nametransform: reject names longer than 255 chars

Looks like we allowed creating longer names by accident.
Fix that, and add a test that verifies it.

internal/fusefrontend/openbackingdir.go

@@ -38,7 +38,11 @@ func (fs *FS) openBackingDir(relPath string) (dirfd int, cName string, err error
 			return dirfd, ".", nil
 		}
 		name := filepath.Base(relPath)
-		cName = fs.nameTransform.EncryptAndHashName(name, iv)
+		cName, err = fs.nameTransform.EncryptAndHashName(name, iv)
+		if err != nil {
+			syscall.Close(dirfd)
+			return -1, "", err
+		}
 		return dirfd, cName, nil
 	}
 	// Open cipherdir (following symlinks)
@@ -58,7 +62,11 @@ func (fs *FS) openBackingDir(relPath string) (dirfd int, cName string, err error
 			syscall.Close(dirfd)
 			return -1, "", err
 		}
-		cName = fs.nameTransform.EncryptAndHashName(name, iv)
+		cName, err = fs.nameTransform.EncryptAndHashName(name, iv)
+		if err != nil {
+			syscall.Close(dirfd)
+			return -1, "", err
+		}
 		// Last part? We are done.
 		if i == len(parts)-1 {
 			fs.dirCache.Store(dirRelPath, dirfd, iv)

internal/nametransform/diriv.go

@@ -8,8 +8,6 @@ import (
 	"path/filepath"
 	"syscall"
 
-	"golang.org/x/sys/unix"
-
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
@@ -97,12 +95,17 @@ func WriteDirIVAt(dirfd int) error {
 
 // encryptAndHashName encrypts "name" and hashes it to a longname if it is
 // too long.
-func (be *NameTransform) EncryptAndHashName(name string, iv []byte) string {
-	cName := be.EncryptName(name, iv)
-	if be.longNames && len(cName) > unix.NAME_MAX {
-		return be.HashLongName(cName)
+// 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
 	}
-	return cName
+	cName := be.EncryptName(name, iv)
+	if be.longNames && len(cName) > NameMax {
+		return be.HashLongName(cName), nil
+	}
+	return cName, nil
 }
 
 // Dir is like filepath.Dir but returns "" instead of ".".

internal/nametransform/names.go

@@ -12,6 +12,11 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
+const (
+	// Like ext4, we allow at most 255 bytes for a file name.
+	NameMax = 255
+)
+
 // NameTransform is used to transform filenames.
 type NameTransform struct {
 	emeCipher *eme.EMECipher

tests/matrix/matrix_test.go

@@ -377,6 +377,57 @@ func TestRename(t *testing.T) {
 	test_helpers.TestRename(t, test_helpers.DefaultPlainDir)
 }
 
+// Test that names of all lengths work
+func TestNameLengths(t *testing.T) {
+	f, err := os.Open(test_helpers.DefaultPlainDir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	entries, err := f.Readdirnames(0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+	cnt1 := len(entries)
+
+	wd := test_helpers.DefaultPlainDir + "/"
+	name := "x"
+	for len(name) < 2000 {
+		f, err := os.Create(wd + name + "x")
+		if err != nil {
+			break
+		}
+		name = name + "x"
+		f.Close()
+		f, err = os.Open(test_helpers.DefaultPlainDir)
+		if err != nil {
+			t.Fatal(err)
+		}
+		// In v1.7-rc2, we had a bug that allowed creation of too-long names.
+		// This threw errors in like this in READDIR:
+		//
+		//   OpenDir ".": invalid entry "gocryptfs.longname.wrE-izsR9ciEkP7JSCFDrk_d_Nj4mQo1dGY6hjuixAU=":
+		//   Could not read .name: ReadLongName: size=345 > limit=344
+		//
+		entries, err = f.Readdirnames(0)
+		if err != nil {
+			t.Fatal(err)
+		}
+		f.Close()
+		cnt2 := len(entries)
+		if cnt2 != cnt1+1 {
+			t.Fatalf("len=%d: expected %d dir entries, have %d: %v", len(name), cnt1+1, cnt2, entries)
+		}
+		err = syscall.Unlink(wd + name)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+	if len(name) != 255 {
+		t.Errorf("maxlen=%d", len(name))
+	}
+}
+
 func TestLongNames(t *testing.T) {
 	fi, err := ioutil.ReadDir(test_helpers.DefaultCipherDir)
 	if err != nil {