fusefrontend_reverse: return ENOENT for undecryptable names

This was working until DecryptName switched to returning
EBADMSG instead of EINVAL.

Add a test to catch the regression next time.

benchmark.bash

@@ -67,7 +67,7 @@ if [[ $OPT_ENCFS -eq 1 ]]; then
 		exit 1
 	fi
 	echo "Testing EncFS at $CRYPT"
-	encfs --extpass="echo test" --standard $CRYPT $MNT > /dev/null
+	/home/jakob.donotbackup/encfs/build/encfs --extpass="echo test" --standard $CRYPT $MNT > /dev/null
 else
 	echo "Testing gocryptfs at $CRYPT"
 	gocryptfs -q -init -extpass="echo test" -scryptn=10 $CRYPT

internal/fusefrontend_reverse/rpath.go

@@ -46,7 +46,7 @@ func (rfs *ReverseFS) rDecryptName(cName string, dirIV []byte, pDir string) (pNa
 			// Stat attempts on the link target of encrypted symlinks.
 			// These are always valid base64 but the length is not a
 			// multiple of 16.
-			if err == syscall.EINVAL {
+			if err == syscall.EBADMSG {
 				return "", syscall.ENOENT
 			}
 			return "", err

tests/reverse/correctness_test.go

@@ -130,3 +130,13 @@ func TestAccessVirtual(t *testing.T) {
 		t.Errorf("should NOT be executable")
 	}
 }
+
+// Opening a nonexistant file name should return ENOENT
+// and not EBADMSG or EIO or anything else.
+func TestEnoent(t *testing.T) {
+	fn := dirB + "/TestEnoent"
+	_, err := syscall.Open(fn, syscall.O_RDONLY, 0)
+	if err != syscall.ENOENT {
+		t.Errorf("want ENOENT, got: %v", err)
+	}
+}