netdev - [PATCH net-next v2 15/15] vhost/vsock: refuse CID assigned to the guest->host transport

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Date:   Thu, 14 Nov 2019 10:57:50 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Stephen Hemminger <sthemmin@...rosoft.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jorgen Hansen <jhansen@...are.com>,
        Jason Wang <jasowang@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        Sasha Levin <sashal@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>, linux-hyperv@...r.kernel.org
Subject: [PATCH net-next v2 15/15] vhost/vsock: refuse CID assigned to the guest->host transport

In a nested VM environment, we have to refuse to assign to a nested
guest the same CID assigned to our guest->host transport.
In this way, the user can use the local CID for loopback.

Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
---
 drivers/vhost/vsock.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index fdda9ec625ad..dde392b91bb3 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -718,6 +718,12 @@ static int vhost_vsock_set_cid(struct vhost_vsock *vsock, u64 guest_cid)
 	if (guest_cid > U32_MAX)
 		return -EINVAL;
 
+	/* Refuse if CID is assigned to the guest->host transport (i.e. nested
+	 * VM), to make the loopback work.
+	 */
+	if (vsock_find_cid(guest_cid))
+		return -EADDRINUSE;
+
 	/* Refuse if CID is already in use */
 	mutex_lock(&vhost_vsock_mutex);
 	other = vhost_vsock_get(guest_cid);
-- 
2.21.0