From: Sebastien Boeuf sebastien.boeuf@intel.com
[ Upstream commit df12eb6d6cd920ab2f0e0a43cd6e1c23a05cea91 ]
Whenever the vsock backend on the host sends a packet through the RX queue, it expects an answer on the TX queue. Unfortunately, there is one case where the host side will hang waiting for the answer and might effectively never recover if no timeout mechanism was implemented.
This issue happens when the guest side starts binding to the socket, which insert a new bound socket into the list of already bound sockets. At this time, we expect the guest to also start listening, which will trigger the sk_state to move from TCP_CLOSE to TCP_LISTEN. The problem occurs if the host side queued a RX packet and triggered an interrupt right between the end of the binding process and the beginning of the listening process. In this specific case, the function processing the packet virtio_transport_recv_pkt() will find a bound socket, which means it will hit the switch statement checking for the sk_state, but the state won't be changed into TCP_LISTEN yet, which leads the code to pick the default statement. This default statement will only free the buffer, while it should also respond to the host side, by sending a packet on its TX queue.
In order to simply fix this unfortunate chain of events, it is important that in case the default statement is entered, and because at this stage we know the host side is waiting for an answer, we must send back a packet containing the operation VIRTIO_VSOCK_OP_RST.
One could say that a proper timeout mechanism on the host side will be enough to avoid the backend to hang. But the point of this patch is to ensure the normal use case will be provided with proper responsiveness when it comes to establishing the connection.
Signed-off-by: Sebastien Boeuf sebastien.boeuf@intel.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/vmw_vsock/virtio_transport_common.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c index fae2bded5d51..5f8a72d34d31 100644 --- a/net/vmw_vsock/virtio_transport_common.c +++ b/net/vmw_vsock/virtio_transport_common.c @@ -1060,6 +1060,7 @@ void virtio_transport_recv_pkt(struct virtio_transport *t, virtio_transport_free_pkt(pkt); break; default: + (void)virtio_transport_reset_no_sock(t, pkt); virtio_transport_free_pkt(pkt); break; }