nametransform: gather badname functions in badname.go

1 files changed, 91 insertions, 0 deletions

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
+}