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package nametransform
import (
"bytes"
"fmt"
"io"
"os"
"path/filepath"
"strings"
"syscall"
"github.com/rfjakob/gocryptfs/internal/cryptocore"
"github.com/rfjakob/gocryptfs/internal/syscallcompat"
"github.com/rfjakob/gocryptfs/internal/tlog"
"golang.org/x/sys/unix"
)
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"
)
// ReadDirIVAt reads "gocryptfs.diriv" from the directory that is opened as "dirfd".
// Using the dirfd makes it immune to concurrent renames of the directory.
// Retries on EINTR.
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, 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
}
// WriteDirIVAt - create a new gocryptfs.diriv file in the directory opened at
// "dirfd". On error we try to delete the incomplete file.
// This function is exported because it is used from fusefrontend, main,
// and also the automated tests.
func WriteDirIVAt(dirfd int) error {
iv := cryptocore.RandBytes(DirIVLen)
// 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/commit/7d38f80a78644c8ec4900cc990bfb894387112ed
fd, err := syscallcompat.Openat(dirfd, DirIVFilename, os.O_WRONLY|os.O_CREATE|os.O_EXCL, dirivPerms)
if err != nil {
tlog.Warn.Printf("WriteDirIV: Openat: %v", err)
return err
}
// Wrap the fd in an os.File - we need the write retry logic.
f := os.NewFile(uintptr(fd), DirIVFilename)
_, err = f.Write(iv)
if err != nil {
f.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, DirIVFilename, 0)
return err
}
err = f.Close()
if err != nil {
tlog.Warn.Printf("WriteDirIV: Close: %v", err)
// Delete incomplete gocryptfs.diriv file
syscallcompat.Unlinkat(dirfd, DirIVFilename, 0)
return err
}
return nil
}
// encryptAndHashName encrypts "name" and hashes it to a longname if it is
// too long.
// Returns ENAMETOOLONG if "name" is longer than 255 bytes.
func (be *NameTransform) EncryptAndHashName(name string, iv []byte) (string, error) {
// Prevent the user from creating files longer than 255 chars.
if len(name) > NameMax {
return "", syscall.ENAMETOOLONG
}
cName, err := be.EncryptName(name, iv)
if err != nil {
return "", err
}
if be.longNames && len(cName) > NameMax {
return be.HashLongName(cName), nil
}
return cName, nil
}
// EncryptAndHashBadName tries to find the "name" substring, which (encrypted and hashed)
// leads to an unique existing file
// Returns ENOENT if cipher file does not exist or is not unique
func (be *NameTransform) EncryptAndHashBadName(name string, iv []byte, dirfd int) (cName string, err error) {
var st unix.Stat_t
var filesFound int
lastFoundName, err := be.EncryptAndHashName(name, iv)
if !strings.HasSuffix(name, BadNameFlag) || err != nil {
//Default mode: same behaviour on error or no BadNameFlag on "name"
return lastFoundName, err
}
//Default mode: Check if File extists without modifications
err = syscallcompat.Fstatat(dirfd, lastFoundName, &st, unix.AT_SYMLINK_NOFOLLOW)
if err == nil {
//file found, return result
return lastFoundName, nil
}
//BadName Mode: check if the name was tranformed without change (badname suffix and undecryptable cipher name)
err = syscallcompat.Fstatat(dirfd, name[:len(name)-len(BadNameFlag)], &st, unix.AT_SYMLINK_NOFOLLOW)
if err == nil {
filesFound++
lastFoundName = name[:len(name)-len(BadNameFlag)]
}
// search for the longest badname pattern match
for charpos := len(name) - len(BadNameFlag); charpos > 0; charpos-- {
//only use original cipher name and append assumed suffix (without badname flag)
cNamePart, err := be.EncryptName(name[:charpos], iv)
if err != nil {
//expand suffix on error
continue
}
if be.longNames && len(cName) > NameMax {
cNamePart = be.HashLongName(cName)
}
cNameBadReverse := cNamePart + name[charpos:len(name)-len(BadNameFlag)]
err = syscallcompat.Fstatat(dirfd, cNameBadReverse, &st, unix.AT_SYMLINK_NOFOLLOW)
if err == nil {
filesFound++
lastFoundName = cNameBadReverse
}
}
if filesFound == 1 {
return lastFoundName, nil
}
// more than 1 possible file found, ignore
return "", syscall.ENOENT
}
// 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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