[PATCH 8/9] vhost-scsi: protect vq->log_used with vq->mutex

[Dongli Zhang]

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 <dongli.zhang@xxxxxxxxxx>
---
 drivers/vhost/scsi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 40268b88f470..3b87d698adaf 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -645,7 +645,9 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
 		if (likely(ret == sizeof(v_rsp))) {
 			signal = true;
 
+			mutex_lock(&cmd->tvc_vq->mutex);
 			vhost_add_used(cmd->tvc_vq, cmd->tvc_vq_desc, 0);
+			mutex_unlock(&cmd->tvc_vq->mutex);
 		} else
 			pr_err("Faulted on virtio_scsi_cmd_resp\n");
 
@@ -1371,8 +1373,10 @@ 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);
 
 	if (unlikely(tmf->tmf_log_num)) {
 		mutex_lock(&tmf->svq->vq.mutex);
-- 
2.39.3