static int count_cow_clusters(BDRVQcowState *s, int nb_clusters,
    uint64_t *l2_table, int l2_index)
{
    int i;

    for (i = 0; i < nb_clusters; i++) {
        uint64_t l2_entry = be64_to_cpu(l2_table[l2_index + i]);
        int cluster_type = qcow2_get_cluster_type(l2_entry);

        switch(cluster_type) {
        case QCOW2_CLUSTER_NORMAL:
            if (l2_entry & QCOW_OFLAG_COPIED) {
                goto out;
            }
            break;
        case QCOW2_CLUSTER_UNALLOCATED:
        case QCOW2_CLUSTER_COMPRESSED:
        case QCOW2_CLUSTER_ZERO:
            break;
        default:
            abort();
        }
    }

out:
    assert(i <= nb_clusters);
    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.