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package nametransform
import (
"bytes"
"io"
"os"
"path/filepath"
"strings"
"syscall"
"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.
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.
return nil, 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 *os.File) (iv []byte, err error) {
fdRaw, err := syscallcompat.Openat(int(dirfd.Fd()), DirIVFilename, syscall.O_RDONLY, 0)
if err != nil {
tlog.Warn.Printf("ReadDirIVAt: opening %q in dir %q failed: %v",
DirIVFilename, dirfd.Name(), err)
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 {
tlog.Warn.Printf("ReadDirIVAt: Read failed: %v", err)
return nil, err
}
iv = iv[0:n]
if len(iv) != DirIVLen {
tlog.Warn.Printf("ReadDirIVAt: wanted %d bytes, got %d. Returning EINVAL.", DirIVLen, len(iv))
return nil, syscall.EINVAL
}
if bytes.Equal(iv, allZeroDirIV) {
tlog.Warn.Printf("ReadDirIVAt: diriv is all-zero. Returning EINVAL.")
return nil, syscall.EINVAL
}
return iv, nil
}
// WriteDirIV - create diriv file inside "dir" (absolute ciphertext path)
// This function is exported because it is used from pathfs_frontend, main,
// and also the automated tests.
func WriteDirIV(dir string) error {
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
fd, err := os.OpenFile(file, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0400)
if err != nil {
tlog.Warn.Printf("WriteDirIV: OpenFile: %v", err)
return err
}
_, err = fd.Write(iv)
if err != nil {
tlog.Warn.Printf("WriteDirIV: Write: %v", err)
return err
}
err = fd.Close()
if err != nil {
tlog.Warn.Printf("WriteDirIV: Close: %v", err)
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) > syscall.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) (cipherPath string, err error) {
// Empty string means root directory
if plainPath == "" {
return plainPath, nil
}
// Reject names longer than 255 bytes already here. This relieves everybody
// who uses hashed long names from checking for that later.
baseName := filepath.Base(plainPath)
if len(baseName) > syscall.NAME_MAX {
return "", syscall.ENAMETOOLONG
}
// Check if the DirIV is cached. This catches the case of the user iterating
// over files in a directory pretty well.
parentDir := filepath.Dir(plainPath)
iv, cParentDir := be.DirIVCache.lookup(parentDir)
if iv != nil {
cBaseName := be.encryptAndHashName(baseName, iv)
return filepath.Join(cParentDir, cBaseName), nil
}
// We have to walk the directory tree, in the worst case starting at the root
// directory.
wd := rootDir
plainNames := strings.Split(plainPath, "/")
// So the DirIV we need is not cached. But maybe one level higher is
// cached. Then we can skip a few items in the directory walk.
// This catches the case of walking directories recursively.
parentDir2 := filepath.Dir(parentDir)
iv, cParentDir = be.DirIVCache.lookup(parentDir2)
if iv != nil {
parentDirBase := filepath.Base(parentDir)
cBaseName := be.encryptAndHashName(parentDirBase, iv)
wd = filepath.Join(wd, cParentDir, cBaseName)
cipherPath = filepath.Join(cParentDir, cBaseName)
skip := len(strings.Split(cipherPath, "/"))
plainNames = plainNames[skip:]
}
// Walk the directory tree starting at "wd"
for _, plainName := range plainNames {
iv, err = ReadDirIV(wd)
if err != nil {
return "", err
}
encryptedName := be.encryptAndHashName(plainName, iv)
cipherPath = filepath.Join(cipherPath, encryptedName)
wd = filepath.Join(wd, encryptedName)
}
// Cache the final DirIV
cParentDir = filepath.Dir(cipherPath)
be.DirIVCache.store(parentDir, iv, cParentDir)
return cipherPath, nil
}
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