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

91 lines
3.0 KiB

package nametransform
import (
"crypto/aes"
"path/filepath"
"strings"
"syscall"
"golang.org/x/sys/unix"
"libgocryptfs/v2/internal/syscallcompat"
)
const (
// BadnameSuffix is appended to filenames in plaintext view if a corrupt
// ciphername is shown due to a matching `-badname` pattern
BadnameSuffix = " 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, BadnameSuffix) || 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(BadnameSuffix)], &st, unix.AT_SYMLINK_NOFOLLOW)
if err == nil {
filesFound++
lastFoundName = name[:len(name)-len(BadnameSuffix)]
}
// search for the longest badname pattern match
for charpos := len(name) - len(BadnameSuffix); 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(BadnameSuffix)]
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:] + BadnameSuffix, nil
}
}
return cipherName + BadnameSuffix, nil
}
}
return "", syscall.EBADMSG
}
// HaveBadnamePatterns returns true if `-badname` patterns were provided
func (n *NameTransform) HaveBadnamePatterns() bool {
return len(n.badnamePatterns) > 0
}