nametransform: gather badname functions in badname.go

This commit is contained in:
Jakob Unterwurzacher 2021-06-21 12:08:18 +02:00
parent 2efef1e270
commit 689b74835b
3 changed files with 118 additions and 99 deletions

View File

@ -0,0 +1,91 @@
package nametransform
import (
"crypto/aes"
"path/filepath"
"strings"
"syscall"
"golang.org/x/sys/unix"
"github.com/rfjakob/gocryptfs/internal/syscallcompat"
)
const (
// BadNameFlag is appended to filenames in plaintext view if a corrupt
// ciphername is shown due to a matching `-badname` pattern
BadNameFlag = " GOCRYPTFS_BAD_NAME"
)
// 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
}
func (n *NameTransform) decryptBadname(cipherName string, iv []byte) (string, error) {
for _, pattern := range n.badnamePatterns {
match, err := filepath.Match(pattern, cipherName)
// Pattern should have been validated already
if err == nil && match {
// Find longest decryptable substring
// At least 16 bytes due to AES --> at least 22 characters in base64
nameMin := n.B64.EncodedLen(aes.BlockSize)
for charpos := len(cipherName) - 1; charpos >= nameMin; charpos-- {
res, err := n.decryptName(cipherName[:charpos], iv)
if err == nil {
return res + cipherName[charpos:] + BadNameFlag, nil
}
}
return cipherName + BadNameFlag, nil
}
}
return "", syscall.EBADMSG
}
// HaveBadnamePatterns returns true if `-badname` patterns were provided
func (n *NameTransform) HaveBadnamePatterns() bool {
return len(n.badnamePatterns) > 0
}

View File

@ -5,14 +5,11 @@ import (
"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 (
@ -95,78 +92,3 @@ func WriteDirIVAt(dirfd int) error {
}
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
}

View File

@ -15,8 +15,6 @@ import (
const (
// Like ext4, we allow at most 255 bytes for a file name.
NameMax = 255
//BadNameFlag is appended to filenames in plain mode if a ciphername is inavlid but is shown
BadNameFlag = " GOCRYPTFS_BAD_NAME"
)
// NameTransform is used to transform filenames.
@ -51,22 +49,8 @@ func New(e *eme.EMECipher, longNames bool, raw64 bool, badname []string) *NameTr
// filename "cipherName", and failing that checks if it can be bypassed
func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
res, err := n.decryptName(cipherName, iv)
if err != nil {
for _, pattern := range n.badnamePatterns {
match, err := filepath.Match(pattern, cipherName)
if err == nil && match { // Pattern should have been validated already
// Find longest decryptable substring
// At least 16 bytes due to AES --> at least 22 characters in base64
nameMin := n.B64.EncodedLen(aes.BlockSize)
for charpos := len(cipherName) - 1; charpos >= nameMin; charpos-- {
res, err = n.decryptName(cipherName[:charpos], iv)
if err == nil {
return res + cipherName[charpos:] + BadNameFlag, nil
}
}
return cipherName + BadNameFlag, nil
}
}
if err != nil && n.HaveBadnamePatterns() {
return n.decryptBadname(cipherName, iv)
}
return res, err
}
@ -117,6 +101,24 @@ func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 s
return cipherName64, 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
}
// B64EncodeToString returns a Base64-encoded string
func (n *NameTransform) B64EncodeToString(src []byte) string {
return n.B64.EncodeToString(src)
@ -127,7 +129,11 @@ func (n *NameTransform) B64DecodeString(s string) ([]byte, error) {
return n.B64.DecodeString(s)
}
// HaveBadnamePatterns returns true if BadName patterns were provided
func (n *NameTransform) HaveBadnamePatterns() bool {
return len(n.badnamePatterns) > 0
// Dir is like filepath.Dir but returns "" instead of ".".
func Dir(path string) string {
d := filepath.Dir(path)
if d == "." {
return ""
}
return d
}