nametransform: add longNameMax parameter

Determines when to start hashing long names instead
of hardcoded 255. Will be used to alleviate "name too long"
issues some users see on cloud storage.

https://github.com/rfjakob/gocryptfs/issues/499

internal/fusefrontend/xattr_unit_test.go

@@ -19,7 +19,7 @@ func newTestFS(args Args) *RootNode {
 	key := make([]byte, cryptocore.KeyLen)
 	cCore := cryptocore.New(key, cryptocore.BackendGoGCM, contentenc.DefaultIVBits, true)
 	cEnc := contentenc.New(cCore, contentenc.DefaultBS)
-	n := nametransform.New(cCore.EMECipher, true, true, nil, false)
+	n := nametransform.New(cCore.EMECipher, true, 0, true, nil, false)
 	rn := NewRootNode(args, cEnc, n)
 	oneSec := time.Second
 	options := &fs.Options{

internal/nametransform/badname.go

@@ -48,7 +48,7 @@ func (be *NameTransform) EncryptAndHashBadName(name string, iv []byte, dirfd int
 			//expand suffix on error
 			continue
 		}
-		if be.longNames && len(cName) > NameMax {
+		if len(cName) > be.longNameMax {
 			cNamePart = be.HashLongName(cName)
 		}
 		cNameBadReverse := cNamePart + name[charpos:len(name)-len(BadnameSuffix)]

internal/nametransform/longnames_test.go

@@ -1,7 +1,11 @@
 package nametransform
 
 import (
+	"strings"
 	"testing"
+
+	"github.com/rfjakob/gocryptfs/v2/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/v2/internal/cryptocore"
 )
 
 func TestIsLongName(t *testing.T) {
@@ -28,3 +32,40 @@ func TestRemoveLongNameSuffix(t *testing.T) {
 		t.Error(".name suffix not removed")
 	}
 }
+
+func newLognamesTestInstance(longNameMax uint8) *NameTransform {
+	key := make([]byte, cryptocore.KeyLen)
+	cCore := cryptocore.New(key, cryptocore.BackendGoGCM, contentenc.DefaultIVBits, true)
+	return New(cCore.EMECipher, true, longNameMax, true, nil, false)
+}
+
+func TestLongNameMax(t *testing.T) {
+	iv := make([]byte, 16)
+	for max := 0; max <= NameMax; max++ {
+		n := newLognamesTestInstance(uint8(max))
+		if max == 0 {
+			// effective value is 255
+			max = NameMax
+		}
+		for l := 0; l <= NameMax+10; l++ {
+			name := strings.Repeat("x", l)
+			out, err := n.EncryptAndHashName(name, iv)
+			if l == 0 || l > NameMax {
+				if err == nil {
+					t.Errorf("should have rejected a name of length %d, but did not", l)
+				}
+				continue
+			}
+			cName, _ := n.EncryptName(name, iv)
+			rawLen := len(cName)
+			want := LongNameNone
+			if rawLen > max {
+				want = LongNameContent
+			}
+			have := NameType(out)
+			if have != want {
+				t.Errorf("l=%d max=%d: wanted %v, got %v\nname=%q\nout=%q", l, max, want, have, name, out)
+			}
+		}
+	}
+}

internal/nametransform/names.go

@@ -4,6 +4,7 @@ package nametransform
 import (
 	"crypto/aes"
 	"encoding/base64"
+	"math"
 	"path/filepath"
 	"syscall"
 
@@ -20,7 +21,9 @@ const (
 // NameTransform is used to transform filenames.
 type NameTransform struct {
 	emeCipher *eme.EMECipher
-	longNames bool
+	// Names longer than `longNameMax` are hashed. Set to MaxInt when
+	// longnames are disabled.
+	longNameMax int
 	// B64 = either base64.URLEncoding or base64.RawURLEncoding, depending
 	// on the Raw64 feature flag
 	B64 *base64.Encoding
@@ -30,17 +33,28 @@ type NameTransform struct {
 }
 
 // New returns a new NameTransform instance.
-func New(e *eme.EMECipher, longNames bool, raw64 bool, badname []string, deterministicNames bool) *NameTransform {
-	tlog.Debug.Printf("nametransform.New: longNames=%v, raw64=%v, badname=%q",
-		longNames, raw64, badname)
-
+//
+// If `longNames` is set, names longer than `longNameMax` are hashed to
+// `gocryptfs.longname.[sha256]`.
+// Pass `longNameMax = 0` to use the default value (255).
+func New(e *eme.EMECipher, longNames bool, longNameMax uint8, raw64 bool, badname []string, deterministicNames bool) *NameTransform {
+	tlog.Debug.Printf("nametransform.New: longNameMax=%v, raw64=%v, badname=%q",
+		longNameMax, raw64, badname)
 	b64 := base64.URLEncoding
 	if raw64 {
 		b64 = base64.RawURLEncoding
 	}
+	var effectiveLongNameMax int = math.MaxInt
+	if longNames {
+		if longNameMax == 0 {
+			effectiveLongNameMax = NameMax
+		} else {
+			effectiveLongNameMax = int(longNameMax)
+		}
+	}
 	return &NameTransform{
 		emeCipher:          e,
-		longNames:          longNames,
+		longNameMax:        effectiveLongNameMax,
 		B64:                b64,
 		badnamePatterns:    badname,
 		deterministicNames: deterministicNames,
@@ -115,7 +129,7 @@ func (be *NameTransform) EncryptAndHashName(name string, iv []byte) (string, err
 	if err != nil {
 		return "", err
 	}
-	if be.longNames && len(cName) > NameMax {
+	if len(cName) > be.longNameMax {
 		return be.HashLongName(cName), nil
 	}
 	return cName, nil

mount.go

@@ -324,7 +324,7 @@ func initFuseFrontend(args *argContainer) (rootNode fs.InodeEmbedder, wipeKeys f
 	// Init crypto backend
 	cCore := cryptocore.New(masterkey, cryptoBackend, IVBits, args.hkdf)
 	cEnc := contentenc.New(cCore, contentenc.DefaultBS)
-	nameTransform := nametransform.New(cCore.EMECipher, frontendArgs.LongNames,
+	nameTransform := nametransform.New(cCore.EMECipher, frontendArgs.LongNames, 0,
 		args.raw64, []string(args.badname), frontendArgs.DeterministicNames)
 	// After the crypto backend is initialized,
 	// we can purge the master key from memory.