int qcow2_update_cluster_refcount(BlockDriverState *bs,
                                  int64_t cluster_index,
                                  int addend,
                                  enum qcow2_discard_type type)
{
    BDRVQcowState *s = bs->opaque;
    int ret;

    ret = update_refcount(bs, cluster_index << s->cluster_bits, 1, addend,
                          type);
    if (ret < 0) {
        return ret;
    }

    return get_refcount(bs, cluster_index);
}

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.