Fix integer overflow in allocation size calculation

Passing a large integer value as the first argument to `Array#ary_combination_init` could cause an incorrect memory allocation due to integer overflow.
This would result in an invalid write during the subsequent zero-fill of the memory.

To resolve the issue, it has been replaced with `mrb_calloc()`.
However, since the current `mrb_calloc()` returns `NULL` due to overflow, it has been modified to raise an exception as a clear error.

mrbgems/mruby-array-ext/src/array.c

@@ -1315,6 +1315,11 @@ ary_combination_init(mrb_state *mrb, mrb_value self)
   mrb_bool permutation;
 
   mrb_get_args(mrb, "ib", &n, &permutation);
+#if MRB_INT_MAX > SIZE_MAX
+  if (n > SIZE_MAX) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "number too large");
+  }
+#endif
 
   struct mrb_combination_state *state = (struct mrb_combination_state*)mrb_malloc(mrb, sizeof(*state));
   state->n = n;
@@ -1323,10 +1328,7 @@ ary_combination_init(mrb_state *mrb, mrb_value self)
   state->finished = (n <= 0 && n != 0);
 
   if (n > 0) {
-    state->indices = (mrb_int*)mrb_malloc(mrb, sizeof(mrb_int) * n);
-    for (mrb_int i = 0; i < n; i++) {
-      state->indices[i] = 0;
-    }
+    state->indices = (mrb_int*)mrb_calloc(mrb, n, sizeof(mrb_int));
   }
   else {
     state->indices = NULL;

src/gc.c

@@ -243,15 +243,17 @@ mrb_calloc(mrb_state *mrb, size_t nelem, size_t len)
 {
   void *p;
 
-  if (nelem > 0 && len > 0 &&
-      nelem <= SIZE_MAX / len) {
+  if (nelem == 0 || len == 0) {
+    p = NULL;
+  }
+  else if (nelem <= SIZE_MAX / len) {
     size_t size = nelem * len;
     p = mrb_malloc(mrb, size);
 
     memset(p, 0, size);
   }
   else {
-    p = NULL;
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "memory allocation overflow");
   }
 
   return p;