On Thu, Jan 28, 2021 at 03:41:25PM +0100, Stefano Garzarella wrote:

+static void vdpasim_blk_work(struct work_struct *work)
+{
+	struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
+	u8 status = VIRTIO_BLK_S_OK;
+	int i;
+
+	spin_lock(&vdpasim->lock);
+
+	if (!(vdpasim->status & VIRTIO_CONFIG_S_DRIVER_OK))
+		goto out;
+
+	for (i = 0; i < VDPASIM_BLK_VQ_NUM; i++) {
+		struct vdpasim_virtqueue *vq = &vdpasim->vqs[i];
+
+		if (!vq->ready)
+			continue;
+
+		while (vringh_getdesc_iotlb(&vq->vring, &vq->out_iov,
+					    &vq->in_iov, &vq->head,
+					    GFP_ATOMIC) > 0) {
+			int write;
+
+			vq->in_iov.i = vq->in_iov.used - 1;
+			write = vringh_iov_push_iotlb(&vq->vring, &vq->in_iov,
+						      &status, 1);
+			if (write <= 0)
+				break;

This code looks fragile:

1. Relying on unsigned underflow and the while loop in
   vringh_iov_push_iotlb() to handle the case where in_iov.used == 0 is
   risky and could break.

2. Does this assume that the last in_iov element has size 1? For
   example, the guest driver may send a single "in" iovec with size 513
   when reading 512 bytes (with an extra byte for the request status).

Please validate inputs fully, even in test/development code, because
it's likely to be copied by others when writing production code (or
deployed in production by unsuspecting users) :).