static int coroutine_fn copy_sectors(BlockDriverState *bs,
                                     uint64_t start_sect,
                                     uint64_t cluster_offset,
                                     int n_start, int n_end)
{
    BDRVQcowState *s = bs->opaque;
    QEMUIOVector qiov;
    struct iovec iov;
    int n, ret;

    /*
     * If this is the last cluster and it is only partially used, we must only
     * copy until the end of the image, or bdrv_check_request will fail for the
     * bdrv_read/write calls below.
     */
    if (start_sect + n_end > bs->total_sectors) {
        n_end = bs->total_sectors - start_sect;
    }

    n = n_end - n_start;
    if (n <= 0) {
        return 0;
    }

    iov.iov_len = n * BDRV_SECTOR_SIZE;
    iov.iov_base = qemu_blockalign(bs, iov.iov_len);

    qemu_iovec_init_external(&qiov, &iov, 1);

    BLKDBG_EVENT(bs->file, BLKDBG_COW_READ);

    if (!bs->drv) {
        return -ENOMEDIUM;
    }

    /* Call .bdrv_co_readv() directly instead of using the public block-layer
     * interface.  This avoids double I/O throttling and request tracking,
     * which can lead to deadlock when block layer copy-on-read is enabled.
     */
    ret = bs->drv->bdrv_co_readv(bs, start_sect + n_start, n, &qiov);
    if (ret < 0) {
        goto out;
    }

    if (s->crypt_method) {
        qcow2_encrypt_sectors(s, start_sect + n_start,
                        iov.iov_base, iov.iov_base, n, 1,
                        &s->aes_encrypt_key);
    }

    ret = qcow2_pre_write_overlap_check(bs, 0,
            cluster_offset + n_start * BDRV_SECTOR_SIZE, n * BDRV_SECTOR_SIZE);
    if (ret < 0) {
        goto out;
    }

    BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);
    ret = bdrv_co_writev(bs->file, (cluster_offset >> 9) + n_start, n, &qiov);
    if (ret < 0) {
        goto out;
    }

    ret = 0;
out:
    qemu_vfree(iov.iov_base);
    return ret;
}

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.