libgocryptfs/pathfs_frontend/fs.go

package pathfs_frontend

import (
	"encoding/base64"
	"fmt"
	"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/cryptfs"
)

type FS struct {
	*cryptfs.CryptFS
	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
}

// Encrypted FUSE overlay filesystem
func NewFS(args Args) *FS {
	return &FS{
		CryptFS:    cryptfs.NewCryptFS(args.Masterkey, args.OpenSSL, args.PlaintextNames),
		FileSystem: pathfs.NewLoopbackFileSystem(args.Cipherdir),
		args: args,
	}
}

// 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)
	cryptfs.Debug.Printf("getBackingPath: %s + %s -> %s\n", fs.args.Cipherdir, relPath, cAbsPath)
	return cAbsPath, nil
}

func (fs *FS) GetAttr(name string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
	cryptfs.Debug.Printf("FS.GetAttr('%s')\n", name)
	if fs.CryptFS.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 {
		cryptfs.Debug.Printf("FS.GetAttr failed: %s\n", status.String())
		return a, status
	}
	if a.IsRegular() {
		a.Size = fs.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) {
	cryptfs.Debug.Printf("OpenDir(%s)\n", 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 zero if DirIV if off)
	cachedIV := make([]byte, cryptfs.DIRIV_LEN)
	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.CryptFS.ReadDirIV(cDirAbsPath)
		if err != nil {
			return nil, fuse.ToStatus(err)
		}
	}
	// Decrypt filenames
	var plain []fuse.DirEntry
	for i := range cipherEntries {
		cName := cipherEntries[i].Name
		if dirName == "" && cName == cryptfs.ConfDefaultName {
			// silently ignore "gocryptfs.conf" in the top level dir
			continue
		}
		if fs.args.DirIV && cName == cryptfs.DIRIV_FILENAME {
			// silently ignore "gocryptfs.diriv" everywhere if dirIV is enabled
			continue
		}
		var name string
		name, err = fs.CryptFS.DecryptName(cName, cachedIV)
		if err != nil {
			cryptfs.Warn.Printf("Invalid name \"%s\" in dir \"%s\": %s\n", cName, dirName, 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.CryptFS.IsFiltered(path) {
		return nil, fuse.EPERM
	}
	iflags, writeOnly := fs.mangleOpenFlags(flags)
	cPath, err := fs.getBackingPath(path)
	if err != nil {
		cryptfs.Debug.Printf("Open: getBackingPath: %v\n", err)
		return nil, fuse.ToStatus(err)
	}
	cryptfs.Debug.Printf("Open: %s\n", cPath)
	f, err := os.OpenFile(cPath, iflags, 0666)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}

	return NewFile(f, writeOnly, fs.CryptFS), fuse.OK
}

func (fs *FS) Create(path string, flags uint32, mode uint32, context *fuse.Context) (fuseFile nodefs.File, code fuse.Status) {
	if fs.CryptFS.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.CryptFS), fuse.OK
}

func (fs *FS) Chmod(path string, mode uint32, context *fuse.Context) (code fuse.Status) {
	if fs.CryptFS.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.CryptFS.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.CryptFS.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)
}

func (fs *FS) Truncate(path string, offset uint64, context *fuse.Context) (code fuse.Status) {
	cryptfs.Warn.Printf("Truncate of a closed file is not supported, returning ENOSYS\n")
	return fuse.ENOSYS
}

func (fs *FS) Utimens(path string, Atime *time.Time, Mtime *time.Time, context *fuse.Context) (code fuse.Status) {
	if fs.CryptFS.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 {
			cryptfs.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 {
		cryptfs.Warn.Printf("Readlink: %v\n", err)
		return "", fuse.EIO
	}
	target, err := fs.CryptFS.DecryptBlock([]byte(cBinTarget), 0, nil)
	if err != nil {
		cryptfs.Warn.Printf("Readlink: %v\n", err)
		return "", fuse.EIO
	}
	return string(target), fuse.OK
}

func (fs *FS) Mkdir(relPath string, mode uint32, context *fuse.Context) (code fuse.Status) {
	if fs.CryptFS.IsFiltered(relPath) {
		return fuse.EPERM
	}
	encPath, err := fs.getBackingPath(relPath)
	if err != nil {
		return fuse.ToStatus(err)
	}
	// The new directory may take the place of an older one that is still in the cache
	fs.CryptFS.DirIVCacheEnc.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 = cryptfs.WriteDirIV(encPath)
	if err != nil {
		// This should not happen
		cryptfs.Warn.Printf("Creating %s in dir %s failed: %v\n", cryptfs.DIRIV_FILENAME, encPath, err)
		err2 := syscall.Rmdir(encPath)
		if err2 != nil {
			cryptfs.Warn.Printf("Mkdir: Rollback failed: %v\n", err2)
		}
		return fuse.ToStatus(err)
	}
	return fuse.OK
}

func (fs *FS) Unlink(path string, context *fuse.Context) (code fuse.Status) {
	if fs.CryptFS.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) Rmdir(name string, context *fuse.Context) (code fuse.Status) {
	encPath, err := fs.getBackingPath(name)
	if err != nil {
		return fuse.ToStatus(err)
	}

	// If the directory is not empty besides gocryptfs.diriv, do not even
	// attempt the dance around gocryptfs.diriv.
	fd, err := os.Open(encPath)
	if err != nil {
		return fuse.ToStatus(err)
	}
	defer fd.Close()
	list, err := fd.Readdirnames(10)
	if err != nil {
		return fuse.ToStatus(err)
	}
	if len(list) > 1 {
		return fuse.ToStatus(syscall.ENOTEMPTY)
	}

	// Move "gocryptfs.diriv" to the parent dir under name "gocryptfs.diriv.rmdir.INODENUMBER"
	var st syscall.Stat_t
	err = syscall.Fstat(int(fd.Fd()), &st)
	if err != nil {
		return fuse.ToStatus(err)
	}
	dirivPath := filepath.Join(encPath, cryptfs.DIRIV_FILENAME)
	parentDir := filepath.Dir(encPath)
	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)
	// 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 {
		cryptfs.Warn.Printf("Rmdir: Renaming %s to %s failed: %v\n", cryptfs.DIRIV_FILENAME, 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 {
			cryptfs.Warn.Printf("Rmdir: Rollback failed: %v\n", err2)
		}
		return fuse.ToStatus(err)
	}
	// Delete "gocryptfs.diriv.rmdir.INODENUMBER"
	err = syscall.Unlink(tmpDirivPath)
	if err != nil {
		cryptfs.Warn.Printf("Rmdir: Could not clean up %s: %v\n", tmpName, err)
	}
	// The now-deleted directory may have been in the DirIV cache. Clear it.
	fs.CryptFS.DirIVCacheEnc.Clear()
	return fuse.OK
}

func (fs *FS) Symlink(target string, linkName string, context *fuse.Context) (code fuse.Status) {
	cryptfs.Debug.Printf("Symlink(\"%s\", \"%s\")\n", target, linkName)
	if fs.CryptFS.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 {
			cryptfs.Warn.Printf("Symlink: BUG: we should not get an error here: %v\n", 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.CryptFS.EncryptBlock([]byte(target), 0, nil)
	cTarget := base64.URLEncoding.EncodeToString(cBinTarget)

	err = os.Symlink(cTarget, cPath)
	cryptfs.Debug.Printf("Symlink: os.Symlink(%s, %s) = %v\n", cTarget, cPath, err)
	return fuse.ToStatus(err)
}

func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
	if fs.CryptFS.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.CryptFS.DirIVCacheEnc.Clear()

	return fs.FileSystem.Rename(cOldPath, cNewPath, context)
}

func (fs *FS) Link(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
	if fs.CryptFS.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.CryptFS.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
}