[PATCH RFC v2 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.

Reject guest datagrams on ingress unless the receiving virtqueue
acknowledged the feature. Complete rejected descriptors normally so the
queue can continue processing subsequent traffic.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 drivers/vhost/vsock.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 0cb87971d749..7971f6f0b6a2 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,
@@ -573,10 +595,12 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
 
 		hdr = virtio_vsock_hdr(skb);
 
-		/* Only accept correctly addressed packets */
+		/* Check addressing and datagram feature negotiation. */
 		if (le64_to_cpu(hdr->src_cid) == vsock->guest_cid &&
 		    le64_to_cpu(hdr->dst_cid) ==
-		    vhost_transport_get_local_cid())
+		    vhost_transport_get_local_cid() &&
+		    (le16_to_cpu(hdr->type) != VIRTIO_VSOCK_TYPE_DGRAM ||
+		     vhost_has_feature(vq, VIRTIO_VSOCK_F_DGRAM)))
 			virtio_transport_recv_pkt(&vhost_transport, skb,
 						  vsock->net);
 		else
@@ -737,6 +761,7 @@ 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 +915,7 @@ 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