nametransform: gather badname functions in badname.go
This commit is contained in:
Jakob Unterwurzacher
parent
2efef1e270
commit
689b74835b
91
internal/nametransform/badname.go
Normal file
91
internal/nametransform/badname.go
Normal file
@ -0,0 +1,91 @@
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package nametransform
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import (
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"crypto/aes"
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"path/filepath"
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"strings"
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"syscall"
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"golang.org/x/sys/unix"
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"github.com/rfjakob/gocryptfs/internal/syscallcompat"
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)
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const (
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// BadNameFlag is appended to filenames in plaintext view if a corrupt
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// ciphername is shown due to a matching `-badname` pattern
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BadNameFlag = " GOCRYPTFS_BAD_NAME"
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)
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// EncryptAndHashBadName tries to find the "name" substring, which (encrypted and hashed)
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// leads to an unique existing file
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// Returns ENOENT if cipher file does not exist or is not unique
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func (be *NameTransform) EncryptAndHashBadName(name string, iv []byte, dirfd int) (cName string, err error) {
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var st unix.Stat_t
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var filesFound int
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lastFoundName, err := be.EncryptAndHashName(name, iv)
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if !strings.HasSuffix(name, BadNameFlag) || err != nil {
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//Default mode: same behaviour on error or no BadNameFlag on "name"
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return lastFoundName, err
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}
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//Default mode: Check if File extists without modifications
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err = syscallcompat.Fstatat(dirfd, lastFoundName, &st, unix.AT_SYMLINK_NOFOLLOW)
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if err == nil {
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//file found, return result
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return lastFoundName, nil
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}
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//BadName Mode: check if the name was tranformed without change (badname suffix and undecryptable cipher name)
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err = syscallcompat.Fstatat(dirfd, name[:len(name)-len(BadNameFlag)], &st, unix.AT_SYMLINK_NOFOLLOW)
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if err == nil {
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filesFound++
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lastFoundName = name[:len(name)-len(BadNameFlag)]
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}
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// search for the longest badname pattern match
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for charpos := len(name) - len(BadNameFlag); charpos > 0; charpos-- {
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//only use original cipher name and append assumed suffix (without badname flag)
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cNamePart, err := be.EncryptName(name[:charpos], iv)
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if err != nil {
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//expand suffix on error
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continue
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}
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if be.longNames && len(cName) > NameMax {
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cNamePart = be.HashLongName(cName)
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}
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cNameBadReverse := cNamePart + name[charpos:len(name)-len(BadNameFlag)]
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err = syscallcompat.Fstatat(dirfd, cNameBadReverse, &st, unix.AT_SYMLINK_NOFOLLOW)
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if err == nil {
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filesFound++
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lastFoundName = cNameBadReverse
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}
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}
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if filesFound == 1 {
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return lastFoundName, nil
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}
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// more than 1 possible file found, ignore
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return "", syscall.ENOENT
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}
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func (n *NameTransform) decryptBadname(cipherName string, iv []byte) (string, error) {
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for _, pattern := range n.badnamePatterns {
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match, err := filepath.Match(pattern, cipherName)
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// Pattern should have been validated already
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if err == nil && match {
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// Find longest decryptable substring
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// At least 16 bytes due to AES --> at least 22 characters in base64
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nameMin := n.B64.EncodedLen(aes.BlockSize)
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for charpos := len(cipherName) - 1; charpos >= nameMin; charpos-- {
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res, err := n.decryptName(cipherName[:charpos], iv)
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if err == nil {
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return res + cipherName[charpos:] + BadNameFlag, nil
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}
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}
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return cipherName + BadNameFlag, nil
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}
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}
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return "", syscall.EBADMSG
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}
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// HaveBadnamePatterns returns true if `-badname` patterns were provided
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func (n *NameTransform) HaveBadnamePatterns() bool {
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return len(n.badnamePatterns) > 0
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}
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@ -5,14 +5,11 @@ import (
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"fmt"
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"io"
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"os"
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"path/filepath"
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"strings"
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"syscall"
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"github.com/rfjakob/gocryptfs/internal/cryptocore"
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"github.com/rfjakob/gocryptfs/internal/syscallcompat"
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"github.com/rfjakob/gocryptfs/internal/tlog"
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"golang.org/x/sys/unix"
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)
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const (
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@ -95,78 +92,3 @@ func WriteDirIVAt(dirfd int) error {
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}
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return nil
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}
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// encryptAndHashName encrypts "name" and hashes it to a longname if it is
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// too long.
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// Returns ENAMETOOLONG if "name" is longer than 255 bytes.
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func (be *NameTransform) EncryptAndHashName(name string, iv []byte) (string, error) {
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// Prevent the user from creating files longer than 255 chars.
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if len(name) > NameMax {
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return "", syscall.ENAMETOOLONG
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}
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cName, err := be.EncryptName(name, iv)
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if err != nil {
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return "", err
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}
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if be.longNames && len(cName) > NameMax {
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return be.HashLongName(cName), nil
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}
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return cName, nil
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}
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// EncryptAndHashBadName tries to find the "name" substring, which (encrypted and hashed)
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// leads to an unique existing file
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// Returns ENOENT if cipher file does not exist or is not unique
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func (be *NameTransform) EncryptAndHashBadName(name string, iv []byte, dirfd int) (cName string, err error) {
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var st unix.Stat_t
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var filesFound int
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lastFoundName, err := be.EncryptAndHashName(name, iv)
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if !strings.HasSuffix(name, BadNameFlag) || err != nil {
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//Default mode: same behaviour on error or no BadNameFlag on "name"
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return lastFoundName, err
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}
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//Default mode: Check if File extists without modifications
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err = syscallcompat.Fstatat(dirfd, lastFoundName, &st, unix.AT_SYMLINK_NOFOLLOW)
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if err == nil {
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//file found, return result
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return lastFoundName, nil
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}
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//BadName Mode: check if the name was tranformed without change (badname suffix and undecryptable cipher name)
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err = syscallcompat.Fstatat(dirfd, name[:len(name)-len(BadNameFlag)], &st, unix.AT_SYMLINK_NOFOLLOW)
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if err == nil {
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filesFound++
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lastFoundName = name[:len(name)-len(BadNameFlag)]
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}
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// search for the longest badname pattern match
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for charpos := len(name) - len(BadNameFlag); charpos > 0; charpos-- {
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//only use original cipher name and append assumed suffix (without badname flag)
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cNamePart, err := be.EncryptName(name[:charpos], iv)
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if err != nil {
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//expand suffix on error
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continue
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}
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if be.longNames && len(cName) > NameMax {
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cNamePart = be.HashLongName(cName)
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}
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cNameBadReverse := cNamePart + name[charpos:len(name)-len(BadNameFlag)]
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err = syscallcompat.Fstatat(dirfd, cNameBadReverse, &st, unix.AT_SYMLINK_NOFOLLOW)
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if err == nil {
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filesFound++
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lastFoundName = cNameBadReverse
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}
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}
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if filesFound == 1 {
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return lastFoundName, nil
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}
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// more than 1 possible file found, ignore
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return "", syscall.ENOENT
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}
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// Dir is like filepath.Dir but returns "" instead of ".".
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func Dir(path string) string {
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d := filepath.Dir(path)
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if d == "." {
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return ""
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}
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return d
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}
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@ -15,8 +15,6 @@ import (
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const (
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// Like ext4, we allow at most 255 bytes for a file name.
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NameMax = 255
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//BadNameFlag is appended to filenames in plain mode if a ciphername is inavlid but is shown
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BadNameFlag = " GOCRYPTFS_BAD_NAME"
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)
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// NameTransform is used to transform filenames.
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@ -51,22 +49,8 @@ func New(e *eme.EMECipher, longNames bool, raw64 bool, badname []string) *NameTr
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// filename "cipherName", and failing that checks if it can be bypassed
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func (n *NameTransform) DecryptName(cipherName string, iv []byte) (string, error) {
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res, err := n.decryptName(cipherName, iv)
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if err != nil {
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for _, pattern := range n.badnamePatterns {
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match, err := filepath.Match(pattern, cipherName)
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if err == nil && match { // Pattern should have been validated already
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// Find longest decryptable substring
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// At least 16 bytes due to AES --> at least 22 characters in base64
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nameMin := n.B64.EncodedLen(aes.BlockSize)
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for charpos := len(cipherName) - 1; charpos >= nameMin; charpos-- {
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res, err = n.decryptName(cipherName[:charpos], iv)
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if err == nil {
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return res + cipherName[charpos:] + BadNameFlag, nil
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}
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}
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return cipherName + BadNameFlag, nil
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}
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}
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if err != nil && n.HaveBadnamePatterns() {
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return n.decryptBadname(cipherName, iv)
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}
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return res, err
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}
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@ -117,6 +101,24 @@ func (n *NameTransform) EncryptName(plainName string, iv []byte) (cipherName64 s
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return cipherName64, nil
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}
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// EncryptAndHashName encrypts "name" and hashes it to a longname if it is
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// too long.
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// Returns ENAMETOOLONG if "name" is longer than 255 bytes.
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func (be *NameTransform) EncryptAndHashName(name string, iv []byte) (string, error) {
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// Prevent the user from creating files longer than 255 chars.
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if len(name) > NameMax {
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return "", syscall.ENAMETOOLONG
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}
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cName, err := be.EncryptName(name, iv)
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if err != nil {
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return "", err
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}
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if be.longNames && len(cName) > NameMax {
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return be.HashLongName(cName), nil
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}
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return cName, nil
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}
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// B64EncodeToString returns a Base64-encoded string
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func (n *NameTransform) B64EncodeToString(src []byte) string {
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return n.B64.EncodeToString(src)
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@ -127,7 +129,11 @@ func (n *NameTransform) B64DecodeString(s string) ([]byte, error) {
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return n.B64.DecodeString(s)
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}
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// HaveBadnamePatterns returns true if BadName patterns were provided
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func (n *NameTransform) HaveBadnamePatterns() bool {
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return len(n.badnamePatterns) > 0
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// Dir is like filepath.Dir but returns "" instead of ".".
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func Dir(path string) string {
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d := filepath.Dir(path)
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if d == "." {
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return ""
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}
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return d
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}
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