 static int get_refcount(BlockDriverState *bs, int64_t cluster_index)
 {
     BDRVQcowState *s = bs->opaque;
    int refcount_table_index, block_index;
     int64_t refcount_block_offset;
     int ret;
     uint16_t *refcount_block;
    uint16_t refcount;

    refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
    if (refcount_table_index >= s->refcount_table_size)
        return 0;
    refcount_block_offset =
        s->refcount_table[refcount_table_index] & REFT_OFFSET_MASK;
    if (!refcount_block_offset)
        return 0;

    ret = qcow2_cache_get(bs, s->refcount_block_cache, refcount_block_offset,
        (void**) &refcount_block);
    if (ret < 0) {
        return ret;
    }

    block_index = cluster_index &
        ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
    refcount = be16_to_cpu(refcount_block[block_index]);

    ret = qcow2_cache_put(bs, s->refcount_block_cache,
        (void**) &refcount_block);
    if (ret < 0) {
        return ret;
    }

    return refcount;
}

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.