vhost/scsi: Use copy_to_iter() to send control queue response

Uses copy_to_iter() instead of __copy_to_user() in order to ensure we
support arbitrary layouts and an input buffer split across iov entries.

Fixes: 0d02dbd68c47b ("vhost/scsi: Respond to control queue operations")
Signed-off-by: Bijan Mottahedeh <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>

drivers/vhost/scsi.c

···
 			   struct vhost_virtqueue *vq,
 			   struct vhost_scsi_ctx *vc)
 {
-	struct virtio_scsi_ctrl_tmf_resp __user *resp;
 	struct virtio_scsi_ctrl_tmf_resp rsp;
+	struct iov_iter iov_iter;
 	int ret;
 
 	pr_debug("%s\n", __func__);
 	memset(&rsp, 0, sizeof(rsp));
 	rsp.response = VIRTIO_SCSI_S_FUNCTION_REJECTED;
-	resp = vq->iov[vc->out].iov_base;
-	ret = __copy_to_user(resp, &rsp, sizeof(rsp));
-	if (!ret)
+
+	iov_iter_init(&iov_iter, READ, &vq->iov[vc->out], vc->in, sizeof(rsp));
+
+	ret = copy_to_iter(&rsp, sizeof(rsp), &iov_iter);
+	if (likely(ret == sizeof(rsp)))
 		vhost_add_used_and_signal(&vs->dev, vq, vc->head, 0);
 	else
 		pr_err("Faulted on virtio_scsi_ctrl_tmf_resp\n");
···
 			struct vhost_virtqueue *vq,
 			struct vhost_scsi_ctx *vc)
 {
-	struct virtio_scsi_ctrl_an_resp __user *resp;
 	struct virtio_scsi_ctrl_an_resp rsp;
+	struct iov_iter iov_iter;
 	int ret;
 
 	pr_debug("%s\n", __func__);
 	memset(&rsp, 0, sizeof(rsp));	/* event_actual = 0 */
 	rsp.response = VIRTIO_SCSI_S_OK;
-	resp = vq->iov[vc->out].iov_base;
-	ret = __copy_to_user(resp, &rsp, sizeof(rsp));
-	if (!ret)
+
+	iov_iter_init(&iov_iter, READ, &vq->iov[vc->out], vc->in, sizeof(rsp));
+
+	ret = copy_to_iter(&rsp, sizeof(rsp), &iov_iter);
+	if (likely(ret == sizeof(rsp)))
 		vhost_add_used_and_signal(&vs->dev, vq, vc->head, 0);
 	else
 		pr_err("Faulted on virtio_scsi_ctrl_an_resp\n");