package sftp // sftp server counterpart import ( "encoding" "fmt" "io" "io/ioutil" "os" "path/filepath" "strconv" "sync" "syscall" "time" "github.com/pkg/errors" ) const ( sftpServerWorkerCount = 8 ) // Server is an SSH File Transfer Protocol (sftp) server. // This is intended to provide the sftp subsystem to an ssh server daemon. // This implementation currently supports most of sftp server protocol version 3, // as specified at http://tools.ietf.org/html/draft-ietf-secsh-filexfer-02 type Server struct { *serverConn debugStream io.Writer readOnly bool pktMgr packetManager openFiles map[string]*os.File openFilesLock sync.RWMutex handleCount int maxTxPacket uint32 } func (svr *Server) nextHandle(f *os.File) string { svr.openFilesLock.Lock() defer svr.openFilesLock.Unlock() svr.handleCount++ handle := strconv.Itoa(svr.handleCount) svr.openFiles[handle] = f return handle } func (svr *Server) closeHandle(handle string) error { svr.openFilesLock.Lock() defer svr.openFilesLock.Unlock() if f, ok := svr.openFiles[handle]; ok { delete(svr.openFiles, handle) return f.Close() } return syscall.EBADF } func (svr *Server) getHandle(handle string) (*os.File, bool) { svr.openFilesLock.RLock() defer svr.openFilesLock.RUnlock() f, ok := svr.openFiles[handle] return f, ok } type serverRespondablePacket interface { encoding.BinaryUnmarshaler id() uint32 respond(svr *Server) error } // NewServer creates a new Server instance around the provided streams, serving // content from the root of the filesystem. Optionally, ServerOption // functions may be specified to further configure the Server. // // A subsequent call to Serve() is required to begin serving files over SFTP. func NewServer(rwc io.ReadWriteCloser, options ...ServerOption) (*Server, error) { svrConn := &serverConn{ conn: conn{ Reader: rwc, WriteCloser: rwc, }, } s := &Server{ serverConn: svrConn, debugStream: ioutil.Discard, pktMgr: newPktMgr(svrConn), openFiles: make(map[string]*os.File), maxTxPacket: 1 << 15, } for _, o := range options { if err := o(s); err != nil { return nil, err } } return s, nil } // A ServerOption is a function which applies configuration to a Server. type ServerOption func(*Server) error // WithDebug enables Server debugging output to the supplied io.Writer. func WithDebug(w io.Writer) ServerOption { return func(s *Server) error { s.debugStream = w return nil } } // ReadOnly configures a Server to serve files in read-only mode. func ReadOnly() ServerOption { return func(s *Server) error { s.readOnly = true return nil } } type rxPacket struct { pktType fxp pktBytes []byte } // Up to N parallel servers func (svr *Server) sftpServerWorker(pktChan chan requestPacket) error { for pkt := range pktChan { // readonly checks readonly := true switch pkt := pkt.(type) { case notReadOnly: readonly = false case *sshFxpOpenPacket: readonly = pkt.readonly() case *sshFxpExtendedPacket: readonly = pkt.SpecificPacket.readonly() } // If server is operating read-only and a write operation is requested, // return permission denied if !readonly && svr.readOnly { if err := svr.sendError(pkt, syscall.EPERM); err != nil { return errors.Wrap(err, "failed to send read only packet response") } continue } if err := handlePacket(svr, pkt); err != nil { return err } } return nil } func handlePacket(s *Server, p interface{}) error { switch p := p.(type) { case *sshFxInitPacket: return s.sendPacket(sshFxVersionPacket{sftpProtocolVersion, nil}) case *sshFxpStatPacket: // stat the requested file info, err := os.Stat(p.Path) if err != nil { return s.sendError(p, err) } return s.sendPacket(sshFxpStatResponse{ ID: p.ID, info: info, }) case *sshFxpLstatPacket: // stat the requested file info, err := os.Lstat(p.Path) if err != nil { return s.sendError(p, err) } return s.sendPacket(sshFxpStatResponse{ ID: p.ID, info: info, }) case *sshFxpFstatPacket: f, ok := s.getHandle(p.Handle) if !ok { return s.sendError(p, syscall.EBADF) } info, err := f.Stat() if err != nil { return s.sendError(p, err) } return s.sendPacket(sshFxpStatResponse{ ID: p.ID, info: info, }) case *sshFxpMkdirPacket: // TODO FIXME: ignore flags field err := os.Mkdir(p.Path, 0755) return s.sendError(p, err) case *sshFxpRmdirPacket: err := os.Remove(p.Path) return s.sendError(p, err) case *sshFxpRemovePacket: err := os.Remove(p.Filename) return s.sendError(p, err) case *sshFxpRenamePacket: err := os.Rename(p.Oldpath, p.Newpath) return s.sendError(p, err) case *sshFxpSymlinkPacket: err := os.Symlink(p.Targetpath, p.Linkpath) return s.sendError(p, err) case *sshFxpClosePacket: return s.sendError(p, s.closeHandle(p.Handle)) case *sshFxpReadlinkPacket: f, err := os.Readlink(p.Path) if err != nil { return s.sendError(p, err) } return s.sendPacket(sshFxpNamePacket{ ID: p.ID, NameAttrs: []sshFxpNameAttr{{ Name: f, LongName: f, Attrs: emptyFileStat, }}, }) case *sshFxpRealpathPacket: f, err := filepath.Abs(p.Path) if err != nil { return s.sendError(p, err) } f = filepath.Clean(f) f = filepath.ToSlash(f) // make path more Unix like on windows servers return s.sendPacket(sshFxpNamePacket{ ID: p.ID, NameAttrs: []sshFxpNameAttr{{ Name: f, LongName: f, Attrs: emptyFileStat, }}, }) case *sshFxpOpendirPacket: return sshFxpOpenPacket{ ID: p.ID, Path: p.Path, Pflags: ssh_FXF_READ, }.respond(s) case *sshFxpReadPacket: f, ok := s.getHandle(p.Handle) if !ok { return s.sendError(p, syscall.EBADF) } data := make([]byte, clamp(p.Len, s.maxTxPacket)) n, err := f.ReadAt(data, int64(p.Offset)) if err != nil && (err != io.EOF || n == 0) { return s.sendError(p, err) } return s.sendPacket(sshFxpDataPacket{ ID: p.ID, Length: uint32(n), Data: data[:n], }) case *sshFxpWritePacket: f, ok := s.getHandle(p.Handle) if !ok { return s.sendError(p, syscall.EBADF) } _, err := f.WriteAt(p.Data, int64(p.Offset)) return s.sendError(p, err) case serverRespondablePacket: err := p.respond(s) return errors.Wrap(err, "pkt.respond failed") default: return errors.Errorf("unexpected packet type %T", p) } } // Serve serves SFTP connections until the streams stop or the SFTP subsystem // is stopped. func (svr *Server) Serve() error { var wg sync.WaitGroup runWorker := func(ch requestChan) { wg.Add(1) go func() { defer wg.Done() if err := svr.sftpServerWorker(ch); err != nil { svr.conn.Close() // shuts down recvPacket } }() } pktChan := svr.pktMgr.workerChan(runWorker) var err error var pkt requestPacket var pktType uint8 var pktBytes []byte for { pktType, pktBytes, err = svr.recvPacket() if err != nil { break } pkt, err = makePacket(rxPacket{fxp(pktType), pktBytes}) if err != nil { debug("makePacket err: %v", err) svr.conn.Close() // shuts down recvPacket break } pktChan <- pkt } close(pktChan) // shuts down sftpServerWorkers wg.Wait() // wait for all workers to exit // close any still-open files for handle, file := range svr.openFiles { fmt.Fprintf(svr.debugStream, "sftp server file with handle %q left open: %v\n", handle, file.Name()) file.Close() } return err // error from recvPacket } // Wrap underlying connection methods to use packetManager func (svr *Server) sendPacket(m encoding.BinaryMarshaler) error { if pkt, ok := m.(responsePacket); ok { svr.pktMgr.readyPacket(pkt) } else { return errors.Errorf("unexpected packet type %T", m) } return nil } func (svr *Server) sendError(p ider, err error) error { return svr.sendPacket(statusFromError(p, err)) } type ider interface { id() uint32 } // The init packet has no ID, so we just return a zero-value ID func (p sshFxInitPacket) id() uint32 { return 0 } type sshFxpStatResponse struct { ID uint32 info os.FileInfo } func (p sshFxpStatResponse) MarshalBinary() ([]byte, error) { b := []byte{ssh_FXP_ATTRS} b = marshalUint32(b, p.ID) b = marshalFileInfo(b, p.info) return b, nil } var emptyFileStat = []interface{}{uint32(0)} func (p sshFxpOpenPacket) readonly() bool { return !p.hasPflags(ssh_FXF_WRITE) } func (p sshFxpOpenPacket) hasPflags(flags ...uint32) bool { for _, f := range flags { if p.Pflags&f == 0 { return false } } return true } func (p sshFxpOpenPacket) respond(svr *Server) error { var osFlags int if p.hasPflags(ssh_FXF_READ, ssh_FXF_WRITE) { osFlags |= os.O_RDWR } else if p.hasPflags(ssh_FXF_WRITE) { osFlags |= os.O_WRONLY } else if p.hasPflags(ssh_FXF_READ) { osFlags |= os.O_RDONLY } else { // how are they opening? return svr.sendError(p, syscall.EINVAL) } if p.hasPflags(ssh_FXF_APPEND) { osFlags |= os.O_APPEND } if p.hasPflags(ssh_FXF_CREAT) { osFlags |= os.O_CREATE } if p.hasPflags(ssh_FXF_TRUNC) { osFlags |= os.O_TRUNC } if p.hasPflags(ssh_FXF_EXCL) { osFlags |= os.O_EXCL } f, err := os.OpenFile(p.Path, osFlags, 0644) if err != nil { return svr.sendError(p, err) } handle := svr.nextHandle(f) return svr.sendPacket(sshFxpHandlePacket{p.ID, handle}) } func (p sshFxpReaddirPacket) respond(svr *Server) error { f, ok := svr.getHandle(p.Handle) if !ok { return svr.sendError(p, syscall.EBADF) } dirname := f.Name() dirents, err := f.Readdir(128) if err != nil { return svr.sendError(p, err) } ret := sshFxpNamePacket{ID: p.ID} for _, dirent := range dirents { ret.NameAttrs = append(ret.NameAttrs, sshFxpNameAttr{ Name: dirent.Name(), LongName: runLs(dirname, dirent), Attrs: []interface{}{dirent}, }) } return svr.sendPacket(ret) } func (p sshFxpSetstatPacket) respond(svr *Server) error { // additional unmarshalling is required for each possibility here b := p.Attrs.([]byte) var err error debug("setstat name \"%s\"", p.Path) if (p.Flags & ssh_FILEXFER_ATTR_SIZE) != 0 { var size uint64 if size, b, err = unmarshalUint64Safe(b); err == nil { err = os.Truncate(p.Path, int64(size)) } } if (p.Flags & ssh_FILEXFER_ATTR_PERMISSIONS) != 0 { var mode uint32 if mode, b, err = unmarshalUint32Safe(b); err == nil { err = os.Chmod(p.Path, os.FileMode(mode)) } } if (p.Flags & ssh_FILEXFER_ATTR_ACMODTIME) != 0 { var atime uint32 var mtime uint32 if atime, b, err = unmarshalUint32Safe(b); err != nil { } else if mtime, b, err = unmarshalUint32Safe(b); err != nil { } else { atimeT := time.Unix(int64(atime), 0) mtimeT := time.Unix(int64(mtime), 0) err = os.Chtimes(p.Path, atimeT, mtimeT) } } if (p.Flags & ssh_FILEXFER_ATTR_UIDGID) != 0 { var uid uint32 var gid uint32 if uid, b, err = unmarshalUint32Safe(b); err != nil { } else if gid, b, err = unmarshalUint32Safe(b); err != nil { } else { err = os.Chown(p.Path, int(uid), int(gid)) } } return svr.sendError(p, err) } func (p sshFxpFsetstatPacket) respond(svr *Server) error { f, ok := svr.getHandle(p.Handle) if !ok { return svr.sendError(p, syscall.EBADF) } // additional unmarshalling is required for each possibility here b := p.Attrs.([]byte) var err error debug("fsetstat name \"%s\"", f.Name()) if (p.Flags & ssh_FILEXFER_ATTR_SIZE) != 0 { var size uint64 if size, b, err = unmarshalUint64Safe(b); err == nil { err = f.Truncate(int64(size)) } } if (p.Flags & ssh_FILEXFER_ATTR_PERMISSIONS) != 0 { var mode uint32 if mode, b, err = unmarshalUint32Safe(b); err == nil { err = f.Chmod(os.FileMode(mode)) } } if (p.Flags & ssh_FILEXFER_ATTR_ACMODTIME) != 0 { var atime uint32 var mtime uint32 if atime, b, err = unmarshalUint32Safe(b); err != nil { } else if mtime, b, err = unmarshalUint32Safe(b); err != nil { } else { atimeT := time.Unix(int64(atime), 0) mtimeT := time.Unix(int64(mtime), 0) err = os.Chtimes(f.Name(), atimeT, mtimeT) } } if (p.Flags & ssh_FILEXFER_ATTR_UIDGID) != 0 { var uid uint32 var gid uint32 if uid, b, err = unmarshalUint32Safe(b); err != nil { } else if gid, b, err = unmarshalUint32Safe(b); err != nil { } else { err = f.Chown(int(uid), int(gid)) } } return svr.sendError(p, err) } // translateErrno translates a syscall error number to a SFTP error code. func translateErrno(errno syscall.Errno) uint32 { switch errno { case 0: return ssh_FX_OK case syscall.ENOENT: return ssh_FX_NO_SUCH_FILE case syscall.EPERM: return ssh_FX_PERMISSION_DENIED } return ssh_FX_FAILURE } func statusFromError(p ider, err error) sshFxpStatusPacket { ret := sshFxpStatusPacket{ ID: p.id(), StatusError: StatusError{ // ssh_FX_OK = 0 // ssh_FX_EOF = 1 // ssh_FX_NO_SUCH_FILE = 2 ENOENT // ssh_FX_PERMISSION_DENIED = 3 // ssh_FX_FAILURE = 4 // ssh_FX_BAD_MESSAGE = 5 // ssh_FX_NO_CONNECTION = 6 // ssh_FX_CONNECTION_LOST = 7 // ssh_FX_OP_UNSUPPORTED = 8 Code: ssh_FX_OK, }, } if err != nil { debug("statusFromError: error is %T %#v", err, err) ret.StatusError.Code = ssh_FX_FAILURE ret.StatusError.msg = err.Error() if err == io.EOF { ret.StatusError.Code = ssh_FX_EOF } else if errno, ok := err.(syscall.Errno); ok { ret.StatusError.Code = translateErrno(errno) } else if pathError, ok := err.(*os.PathError); ok { debug("statusFromError: error is %T %#v", pathError.Err, pathError.Err) if errno, ok := pathError.Err.(syscall.Errno); ok { ret.StatusError.Code = translateErrno(errno) } } } return ret } func clamp(v, max uint32) uint32 { if v > max { return max } return v }