[PATCH net-next v2 1/5] vsock/virtio: split socket lookup from locked RX processing

[Jia Jia <physicalmtea@gmail.com>]

Split virtio_transport_recv_pkt() so socket lookup is separate from the
receive state machine that runs under the socket lock.

Keep virtio_transport_recv_pkt() on its existing per-packet locking path.
Pass the source and destination addresses used for lookup to the locked
receive path so they are decoded only once.

Pass the network namespace and decoded address tuple through a packet
context to the locked receive path.

Preserve source validation and failure handling. Keep the lookup reference
separate from the skb owner reference so the locked receive path can manage
the two lifetimes independently.

Signed-off-by: Jia Jia <physicalmtea@gmail.com>
---
 net/vmw_vsock/virtio_transport_common.c | 139 ++++++++++++++++--------
 1 file changed, 96 insertions(+), 43 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index f225f53..e3e75e5 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1774,81 +1774,97 @@ static bool virtio_transport_valid_type(u16 type)
 	       (type == VIRTIO_VSOCK_TYPE_SEQPACKET);
 }
 
-/* We are under the virtio-vsock's vsock->rx_lock or vhost-vsock's vq->mutex
- * lock.
- */
-void virtio_transport_recv_pkt(struct virtio_transport *t,
-			       struct sk_buff *skb, struct net *net)
+static void
+virtio_transport_recv_pkt_init_addrs(struct sk_buff *skb,
+				     struct sockaddr_vm *src,
+				     struct sockaddr_vm *dst)
 {
 	struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
-	struct sockaddr_vm src, dst;
-	struct vsock_sock *vsk;
-	struct sock *sk;
-	bool space_available;
 
-	vsock_addr_init(&src, le64_to_cpu(hdr->src_cid),
+	vsock_addr_init(src, le64_to_cpu(hdr->src_cid),
 			le32_to_cpu(hdr->src_port));
-	vsock_addr_init(&dst, le64_to_cpu(hdr->dst_cid),
+	vsock_addr_init(dst, le64_to_cpu(hdr->dst_cid),
 			le32_to_cpu(hdr->dst_port));
+}
+
+static void
+virtio_transport_trace_recv_pkt(struct sk_buff *skb,
+				const struct sockaddr_vm *src,
+				const struct sockaddr_vm *dst)
+{
+	struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
 
-	trace_virtio_transport_recv_pkt(src.svm_cid, src.svm_port,
-					dst.svm_cid, dst.svm_port,
+	trace_virtio_transport_recv_pkt(src->svm_cid, src->svm_port,
+					dst->svm_cid, dst->svm_port,
 					le32_to_cpu(hdr->len),
 					le16_to_cpu(hdr->type),
 					le16_to_cpu(hdr->op),
 					le32_to_cpu(hdr->flags),
 					le32_to_cpu(hdr->buf_alloc),
 					le32_to_cpu(hdr->fwd_cnt));
+}
 
-	if (!virtio_transport_valid_type(le16_to_cpu(hdr->type))) {
-		(void)virtio_transport_reset_no_sock(t, skb, net);
-		goto free_pkt;
-	}
+static struct sock *
+virtio_transport_recv_pkt_find_socket(struct sk_buff *skb,
+				      struct sockaddr_vm *src,
+				      struct sockaddr_vm *dst,
+				      struct net *net)
+{
+	struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
+	struct sock *sk;
 
-	/* The socket must be in connected or bound table
-	 * otherwise send reset back
-	 */
-	sk = vsock_find_connected_socket_net(&src, &dst, net);
-	if (!sk) {
-		sk = vsock_find_bound_socket_net(&dst, net);
-		if (!sk) {
-			(void)virtio_transport_reset_no_sock(t, skb, net);
-			goto free_pkt;
-		}
-	}
+	if (!virtio_transport_valid_type(le16_to_cpu(hdr->type)))
+		return NULL;
+
+	sk = vsock_find_connected_socket_net(src, dst, net);
+	if (!sk)
+		sk = vsock_find_bound_socket_net(dst, net);
+	if (!sk)
+		return NULL;
 
 	if (virtio_transport_get_type(sk) != le16_to_cpu(hdr->type)) {
-		(void)virtio_transport_reset_no_sock(t, skb, net);
 		sock_put(sk);
-		goto free_pkt;
+		return NULL;
 	}
 
-	if (!skb_set_owner_sk_safe(skb, sk)) {
-		WARN_ONCE(1, "receiving vsock socket has sk_refcnt == 0\n");
-		goto free_pkt;
-	}
+	return sk;
+}
 
-	vsk = vsock_sk(sk);
+struct virtio_transport_rx_pkt_ctx {
+	struct net *net;
+	const struct sockaddr_vm *src;
+	const struct sockaddr_vm *dst;
+};
 
-	lock_sock(sk);
+/*
+ * The caller holds sk's socket lock and must free skb if this returns true.
+ */
+static bool
+virtio_transport_recv_pkt_locked(struct virtio_transport *t,
+				 struct sk_buff *skb, struct sock *sk,
+				 const struct virtio_transport_rx_pkt_ctx *ctx)
+{
+	const struct sockaddr_vm *src = ctx->src;
+	const struct sockaddr_vm *dst = ctx->dst;
+	struct vsock_sock *vsk = vsock_sk(sk);
+	struct net *net = ctx->net;
+	bool space_available;
 
-	/* Check if sk has been closed or assigned to another transport before
-	 * lock_sock (note: listener sockets are not assigned to any transport)
+	/* Check after acquiring the socket lock. Listener sockets accept packets
+	 * from any source and are not assigned to a transport.
 	 */
 	if (sock_flag(sk, SOCK_DONE) ||
 	    (sk->sk_state != TCP_LISTEN &&
-	     !vsock_check_source(vsk, &t->transport, &src))) {
+	     !vsock_check_source(vsk, &t->transport, src))) {
 		(void)virtio_transport_reset_no_sock(t, skb, net);
-		release_sock(sk);
-		sock_put(sk);
-		goto free_pkt;
+		return true;
 	}
 
 	space_available = virtio_transport_space_update(sk, skb);
 
 	/* Update CID in case it has changed after a transport reset event */
 	if (vsk->local_addr.svm_cid != VMADDR_CID_ANY)
-		vsk->local_addr.svm_cid = dst.svm_cid;
+		vsk->local_addr.svm_cid = dst->svm_cid;
 
 	if (space_available)
 		sk->sk_write_space(sk);
@@ -1875,12 +1891,49 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
 		break;
 	}
 
+	return false;
+}
+
+/* We are under the virtio-vsock's vsock->rx_lock or vhost-vsock's vq->mutex
+ * lock.
+ */
+void virtio_transport_recv_pkt(struct virtio_transport *t,
+			       struct sk_buff *skb, struct net *net)
+{
+	struct virtio_transport_rx_pkt_ctx ctx;
+	struct sockaddr_vm src, dst;
+	struct sock *sk;
+	bool free_pkt;
+
+	virtio_transport_recv_pkt_init_addrs(skb, &src, &dst);
+	virtio_transport_trace_recv_pkt(skb, &src, &dst);
+
+	sk = virtio_transport_recv_pkt_find_socket(skb, &src, &dst, net);
+	if (!sk) {
+		(void)virtio_transport_reset_no_sock(t, skb, net);
+		goto free_pkt;
+	}
+
+	if (!skb_set_owner_sk_safe(skb, sk)) {
+		WARN_ONCE(1, "receiving vsock socket has sk_refcnt == 0\n");
+		goto free_pkt;
+	}
+
+	lock_sock(sk);
+	ctx = (struct virtio_transport_rx_pkt_ctx) {
+		.net = net,
+		.src = &src,
+		.dst = &dst,
+	};
+	free_pkt = virtio_transport_recv_pkt_locked(t, skb, sk, &ctx);
 	release_sock(sk);
 
 	/* Release refcnt obtained when we fetched this socket out of the
 	 * bound or connected list.
 	 */
 	sock_put(sk);
+	if (free_pkt)
+		kfree_skb(skb);
 	return;
 
 free_pkt:
-- 
2.34.1