Re-design of the original gocryptfs code to work as a library.
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libgocryptfs/internal/nametransform/longnames.go

157 lines
4.6 KiB

package nametransform
import (
"crypto/sha256"
"fmt"
"io"
"os"
"path/filepath"
"strings"
"syscall"
"libgocryptfs/v2/internal/syscallcompat"
)
const (
// LongNameSuffix is the suffix used for files with long names.
// Files with long names are stored in two files:
// gocryptfs.longname.[sha256] <--- File content, prefix = gocryptfs.longname.
// gocryptfs.longname.[sha256].name <--- File name, suffix = .name
LongNameSuffix = ".name"
longNamePrefix = "gocryptfs.longname."
)
// HashLongName - take the hash of a long string "name" and return
// "gocryptfs.longname.[sha256]"
//
// This function does not do any I/O.
func (n *NameTransform) HashLongName(name string) string {
hashBin := sha256.Sum256([]byte(name))
hashBase64 := n.B64.EncodeToString(hashBin[:])
return longNamePrefix + hashBase64
}
// Values returned by IsLongName
const (
// LongNameContent is the file that stores the file content.
// Example: gocryptfs.longname.URrM8kgxTKYMgCk4hKk7RO9Lcfr30XQof4L_5bD9Iro=
LongNameContent = iota
// LongNameFilename is the file that stores the full encrypted filename.
// Example: gocryptfs.longname.URrM8kgxTKYMgCk4hKk7RO9Lcfr30XQof4L_5bD9Iro=.name
LongNameFilename = iota
// LongNameNone is used when the file does not have a long name.
// Example: i1bpTaVLZq7sRNA9mL_2Ig==
LongNameNone = iota
)
// NameType - detect if cName is
// gocryptfs.longname.[sha256] ........ LongNameContent (content of a long name file)
// gocryptfs.longname.[sha256].name .... LongNameFilename (full file name of a long name file)
// else ................................ LongNameNone (normal file)
//
// This function does not do any I/O.
func NameType(cName string) int {
if !strings.HasPrefix(cName, longNamePrefix) {
return LongNameNone
}
if strings.HasSuffix(cName, LongNameSuffix) {
return LongNameFilename
}
return LongNameContent
}
// IsLongContent returns true if "cName" is the content store of a long name
// file (looks like "gocryptfs.longname.[sha256]").
//
// This function does not do any I/O.
func IsLongContent(cName string) bool {
return NameType(cName) == LongNameContent
}
// RemoveLongNameSuffix removes the ".name" suffix from cName, returning the corresponding
// content file name.
// No check is made if cName actually is a LongNameFilename.
func RemoveLongNameSuffix(cName string) string {
return cName[:len(cName)-len(LongNameSuffix)]
}
// ReadLongName - read cName + ".name" from the directory opened as dirfd.
//
// Symlink-safe through Openat().
func ReadLongNameAt(dirfd int, cName string) (string, error) {
cName += LongNameSuffix
var f *os.File
{
fd, err := syscallcompat.Openat(dirfd, cName, syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
if err != nil {
return "", err
}
f = os.NewFile(uintptr(fd), "")
// fd runs out of scope here
}
defer f.Close()
// 256 (=255 padded to 16) bytes base64-encoded take 344 bytes: "AAAAAAA...AAA=="
lim := 344
// Allocate a bigger buffer so we see whether the file is too big
buf := make([]byte, lim+1)
n, err := f.ReadAt(buf, 0)
if err != nil && err != io.EOF {
return "", err
}
if n == 0 {
return "", fmt.Errorf("ReadLongName: empty file")
}
if n > lim {
return "", fmt.Errorf("ReadLongName: size=%d > limit=%d", n, lim)
}
return string(buf[0:n]), nil
}
// DeleteLongName deletes "hashName.name" in the directory opened at "dirfd".
//
// This function is symlink-safe through the use of Unlinkat().
func DeleteLongNameAt(dirfd int, hashName string) error {
err := syscallcompat.Unlinkat(dirfd, hashName+LongNameSuffix, 0)
return err
}
// WriteLongName encrypts plainName and writes it into "hashName.name".
// For the convenience of the caller, plainName may also be a path and will be
// Base()named internally.
//
// This function is symlink-safe through the use of Openat().
func (n *NameTransform) WriteLongNameAt(dirfd int, hashName string, plainName string) (err error) {
plainName = filepath.Base(plainName)
// Encrypt the basename
dirIV, err := n.ReadDirIVAt(dirfd)
if err != nil {
return err
}
cName, err := n.EncryptName(plainName, dirIV)
if err != nil {
return err
}
// Write the encrypted name into hashName.name
fdRaw, err := syscallcompat.Openat(dirfd, hashName+LongNameSuffix,
syscall.O_WRONLY|syscall.O_CREAT|syscall.O_EXCL, namePerms)
if err != nil {
return err
}
fd := os.NewFile(uintptr(fdRaw), hashName+LongNameSuffix)
_, err = fd.Write([]byte(cName))
if err != nil {
fd.Close()
// Delete incomplete longname file
syscallcompat.Unlinkat(dirfd, hashName+LongNameSuffix, 0)
return err
}
err = fd.Close()
if err != nil {
// Delete incomplete longname file
syscallcompat.Unlinkat(dirfd, hashName+LongNameSuffix, 0)
return err
}
return nil
}