Subject: Re: [PATCH 1/2] vsock: each transport cycles only on its own sockets

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 10 Mar 2022 08:01:53 -0500

On Thu, Mar 10, 2022 at 09:54:24PM +0900, Jiyong Park wrote:
> When iterating over sockets using vsock_for_each_connected_socket, make
> sure that a transport filters out sockets that don't belong to the
> transport.
> 
> There actually was an issue caused by this; in a nested VM
> configuration, destroying the nested VM (which often involves the
> closing of /dev/vhost-vsock if there was h2g connections to the nested
> VM) kills not only the h2g connections, but also all existing g2h
> connections to the (outmost) host which are totally unrelated.
> 
> Tested: Executed the following steps on Cuttlefish (Android running on a
> VM) [1]: (1) Enter into an `adb shell` session - to have a g2h
> connection inside the VM, (2) open and then close /dev/vhost-vsock by
> `exec 3< /dev/vhost-vsock && exec 3<&-`, (3) observe that the adb
> session is not reset.
> 
> [1] https://android.googlesource.com/device/google/cuttlefish/
> 
> Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
> Signed-off-by: Jiyong Park <[email-masked]>
> ---
>  drivers/vhost/vsock.c            | 4 ++++
>  net/vmw_vsock/virtio_transport.c | 7 +++++++
>  net/vmw_vsock/vmci_transport.c   | 5 +++++
>  3 files changed, 16 insertions(+)
> 
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 37f0b4274113..853ddac00d5b 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -722,6 +722,10 @@ static void vhost_vsock_reset_orphans(struct sock *sk)
>  	 * executing.
>  	 */
>  
> +	/* Only handle our own sockets */
> +	if (vsk->transport != &vhost_transport.transport)
> +		return;
> +
>  	/* If the peer is still valid, no need to reset connection */
>  	if (vhost_vsock_get(vsk->remote_addr.svm_cid))
>  		return;

We know this is incomplete though. So I think it's the wrong thing to do
when you backport, too. If all you worry about is breaking a binary
module interface, how about simply exporting a new function when you
backport. Thus you will have downstream both:

void vsock_for_each_connected_socket(void (*fn)(struct sock *sk));

void vsock_for_each_connected_socket_new(struct vsock_transport *transport,
                                    void (*fn)(struct sock *sk));

and then upstream we can squash these two patches.

Hmm?

> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index fb3302fff627..61b24eb31d4b 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -24,6 +24,7 @@
>  static struct workqueue_struct *virtio_vsock_workqueue;
>  static struct virtio_vsock __rcu *the_virtio_vsock;
>  static DEFINE_MUTEX(the_virtio_vsock_mutex); /* protects the_virtio_vsock */
> +static struct virtio_transport virtio_transport; /* forward declaration */
>  
>  struct virtio_vsock {
>  	struct virtio_device *vdev;
> @@ -357,11 +358,17 @@ static void virtio_vsock_event_fill(struct virtio_vsock *vsock)
>  
>  static void virtio_vsock_reset_sock(struct sock *sk)
>  {
> +	struct vsock_sock *vsk = vsock_sk(sk);
> +
>  	/* vmci_transport.c doesn't take sk_lock here either.  At least we're
>  	 * under vsock_table_lock so the sock cannot disappear while we're
>  	 * executing.
>  	 */
>  
> +	/* Only handle our own sockets */
> +	if (vsk->transport != &virtio_transport.transport)
> +		return;
> +
>  	sk->sk_state = TCP_CLOSE;
>  	sk->sk_err = ECONNRESET;
>  	sk_error_report(sk);
> diff --git a/net/vmw_vsock/vmci_transport.c b/net/vmw_vsock/vmci_transport.c
> index 7aef34e32bdf..cd2f01513fae 100644
> --- a/net/vmw_vsock/vmci_transport.c
> +++ b/net/vmw_vsock/vmci_transport.c
> @@ -803,6 +803,11 @@ static void vmci_transport_handle_detach(struct sock *sk)
>  	struct vsock_sock *vsk;
>  
>  	vsk = vsock_sk(sk);
> +
> +	/* Only handle our own sockets */
> +	if (vsk->transport != &vmci_transport)
> +		return;
> +
>  	if (!vmci_handle_is_invalid(vmci_trans(vsk)->qp_handle)) {
>  		sock_set_flag(sk, SOCK_DONE);
>  
> -- 
> 2.35.1.723.g4982287a31-goog