libgocryptfs/internal/fusefrontend_reverse/rfs.go

package fusefrontend_reverse

import (
	"fmt"
	"os"
	"path/filepath"
	"syscall"

	"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/contentenc"
	"github.com/rfjakob/gocryptfs/internal/cryptocore"
	"github.com/rfjakob/gocryptfs/internal/fusefrontend"
	"github.com/rfjakob/gocryptfs/internal/nametransform"
)

const (
	DirIVMode = syscall.S_IFREG | 0400
)

type reverseFS struct {
	// Embed pathfs.defaultFileSystem for a ENOSYS implementation of all methods
	pathfs.FileSystem
	// pathfs.loopbackFileSystem, see go-fuse/fuse/pathfs/loopback.go
	loopbackfs pathfs.FileSystem
	// Stores configuration arguments
	args fusefrontend.Args
	// Filename encryption helper
	nameTransform *nametransform.NameTransform
	// Content encryption helper
	contentEnc *contentenc.ContentEnc
}

// Encrypted FUSE overlay filesystem
func NewFS(args fusefrontend.Args) *reverseFS {
	cryptoCore := cryptocore.New(args.Masterkey, args.OpenSSL, true)
	contentEnc := contentenc.New(cryptoCore, contentenc.DefaultBS)
	nameTransform := nametransform.New(cryptoCore, args.LongNames)

	return &reverseFS{
		// pathfs.defaultFileSystem returns ENOSYS for all operations
		FileSystem:    pathfs.NewDefaultFileSystem(),
		loopbackfs:    pathfs.NewLoopbackFileSystem(args.Cipherdir),
		args:          args,
		nameTransform: nameTransform,
		contentEnc:    contentEnc,
	}
}

// relDir is identical to filepath.Dir excepts that it returns "" when
// filepath.Dir would return ".".
// In the FUSE API, the root directory is called "", and we actually want that.
func relDir(path string) string {
	dir := filepath.Dir(path)
	if dir == "." {
		return ""
	}
	return dir
}

// dirIVAttr handles GetAttr requests for the virtual gocryptfs.diriv files.
func (rfs *reverseFS) dirIVAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
	cDir := relDir(relPath)
	dir, err := rfs.decryptPath(cDir)
	if err != nil {
		fmt.Printf("decrypt err %q\n", cDir)
		return nil, fuse.ToStatus(err)
	}
	// Does the parent dir exist?
	a, status := rfs.loopbackfs.GetAttr(dir, context)
	if !status.Ok() {
		fmt.Printf("missing parent\n")
		return nil, status
	}
	// Is it a dir at all?
	if !a.IsDir() {
		fmt.Printf("not isdir\n")
		return nil, fuse.ENOTDIR
	}
	// Does the user have execute permissions?
	if a.Mode&syscall.S_IXUSR == 0 {
		fmt.Printf("not exec")
		return nil, fuse.EPERM
	}
	// All good. Let's fake the file.
	// We use the inode number of the parent dir (can this cause problems?).
	a.Mode = DirIVMode
	a.Size = nametransform.DirIVLen
	a.Nlink = 1

	return a, fuse.OK
}

// isDirIV determines if the path points to a gocryptfs.diriv file
func isDirIV(relPath string) bool {
	return filepath.Base(relPath) == nametransform.DirIVFilename
}

func (rfs *reverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
	if isDirIV(relPath) {
		return rfs.dirIVAttr(relPath, context)
	}
	if rfs.isFiltered(relPath) {
		return nil, fuse.EPERM
	}
	relPath, err := rfs.decryptPath(relPath)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	a, status := rfs.loopbackfs.GetAttr(relPath, context)
	if !status.Ok() {
		return nil, status
	}
	// Calculate encrypted file size
	if a.IsRegular() {
		a.Size = rfs.contentEnc.PlainSizeToCipherSize(a.Size)
	}
	return a, fuse.OK
}

func (rfs *reverseFS) Access(relPath string, mode uint32, context *fuse.Context) fuse.Status {
	if isDirIV(relPath) {
		return fuse.OK
	}
	if rfs.isFiltered(relPath) {
		return fuse.EPERM
	}
	absPath, err := rfs.abs(rfs.decryptPath(relPath))
	if err != nil {
		return fuse.ToStatus(err)
	}
	return fuse.ToStatus(syscall.Access(absPath, mode))
}

func (rfs *reverseFS) Open(relPath string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) {
	if isDirIV(relPath) {
		return NewDirIVFile(relDir(relPath))
	}
	if rfs.isFiltered(relPath) {
		return nil, fuse.EPERM
	}
	absPath, err := rfs.abs(rfs.decryptPath(relPath))
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	f, err := os.OpenFile(absPath, int(flags), 0666)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	return NewFile(f, rfs.contentEnc)
}

func (rfs *reverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.DirEntry, fuse.Status) {
	relPath, err := rfs.decryptPath(cipherPath)
	if err != nil {
		return nil, fuse.ToStatus(err)
	}
	// Read plaintext dir
	entries, status := rfs.loopbackfs.OpenDir(relPath, context)
	if entries == nil {
		return nil, status
	}
	// Encrypt names
	dirIV := deriveDirIV(cipherPath)
	for i := range entries {
		entries[i].Name = rfs.nameTransform.EncryptName(entries[i].Name, dirIV)
	}
	// Add virtual gocryptfs.diriv
	entries = append(entries, fuse.DirEntry{syscall.S_IFREG | 0400, nametransform.DirIVFilename})

	return entries, fuse.OK
}