From 689b74835bd38ebaf87ba0e205c10b9594e51863 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Mon, 21 Jun 2021 12:08:18 +0200
Subject: nametransform: gather badname functions in badname.go

---
 internal/nametransform/badname.go | 91 +++++++++++++++++++++++++++++++++++++++
 internal/nametransform/diriv.go   | 78 ---------------------------------
 internal/nametransform/names.go   | 48 ++++++++++++---------
 3 files changed, 118 insertions(+), 99 deletions(-)
 create mode 100644 internal/nametransform/badname.go

diff --git a/internal/nametransform/badname.go b/internal/nametransform/badname.go
new file mode 100644
index 0000000..5cc9799
--- /dev/null
+++ b/internal/nametransform/badname.go
@@ -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
+}
diff --git a/internal/nametransform/diriv.go b/internal/nametransform/diriv.go
index d62b3fb..b10c899 100644
--- a/internal/nametransform/diriv.go
+++ b/internal/nametransform/diriv.go
@@ -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
-}
diff --git a/internal/nametransform/names.go b/internal/nametransform/names.go
index 2ee52e4..566f0c7 100644
--- a/internal/nametransform/names.go
+++ b/internal/nametransform/names.go
@@ -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
 }
-- 
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