From:   Wei Wang <wei.w.wang@intel.com>
To:     mst@redhat.com, stefanha@redhat.com, sgarzare@redhat.com,
        davem@davemloft.net, asias@redhat.com,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org
Cc:     Wei Wang <wei.w.wang@intel.com>
Subject: [PATCH] virtio/vsock: fix the transport to work with VMADDR_CID_ANY
Date:   Thu, 25 Nov 2021 02:15:54 -0500
Message-Id: <20211125071554.16969-1-wei.w.wang@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The VMADDR_CID_ANY flag used by a socket means that the socket isn't bound
to any specific CID. For example, a host vsock server may want to be bound
with VMADDR_CID_ANY, so that a guest vsock client can connect to the host
server with CID=VMADDR_CID_HOST (i.e. 2), and meanwhile, a host vsock
client can connect to the same local server with CID=VMADDR_CID_LOCAL
(i.e. 1).

The current implementation sets the destination socket's svm_cid to a
fixed CID value after the first client's connection, which isn't an
expected operation. For example, if the guest client first connects to the
host server, the server's svm_cid gets set to VMADDR_CID_HOST, then other
host clients won't be able to connect to the server anymore.

Reproduce steps:
1. Run the host server:
   socat VSOCK-LISTEN:1234,fork -
2. Run a guest client to connect to the host server:
   socat - VSOCK-CONNECT:2:1234
3. Run a host client to connect to the host server:
   socat - VSOCK-CONNECT:1:1234

Without this patch, step 3. above fails to connect, and socat complains
"socat[1720] E connect(5, AF=40 cid:1 port:1234, 16): Connection
reset by peer".
With this patch, the above works well.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
---
 net/vmw_vsock/virtio_transport_common.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 59ee1be5a6dd..5c60fae10569 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1298,9 +1298,6 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
 
 	space_available = virtio_transport_space_update(sk, pkt);
 
-	/* Update CID in case it has changed after a transport reset event */
-	vsk->local_addr.svm_cid = dst.svm_cid;
-
 	if (space_available)
 		sk->sk_write_space(sk);
 
-- 
2.25.1