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libgocryptfs
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reverse: implement dynamic diriv 

Introduce a unique per-directory diriv that is generated
by hashing the encrypted directory path.
This commit is contained in:
Jakob Unterwurzacher 2016-09-19 23:40:43 +02:00
parent 10f38e8870
commit be9dfe3a89
3 changed files with 116 additions and 86 deletions
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42
internal/fusefrontend_reverse/diriv.go Normal file
View File

@ -0,0 +1,42 @@
package fusefrontend_reverse
import (
"crypto/sha256"
"github.com/hanwen/go-fuse/fuse"
"github.com/hanwen/go-fuse/fuse/nodefs"
"github.com/rfjakob/gocryptfs/internal/nametransform"
)
// deriveDirIV derives the DirIV from the directory path by simply hashing it
func deriveDirIV(dirPath string) []byte {
hash := sha256.Sum256([]byte(dirPath))
return hash[:nametransform.DirIVLen]
}
type dirIVFile struct {
// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
nodefs.File
// file content
content []byte
}
func NewDirIVFile(dirPath string) (nodefs.File, fuse.Status) {
return &dirIVFile{
File: nodefs.NewDefaultFile(),
content: deriveDirIV(dirPath),
}, fuse.OK
}
// Read - FUSE call
func (f *dirIVFile) Read(buf []byte, off int64) (resultData fuse.ReadResult, status fuse.Status) {
if off >= int64(len(f.content)) {
return nil, fuse.OK
}
end := int(off) + len(buf)
if end > len(f.content) {
end = len(f.content)
}
return fuse.ReadResultData(f.content[off:end]), fuse.OK
}

113
internal/fusefrontend_reverse/rfs.go
View File

@ -3,8 +3,7 @@ package fusefrontend_reverse
import (
"fmt"
"os"
"path"
"strings"
"path/filepath"
"syscall"
"github.com/hanwen/go-fuse/fuse"
@ -50,47 +49,59 @@ func NewFS(args fusefrontend.Args) *reverseFS {
}
}
func (rfs *reverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
// Handle gocryptfs.diriv
if relPath == nametransform.DirIVFilename ||
strings.HasSuffix(relPath, nametransform.DirIVFilename) {
fmt.Printf("Handling gocryptfs.diriv\n")
cDir := path.Dir(relPath)
if cDir == "." {
cDir = ""
}
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
// 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
}
@ -110,17 +121,23 @@ func (rfs *reverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr
}
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
}
cPath, err := rfs.abs(rfs.encryptPath(relPath))
absPath, err := rfs.abs(rfs.decryptPath(relPath))
if err != nil {
return fuse.ToStatus(err)
}
return fuse.ToStatus(syscall.Access(cPath, mode))
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(relPath)
}
if rfs.isFiltered(relPath) {
return nil, fuse.EPERM
}
@ -135,8 +152,8 @@ func (rfs *reverseFS) Open(relPath string, flags uint32, context *fuse.Context)
return NewFile(f, rfs.contentEnc)
}
func (rfs *reverseFS) OpenDir(relPath string, context *fuse.Context) ([]fuse.DirEntry, fuse.Status) {
relPath, err := rfs.decryptPath(relPath)
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)
}
@ -146,11 +163,9 @@ func (rfs *reverseFS) OpenDir(relPath string, context *fuse.Context) ([]fuse.Dir
return nil, status
}
// Encrypt names
dirIV := deriveDirIV(cipherPath)
for i := range entries {
entries[i].Name, err = rfs.encryptPath(entries[i].Name)
if err != nil {
return nil, fuse.ToStatus(err)
}
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})

47
internal/fusefrontend_reverse/rpath.go
View File

@ -2,18 +2,11 @@ package fusefrontend_reverse
import (
"encoding/base64"
"fmt"
"path/filepath"
"strings"
"syscall"
)
var zeroDirIV []byte
func init() {
zeroDirIV = make([]byte, 16)
}
func (rfs *reverseFS) abs(relPath string, err error) (string, error) {
if err != nil {
return "", err
@ -21,45 +14,25 @@ func (rfs *reverseFS) abs(relPath string, err error) (string, error) {
return filepath.Join(rfs.args.Cipherdir, relPath), nil
}
const (
ENCRYPT = iota
DECRYPT
)
func (rfs *reverseFS) encryptPath(relPath string) (string, error) {
return rfs.transformPath(relPath, ENCRYPT)
}
func (rfs *reverseFS) decryptPath(relPath string) (string, error) {
return rfs.transformPath(relPath, DECRYPT)
}
func (rfs *reverseFS) transformPath(relPath string, direction int) (string, error) {
if rfs.args.PlaintextNames || relPath == "" {
return relPath, nil
}
var err error
var transformedParts []string
parts := strings.Split(relPath, "/")
for _, part := range parts {
for i, part := range parts {
var transformedPart string
switch direction {
case ENCRYPT:
transformedPart = rfs.nameTransform.EncryptName(part, zeroDirIV)
case DECRYPT:
transformedPart, err = rfs.nameTransform.DecryptName(part, zeroDirIV)
if err != nil {
// We get lots of decrypt requests for names like ".Trash" that
// are invalid base64. Convert them to ENOENT so the correct
// error gets returned to the user.
if _, ok := err.(base64.CorruptInputError); ok {
fmt.Printf("converting to ENOENT\n")
return "", syscall.ENOENT
}
return "", err
dirIV := deriveDirIV(filepath.Join(parts[:i]...))
transformedPart, err = rfs.nameTransform.DecryptName(part, dirIV)
if err != nil {
// We get lots of decrypt requests for names like ".Trash" that
// are invalid base64. Convert them to ENOENT so the correct
// error gets returned to the user.
if _, ok := err.(base64.CorruptInputError); ok {
return "", syscall.ENOENT
}
default:
panic("bug: invalid direction value")
return "", err
}
transformedParts = append(transformedParts, transformedPart)
}