Re: [PATCH v2 3/3] vsock/virtio: fix flush of works during the .remove()

[Stefan Hajnoczi]

On Fri, Jun 28, 2019 at 02:36:59PM +0200, Stefano Garzarella wrote:
> 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.

Nevermind, I looked back at Patch 2 and saw the send_pkt and loopback
work functions were also updated.  Thanks!

Stefan


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Re: [PATCH v2 3/3] vsock/virtio: fix flush of works during the .remove()

[Stefan Hajnoczi]

On Fri, Jun 28, 2019 at 02:36:59PM +0200, Stefano Garzarella wrote:
> 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.

What about send_pkt and loopback work?  How were they stopped safely?

For example, if send_pkt work executes then we're in trouble since it
accesses the tx virtqueue which is deleted by ->del_vqs().


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[PATCH v2 3/3] vsock/virtio: fix flush of works during the .remove()

[Stefano Garzarella]

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 
Signed-off-by: Stefano Garzarella 
---
 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 1b44ec6f3f6c..96dafa978268 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -680,12 +680,6 @@ static void virtio_vsock_remove(struct virtio_device *vdev)
rcu_assign_pointer(the_virtio_vsock, NULL);
synchronize_rcu();
 
-   flush_work(>loopback_work);
-   flush_work(>rx_work);
-   flush_work(>tx_work);
-   flush_work(>event_work);
-   flush_work(>send_pkt_work);
-
/* Reset all connected sockets when the device disappear */
vsock_for_each_connected_socket(virtio_vsock_reset_sock);
 
@@ -740,6 +734,15 @@ 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(>loopback_work);
+   flush_work(>rx_work);
+   flush_work(>tx_work);
+   flush_work(>event_work);
+   flush_work(>send_pkt_work);
+
mutex_unlock(_virtio_vsock_mutex);
 
kfree(vsock);
-- 
2.20.1