int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
{
    char backing_filename[PATH_MAX];
    int back_flags, ret;
    BlockDriver *back_drv = NULL;
    Error *local_err = NULL;

    if (bs->backing_hd != NULL) {
        QDECREF(options);
        return 0;
    }

    /* NULL means an empty set of options */
    if (options == NULL) {
        options = qdict_new();
    }

    bs->open_flags &= ~BDRV_O_NO_BACKING;
    if (qdict_haskey(options, "file.filename")) {
        backing_filename[0] = '\0';
    } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
        QDECREF(options);
        return 0;
    } else {
        bdrv_get_full_backing_filename(bs, backing_filename,
                                       sizeof(backing_filename));
    }

    if (bs->backing_format[0] != '\0') {
        back_drv = bdrv_find_format(bs->backing_format);
    }

    /* backing files always opened read-only */
    back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT |
                                    BDRV_O_COPY_ON_READ);

    assert(bs->backing_hd == NULL);
    ret = bdrv_open(&bs->backing_hd,
                    *backing_filename ? backing_filename : NULL, NULL, options,
                    back_flags, back_drv, &local_err);
    if (ret < 0) {
        bs->backing_hd = NULL;
        bs->open_flags |= BDRV_O_NO_BACKING;
        error_setg(errp, "Could not open backing file: %s",
                   error_get_pretty(local_err));
        error_free(local_err);
        return ret;
    }

    if (bs->backing_hd->file) {
        pstrcpy(bs->backing_file, sizeof(bs->backing_file),
                bs->backing_hd->file->filename);
    }

    /* Recalculate the BlockLimits with the backing file */
    bdrv_refresh_limits(bs);

    return 0;
}

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.