Backtrace list must be an array of strings; fix #3408

src/error.c

@@ -208,6 +208,19 @@ exc_set_backtrace(mrb_state *mrb, mrb_value exc)
   mrb_value backtrace;
 
   mrb_get_args(mrb, "o", &backtrace);
+  if (!mrb_array_p(backtrace)) {
+  type_err:
+    mrb_raise(mrb, E_TYPE_ERROR, "backtrace must be Array of String");
+  }
+  else {
+    const mrb_value *p = RARRAY_PTR(backtrace);
+    const mrb_value *pend = p + RARRAY_LEN(backtrace);
+
+    while (p < pend) {
+      if (!mrb_string_p(*p)) goto type_err;
+      p++;
+    }
+  }
   mrb_iv_set(mrb, exc, mrb_intern_lit(mrb, "backtrace"), backtrace);
 
   return backtrace;