int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset,
    int nb_clusters)
{
    BDRVQcowState *s = bs->opaque;
    uint64_t cluster_index;
    uint64_t i;
    int refcount, ret;

    assert(nb_clusters >= 0);
    if (nb_clusters == 0) {
        return 0;
    }

    do {
        /* Check how many clusters there are free */
        cluster_index = offset >> s->cluster_bits;
        for(i = 0; i < nb_clusters; i++) {
            refcount = get_refcount(bs, cluster_index++);

            if (refcount < 0) {
                return refcount;
            } else if (refcount != 0) {
                break;
            }
        }

        /* And then allocate them */
        ret = update_refcount(bs, offset, i << s->cluster_bits, 1,
                              QCOW2_DISCARD_NEVER);
    } while (ret == -EAGAIN);

    if (ret < 0) {
        return ret;
    }

    return i;
}

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.