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Subject[PATCH v3 3/3] vsock/virtio: fix flush of works during the .remove()
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This patch moves the flush of works after vdev->config->del_vqs(vdev),
because we need to be sure that no workers run before to free the
'vsock' object.

Since we stopped the workers using the [tx|rx|event]_run flags,
we are sure no one is accessing the device while we are calling
vdev->config->reset(vdev), so we can safely move the workers' flush.

Before the vdev->config->del_vqs(vdev), workers can be scheduled
by VQ callbacks, so we must flush them after del_vqs(), to avoid
use-after-free of 'vsock' object.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
net/vmw_vsock/virtio_transport.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 4dbdce7746bd..0815d1357861 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -681,12 +681,6 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
rcu_assign_pointer(the_virtio_vsock, NULL);
synchronize_rcu();

- flush_work(&vsock->loopback_work);
- flush_work(&vsock->rx_work);
- flush_work(&vsock->tx_work);
- flush_work(&vsock->event_work);
- flush_work(&vsock->send_pkt_work);
-
/* Reset all connected sockets when the device disappear */
vsock_for_each_connected_socket(virtio_vsock_reset_sock);

@@ -741,6 +735,15 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
/* Delete virtqueues and flush outstanding callbacks if any */
vdev->config->del_vqs(vdev);

+ /* Other works can be queued before 'config->del_vqs()', so we flush
+ * all works before to free the vsock object to avoid use after free.
+ */
+ flush_work(&vsock->loopback_work);
+ flush_work(&vsock->rx_work);
+ flush_work(&vsock->tx_work);
+ flush_work(&vsock->event_work);
+ flush_work(&vsock->send_pkt_work);
+
mutex_unlock(&the_virtio_vsock_mutex);

kfree(vsock);
--
2.20.1
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