test: add a simple fuzzer for manager serialization

src/core/fuzz-manager-serialize.c

@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <stdio.h>
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "fuzz.h"
+#include "manager-serialize.h"
+#include "manager.h"
+#include "service.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        _cleanup_(manager_freep) Manager *m = NULL;
+        _cleanup_fclose_ FILE *f = NULL, *null = NULL;
+        _cleanup_fdset_free_ FDSet *fdset = NULL;
+
+        /* We don't want to fill the logs with messages about parse errors.
+         * Disable most logging if not running standalone. */
+        if (!getenv("SYSTEMD_LOG_LEVEL")) {
+                log_set_max_level(LOG_CRIT);
+                log_set_target(LOG_TARGET_NULL);
+        }
+
+        assert_se(manager_new(RUNTIME_SCOPE_SYSTEM, MANAGER_TEST_RUN_BASIC, &m) >= 0);
+        /* Set log overrides as well to make it harder for a serialization file
+         * to switch log levels/targets during fuzzing */
+        manager_override_log_level(m, log_get_max_level());
+        manager_override_log_target(m, log_get_target());
+        assert_se(null = fopen("/dev/null", "we"));
+        assert_se(fdset = fdset_new());
+        assert_se(f = data_to_file(data, size));
+
+        (void) manager_deserialize(m, f, fdset);
+        (void) manager_serialize(m, null, fdset, true);
+        (void) manager_serialize(m, null, fdset, false);
+
+        return 0;
+}

src/core/meson.build

@@ -192,4 +192,11 @@ fuzzers += [
                 ],
                 'dependencies' : libmount,
         },
+        {
+                'sources' : files('fuzz-manager-serialize.c'),
+                'link_with' : [
+                        libcore,
+                        libshared
+                ],
+        },
 ]