Re-design of the original gocryptfs code to work as a library.
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package fusefrontend
import (
// RootNode is the root of the filesystem tree of Nodes.
type RootNode struct {
// args stores configuration arguments
args Args
// dirIVLock: Lock()ed if any "gocryptfs.diriv" file is modified
// Readers must RLock() it to prevent them from seeing intermediate
// states
dirIVLock sync.RWMutex
// Filename encryption helper
nameTransform *nametransform.NameTransform
// Content encryption helper
contentEnc *contentenc.ContentEnc
// This lock is used by openWriteOnlyFile() to block concurrent opens while
// it relaxes the permissions on a file.
openWriteOnlyLock sync.RWMutex
// MitigatedCorruptions is used to report data corruption that is internally
// mitigated by ignoring the corrupt item. For example, when OpenDir() finds
// a corrupt filename, we still return the other valid filenames.
// The corruption is logged to syslog to inform the user, and in addition,
// the corrupt filename is logged to this channel via
// reportMitigatedCorruption().
// "gocryptfs -fsck" reads from the channel to also catch these transparently-
// mitigated corruptions.
MitigatedCorruptions chan string
// IsIdle flag is set to zero each time fs.isFiltered() is called
// (uint32 so that it can be reset with CompareAndSwapUint32).
// When -idle was used when mounting, idleMonitor() sets it to 1
// periodically.
IsIdle uint32
// dirCache caches directory fds
dirCache dirCache
// inoMap translates inode numbers from different devices to unique inode
// numbers.
inoMap *inomap.InoMap
// gen is the node generation numbers. Normally, it is always set to 1,
// but -sharestorage uses an incrementing counter for new nodes.
// This makes each directory entry unique (even hard links),
// makes go-fuse hand out separate FUSE Node IDs for each, and prevents
// bizarre problems when inode numbers are reused behind our back.
gen uint64
// quirks is a bitmap that enables workaround for quirks in the filesystem
// backing the cipherdir
quirks uint64
func NewRootNode(args Args, c *contentenc.ContentEnc, n *nametransform.NameTransform) *RootNode {
var rootDev uint64
var st syscall.Stat_t
if err := syscall.Stat(args.Cipherdir, &st); err != nil {
tlog.Warn.Printf("Could not stat backing directory %q: %v", args.Cipherdir, err)
} else {
rootDev = uint64(st.Dev)
if len(args.Exclude) > 0 {
tlog.Warn.Printf("Forward mode does not support -exclude")
ivLen := nametransform.DirIVLen
if args.PlaintextNames {
ivLen = 0
rn := &RootNode{
args: args,
nameTransform: n,
contentEnc: c,
inoMap: inomap.New(rootDev),
dirCache: dirCache{ivLen: ivLen},
quirks: syscallcompat.DetectQuirks(args.Cipherdir),
return rn
// main.doMount() calls this after unmount
func (rn *RootNode) AfterUnmount() {
// print stats before we exit
// mangleOpenFlags is used by Create() and Open() to convert the open flags the user
// wants to the flags we internally use to open the backing file.
// The returned flags always contain O_NOFOLLOW.
func (rn *RootNode) mangleOpenFlags(flags uint32) (newFlags int) {
newFlags = int(flags)
// Convert WRONLY to RDWR. We always need read access to do read-modify-write cycles.
if (newFlags & syscall.O_ACCMODE) == syscall.O_WRONLY {
newFlags = newFlags ^ os.O_WRONLY | os.O_RDWR
// We also cannot open the file in append mode, we need to seek back for RMW
newFlags = newFlags &^ os.O_APPEND
// O_DIRECT accesses must be aligned in both offset and length. Due to our
// crypto header, alignment will be off, even if userspace makes aligned
// accesses. Running xfstests generic/013 on ext4 used to trigger lots of
// EINVAL errors due to missing alignment. Just fall back to buffered IO.
newFlags = newFlags &^ syscallcompat.O_DIRECT
// Create and Open are two separate FUSE operations, so O_CREAT should not
// be part of the open flags.
newFlags = newFlags &^ syscall.O_CREAT
// We always want O_NOFOLLOW to be safe against symlink races
newFlags |= syscall.O_NOFOLLOW
return newFlags
// reportMitigatedCorruption is used to report a corruption that was transparently
// mitigated and did not return an error to the user. Pass the name of the corrupt
// item (filename for OpenDir(), xattr name for ListXAttr() etc).
// See the MitigatedCorruptions channel for more info.
func (rn *RootNode) reportMitigatedCorruption(item string) {
if rn.MitigatedCorruptions == nil {
select {
case rn.MitigatedCorruptions <- item:
case <-time.After(1 * time.Second):
tlog.Warn.Printf("BUG: reportCorruptItem: timeout")
// isFiltered - check if plaintext file "child" should be forbidden
// Prevents name clashes with internal files when file names are not encrypted
func (rn *RootNode) isFiltered(child string) bool {
if !rn.args.PlaintextNames {
return false
// gocryptfs.conf in the root directory is forbidden
if child == configfile.ConfDefaultName {
tlog.Info.Printf("The name /%s is reserved when -plaintextnames is used\n",
return true
// Note: gocryptfs.diriv is NOT forbidden because diriv and plaintextnames
// are exclusive
return false
// decryptSymlinkTarget: "cData64" is base64-decoded and decrypted
// like file contents (GCM).
// The empty string decrypts to the empty string.
// This function does not do any I/O and is hence symlink-safe.
func (rn *RootNode) decryptSymlinkTarget(cData64 string) (string, error) {
if cData64 == "" {
return "", nil
cData, err := rn.nameTransform.B64DecodeString(cData64)
if err != nil {
return "", err
data, err := rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
if err != nil {
return "", err
return string(data), nil
// Due to RMW, we always need read permissions on the backing file. This is a
// problem if the file permissions do not allow reading (i.e. 0200 permissions).
// This function works around that problem by chmod'ing the file, obtaining a fd,
// and chmod'ing it back.
func (rn *RootNode) openWriteOnlyFile(dirfd int, cName string, newFlags int) (rwFd int, err error) {
woFd, err := syscallcompat.Openat(dirfd, cName, syscall.O_WRONLY|syscall.O_NOFOLLOW, 0)
if err != nil {
defer syscall.Close(woFd)
var st syscall.Stat_t
err = syscall.Fstat(woFd, &st)
if err != nil {
// The cast to uint32 fixes a build failure on Darwin, where st.Mode is uint16.
perms := uint32(st.Mode)
// Verify that we don't have read permissions
if perms&0400 != 0 {
tlog.Warn.Printf("openWriteOnlyFile: unexpected permissions %#o, returning EPERM", perms)
err = syscall.EPERM
// Upgrade the lock to block other Open()s and downgrade again on return
defer func() {
// Relax permissions and revert on return
err = syscall.Fchmod(woFd, perms|0400)
if err != nil {
tlog.Warn.Printf("openWriteOnlyFile: changing permissions failed: %v", err)
defer func() {
err2 := syscall.Fchmod(woFd, perms)
if err2 != nil {
tlog.Warn.Printf("openWriteOnlyFile: reverting permissions failed: %v", err2)
return syscallcompat.Openat(dirfd, cName, newFlags, 0)
// encryptSymlinkTarget: "data" is encrypted like file contents (GCM)
// and base64-encoded.
// The empty string encrypts to the empty string.
// Symlink-safe because it does not do any I/O.
func (rn *RootNode) encryptSymlinkTarget(data string) (cData64 string) {
if data == "" {
return ""
cData := rn.contentEnc.EncryptBlock([]byte(data), 0, nil)
cData64 = rn.nameTransform.B64EncodeToString(cData)
return cData64
// encryptXattrValue encrypts the xattr value "data".
// The data is encrypted like a file content block, but without binding it to
// a file location (block number and file id are set to zero).
// Special case: an empty value is encrypted to an empty value.
func (rn *RootNode) encryptXattrValue(data []byte) (cData []byte) {
if len(data) == 0 {
return []byte{}
return rn.contentEnc.EncryptBlock(data, 0, nil)
// decryptXattrValue decrypts the xattr value "cData".
func (rn *RootNode) decryptXattrValue(cData []byte) (data []byte, err error) {
if len(cData) == 0 {
return []byte{}, nil
data, err1 := rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
if err1 == nil {
return data, nil
// This backward compatibility is needed to support old
// file systems having xattr values base64-encoded.
cData, err2 := rn.nameTransform.B64DecodeString(string(cData))
if err2 != nil {
// Looks like the value was not base64-encoded, but just corrupt.
// Return the original decryption error: err1
return nil, err1
return rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
// encryptXattrName transforms "" to "user.gocryptfs.a5sAd4XAa47f5as6dAf"
func (rn *RootNode) encryptXattrName(attr string) (string, error) {
// xattr names are encrypted like file names, but with a fixed IV.
cAttr, err := rn.nameTransform.EncryptName(attr, xattrNameIV)
if err != nil {
return "", err
return xattrStorePrefix + cAttr, nil
func (rn *RootNode) decryptXattrName(cAttr string) (attr string, err error) {
// Reject anything that does not start with "user.gocryptfs."
if !strings.HasPrefix(cAttr, xattrStorePrefix) {
return "", syscall.EINVAL
// Strip "user.gocryptfs." prefix
cAttr = cAttr[len(xattrStorePrefix):]
attr, err = rn.nameTransform.DecryptName(cAttr, xattrNameIV)
if err != nil {
return "", err
return attr, nil