OSS-Fuzz: Add new fuzzer targets unmarshal (#1762)

Signed-off-by: Arthur Chan <arthur.chan@adalogics.com>

Author: arthurscchan

test/fuzzers/fuzz_unmarshal.c

@@ -0,0 +1,25 @@
+#include <stdint.h>
+#include <janet.h>
+
+/* Disable leak sanitizer */
+int __lsan_is_turned_off(void) { return 1; }
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+
+    /* init Janet */
+    janet_init();
+
+    /* fuzz the binary unmarshal (deserialization) path in src/core/marsh.c */
+    JanetTable *reg = janet_env_lookup(janet_core_env(NULL));
+    JanetTryState tstate;
+    if (janet_try(&tstate) == JANET_SIGNAL_OK) {
+        const uint8_t *next = NULL;
+        janet_unmarshal(data, size, 0, reg, &next);
+    }
+    janet_restore(&tstate);
+
+    /* cleanup Janet */
+    janet_deinit();
+
+    return 0;
+}