static void scsi_read_data(SCSIRequest *req)
{
    SCSIDiskReq *r = DO_UPCAST(SCSIDiskReq, req, req);
    SCSIDiskState *s = DO_UPCAST(SCSIDiskState, qdev, r->req.dev);
    uint32_t n;

    if (r->sector_count == (uint32_t)-1) {
        DPRINTF("Read buf_len=%zd\n", r->iov.iov_len);
        r->sector_count = 0;
        scsi_req_data(&r->req, r->iov.iov_len);
        return;
    }
    DPRINTF("Read sector_count=%d\n", r->sector_count);
    if (r->sector_count == 0) {
        /* This also clears the sense buffer for REQUEST SENSE.  */
        scsi_req_complete(&r->req, GOOD);
        return;
    }

    /* No data transfer may already be in progress */
    assert(r->req.aiocb == NULL);

    if (r->req.cmd.mode == SCSI_XFER_TO_DEV) {
        DPRINTF("Data transfer direction invalid\n");
        scsi_read_complete(r, -EINVAL);
        return;
    }

    if (s->tray_open) {
        scsi_read_complete(r, -ENOMEDIUM);
    }
    n = scsi_init_iovec(r);
    bdrv_acct_start(s->bs, &r->acct, n * BDRV_SECTOR_SIZE, BDRV_ACCT_READ);
    r->req.aiocb = bdrv_aio_readv(s->bs, r->sector, &r->qiov, n,
                              scsi_read_complete, r);
    if (r->req.aiocb == NULL) {
        scsi_read_complete(r, -EIO);
    }
}
The software performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.