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[PATCH 4.9 22/31] vhost: synchronize IOTLB message with dev cleanup




4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasowang@xxxxxxxxxx>

[ Upstream commit 1b15ad683ab42a203f98b67045b40720e99d0e9a ]

DaeRyong Jeong reports a race between vhost_dev_cleanup() and
vhost_process_iotlb_msg():

Thread interleaving:
CPU0 (vhost_process_iotlb_msg)			CPU1 (vhost_dev_cleanup)
(In the case of both VHOST_IOTLB_UPDATE and
VHOST_IOTLB_INVALIDATE)

=====						=====
						vhost_umem_clean(dev->iotlb);
if (!dev->iotlb) {
	        ret = -EFAULT;
		        break;
}
						dev->iotlb = NULL;

The reason is we don't synchronize between them, fixing by protecting
vhost_process_iotlb_msg() with dev mutex.

Reported-by: DaeRyong Jeong <threeearcat@xxxxxxxxx>
Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/vhost/vhost.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -938,6 +938,7 @@ int vhost_process_iotlb_msg(struct vhost
 {
 	int ret = 0;
 
+	mutex_lock(&dev->mutex);
 	vhost_dev_lock_vqs(dev);
 	switch (msg->type) {
 	case VHOST_IOTLB_UPDATE:
@@ -967,6 +968,8 @@ int vhost_process_iotlb_msg(struct vhost
 	}
 
 	vhost_dev_unlock_vqs(dev);
+	mutex_unlock(&dev->mutex);
+
 	return ret;
 }
 ssize_t vhost_chr_write_iter(struct vhost_dev *dev,