Add a test to prove that hardened_malloc handles too-large-to-be-true allocations

This pattern, used by https://github.com/kaist-hacking/HardsHeap,
uncovered bugs in other memory allocators.

test/simple-memory-corruption/Makefile

@@ -45,7 +45,8 @@ EXECUTABLES := \
     malloc_object_size \
     malloc_object_size_offset \
     invalid_malloc_object_size_small \
-    invalid_malloc_object_size_small_quarantine
+    invalid_malloc_object_size_small_quarantine \
+    impossibly_large_malloc
 
 all: $(EXECUTABLES)
 

test/simple-memory-corruption/impossibly_large_malloc.c

@@ -0,0 +1,9 @@
+#include <malloc.h>
+#include <stddef.h>
+
+#include "../test_util.h"
+
+OPTNONE int main(void) {
+    char *p = malloc(-8);
+    return !(p == NULL);
+}

test/simple-memory-corruption/test_smc.py

@@ -206,6 +206,12 @@ class TestSimpleMemoryCorruption(unittest.TestCase):
         self.assertEqual(stderr.decode(
             "utf-8"), "fatal allocator error: invalid malloc_object_size (quarantine)\n")
 
+    def test_impossibly_large_malloc(self):
+        _stdout, stderr, returncode = self.run_test(
+            "impossibly_large_malloc")
+        self.assertEqual(returncode, 0)
+
+
 
 if __name__ == '__main__':
     unittest.main()