fuzzing: Add a new fuzz test for g_variant_byteswap()

The behaviour of `g_variant_byteswap()` is largely dominated by its call
to `g_variant_get_normal_form()`, but it does do an additional call to
`g_variant_serialised_byteswap()` which we should probably be fuzzing.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

fuzzing/fuzz_variant_binary_byteswap.c

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2018 pdknsk
+ * Copyright 2022 Endless OS Foundation, LLC
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "fuzz.h"
+
+int
+LLVMFuzzerTestOneInput (const unsigned char *data, size_t size)
+{
+  GVariant *variant = NULL, *swapped_variant = NULL;
+
+  fuzz_set_logging_func ();
+
+  variant = g_variant_new_from_data (G_VARIANT_TYPE_VARIANT, data, size, FALSE,
+                                     NULL, NULL);
+  if (variant == NULL)
+    return 0;
+
+  swapped_variant = g_variant_byteswap (variant);
+  g_variant_get_data (swapped_variant);
+
+  g_variant_unref (swapped_variant);
+  g_variant_unref (variant);
+  return 0;
+}

fuzzing/meson.build

@@ -35,6 +35,7 @@ fuzz_targets = [
   'fuzz_uri_parse_params',
   'fuzz_uuid_string_is_valid',
   'fuzz_variant_binary',
+  'fuzz_variant_binary_byteswap',
   'fuzz_variant_text',
 ]