vhost-scsi: protect vq->log_used with vq->mutex

commit f591cf9fce724e5075cc67488c43c6e39e8cbe27 upstream.

The vhost-scsi completion path may access vq->log_base when vq->log_used is
already set to false.

    vhost-thread                       QEMU-thread

vhost_scsi_complete_cmd_work()
-> vhost_add_used()
   -> vhost_add_used_n()
      if (unlikely(vq->log_used))
                                      QEMU disables vq->log_used
                                      via VHOST_SET_VRING_ADDR.
                                      mutex_lock(&vq->mutex);
                                      vq->log_used = false now!
                                      mutex_unlock(&vq->mutex);

				      QEMU gfree(vq->log_base)
        log_used()
        -> log_write(vq->log_base)

Assuming the VMM is QEMU. The vq->log_base is from QEMU userpace and can be
reclaimed via gfree(). As a result, this causes invalid memory writes to
QEMU userspace.

The control queue path has the same issue.

Signed-off-by: Dongli Zhang <[email protected]>
Acked-by: Jason Wang <[email protected]>
Reviewed-by: Mike Christie <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
[ resoloved conflicts in drivers/vhost/scsi.c
  bacause vhost_scsi_complete_cmd_work() has been refactored. ]
Signed-off-by: Xinyu Zheng <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Dongli Zhang

drivers/vhost/scsi.c

@@ -568,8 +568,10 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
 		ret = copy_to_iter(&v_rsp, sizeof(v_rsp), &iov_iter);
 		if (likely(ret == sizeof(v_rsp))) {
 			struct vhost_scsi_virtqueue *q;
-			vhost_add_used(cmd->tvc_vq, cmd->tvc_vq_desc, 0);
 			q = container_of(cmd->tvc_vq, struct vhost_scsi_virtqueue, vq);
+			mutex_lock(&q->vq.mutex);
+			vhost_add_used(cmd->tvc_vq, cmd->tvc_vq_desc, 0);
+			mutex_unlock(&q->vq.mutex);
 			vq = q - vs->vqs;
 			__set_bit(vq, vs->compl_bitmap);
 		} else
@@ -1173,8 +1175,11 @@ static void vhost_scsi_tmf_resp_work(struct vhost_work *work)
 	else
 		resp_code = VIRTIO_SCSI_S_FUNCTION_REJECTED;
 
+	mutex_lock(&tmf->svq->vq.mutex);
 	vhost_scsi_send_tmf_resp(tmf->vhost, &tmf->svq->vq, tmf->in_iovs,
 				 tmf->vq_desc, &tmf->resp_iov, resp_code);
+	mutex_unlock(&tmf->svq->vq.mutex);
+
 	vhost_scsi_release_tmf_res(tmf);
 }