[PATCH 4/4] vhost: scsi: add weight support

[Tyler Hicks]

From: Jason Wang <jasowang at redhat.com>

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

CVE-2019-3900

(cherry picked from commit c1ea02f15ab5efb3e93fc3144d895410bf79fcf2)
Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 drivers/vhost/scsi.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 2f6154469f32..8bbe575ea568 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -923,7 +923,7 @@ 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);
@@ -943,7 +943,7 @@ 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;
@@ -1123,7 +1123,7 @@ 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);
 }
@@ -1182,7 +1182,7 @@ 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);
 	/*
@@ -1196,7 +1196,7 @@ 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;
@@ -1275,7 +1275,7 @@ 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);
 }
-- 
2.7.4