static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
    int64_t offset, int64_t length, int addend, enum qcow2_discard_type type)
{
    BDRVQcowState *s = bs->opaque;
    int64_t start, last, cluster_offset;
    uint16_t *refcount_block = NULL;
    int64_t old_table_index = -1;
    int ret;

#ifdef DEBUG_ALLOC2
    fprintf(stderr, "update_refcount: offset=%" PRId64 " size=%" PRId64 " addend=%d\n",
           offset, length, addend);
#endif
    if (length < 0) {
        return -EINVAL;
    } else if (length == 0) {
        return 0;
    }

    if (addend < 0) {
        qcow2_cache_set_dependency(bs, s->refcount_block_cache,
            s->l2_table_cache);
    }

    start = start_of_cluster(s, offset);
    last = start_of_cluster(s, offset + length - 1);
    for(cluster_offset = start; cluster_offset <= last;
        cluster_offset += s->cluster_size)
    {
        int block_index, refcount;
        int64_t cluster_index = cluster_offset >> s->cluster_bits;
        int64_t table_index =
            cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);

        /* Load the refcount block and allocate it if needed */
        if (table_index != old_table_index) {
            if (refcount_block) {
                ret = qcow2_cache_put(bs, s->refcount_block_cache,
                    (void**) &refcount_block);
                if (ret < 0) {
                    goto fail;
                }
            }

            ret = alloc_refcount_block(bs, cluster_index, &refcount_block);
            if (ret < 0) {
                goto fail;
            }
        }
        old_table_index = table_index;

        qcow2_cache_entry_mark_dirty(s->refcount_block_cache, refcount_block);

        /* we can update the count and save it */
        block_index = cluster_index &
            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);

        refcount = be16_to_cpu(refcount_block[block_index]);
        refcount += addend;
        if (refcount < 0 || refcount > 0xffff) {
            ret = -EINVAL;
            goto fail;
        }
        if (refcount == 0 && cluster_index < s->free_cluster_index) {
            s->free_cluster_index = cluster_index;
        }
        refcount_block[block_index] = cpu_to_be16(refcount);

        if (refcount == 0 && s->discard_passthrough[type]) {
            update_refcount_discard(bs, cluster_offset, s->cluster_size);
        }
    }

    ret = 0;
fail:
    if (!s->cache_discards) {
        qcow2_process_discards(bs, ret);
    }

    /* Write last changed block to disk */
    if (refcount_block) {
        int wret;
        wret = qcow2_cache_put(bs, s->refcount_block_cache,
            (void**) &refcount_block);
        if (wret < 0) {
            return ret < 0 ? ret : wret;
        }
    }

    /*
     * Try do undo any updates if an error is returned (This may succeed in
     * some cases like ENOSPC for allocating a new refcount block)
     */
    if (ret < 0) {
        int dummy;
        dummy = update_refcount(bs, offset, cluster_offset - offset, -addend,
                                QCOW2_DISCARD_NEVER);
        (void)dummy;
    }

    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.