9 files changed, 1228 insertions, 0 deletions
diff --git a/internal/fusefrontend/args.go b/internal/fusefrontend/args.go
new file mode 100644
index 0000000..e8cab04
--- /dev/null
+++ b/internal/fusefrontend/args.go
@@ -0,0 +1,12 @@
+package fusefrontend
+
+// Container for arguments that are passed from main() to fusefrontend
+type Args struct {
+	Masterkey      []byte
+	Cipherdir      string
+	OpenSSL        bool
+	PlaintextNames bool
+	DirIV          bool
+	EMENames       bool
+	GCMIV128       bool
+}
diff --git a/internal/fusefrontend/compat_darwin.go b/internal/fusefrontend/compat_darwin.go
new file mode 100644
index 0000000..445fb45
--- /dev/null
+++ b/internal/fusefrontend/compat_darwin.go
@@ -0,0 +1,12 @@
+package fusefrontend
+
+// prealloc - preallocate space without changing the file size. This prevents
+// us from running out of space in the middle of an operation.
+func prealloc(fd int, off int64, len int64) (err error) {
+	//
+	// Sorry, fallocate is not available on OSX at all and
+	// fcntl F_PREALLOCATE is not accessible from Go.
+	//
+	// See https://github.com/rfjakob/gocryptfs/issues/18 if you want to help.
+	return nil
+}
diff --git a/internal/fusefrontend/compat_linux.go b/internal/fusefrontend/compat_linux.go
new file mode 100644
index 0000000..4108792
--- /dev/null
+++ b/internal/fusefrontend/compat_linux.go
@@ -0,0 +1,18 @@
+package fusefrontend
+
+import "syscall"
+
+// prealloc - preallocate space without changing the file size. This prevents
+// us from running out of space in the middle of an operation.
+func prealloc(fd int, off int64, len int64) (err error) {
+	for {
+		err = syscall.Fallocate(fd, FALLOC_FL_KEEP_SIZE, off, len)
+		if err == syscall.EINTR {
+			// fallocate, like many syscalls, can return EINTR. This is not an
+			// error and just signifies that the operation was interrupted by a
+			// signal and we should try again.
+			continue
+		}
+		return err
+	}
+}
diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
new file mode 100644
index 0000000..2e0b504
--- /dev/null
+++ b/internal/fusefrontend/file.go
@@ -0,0 +1,501 @@
+package fusefrontend
+
+// FUSE operations on file handles
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/hanwen/go-fuse/fuse"
+	"github.com/hanwen/go-fuse/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
+)
+
+// File - based on loopbackFile in go-fuse/fuse/nodefs/files.go
+type file struct {
+	fd *os.File
+
+	// fdLock prevents the fd to be closed while we are in the middle of
+	// an operation.
+	// Every FUSE entrypoint should RLock(). The only user of Lock() is
+	// Release(), which closes the fd, hence has to acquire an exclusive lock.
+	fdLock sync.RWMutex
+
+	// Was the file opened O_WRONLY?
+	writeOnly bool
+
+	// Content encryption helper
+	contentEnc *contentenc.ContentEnc
+
+	// Inode number
+	ino uint64
+
+	// File header
+	header *contentenc.FileHeader
+
+	forgotten bool
+}
+
+func NewFile(fd *os.File, writeOnly bool, contentEnc *contentenc.ContentEnc) nodefs.File {
+	var st syscall.Stat_t
+	syscall.Fstat(int(fd.Fd()), &st)
+	wlock.register(st.Ino)
+
+	return &file{
+		fd:        fd,
+		writeOnly: writeOnly,
+		contentEnc: contentEnc,
+		ino:       st.Ino,
+	}
+}
+
+// intFd - return the backing file descriptor as an integer. Used for debug
+// messages.
+func (f *file) intFd() int {
+	return int(f.fd.Fd())
+}
+
+func (f *file) InnerFile() nodefs.File {
+	return nil
+}
+
+func (f *file) SetInode(n *nodefs.Inode) {
+}
+
+// readHeader - load the file header from disk
+//
+// Returns io.EOF if the file is empty
+func (f *file) readHeader() error {
+	buf := make([]byte, contentenc.HEADER_LEN)
+	_, err := f.fd.ReadAt(buf, 0)
+	if err != nil {
+		return err
+	}
+	h, err := contentenc.ParseHeader(buf)
+	if err != nil {
+		return err
+	}
+	f.header = h
+
+	return nil
+}
+
+// createHeader - create a new random header and write it to disk
+func (f *file) createHeader() error {
+	h := contentenc.RandomHeader()
+	buf := h.Pack()
+
+	// Prevent partially written (=corrupt) header by preallocating the space beforehand
+	err := prealloc(int(f.fd.Fd()), 0, contentenc.HEADER_LEN)
+	if err != nil {
+		toggledlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.ino, err.Error())
+		return err
+	}
+
+	// Actually write header
+	_, err = f.fd.WriteAt(buf, 0)
+	if err != nil {
+		return err
+	}
+	f.header = h
+
+	return nil
+}
+
+func (f *file) String() string {
+	return fmt.Sprintf("cryptFile(%s)", f.fd.Name())
+}
+
+// doRead - returns "length" plaintext bytes from plaintext offset "off".
+// Arguments "length" and "off" do not have to be block-aligned.
+//
+// doRead reads the corresponding ciphertext blocks from disk, decrypts them and
+// returns the requested part of the plaintext.
+//
+// Called by Read() for normal reading,
+// by Write() and Truncate() for Read-Modify-Write
+func (f *file) doRead(off uint64, length uint64) ([]byte, fuse.Status) {
+
+	// Read file header
+	if f.header == nil {
+		err := f.readHeader()
+		if err == io.EOF {
+			return nil, fuse.OK
+		}
+		if err != nil {
+			return nil, fuse.ToStatus(err)
+		}
+	}
+
+	// Read the backing ciphertext in one go
+	blocks := f.contentEnc.ExplodePlainRange(off, length)
+	alignedOffset, alignedLength := blocks[0].JointCiphertextRange(blocks)
+	skip := blocks[0].Skip
+	toggledlog.Debug.Printf("JointCiphertextRange(%d, %d) -> %d, %d, %d", off, length, alignedOffset, alignedLength, skip)
+	ciphertext := make([]byte, int(alignedLength))
+	n, err := f.fd.ReadAt(ciphertext, int64(alignedOffset))
+	if err != nil && err != io.EOF {
+		toggledlog.Warn.Printf("read: ReadAt: %s", err.Error())
+		return nil, fuse.ToStatus(err)
+	}
+	// Truncate ciphertext buffer down to actually read bytes
+	ciphertext = ciphertext[0:n]
+
+	firstBlockNo := blocks[0].BlockNo
+	toggledlog.Debug.Printf("ReadAt offset=%d bytes (%d blocks), want=%d, got=%d", alignedOffset, firstBlockNo, alignedLength, n)
+
+	// Decrypt it
+	plaintext, err := f.contentEnc.DecryptBlocks(ciphertext, firstBlockNo, f.header.Id)
+	if err != nil {
+		curruptBlockNo := firstBlockNo + f.contentEnc.PlainOffToBlockNo(uint64(len(plaintext)))
+		cipherOff := f.contentEnc.BlockNoToCipherOff(curruptBlockNo)
+		plainOff := f.contentEnc.BlockNoToPlainOff(curruptBlockNo)
+		toggledlog.Warn.Printf("ino%d: doRead: corrupt block #%d (plainOff=%d, cipherOff=%d)",
+			f.ino, curruptBlockNo, plainOff, cipherOff)
+		return nil, fuse.EIO
+	}
+
+	// Crop down to the relevant part
+	var out []byte
+	lenHave := len(plaintext)
+	lenWant := int(skip + length)
+	if lenHave > lenWant {
+		out = plaintext[skip:lenWant]
+	} else if lenHave > int(skip) {
+		out = plaintext[skip:lenHave]
+	}
+	// else: out stays empty, file was smaller than the requested offset
+
+	return out, fuse.OK
+}
+
+// Read - FUSE call
+func (f *file) Read(buf []byte, off int64) (resultData fuse.ReadResult, code fuse.Status) {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+
+	toggledlog.Debug.Printf("ino%d: FUSE Read: offset=%d length=%d", f.ino, len(buf), off)
+
+	if f.writeOnly {
+		toggledlog.Warn.Printf("ino%d: Tried to read from write-only file", f.ino)
+		return nil, fuse.EBADF
+	}
+
+	out, status := f.doRead(uint64(off), uint64(len(buf)))
+
+	if status == fuse.EIO {
+		toggledlog.Warn.Printf("ino%d: Read failed with EIO, offset=%d, length=%d", f.ino, len(buf), off)
+	}
+	if status != fuse.OK {
+		return nil, status
+	}
+
+	toggledlog.Debug.Printf("ino%d: Read: status %v, returning %d bytes", f.ino, status, len(out))
+	return fuse.ReadResultData(out), status
+}
+
+const FALLOC_FL_KEEP_SIZE = 0x01
+
+// doWrite - encrypt "data" and write it to plaintext offset "off"
+//
+// Arguments do not have to be block-aligned, read-modify-write is
+// performed internally as neccessary
+//
+// Called by Write() for normal writing,
+// and by Truncate() to rewrite the last file block.
+func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
+
+	// Read header from disk, create a new one if the file is empty
+	if f.header == nil {
+		err := f.readHeader()
+		if err == io.EOF {
+			err = f.createHeader()
+
+		}
+		if err != nil {
+			return 0, fuse.ToStatus(err)
+		}
+	}
+
+	var written uint32
+	status := fuse.OK
+	dataBuf := bytes.NewBuffer(data)
+	blocks := f.contentEnc.ExplodePlainRange(uint64(off), uint64(len(data)))
+	for _, b := range blocks {
+
+		blockData := dataBuf.Next(int(b.Length))
+
+		// Incomplete block -> Read-Modify-Write
+		if b.IsPartial() {
+			// Read
+			o, _ := b.PlaintextRange()
+			oldData, status := f.doRead(o, f.contentEnc.PlainBS())
+			if status != fuse.OK {
+				toggledlog.Warn.Printf("ino%d fh%d: RMW read failed: %s", f.ino, f.intFd(), status.String())
+				return written, status
+			}
+			// Modify
+			blockData = f.contentEnc.MergeBlocks(oldData, blockData, int(b.Skip))
+			toggledlog.Debug.Printf("len(oldData)=%d len(blockData)=%d", len(oldData), len(blockData))
+		}
+
+		// Encrypt
+		blockOffset, blockLen := b.CiphertextRange()
+		blockData = f.contentEnc.EncryptBlock(blockData, b.BlockNo, f.header.Id)
+		toggledlog.Debug.Printf("ino%d: Writing %d bytes to block #%d",
+			f.ino, uint64(len(blockData))-f.contentEnc.BlockOverhead(), b.BlockNo)
+
+		// Prevent partially written (=corrupt) blocks by preallocating the space beforehand
+		err := prealloc(int(f.fd.Fd()), int64(blockOffset), int64(blockLen))
+		if err != nil {
+			toggledlog.Warn.Printf("ino%d fh%d: doWrite: prealloc failed: %s", f.ino, f.intFd(), err.Error())
+			status = fuse.ToStatus(err)
+			break
+		}
+
+		// Write
+		_, err = f.fd.WriteAt(blockData, int64(blockOffset))
+
+		if err != nil {
+			toggledlog.Warn.Printf("doWrite: Write failed: %s", err.Error())
+			status = fuse.ToStatus(err)
+			break
+		}
+		written += uint32(b.Length)
+	}
+	return written, status
+}
+
+// Write - FUSE call
+func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+	wlock.lock(f.ino)
+	defer wlock.unlock(f.ino)
+
+	toggledlog.Debug.Printf("ino%d: FUSE Write: offset=%d length=%d", f.ino, off, len(data))
+
+	fi, err := f.fd.Stat()
+	if err != nil {
+		toggledlog.Warn.Printf("Write: Fstat failed: %v", err)
+		return 0, fuse.ToStatus(err)
+	}
+	plainSize := f.contentEnc.CipherSizeToPlainSize(uint64(fi.Size()))
+	if f.createsHole(plainSize, off) {
+		status := f.zeroPad(plainSize)
+		if status != fuse.OK {
+			toggledlog.Warn.Printf("zeroPad returned error %v", status)
+			return 0, status
+		}
+	}
+	return f.doWrite(data, off)
+}
+
+// Release - FUSE call, close file
+func (f *file) Release() {
+	f.fdLock.Lock()
+	defer f.fdLock.Unlock()
+
+	f.fd.Close()
+	f.forgotten = true
+}
+
+// Flush - FUSE call
+func (f *file) Flush() fuse.Status {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+
+	// Since Flush() may be called for each dup'd fd, we don't
+	// want to really close the file, we just want to flush. This
+	// is achieved by closing a dup'd fd.
+	newFd, err := syscall.Dup(int(f.fd.Fd()))
+
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	err = syscall.Close(newFd)
+	return fuse.ToStatus(err)
+}
+
+func (f *file) Fsync(flags int) (code fuse.Status) {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+
+	return fuse.ToStatus(syscall.Fsync(int(f.fd.Fd())))
+}
+
+// Truncate - FUSE call
+func (f *file) Truncate(newSize uint64) fuse.Status {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+	wlock.lock(f.ino)
+	defer wlock.unlock(f.ino)
+
+	if f.forgotten {
+		toggledlog.Warn.Printf("ino%d fh%d: Truncate on forgotten file", f.ino, f.intFd())
+	}
+
+	// Common case first: Truncate to zero
+	if newSize == 0 {
+		err := syscall.Ftruncate(int(f.fd.Fd()), 0)
+		if err != nil {
+			toggledlog.Warn.Printf("ino%d fh%d: Ftruncate(fd, 0) returned error: %v", f.ino, f.intFd(), err)
+			return fuse.ToStatus(err)
+		}
+		// Truncate to zero kills the file header
+		f.header = nil
+		return fuse.OK
+	}
+
+	// We need the old file size to determine if we are growing or shrinking
+	// the file
+	fi, err := f.fd.Stat()
+	if err != nil {
+		toggledlog.Warn.Printf("ino%d fh%d: Truncate: Fstat failed: %v", f.ino, f.intFd(), err)
+		return fuse.ToStatus(err)
+	}
+	oldSize := f.contentEnc.CipherSizeToPlainSize(uint64(fi.Size()))
+	{
+		oldB := float32(oldSize) / float32(f.contentEnc.PlainBS())
+		newB := float32(newSize) / float32(f.contentEnc.PlainBS())
+		toggledlog.Debug.Printf("ino%d: FUSE Truncate from %.2f to %.2f blocks (%d to %d bytes)", f.ino, oldB, newB, oldSize, newSize)
+	}
+
+	// File size stays the same - nothing to do
+	if newSize == oldSize {
+		return fuse.OK
+	}
+
+	// File grows
+	if newSize > oldSize {
+
+		// File was empty, create new header
+		if oldSize == 0 {
+			err := f.createHeader()
+			if err != nil {
+				return fuse.ToStatus(err)
+			}
+		}
+
+		blocks := f.contentEnc.ExplodePlainRange(oldSize, newSize-oldSize)
+		for _, b := range blocks {
+			// First and last block may be partial
+			if b.IsPartial() {
+				off, _ := b.PlaintextRange()
+				off += b.Skip
+				_, status := f.doWrite(make([]byte, b.Length), int64(off))
+				if status != fuse.OK {
+					return status
+				}
+			} else {
+				off, length := b.CiphertextRange()
+				err := syscall.Ftruncate(int(f.fd.Fd()), int64(off+length))
+				if err != nil {
+					toggledlog.Warn.Printf("grow Ftruncate returned error: %v", err)
+					return fuse.ToStatus(err)
+				}
+			}
+		}
+		return fuse.OK
+	} else {
+		// File shrinks
+		blockNo := f.contentEnc.PlainOffToBlockNo(newSize)
+		cipherOff := f.contentEnc.BlockNoToCipherOff(blockNo)
+		plainOff := f.contentEnc.BlockNoToPlainOff(blockNo)
+		lastBlockLen := newSize - plainOff
+		var data []byte
+		if lastBlockLen > 0 {
+			var status fuse.Status
+			data, status = f.doRead(plainOff, lastBlockLen)
+			if status != fuse.OK {
+				toggledlog.Warn.Printf("shrink doRead returned error: %v", err)
+				return status
+			}
+		}
+		// Truncate down to last complete block
+		err = syscall.Ftruncate(int(f.fd.Fd()), int64(cipherOff))
+		if err != nil {
+			toggledlog.Warn.Printf("shrink Ftruncate returned error: %v", err)
+			return fuse.ToStatus(err)
+		}
+		// Append partial block
+		if lastBlockLen > 0 {
+			_, status := f.doWrite(data, int64(plainOff))
+			return status
+		}
+		return fuse.OK
+	}
+}
+
+func (f *file) Chmod(mode uint32) fuse.Status {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+
+	return fuse.ToStatus(f.fd.Chmod(os.FileMode(mode)))
+}
+
+func (f *file) Chown(uid uint32, gid uint32) fuse.Status {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+
+	return fuse.ToStatus(f.fd.Chown(int(uid), int(gid)))
+}
+
+func (f *file) GetAttr(a *fuse.Attr) fuse.Status {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+
+	toggledlog.Debug.Printf("file.GetAttr()")
+	st := syscall.Stat_t{}
+	err := syscall.Fstat(int(f.fd.Fd()), &st)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	a.FromStat(&st)
+	a.Size = f.contentEnc.CipherSizeToPlainSize(a.Size)
+
+	return fuse.OK
+}
+
+// Allocate - FUSE call, fallocate(2)
+var allocateWarned bool
+
+func (f *file) Allocate(off uint64, sz uint64, mode uint32) fuse.Status {
+	// Only warn once
+	if !allocateWarned {
+		toggledlog.Warn.Printf("fallocate(2) is not supported, returning ENOSYS - see https://github.com/rfjakob/gocryptfs/issues/1")
+		allocateWarned = true
+	}
+	return fuse.ENOSYS
+}
+
+const _UTIME_OMIT = ((1 << 30) - 2)
+
+func (f *file) Utimens(a *time.Time, m *time.Time) fuse.Status {
+	f.fdLock.RLock()
+	defer f.fdLock.RUnlock()
+
+	ts := make([]syscall.Timespec, 2)
+
+	if a == nil {
+		ts[0].Nsec = _UTIME_OMIT
+	} else {
+		ts[0].Sec = a.Unix()
+	}
+
+	if m == nil {
+		ts[1].Nsec = _UTIME_OMIT
+	} else {
+		ts[1].Sec = m.Unix()
+	}
+
+	fn := fmt.Sprintf("/proc/self/fd/%d", f.fd.Fd())
+	return fuse.ToStatus(syscall.UtimesNano(fn, ts))
+}
diff --git a/internal/fusefrontend/file_holes.go b/internal/fusefrontend/file_holes.go
new file mode 100644
index 0000000..0259ae9
--- /dev/null
+++ b/internal/fusefrontend/file_holes.go
@@ -0,0 +1,29 @@
+package fusefrontend
+
+// Helper functions for sparse files (files with holes)
+
+import (
+	"github.com/hanwen/go-fuse/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
+)
+
+// Will a write to offset "off" create a file hole?
+func (f *file) createsHole(plainSize uint64, off int64) bool {
+	nextBlock := f.contentEnc.PlainOffToBlockNo(plainSize)
+	targetBlock := f.contentEnc.PlainOffToBlockNo(uint64(off))
+	if targetBlock > nextBlock {
+		return true
+	}
+	return false
+}
+
+// Zero-pad the file of size plainSize to the next block boundary
+func (f *file) zeroPad(plainSize uint64) fuse.Status {
+	lastBlockLen := plainSize % f.contentEnc.PlainBS()
+	missing := f.contentEnc.PlainBS() - lastBlockLen
+	pad := make([]byte, missing)
+	toggledlog.Debug.Printf("zeroPad: Writing %d bytes\n", missing)
+	_, status := f.doWrite(pad, int64(plainSize))
+	return status
+}
diff --git a/internal/fusefrontend/fs.go b/internal/fusefrontend/fs.go
new file mode 100644
index 0000000..0331215
--- /dev/null
+++ b/internal/fusefrontend/fs.go
@@ -0,0 +1,381 @@
+package fusefrontend
+
+// FUSE operations on paths
+
+import (
+	"encoding/base64"
+	"os"
+	"path/filepath"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/hanwen/go-fuse/fuse"
+	"github.com/hanwen/go-fuse/fuse/nodefs"
+	"github.com/hanwen/go-fuse/fuse/pathfs"
+
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
+	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+)
+
+const plainBS = 4096
+
+type FS struct {
+	pathfs.FileSystem      // loopbackFileSystem, see go-fuse/fuse/pathfs/loopback.go
+	args              Args // Stores configuration arguments
+	// 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
+}
+
+// Encrypted FUSE overlay filesystem
+func NewFS(args Args) *FS {
+
+	cryptoCore := cryptocore.New(args.Masterkey, args.OpenSSL, args.GCMIV128)
+	contentEnc := contentenc.New(cryptoCore, plainBS)
+	nameTransform := nametransform.New(cryptoCore, args.EMENames)
+
+	return &FS{
+		FileSystem: pathfs.NewLoopbackFileSystem(args.Cipherdir),
+		args:       args,
+		nameTransform: nameTransform,
+		contentEnc: contentEnc,
+	}
+}
+
+// GetBackingPath - get the absolute encrypted path of the backing file
+// from the relative plaintext path "relPath"
+func (fs *FS) getBackingPath(relPath string) (string, error) {
+	cPath, err := fs.encryptPath(relPath)
+	if err != nil {
+		return "", err
+	}
+	cAbsPath := filepath.Join(fs.args.Cipherdir, cPath)
+	toggledlog.Debug.Printf("getBackingPath: %s + %s -> %s", fs.args.Cipherdir, relPath, cAbsPath)
+	return cAbsPath, nil
+}
+
+func (fs *FS) GetAttr(name string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
+	toggledlog.Debug.Printf("FS.GetAttr('%s')", name)
+	if fs.isFiltered(name) {
+		return nil, fuse.EPERM
+	}
+	cName, err := fs.encryptPath(name)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	a, status := fs.FileSystem.GetAttr(cName, context)
+	if a == nil {
+		toggledlog.Debug.Printf("FS.GetAttr failed: %s", status.String())
+		return a, status
+	}
+	if a.IsRegular() {
+		a.Size = fs.contentEnc.CipherSizeToPlainSize(a.Size)
+	} else if a.IsSymlink() {
+		target, _ := fs.Readlink(name, context)
+		a.Size = uint64(len(target))
+	}
+	return a, status
+}
+
+func (fs *FS) OpenDir(dirName string, context *fuse.Context) ([]fuse.DirEntry, fuse.Status) {
+	toggledlog.Debug.Printf("OpenDir(%s)", dirName)
+	cDirName, err := fs.encryptPath(dirName)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	// Read ciphertext directory
+	cipherEntries, status := fs.FileSystem.OpenDir(cDirName, context)
+	if cipherEntries == nil {
+		return nil, status
+	}
+	// Get DirIV (stays nil if DirIV if off)
+	var cachedIV []byte
+	if fs.args.DirIV {
+		// Read the DirIV once and use it for all later name decryptions
+		cDirAbsPath := filepath.Join(fs.args.Cipherdir, cDirName)
+		cachedIV, err = fs.nameTransform.ReadDirIV(cDirAbsPath)
+		if err != nil {
+			return nil, fuse.ToStatus(err)
+		}
+	}
+	// Filter and decrypt filenames
+	var plain []fuse.DirEntry
+	for i := range cipherEntries {
+		cName := cipherEntries[i].Name
+		if dirName == "" && cName == configfile.ConfDefaultName {
+			// silently ignore "gocryptfs.conf" in the top level dir
+			continue
+		}
+		if fs.args.DirIV && cName == nametransform.DirIVFilename {
+			// silently ignore "gocryptfs.diriv" everywhere if dirIV is enabled
+			continue
+		}
+		var name string = cName
+		if !fs.args.PlaintextNames {
+			name, err = fs.nameTransform.DecryptName(cName, cachedIV)
+			if err != nil {
+				toggledlog.Warn.Printf("Invalid name \"%s\" in dir \"%s\": %s", cName, cDirName, err)
+				continue
+			}
+		}
+		cipherEntries[i].Name = name
+		plain = append(plain, cipherEntries[i])
+	}
+	return plain, status
+}
+
+// We always need read access to do read-modify-write cycles
+func (fs *FS) mangleOpenFlags(flags uint32) (newFlags int, writeOnly bool) {
+	newFlags = int(flags)
+	if newFlags&os.O_WRONLY > 0 {
+		writeOnly = true
+		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
+
+	return newFlags, writeOnly
+}
+
+func (fs *FS) Open(path string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) {
+	if fs.isFiltered(path) {
+		return nil, fuse.EPERM
+	}
+	iflags, writeOnly := fs.mangleOpenFlags(flags)
+	cPath, err := fs.getBackingPath(path)
+	if err != nil {
+		toggledlog.Debug.Printf("Open: getBackingPath: %v", err)
+		return nil, fuse.ToStatus(err)
+	}
+	toggledlog.Debug.Printf("Open: %s", cPath)
+	f, err := os.OpenFile(cPath, iflags, 0666)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+
+	return NewFile(f, writeOnly, fs.contentEnc), fuse.OK
+}
+
+func (fs *FS) Create(path string, flags uint32, mode uint32, context *fuse.Context) (fuseFile nodefs.File, code fuse.Status) {
+	if fs.isFiltered(path) {
+		return nil, fuse.EPERM
+	}
+	iflags, writeOnly := fs.mangleOpenFlags(flags)
+	cPath, err := fs.getBackingPath(path)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	f, err := os.OpenFile(cPath, iflags|os.O_CREATE, os.FileMode(mode))
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	return NewFile(f, writeOnly, fs.contentEnc), fuse.OK
+}
+
+func (fs *FS) Chmod(path string, mode uint32, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(path) {
+		return fuse.EPERM
+	}
+	cPath, err := fs.encryptPath(path)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	return fs.FileSystem.Chmod(cPath, mode, context)
+}
+
+func (fs *FS) Chown(path string, uid uint32, gid uint32, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(path) {
+		return fuse.EPERM
+	}
+	cPath, err := fs.encryptPath(path)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	return fs.FileSystem.Chown(cPath, uid, gid, context)
+}
+
+func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(path) {
+		return fuse.EPERM
+	}
+	cPath, err := fs.encryptPath(path)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	return fs.FileSystem.Mknod(cPath, mode, dev, context)
+}
+
+var truncateWarned bool
+
+func (fs *FS) Truncate(path string, offset uint64, context *fuse.Context) (code fuse.Status) {
+	// Only warn once
+	if !truncateWarned {
+		toggledlog.Warn.Printf("truncate(2) is not supported, returning ENOSYS - use ftruncate(2)")
+		truncateWarned = true
+	}
+	return fuse.ENOSYS
+}
+
+func (fs *FS) Utimens(path string, Atime *time.Time, Mtime *time.Time, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(path) {
+		return fuse.EPERM
+	}
+	cPath, err := fs.encryptPath(path)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	return fs.FileSystem.Utimens(cPath, Atime, Mtime, context)
+}
+
+func (fs *FS) Readlink(path string, context *fuse.Context) (out string, status fuse.Status) {
+	cPath, err := fs.encryptPath(path)
+	if err != nil {
+		return "", fuse.ToStatus(err)
+	}
+	cTarget, status := fs.FileSystem.Readlink(cPath, context)
+	if status != fuse.OK {
+		return "", status
+	}
+	// Old filesystem: symlinks are encrypted like paths (CBC)
+	if !fs.args.DirIV {
+		target, err := fs.decryptPath(cTarget)
+		if err != nil {
+			toggledlog.Warn.Printf("Readlink: CBC decryption failed: %v", err)
+			return "", fuse.EIO
+		}
+		return target, fuse.OK
+	}
+	// Since gocryptfs v0.5 symlinks are encrypted like file contents (GCM)
+	cBinTarget, err := base64.URLEncoding.DecodeString(cTarget)
+	if err != nil {
+		toggledlog.Warn.Printf("Readlink: %v", err)
+		return "", fuse.EIO
+	}
+	target, err := fs.contentEnc.DecryptBlock([]byte(cBinTarget), 0, nil)
+	if err != nil {
+		toggledlog.Warn.Printf("Readlink: %v", err)
+		return "", fuse.EIO
+	}
+	return string(target), fuse.OK
+}
+
+func (fs *FS) Unlink(path string, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(path) {
+		return fuse.EPERM
+	}
+	cPath, err := fs.getBackingPath(path)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	return fuse.ToStatus(syscall.Unlink(cPath))
+}
+
+func (fs *FS) Symlink(target string, linkName string, context *fuse.Context) (code fuse.Status) {
+	toggledlog.Debug.Printf("Symlink(\"%s\", \"%s\")", target, linkName)
+	if fs.isFiltered(linkName) {
+		return fuse.EPERM
+	}
+	cPath, err := fs.getBackingPath(linkName)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	// Old filesystem: symlinks are encrypted like paths (CBC)
+	if !fs.args.DirIV {
+		cTarget, err := fs.encryptPath(target)
+		if err != nil {
+			toggledlog.Warn.Printf("Symlink: BUG: we should not get an error here: %v", err)
+			return fuse.ToStatus(err)
+		}
+		err = os.Symlink(cTarget, cPath)
+		return fuse.ToStatus(err)
+	}
+	// Since gocryptfs v0.5 symlinks are encrypted like file contents (GCM)
+	cBinTarget := fs.contentEnc.EncryptBlock([]byte(target), 0, nil)
+	cTarget := base64.URLEncoding.EncodeToString(cBinTarget)
+
+	err = os.Symlink(cTarget, cPath)
+	toggledlog.Debug.Printf("Symlink: os.Symlink(%s, %s) = %v", cTarget, cPath, err)
+	return fuse.ToStatus(err)
+}
+
+func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(newPath) {
+		return fuse.EPERM
+	}
+	cOldPath, err := fs.getBackingPath(oldPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	cNewPath, err := fs.getBackingPath(newPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	// The Rename may cause a directory to take the place of another directory.
+	// That directory may still be in the DirIV cache, clear it.
+	fs.nameTransform.DirIVCache.Clear()
+
+	err = os.Rename(cOldPath, cNewPath)
+
+	if lerr, ok := err.(*os.LinkError); ok && lerr.Err == syscall.ENOTEMPTY {
+		// If an empty directory is overwritten we will always get
+		// ENOTEMPTY as the "empty" directory will still contain gocryptfs.diriv.
+		// Handle that case by removing the target directory and trying again.
+		toggledlog.Debug.Printf("Rename: Handling ENOTEMPTY")
+		if fs.Rmdir(newPath, context) == fuse.OK {
+			err = os.Rename(cOldPath, cNewPath)
+		}
+	}
+
+	return fuse.ToStatus(err)
+}
+
+func (fs *FS) Link(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(newPath) {
+		return fuse.EPERM
+	}
+	cOldPath, err := fs.getBackingPath(oldPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	cNewPath, err := fs.getBackingPath(newPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	return fuse.ToStatus(os.Link(cOldPath, cNewPath))
+}
+
+func (fs *FS) Access(path string, mode uint32, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(path) {
+		return fuse.EPERM
+	}
+	cPath, err := fs.getBackingPath(path)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	return fuse.ToStatus(syscall.Access(cPath, mode))
+}
+
+func (fs *FS) GetXAttr(name string, attr string, context *fuse.Context) ([]byte, fuse.Status) {
+	return nil, fuse.ENOSYS
+}
+
+func (fs *FS) SetXAttr(name string, attr string, data []byte, flags int, context *fuse.Context) fuse.Status {
+	return fuse.ENOSYS
+}
+
+func (fs *FS) ListXAttr(name string, context *fuse.Context) ([]string, fuse.Status) {
+	return nil, fuse.ENOSYS
+}
+
+func (fs *FS) RemoveXAttr(name string, attr string, context *fuse.Context) fuse.Status {
+	return fuse.ENOSYS
+}
diff --git a/internal/fusefrontend/fs_dir.go b/internal/fusefrontend/fs_dir.go
new file mode 100644
index 0000000..2b1e25d
--- /dev/null
+++ b/internal/fusefrontend/fs_dir.go
@@ -0,0 +1,157 @@
+package fusefrontend
+
+// Mkdir and Rmdir
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	"github.com/hanwen/go-fuse/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
+	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+)
+
+func (fs *FS) Mkdir(relPath string, mode uint32, context *fuse.Context) (code fuse.Status) {
+	if fs.isFiltered(relPath) {
+		return fuse.EPERM
+	}
+	encPath, err := fs.getBackingPath(relPath)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	if !fs.args.DirIV {
+		return fuse.ToStatus(os.Mkdir(encPath, os.FileMode(mode)))
+	}
+
+	// We need write and execute permissions to create gocryptfs.diriv
+	origMode := mode
+	mode = mode | 0300
+
+	// The new directory may take the place of an older one that is still in the cache
+	fs.nameTransform.DirIVCache.Clear()
+	// Create directory
+	fs.dirIVLock.Lock()
+	defer fs.dirIVLock.Unlock()
+	err = os.Mkdir(encPath, os.FileMode(mode))
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	// Create gocryptfs.diriv inside
+	err = nametransform.WriteDirIV(encPath)
+	if err != nil {
+		// This should not happen
+		toggledlog.Warn.Printf("Mkdir: WriteDirIV failed: %v", err)
+		err2 := syscall.Rmdir(encPath)
+		if err2 != nil {
+			toggledlog.Warn.Printf("Mkdir: Rmdir rollback failed: %v", err2)
+		}
+		return fuse.ToStatus(err)
+	}
+
+	// Set permissions back to what the user wanted
+	if origMode != mode {
+		err = os.Chmod(encPath, os.FileMode(origMode))
+		if err != nil {
+			toggledlog.Warn.Printf("Mkdir: Chmod failed: %v", err)
+		}
+	}
+
+	return fuse.OK
+}
+
+func (fs *FS) Rmdir(name string, context *fuse.Context) (code fuse.Status) {
+	encPath, err := fs.getBackingPath(name)
+	if err != nil {
+		return fuse.ToStatus(err)
+	}
+	if !fs.args.DirIV {
+		return fuse.ToStatus(syscall.Rmdir(encPath))
+	}
+
+	// If the directory is not empty besides gocryptfs.diriv, do not even
+	// attempt the dance around gocryptfs.diriv.
+	fd, err := os.Open(encPath)
+	if perr, ok := err.(*os.PathError); ok && perr.Err == syscall.EACCES {
+		// We need permission to read and modify the directory
+		toggledlog.Debug.Printf("Rmdir: handling EACCESS")
+		fi, err2 := os.Stat(encPath)
+		if err2 != nil {
+			toggledlog.Debug.Printf("Rmdir: Stat: %v", err2)
+			return fuse.ToStatus(err2)
+		}
+		origMode := fi.Mode()
+		newMode := origMode | 0700
+		err2 = os.Chmod(encPath, newMode)
+		if err2 != nil {
+			toggledlog.Debug.Printf("Rmdir: Chmod failed: %v", err2)
+			return fuse.ToStatus(err)
+		}
+		defer func() {
+			if code != fuse.OK {
+				// Undo the chmod if removing the directory failed
+				err3 := os.Chmod(encPath, origMode)
+				if err3 != nil {
+					toggledlog.Warn.Printf("Rmdir: Chmod rollback failed: %v", err2)
+				}
+			}
+		}()
+		// Retry open
+		fd, err = os.Open(encPath)
+	}
+	if err != nil {
+		toggledlog.Debug.Printf("Rmdir: Open: %v", err)
+		return fuse.ToStatus(err)
+	}
+	list, err := fd.Readdirnames(10)
+	fd.Close()
+	if err != nil {
+		toggledlog.Debug.Printf("Rmdir: Readdirnames: %v", err)
+		return fuse.ToStatus(err)
+	}
+	if len(list) > 1 {
+		return fuse.ToStatus(syscall.ENOTEMPTY)
+	} else if len(list) == 0 {
+		toggledlog.Warn.Printf("Rmdir: gocryptfs.diriv missing, allowing deletion")
+		return fuse.ToStatus(syscall.Rmdir(encPath))
+	}
+
+	// Move "gocryptfs.diriv" to the parent dir as "gocryptfs.diriv.rmdir.XYZ"
+	dirivPath := filepath.Join(encPath, nametransform.DirIVFilename)
+	parentDir := filepath.Dir(encPath)
+	tmpName := fmt.Sprintf("gocryptfs.diriv.rmdir.%d", cryptocore.RandUint64())
+	tmpDirivPath := filepath.Join(parentDir, tmpName)
+	toggledlog.Debug.Printf("Rmdir: Renaming %s to %s", nametransform.DirIVFilename, tmpDirivPath)
+	// The directory is in an inconsistent state between rename and rmdir. Protect against
+	// concurrent readers.
+	fs.dirIVLock.Lock()
+	defer fs.dirIVLock.Unlock()
+	err = os.Rename(dirivPath, tmpDirivPath)
+	if err != nil {
+		toggledlog.Warn.Printf("Rmdir: Renaming %s to %s failed: %v",
+			nametransform.DirIVFilename, tmpDirivPath, err)
+		return fuse.ToStatus(err)
+	}
+	// Actual Rmdir
+	err = syscall.Rmdir(encPath)
+	if err != nil {
+		// This can happen if another file in the directory was created in the
+		// meantime, undo the rename
+		err2 := os.Rename(tmpDirivPath, dirivPath)
+		if err2 != nil {
+			toggledlog.Warn.Printf("Rmdir: Rename rollback failed: %v", err2)
+		}
+		return fuse.ToStatus(err)
+	}
+	// Delete "gocryptfs.diriv.rmdir.INODENUMBER"
+	err = syscall.Unlink(tmpDirivPath)
+	if err != nil {
+		toggledlog.Warn.Printf("Rmdir: Could not clean up %s: %v", tmpName, err)
+	}
+	// The now-deleted directory may have been in the DirIV cache. Clear it.
+	fs.nameTransform.DirIVCache.Clear()
+	return fuse.OK
+}
diff --git a/internal/fusefrontend/names.go b/internal/fusefrontend/names.go
new file mode 100644
index 0000000..5760c87
--- /dev/null
+++ b/internal/fusefrontend/names.go
@@ -0,0 +1,52 @@
+package fusefrontend
+
+// This file forwards file encryption operations to cryptfs
+
+import (
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	mylog "github.com/rfjakob/gocryptfs/internal/toggledlog"
+)
+
+// isFiltered - check if plaintext "path" should be forbidden
+//
+// Prevents name clashes with internal files when file names are not encrypted
+func (fs *FS) isFiltered(path string) bool {
+	if !fs.args.PlaintextNames {
+		return false
+	}
+	// gocryptfs.conf in the root directory is forbidden
+	if path == configfile.ConfDefaultName {
+		mylog.Info.Printf("The name /%s is reserved when -plaintextnames is used\n",
+			configfile.ConfDefaultName)
+		return true
+	}
+	// Note: gocryptfs.diriv is NOT forbidden because diriv and plaintextnames
+	// are exclusive
+	return false
+}
+
+// encryptPath - encrypt relative plaintext path
+func (fs *FS) encryptPath(plainPath string) (string, error) {
+	if fs.args.PlaintextNames {
+		return plainPath, nil
+	}
+	if !fs.args.DirIV {
+		return fs.nameTransform.EncryptPathNoIV(plainPath), nil
+	}
+	fs.dirIVLock.RLock()
+	defer fs.dirIVLock.RUnlock()
+	return fs.nameTransform.EncryptPathDirIV(plainPath, fs.args.Cipherdir)
+}
+
+// decryptPath - decrypt relative ciphertext path
+func (fs *FS) decryptPath(cipherPath string) (string, error) {
+	if fs.args.PlaintextNames {
+		return cipherPath, nil
+	}
+	if !fs.args.DirIV {
+		return fs.nameTransform.DecryptPathNoIV(cipherPath)
+	}
+	fs.dirIVLock.RLock()
+	defer fs.dirIVLock.RUnlock()
+	return fs.nameTransform.DecryptPathDirIV(cipherPath, fs.args.Cipherdir, fs.args.EMENames)
+}
diff --git a/internal/fusefrontend/write_lock.go b/internal/fusefrontend/write_lock.go
new file mode 100644
index 0000000..a8ec6b6
--- /dev/null
+++ b/internal/fusefrontend/write_lock.go
@@ -0,0 +1,66 @@
+package fusefrontend
+
+import (
+	"sync"
+)
+
+func init() {
+	wlock.m = make(map[uint64]*refCntMutex)
+}
+
+// wlock - serializes write accesses to each file (identified by inode number)
+// Writing partial blocks means we have to do read-modify-write cycles. We
+// really don't want concurrent writes there.
+// Concurrent full-block writes could actually be allowed, but are not to
+// keep the locking simple.
+var wlock wlockMap
+
+// wlockMap - usage:
+// 1) register
+// 2) lock ... unlock ...
+// 3) unregister
+type wlockMap struct {
+	mapMutex sync.RWMutex
+	m        map[uint64]*refCntMutex
+}
+
+func (w *wlockMap) register(ino uint64) {
+	w.mapMutex.Lock()
+	r := w.m[ino]
+	if r == nil {
+		r = &refCntMutex{}
+		w.m[ino] = r
+	}
+	r.refCnt++ // this must happen inside the mapMutex lock
+	w.mapMutex.Unlock()
+}
+
+func (w *wlockMap) unregister(ino uint64) {
+	w.mapMutex.Lock()
+	r := w.m[ino]
+	r.refCnt--
+	if r.refCnt == 0 {
+		delete(w.m, ino)
+	}
+	w.mapMutex.Unlock()
+}
+
+func (w *wlockMap) lock(ino uint64) {
+	w.mapMutex.RLock()
+	r := w.m[ino]
+	w.mapMutex.RUnlock()
+	r.Lock() // this can take a long time - execute outside the mapMutex lock
+}
+
+func (w *wlockMap) unlock(ino uint64) {
+	w.mapMutex.RLock()
+	r := w.m[ino]
+	w.mapMutex.RUnlock()
+	r.Unlock()
+}
+
+// refCntMutex - mutex with reference count
+type refCntMutex struct {
+	sync.Mutex
+	refCnt int
+}