fusefrontend: Handle PlaintextNames mode in Mknod

In PlaintextNames mode the "gocryptfs.longname." prefix does not have any
special meaning. We should not attempt to read the directory IV or to
create special .name files.

Partially fixes https://github.com/rfjakob/gocryptfs/issues/174

internal/fusefrontend/fs.go

@@ -287,9 +287,9 @@ func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context)
 		return fuse.ToStatus(err)
 	}
 	defer dirfd.Close()
-	// Create ".name" file to store long file name
+	// Create ".name" file to store long file name (except in PlaintextNames mode)
 	cName := filepath.Base(cPath)
-	if nametransform.IsLongContent(cName) {
+	if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
 		err = fs.nameTransform.WriteLongName(dirfd, cName, path)
 		if err != nil {
 			return fuse.ToStatus(err)

tests/matrix/matrix_test.go

@@ -789,4 +789,9 @@ func TestMkfifo(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	path = test_helpers.DefaultPlainDir + "/gocryptfs.longname.XXX"
+	err = syscall.Mkfifo(path, 0700)
+	if err != nil {
+		t.Fatal(err)
+	}
 }