vhost: scsi: add weight support

This patch will check the weight and exit the loop if we exceeds the
weight. This is useful for preventing scsi kthread from hogging cpu
which is guest triggerable.

This addresses CVE-2019-3900.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Fixes: 057cbf49a1f0 ("tcm_vhost: Initial merge for vhost level target fabric driver")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 27c9dac9f518c60153561974ca8b180394f413a6..a9caf1bc3c3ef29542530f379d8cc13bd273f30f 100644 (file)
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -918,7 +918,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
        struct iov_iter in_iter, prot_iter, data_iter;
        u64 tag;
        u32 exp_data_len, data_direction;
-       int ret, prot_bytes;
+       int ret, prot_bytes, c = 0;
        u16 lun;
        u8 task_attr;
        bool t10_pi = vhost_has_feature(vq, VIRTIO_SCSI_F_T10_PI);
@@ -938,7 +938,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 
        vhost_disable_notify(&vs->dev, vq);
 
-       for (;;) {
+       do {
                ret = vhost_scsi_get_desc(vs, vq, &vc);
                if (ret)
                        goto err;
@@ -1118,7 +1118,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
                        break;
                else if (ret == -EIO)
                        vhost_scsi_send_bad_target(vs, vq, vc.head, vc.out);
-       }
+       } while (likely(!vhost_exceeds_weight(vq, ++c, 0)));
 out:
        mutex_unlock(&vq->mutex);
 }
@@ -1177,7 +1177,7 @@ vhost_scsi_ctl_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
        } v_req;
        struct vhost_scsi_ctx vc;
        size_t typ_size;
-       int ret;
+       int ret, c = 0;
 
        mutex_lock(&vq->mutex);
        /*
@@ -1191,7 +1191,7 @@ vhost_scsi_ctl_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 
        vhost_disable_notify(&vs->dev, vq);
 
-       for (;;) {
+       do {
                ret = vhost_scsi_get_desc(vs, vq, &vc);
                if (ret)
                        goto err;
@@ -1270,7 +1270,7 @@ vhost_scsi_ctl_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
                        break;
                else if (ret == -EIO)
                        vhost_scsi_send_bad_target(vs, vq, vc.head, vc.out);
-       }
+       } while (likely(!vhost_exceeds_weight(vq, ++c, 0)));
 out:
        mutex_unlock(&vq->mutex);
 }