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package nametransform
import (
const (
// DirIVLen is identical to AES block size
DirIVLen = 16
// DirIVFilename is the filename used to store directory IV.
// Exported because we have to ignore this name in directory listing.
DirIVFilename = "gocryptfs.diriv"
// ReadDirIVAt reads "gocryptfs.diriv" from the directory that is opened as "dirfd".
// Using the dirfd makes it immune to concurrent renames of the directory.
// Retries on EINTR.
// If deterministicNames is set it returns an all-zero slice.
func (n *NameTransform) ReadDirIVAt(dirfd int) (iv []byte, err error) {
if n.deterministicNames {
return make([]byte, DirIVLen), nil
fdRaw, err := syscallcompat.Openat(dirfd, DirIVFilename,
syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
if err != nil {
return nil, err
fd := os.NewFile(uintptr(fdRaw), DirIVFilename)
defer fd.Close()
return fdReadDirIV(fd)
// allZeroDirIV is preallocated to quickly check if the data read from disk is all zero
var allZeroDirIV = make([]byte, DirIVLen)
// fdReadDirIV reads and verifies the DirIV from an opened gocryptfs.diriv file.
func fdReadDirIV(fd *os.File) (iv []byte, err error) {
// We want to detect if the file is bigger than DirIVLen, so
// make the buffer 1 byte bigger than necessary.
iv = make([]byte, DirIVLen+1)
n, err := fd.Read(iv)
if err != nil && err != io.EOF {
return nil, fmt.Errorf("read failed: %v", err)
iv = iv[0:n]
if len(iv) != DirIVLen {
return nil, fmt.Errorf("wanted %d bytes, got %d", DirIVLen, len(iv))
if bytes.Equal(iv, allZeroDirIV) {
return nil, fmt.Errorf("diriv is all-zero")
return iv, nil
// WriteDirIVAt - create a new gocryptfs.diriv file in the directory opened at
// "dirfd". On error we try to delete the incomplete file.
// This function is exported because it is used from fusefrontend, main,
// and also the automated tests.
func WriteDirIVAt(dirfd int) error {
iv := cryptocore.RandBytes(DirIVLen)
// 0400 permissions: gocryptfs.diriv should never be modified after creation.
// Don't use "ioutil.WriteFile", it causes trouble on NFS:
fd, err := syscallcompat.Openat(dirfd, DirIVFilename, os.O_WRONLY|os.O_CREATE|os.O_EXCL, dirivPerms)
if err != nil {
return err
// Wrap the fd in an os.File - we need the write retry logic.
f := os.NewFile(uintptr(fd), DirIVFilename)
_, err = f.Write(iv)
if err != nil {
// It is normal to get ENOSPC here
// Delete incomplete gocryptfs.diriv file
syscallcompat.Unlinkat(dirfd, DirIVFilename, 0)
return err
err = f.Close()
if err != nil {
// Delete incomplete gocryptfs.diriv file
syscallcompat.Unlinkat(dirfd, DirIVFilename, 0)
return err
return nil