory to a remote location
func (cmd *command) GetRemoteShellCmd() (shellCmd string, err error) {
if cmd.RemoteLocation == "" {
return "", trace.BadParameter("missing remote file location")
}
// "impersonate" SCP to a server
// See https://docstore.mik.ua/orelly/networking_2ndEd/ssh/ch03_08.htm, section "scp1 Details"
// about the hidden to/from switches
shellCmd = "/usr/bin/scp -f"
if cmd.Flags.Source {
shellCmd = "/usr/bin/scp -t"
}
if cmd.Flags.Recursive {
shellCmd += " -r"
}
if cmd.Flags.DirectoryMode {
shellCmd += " -d"
}
if cmd.Flags.PreserveAttrs {
shellCmd += " -p"
}
shellCmd += (" " + cmd.RemoteLocation)
return shellCmd, nil
}
func (cmd *command) serveSource(ch io.ReadWriter) (retErr error) {
defer func() {
// If anything goes wrong, notify the remote side so it can terminate
// with an error too.
// This is necessary to emit correct audit events (if the remote end is
// emitting them).
if retErr != nil {
cmd.sendErr(ch, retErr)
}
}()
fileInfos := make([]FileInfo, len(cmd.Flags.Target))
for i := range cmd.Flags.Target {
fileInfo, err := cmd.FileSystem.GetFileInfo(cmd.Flags.Target[i])
if err != nil {
return trace.Errorf("could not access local path %q: %v", cmd.Flags.Target[i], err)
}
if fileInfo.IsDir() && !cmd.Flags.Recursive {
// Note: using any other error constructor (e.g. BadParameter)
// might lead to relogin attempt and a completely obscure
// error message
return trace.Errorf("%v is a directory, use -r flag to copy recursively", fileInfo.GetName())
}
fileInfos[i] = fileInfo
}
r := newReader(ch)
if err := r.read(); err != nil {
return trace.Wrap(err)
}
for i := range fileInfos {
info := fileInfos[i]
if info.IsDir() {
if err := cmd.sendDir(r, ch, info); err != nil {
return trace.Wrap(err)
}
} else {
if err := cmd.sendFile(r, ch, info); err != nil {
return trace.Wrap(err)
}
}
}
cmd.log.Debug("Send completed.")
return nil
}
func (cmd *command) sendDir(r *reader, ch io.ReadWriter, fileInfo FileInfo) error {
if cmd.Config.Flags.PreserveAttrs {
if err := cmd.sendFileTimes(r, ch, fileInfo); err != nil {
return trace.Wrap(err)
}
}
if err := cmd.sendDirMode(r, ch, fileInfo); err != nil {
return trace.Wrap(err)
}
cmd.log.Debug("sendDir got OK")
fileInfos, err := fileInfo.ReadDir()
if err != nil {
return trace.Wrap(err)
}
for i := range fileInfos {
info := fileInfos[i]
if info.IsDir() {
err := cmd.sendDir(r, ch, info)
if err != nil {
return trace.Wrap(err)
}
} else {
err := cmd.sendFile(r, ch, info)
if err != nil {
return trace.Wrap(err)
}
}
}
if _, err = fmt.Fprintf(ch, "E\n"); err != nil {
return trace.Wrap(err)
}
return trace.Wrap(r.read())
}
func (cmd *command) sendFile(r *reader, ch io.ReadWriter, fileInfo FileInfo) error {
reader, err := cmd.FileSystem.OpenFile(fileInfo.GetPath())
if err != nil {
return trace.Wrap(err)
}
defer reader.Close()
if cmd.Config.Flags.PreserveAttrs {
if err := cmd.sendFileTimes(r, ch, fileInfo); err != nil {
return trace.Wrap(err)
}
}
if err := cmd.sendFileMode(r, ch, fileInfo); err != nil {
return trace.Wrap(err)
}
n, err := io.Copy(ch, reader)
if err != nil {
return trace.Wrap(err)
}
if n != fileInfo.GetSize() {
return trace.Errorf("short write: written %v, expected %v", n, fileInfo.GetSize())
}
// report progress:
if cmd.ProgressWriter != nil {
statusMessage := fmt.Sprintf("-> %s (%d)", fileInfo.GetPath(), fileInfo.GetSize())
defer fmt.Fprint(cmd.ProgressWriter, utils.EscapeControl(statusMessage)+"\n")
}
if err := sendOK(ch); err != nil {
return trace.Wrap(err)
}
return trace.Wrap(r.read())
}
func (cmd *command) sendErr(ch io.Writer, err error) {
out := fmt.Sprintf("%c%s\n", byte(ErrByte), err)
if _, err := ch.Write([]byte(out)); err != nil {
cmd.log.Debugf("Failed sending SCP error message to the remote side: %v.", err)
}
}
// serveSink executes file uploading, when a remote server sends file(s)
// via SCP
func (cmd *command) serveSink(ch io.ReadWriter) error {
// Validate that if directory mode flag was sent, the target is an actual
// directory.
if cmd.Flags.DirectoryMode {
if len(cmd.Flags.Target) != 1 {
return trace.BadParameter("in directory mode, only single upload target is allowed but %q provided",
cmd.Flags.Target)
}
if !cmd.FileSystem.IsDir(cmd.Flags.Target[0]) {
return trace.BadParameter("target path must be a directory")
}
}
rootDir := localDir
if cmd.targetDirExists() {
rootDir = newPathFromDir(cmd.Flags.Target[0])
} else if cmd.Flags.Target[0] != "" {
// Extract potential base directory from the target
rootDir = newPathFromDir(filepath.Dir(cmd.Flags.Target[0]))
}
if err := sendOK(ch); err != nil {
return trace.Wrap(err)
}
var st state
st.path = rootDir
var b [1]byte
scanner := bufio.NewScanner(ch)
for {
n, err := ch.Read(b[:])
if err != nil {
if errors.Is(err, io.EOF) {
return nil
}
return trace.Wrap(err)
}
if n < 1 {
return trace.Errorf("unexpected error, read 0 bytes")
}
if b[0] == OKByte {
continue
}
scanner.Scan()
if err := scanner.Err(); err != nil {
return trace.Wrap(err)
}
if err := cmd.processCommand(ch, &st, b[0], scanner.Text()); err != nil {
return trace.Wrap(err)
}
if err := sendOK(ch); err != nil {
return trace.Wrap(err)
}
}
}
func (cmd *command) processCommand(ch io.ReadWriter, st *state, b byte, line string) error {
cmd.log.Debugf("<- %v %v", string(b), line)
switch b {
case WarnByte, ErrByte:
return trace.Errorf("error from sender: %q", line)
case 'C':
f, err := parseNewFile(line)
if err != nil {
return trace.Wrap(err)
}
err = cmd.receiveFile(st, *f, ch)
if err != nil {
return trace.Wrap(err)
}
return nil
case 'D':
d, err := parseNewFile(line)
if err != nil {
return trace.Wrap(err)
}
if err := cmd.receiveDir(st, *d, ch); err != nil {
return trace.Wrap(err)
}
return nil
case 'E':
if len(st.path) == 0 {
return trace.Errorf("empty path")
}
return cmd.updateDirTimes(st.pop())
case 'T':
stat, err := parseFileTimes(line)
if err != nil {
return trace.Wrap(err)
}
st.stat = stat
return nil
}
return trace.Errorf("got unrecognized command: %v", string(b))
}
func (cmd *command) receiveFile(st *state, fc newFileCmd, ch io.ReadWriter) error {
cmd.log.Debugf("scp.receiveFile(%v): %v", cmd.Flags.Target, fc.Name)
// Unless target specifies a file, use the file name from the command
path := cmd.Flags.Target[0]
if cmd.FileSystem.IsDir(cmd.Flags.Target[0]) {
path = st.makePath(fc.Name)
}
writer, err := cmd.FileSystem.CreateFile(path, fc.Length)
if err != nil {
return trace.Wrap(err)
}
defer writer.Close()
// report progress:
if cmd.ProgressWriter != nil {
statusMessage := fmt.Sprintf("<- %s (%d)", path, fc.Length)
defer fmt.Fprint(cmd.ProgressWriter, utils.EscapeControl(statusMessage)+"\n")
}
if err = sendOK(ch); err != nil {
return trace.Wrap(err)
}
n, err := io.CopyN(writer, ch, int64(fc.Length))
if err != nil {
return trace.Wrap(err)
}
if n != int64(fc.Length) {
return trace.Errorf("unexpected file copy length: %v", n)
}
// Change the file permissions only when client requested it.
if cmd.Flags.PreserveAttrs {
if err := cmd.FileSystem.Chmod(path, int(fc.Mode)); err != nil {
return trace.Wrap(err)
}
}
if st.stat != nil {
err = cmd.FileSystem.Chtimes(path, st.stat.Atime, st.stat.Mtime)
if err != nil {
return trace.Wrap(err)
}
}
cmd.log.Debugf("File %v(%v) copied to %v.", fc.Name, fc.Length, path)
return nil
}
func (cmd *command) receiveDir(st *state, fc newFileCmd, ch io.ReadWriter) error {
cmd.log.Debugf("scp.receiveDir(%v): %v", cmd.Flags.Target, fc.Name)
if cmd.FileSystem.IsDir(cmd.Flags.Target[0]) {
// Copying into an existing directory? append to it:
st.push(fc.Name, st.stat)
} else {
// If target specifies a new directory, we need to reset
// state with it
st.path = newPathFromDirAndTimes(cmd.Flags.Target[0], st.stat)
}
targetDir := st.path.join()
err := cmd.FileSystem.MkDir(targetDir, int(fc.Mode))
if err != nil {
return trace.ConvertSystemError(err)
}
return nil
}
func (cmd *command) sendDirMode(r *reader, ch io.Writer, fileInfo FileInfo) error {
out := fmt.Sprintf("D%04o 0 %s\n", fileInfo.GetModePerm(), fileInfo.GetName())
cmd.log.WithField("cmd", out).Debug("Send directory mode.")
_, err := io.WriteString(ch, out)
if err != nil {
return trace.Wrap(err)
}
return trace.Wrap(r.read())
}
func (cmd *command) sendFileTimes(r *reader, ch io.Writer, fileInfo FileInfo) error {
// OpenSSH handles nanoseconds to a certain precision
// which is not sufficient to keep the exact timestamps:
// See these for details:
// https://github.com/openssh/openssh-portable/blob/279261e1ea8150c7c64ab5fe7cb4a4ea17acbb29/scp.c#L619-L621
// https://github.com/openssh/openssh-portable/blob/279261e1ea8150c7c64ab5fe7cb4a4ea17acbb29/scp.c#L1332
// https://github.com/openssh/openssh-portable/blob/279261e1ea8150c7c64ab5fe7cb4a4ea17acbb29/scp.c#L1344
//
// Se we copy its behavior and drop nanoseconds entirely
out := fmt.Sprintf("T%d 0 %d 0\n",
fileInfo.GetModTime().Unix(),
fileInfo.GetAccessTime().Unix(),
)
cmd.log.WithField("cmd", out).Debug("Send file times.")
_, err := io.WriteString(ch, out)
if err != nil {
return trace.Wrap(err)
}
return trace.Wrap(r.read())
}
func (cmd *command) sendFileMode(r *reader, ch io.Writer, fileInfo FileInfo) error {
out := fmt.Sprintf("C%04o %d %s\n",
fileInfo.GetModePerm(),
fileInfo.GetSize(),
fileInfo.GetName(),
)
cmd.log.WithField("cmd", out).Debug("Send file mode.")
_, err := io.WriteString(ch, out)
if err != nil {
return trace.Wrap(err)
}
return trace.Wrap(r.read())
}
func (cmd *command) updateDirTimes(path pathSegments) error {
if stat := path[len(path)-1].stat; stat != nil {
err := cmd.FileSystem.Chtimes(path.join(), stat.Atime, stat.Mtime)
if err != nil {
return trace.ConvertSystemError(err)
}
}
return nil
}
func (cmd *command) targetDirExists() bool {
return len(cmd.Flags.Target) != 0 && cmd.FileSystem.IsDir(cmd.Flags.Target[0])
}
func (r newFileCmd) String() string {
return fmt.Sprintf("newFileCmd(mode=%o,len=%d,name=%v)", r.Mode, r.Length, r.Name)
}
type newFileCmd struct {
Mode int64
Length uint64
Name string
}
func parseNewFile(line string) (*newFileCmd, error) {
parts := strings.SplitN(line, " ", 3)
if len(parts) != 3 {
return nil, trace.Errorf("broken command")
}
c := newFileCmd{}
var err error
if c.Mode, err = strconv.ParseInt(parts[0], 8, 32); err != nil {
return nil, trace.Wrap(err)
}
if c.Length, err = strconv.ParseUint(parts[1], 10, 64); err != nil {
return nil, trace.Wrap(err)
}
// Don't allow malicious servers to send bad directory names. For more
// details, see:
// * https://sintonen.fi/advisories/scp-client-multiple-vulnerabilities.txt
// * https://github.com/openssh/openssh-portable/commit/6010c03
c.Name = parts[2]
if len(c.Name) == 0 || strings.HasPrefix(c.Name, string(filepath.Separator)) || c.Name == "." || c.Name == ".." {
return nil, trace.BadParameter("invalid name")
}
return &c, nil
}
type mtimeCmd struct {
Mtime time.Time
Atime time.Time
}
// parseFileTimes parses the input with access/modification file times:
//
// T<mtime.sec> <mtime.usec> <atime.sec> <atime.usec>
//
// Note that the leading 'T' will not be part of the input as it has already
// been seen and removed
func parseFileTimes(line string) (*mtimeCmd, error) {
parts := strings.SplitN(line, " ", 4)
if len(parts) != 4 {
return nil, trace.Errorf("broken mtime command")
}
var err error
vars := make([]int64, 4)
for i := range vars {
if vars[i], err = strconv.ParseInt(parts[i], 10, 64); err != nil {
return nil, trace.Wrap(err)
}
}
return &mtimeCmd{
Mtime: time.Unix(vars[0], vars[1]),
Atime: time.Unix(vars[2], vars[3]),
}, nil
}
func sendOK(ch io.ReadWriter) error {
_, err := ch.Write([]byte{OKByte})
if err != nil {
return trace.Wrap(err)
}
return nil
}
type state struct {
path pathSegments
// stat optionally specifies access/modification time for the current file/directory
stat *mtimeCmd
}
func (r pathSegments) join(elems ...string) string {
path := make([]string, 0, len(r))
for _, s := range r {
path = append(path, s.dir)
}
return filepath.Join(append(path, elems...)...)
}
var localDir = newPathFromDir(".")
func newPathFromDir(dir string) pathSegments {
return pathSegments{{dir: dir}}
}
func newPathFromDirAndTimes(dir string, stat *mtimeCmd) pathSegments {
return pathSegments{{dir: dir, stat: stat}}
}
type pathSegments []pathSegment
type pathSegment struct {
dir string
// stat optionally specifies access/modification time for the directory
stat *mtimeCmd
}
func (st *state) push(dir string, stat *mtimeCmd) {
st.path = append(st.path, pathSegment{dir: dir, stat: stat})
}
// pop removes the last segment from the current path.
// Returns the old path as a result
func (st *state) pop() pathSegments {
if len(st.path) == 0 {
return nil
}
path := st.path
st.path = st.path[:len(st.path)-1]
st.stat = nil
return path
}
func (st *state) makePath(filename string) string {
return st.path.join(filename)
}
func newReader(r io.Reader) *reader {
return &reader{
b: make([]byte, 1),
s: bufio.NewScanner(r),
r: r,
}
}
type reader struct {
b []byte
s *bufio.Scanner
r io.Reader
}
// read is used to "ask" for response messages after each SCP transmission
// it only reads text data until a newline and returns 'nil' for "OK" responses
// and errors for everything else
func (r *reader) read() error {
n, err := r.r.Read(r.b)
if err != nil {
return trace.Wrap(err)
}
if n < 1 {
return trace.BadParameter("unexpected error, read 0 bytes")
}
switch r.b[0] {
case OKByte:
return nil
case WarnByte, ErrByte:
r.s.Scan()
if err := r.s.Err(); err != nil {
return trace.Wrap(err)
}
return trace.BadParameter("error from receiver: %q", r.s.Text())
}
return trace.BadParameter("unrecognized command: %v", r.b)
}