fuzzing: Add fuzz tests for g_filename_{to,from}_uri()

These functions could be called on untrusted input data, and since they
do URI escaping/unescaping, they have non-trivial string handling code.

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

See: #3827

fuzzing/fuzz_filename_from_uri.c

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2025 GNOME Foundation, Inc.
+ *
+ * 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)
+{
+  unsigned char *nul_terminated_data = NULL;
+  char *filename = NULL;
+  GError *local_error = NULL;
+
+  fuzz_set_logging_func ();
+
+  /* ignore @size (g_filename_from_uri() doesn’t support it); ensure @data is nul-terminated */
+  nul_terminated_data = (unsigned char *) g_strndup ((const char *) data, size);
+  filename = g_filename_from_uri ((const char *) nul_terminated_data, NULL, &local_error);
+  g_free (nul_terminated_data);
+
+  g_free (filename);
+  g_clear_error (&local_error);
+
+  return 0;
+}

fuzzing/fuzz_filename_to_uri.c

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2025 GNOME Foundation, Inc.
+ *
+ * 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)
+{
+  unsigned char *nul_terminated_data = NULL;
+  char *uri = NULL;
+  GError *local_error = NULL;
+
+  fuzz_set_logging_func ();
+
+  /* ignore @size (g_filename_to_uri() doesn’t support it); ensure @data is nul-terminated */
+  nul_terminated_data = (unsigned char *) g_strndup ((const char *) data, size);
+  uri = g_filename_to_uri ((const char *) nul_terminated_data, NULL, &local_error);
+  g_free (nul_terminated_data);
+
+  g_free (uri);
+  g_clear_error (&local_error);
+
+  return 0;
+}

fuzzing/meson.build

@@ -25,6 +25,8 @@ fuzz_targets = [
   'fuzz_date_parse',
   'fuzz_date_time_new_from_iso8601',
   'fuzz_dbus_message',
+  'fuzz_filename_from_uri',
+  'fuzz_filename_to_uri',
   'fuzz_get_locale_variants',
   'fuzz_inet_address_mask_new_from_string',
   'fuzz_inet_address_new_from_string',