diriv: Move WriteDirIV() to cryptfs; add locking to Mkdir, Rmdir

cryptfs/names_diriv.go

@@ -21,6 +21,15 @@ func (be *CryptFS) readDirIV(dir string) (iv []byte, err error) {
 		return iv, nil
 }
 
+// WriteDirIV - create diriv file inside "dir" (absolute path)
+// This function is exported because it is used from pathfs_frontend
+func (be *CryptFS) WriteDirIV(dir string) error {
+	iv := RandBytes(DIRIV_LEN)
+	file := filepath.Join(dir, DIRIV_FILENAME)
+	// 0444 permissions: the file is not secret but should not be written to
+	return ioutil.WriteFile(file, iv, 0444)
+}
+
 // EncryptPathDirIV - encrypt path using CBC with DirIV
 func (be *CryptFS) EncryptPathDirIV(plainPath string, rootDir string) (string, error) {
 	if be.plaintextNames {

pathfs_frontend/fs.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"sync"
 	"syscall"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"time"
@@ -20,7 +19,11 @@ type FS struct {
 	*cryptfs.CryptFS
 	pathfs.FileSystem           // loopbackFileSystem, see go-fuse/fuse/pathfs/loopback.go
 	backingDir           string // Backing directory, cipherdir
-	dirivLock sync.RWMutex      // Global lock that is taken if any "gocryptfs.diriv" file is modified
+	// dirIVLock: Lock()ed if any "gocryptfs.diriv" file is modified
+	// Readers must RLock() it to prevent them from seeing intermediate
+	// states
+	dirIVLock sync.RWMutex
+
 }
 
 // Encrypted FUSE overlay filesystem
@@ -217,16 +220,15 @@ func (fs *FS) Mkdir(relPath string, mode uint32, context *fuse.Context) (code fu
 	if err != nil {
 		return fuse.ToStatus(err)
 	}
-	diriv := cryptfs.RandBytes(cryptfs.DIRIV_LEN)
-	dirivPath := filepath.Join(encPath, cryptfs.DIRIV_FILENAME)
 	// 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
-	// 0444 permissions: the file is not secret but should not be written to
+	err = fs.CryptFS.WriteDirIV(encPath)
-	err = ioutil.WriteFile(dirivPath, diriv, 0444)
 	if err != nil {
 		// This should not happen
 		cryptfs.Warn.Printf("Creating %s in dir %s failed: %v\n", cryptfs.DIRIV_FILENAME, encPath, err)
@@ -282,8 +284,8 @@ func (fs *FS) Rmdir(name string, context *fuse.Context) (code fuse.Status) {
 	tmpName := fmt.Sprintf("gocryptfs.diriv.rmdir.%d", st.Ino)
 	tmpDirivPath := filepath.Join(parentDir, tmpName)
 	cryptfs.Debug.Printf("Rmdir: Renaming %s to %s\n", cryptfs.DIRIV_FILENAME, tmpDirivPath)
-	fs.dirivLock.Lock() // directory will be in an inconsistent state after the rename
+	fs.dirIVLock.Lock() // directory will be in an inconsistent state after the rename
-	defer fs.dirivLock.Unlock()
+	defer fs.dirIVLock.Unlock()
 	err = os.Rename(dirivPath, tmpDirivPath)
 	if err != nil {
 		cryptfs.Warn.Printf("Rmdir: Renaming %s to %s failed: %v\n", cryptfs.DIRIV_FILENAME, tmpDirivPath, err)

pathfs_frontend/names.go

@@ -3,9 +3,13 @@ package pathfs_frontend
 // This file handles filename encryption
 
 func (fs *FS) encryptPath(plainPath string) (string, error) {
+	fs.dirIVLock.RLock()
+	defer fs.dirIVLock.RUnlock()
 	return fs.CryptFS.EncryptPathDirIV(plainPath, fs.backingDir)
 }
 
 func (fs *FS) decryptPath(cipherPath string) (string, error) {
+	fs.dirIVLock.RLock()
+	defer fs.dirIVLock.RUnlock()
 	return fs.CryptFS.DecryptPathDirIV(cipherPath, fs.backingDir)
 }