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package nametransform
import (
"bytes"
"fmt"
"io"
"log"
"os"
"path/filepath"
"strings"
"syscall"
"golang.org/x/sys/unix"
"github.com/rfjakob/gocryptfs/internal/cryptocore"
"github.com/rfjakob/gocryptfs/internal/syscallcompat"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
const (
// DirIVLen is identical to AES block size
DirIVLen = 16
// DirIVFilename is the filename used to store directory IV.
// Exported because we have to ignore this name in directory listing.
DirIVFilename = "gocryptfs.diriv"
)
// ReadDirIV - read the "gocryptfs.diriv" file from "dir" (absolute ciphertext path)
// This function is exported because it allows for an efficient readdir implementation.
// If the directory itself cannot be opened, a syscall error will be returned.
// Otherwise, a fmt.Errorf() error value is returned with the details.
func ReadDirIV(dir string) (iv []byte, err error) {
fd, err := os.Open(filepath.Join(dir, DirIVFilename))
if err != nil {
// Note: getting errors here is normal because of concurrent deletes.
// Strip the useless annotation that os.Open has added and return
// the plain syscall error. The caller will log a nice message.
err2 := err.(*os.PathError)
return nil, err2.Err
}
defer fd.Close()
return fdReadDirIV(fd)
}
// ReadDirIVAt reads "gocryptfs.diriv" from the directory that is opened as "dirfd".
// Using the dirfd makes it immune to concurrent renames of the directory.
func ReadDirIVAt(dirfd int) (iv []byte, err error) {
fdRaw, err := syscallcompat.Openat(dirfd, DirIVFilename,
syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
if err != nil {
return nil, fmt.Errorf("openat failed: %v", err)
}
fd := os.NewFile(uintptr(fdRaw), DirIVFilename)
defer fd.Close()
return fdReadDirIV(fd)
}
// allZeroDirIV is preallocated to quickly check if the data read from disk is all zero
var allZeroDirIV = make([]byte, DirIVLen)
// fdReadDirIV reads and verifies the DirIV from an opened gocryptfs.diriv file.
func fdReadDirIV(fd *os.File) (iv []byte, err error) {
// We want to detect if the file is bigger than DirIVLen, so
// make the buffer 1 byte bigger than necessary.
iv = make([]byte, DirIVLen+1)
n, err := fd.Read(iv)
if err != nil && err != io.EOF {
return nil, fmt.Errorf("read failed: %v", err)
}
iv = iv[0:n]
if len(iv) != DirIVLen {
return nil, fmt.Errorf("wanted %d bytes, got %d", DirIVLen, len(iv))
}
if bytes.Equal(iv, allZeroDirIV) {
return nil, fmt.Errorf("diriv is all-zero")
}
return iv, nil
}
// WriteDirIV - create diriv file inside of the specified directory. If dirfd
// is nil "dir" should be the absolute path to the directory. If dirfd != nil
// "dir" should be a path (without slashes) relative to the directory
// described by "dirfd". This function is exported because it is used from
// pathfs_frontend, main, and also the automated tests.
func WriteDirIV(dirfd int, dir string) error {
// For relative paths we do not expect that "dir" contains slashes
if dirfd >= 0 && strings.Contains(dir, "/") {
log.Panicf("WriteDirIV: Relative path should not contain slashes: %v", dir)
}
iv := cryptocore.RandBytes(DirIVLen)
file := filepath.Join(dir, DirIVFilename)
// 0400 permissions: gocryptfs.diriv should never be modified after creation.
// Don't use "ioutil.WriteFile", it causes trouble on NFS: https://github.com/rfjakob/gocryptfs/issues/105
fdRaw, err := syscallcompat.Openat(dirfd, file, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0400)
if err != nil {
tlog.Warn.Printf("WriteDirIV: Openat: %v", err)
return err
}
fd := os.NewFile(uintptr(fdRaw), file)
_, err = fd.Write(iv)
if err != nil {
fd.Close()
// It is normal to get ENOSPC here
if !syscallcompat.IsENOSPC(err) {
tlog.Warn.Printf("WriteDirIV: Write: %v", err)
}
// Delete incomplete gocryptfs.diriv file
syscallcompat.Unlinkat(dirfd, file, 0)
return err
}
err = fd.Close()
if err != nil {
tlog.Warn.Printf("WriteDirIV: Close: %v", err)
// Delete incomplete gocryptfs.diriv file
syscallcompat.Unlinkat(dirfd, file, 0)
return err
}
return nil
}
// encryptAndHashName encrypts "name" and hashes it to a longname if it is
// too long.
func (be *NameTransform) encryptAndHashName(name string, iv []byte) string {
cName := be.EncryptName(name, iv)
if be.longNames && len(cName) > unix.NAME_MAX {
return be.HashLongName(cName)
}
return cName
}
// EncryptPathDirIV - encrypt relative plaintext path "plainPath" using EME with
// DirIV. "rootDir" is the backing storage root directory.
// Components that are longer than 255 bytes are hashed if be.longnames == true.
func (be *NameTransform) EncryptPathDirIV(plainPath string, rootDir string) (string, error) {
var err error
// Empty string means root directory
if plainPath == "" {
return plainPath, nil
}
// Reject names longer than 255 bytes.
baseName := filepath.Base(plainPath)
if len(baseName) > unix.NAME_MAX {
return "", syscall.ENAMETOOLONG
}
// If we have the iv and the encrypted directory name in the cache, we
// can skip the directory walk. This optimization yields a 10% improvement
// in the tar extract benchmark.
parentDir := Dir(plainPath)
if iv, cParentDir := be.DirIVCache.Lookup(parentDir); iv != nil {
cBaseName := be.encryptAndHashName(baseName, iv)
return filepath.Join(cParentDir, cBaseName), nil
}
// We have to walk the directory tree, starting at the root directory.
// ciphertext working directory (relative path)
cipherWD := ""
// plaintext working directory (relative path)
plainWD := ""
plainNames := strings.Split(plainPath, "/")
for _, plainName := range plainNames {
iv, _ := be.DirIVCache.Lookup(plainWD)
if iv == nil {
iv, err = ReadDirIV(filepath.Join(rootDir, cipherWD))
if err != nil {
return "", err
}
be.DirIVCache.Store(plainWD, iv, cipherWD)
}
cipherName := be.encryptAndHashName(plainName, iv)
cipherWD = filepath.Join(cipherWD, cipherName)
plainWD = filepath.Join(plainWD, plainName)
}
return cipherWD, nil
}
// Dir is like filepath.Dir but returns "" instead of ".".
func Dir(path string) string {
d := filepath.Dir(path)
if d == "." {
return ""
}
return d
}
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