Add overflow checking to array (#111)

src/array.c

@@ -30,8 +30,7 @@ static const size_t data_size_offset = sizeof(size_t);
 static const size_t data_ptr_offset = 2 * sizeof(size_t);
 
 /**
- * Initializes an array. If the multiplication of the element count and the
- * data size overflows, it is undefined behavior.
+ * Initializes an array.
  *
  * @param element_count the number of elements in the array; must not be
  *                      negative
@@ -47,6 +46,12 @@ array array_init(const size_t element_count, const size_t data_size)
     if (data_size == 0) {
         return NULL;
     }
+    if (element_count * data_size / data_size != element_count) {
+        return NULL;
+    }
+    if (data_ptr_offset + element_count * data_size < data_ptr_offset) {
+        return NULL;
+    }
     init = malloc(data_ptr_offset + element_count * data_size);
     if (!init) {
         return NULL;

tst/test_array.c

@@ -5,6 +5,10 @@
 static void test_invalid_init(void)
 {
     assert(!array_init(1, 0));
+    /* These tests rely on this. */
+    assert(sizeof(size_t) == sizeof(unsigned long));
+    assert(!array_init(ULONG_MAX, ULONG_MAX));
+    assert(!array_init(1, ULONG_MAX));
 }
 
 static void test_empty_array(void)