[PATCH RFC 5/8] vhost/vsock: negotiate datagram support with guests

[Sergio Lopez <slp@redhat.com>]

Expose VIRTIO_VSOCK_F_DGRAM in the vhost feature bitmap and retain the
negotiated value for each guest.  Keep datagrams disabled until the
feature is negotiated.

Use a vhost-specific datagram destination check to look up the guest
in the socket's network namespace and require its negotiated datagram
feature. The common virtio implementation supplies the bind and
message operations; destination validation remains in connect() and
sendmsg(), where the remote CID is available.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 drivers/vhost/vsock.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 0cb87971d749..eb2fbdb721aa 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -32,7 +32,8 @@
 static const int vhost_vsock_bits[] = {
 	VHOST_FEATURES,
 	VIRTIO_F_ACCESS_PLATFORM,
-	VIRTIO_VSOCK_F_SEQPACKET
+	VIRTIO_VSOCK_F_SEQPACKET,
+	VIRTIO_VSOCK_F_DGRAM,
 };
 
 #define VHOST_VSOCK_FEATURES VHOST_FEATURES_U64(vhost_vsock_bits, 0)
@@ -62,6 +63,7 @@ struct vhost_vsock {
 	u32 guest_cid;
 	bool seqpacket_allow;
 	bool ever_started; /* set on first SET_RUNNING(1); never cleared */
+	bool dgram_allow;
 };
 
 static u32 vhost_transport_get_local_cid(void)
@@ -436,6 +438,8 @@ static bool vhost_transport_msgzerocopy_allow(void)
 
 static bool vhost_transport_seqpacket_allow(struct vsock_sock *vsk,
 					    u32 remote_cid);
+static bool vhost_transport_dgram_allow(struct vsock_sock *vsk,
+					u32 cid, u32 port);
 
 static bool
 vhost_transport_stream_allow(struct vsock_sock *vsk, u32 cid, u32 port)
@@ -460,7 +464,7 @@ static struct virtio_transport vhost_transport = {
 		.dgram_enqueue            = virtio_transport_dgram_enqueue,
 		.dgram_dequeue            = virtio_transport_dgram_dequeue,
 		.dgram_bind               = virtio_transport_dgram_bind,
-		.dgram_allow              = virtio_transport_dgram_allow,
+		.dgram_allow              = vhost_transport_dgram_allow,
 
 		.stream_enqueue           = virtio_transport_stream_enqueue,
 		.stream_dequeue           = virtio_transport_stream_dequeue,
@@ -516,6 +520,24 @@ static bool vhost_transport_seqpacket_allow(struct vsock_sock *vsk,
 	return seqpacket_allow;
 }
 
+static bool vhost_transport_dgram_allow(struct vsock_sock *vsk,
+					u32 cid, u32 port)
+{
+	struct net *net = sock_net(sk_vsock(vsk));
+	struct vhost_vsock *vsock;
+	bool dgram_allow = false;
+
+	rcu_read_lock();
+	vsock = vhost_vsock_get(cid, net);
+
+	if (vsock)
+		dgram_allow = vsock->dgram_allow;
+
+	rcu_read_unlock();
+
+	return dgram_allow;
+}
+
 static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
 {
 	struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
@@ -737,6 +759,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
 	vsock->guest_cid = 0; /* no CID assigned yet */
 	vsock->seqpacket_allow = false;
 	vsock->ever_started = false;
+	vsock->dgram_allow = false;
 
 	atomic_set(&vsock->queued_replies, 0);
 
@@ -890,6 +913,7 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features)
 	}
 
 	vsock->seqpacket_allow = features & (1ULL << VIRTIO_VSOCK_F_SEQPACKET);
+	vsock->dgram_allow = features & (1ULL << VIRTIO_VSOCK_F_DGRAM);
 
 	for (i = 0; i < ARRAY_SIZE(vsock->vqs); i++) {
 		vq = &vsock->vqs[i];

-- 
2.56.0