Re: [PATCH net-next v20 12/25] ovpn: implement TCP transport

[Sabrina Dubroca <sd@queasysnail.net>]

2025-02-27, 02:21:37 +0100, Antonio Quartulli wrote:
> @@ -94,11 +96,23 @@ void ovpn_socket_release(struct ovpn_peer *peer)
>  	 * detached before it can be picked by a concurrent reader.
>  	 */
>  	lock_sock(sock->sock->sk);
> -	ovpn_socket_put(peer, sock);
> +	released = ovpn_socket_put(peer, sock);
>  	release_sock(sock->sock->sk);
>  
>  	/* align all readers with sk_user_data being NULL */
>  	synchronize_rcu();
> +
> +	/* following cleanup should happen with lock released */
> +	if (released) {
> +		if (sock->sock->sk->sk_protocol == IPPROTO_UDP) {
> +			netdev_put(sock->ovpn->dev, &sock->dev_tracker);
> +		} else if (sock->sock->sk->sk_protocol == IPPROTO_TCP) {
> +			/* wait for TCP jobs to terminate */
> +			ovpn_tcp_socket_wait_finish(sock);
> +			ovpn_peer_put(sock->peer);
> +		}
> +		kfree_rcu(sock, rcu);

kfree_rcu after synchronize_rcu is a bit unexpected. Do we still need
to wait before we free sock, now that we have synchronize_rcu before?

> +	}
>  }
>  



> +static int ovpn_tcp_parse(struct strparser *strp, struct sk_buff *skb)
> +{
> +	struct strp_msg *rxm = strp_msg(skb);
> +	__be16 blen;
> +	u16 len;
> +	int err;
> +
> +	/* when packets are written to the TCP stream, they are prepended with
> +	 * two bytes indicating the actual packet size.
> +	 * Here we read those two bytes and move the skb data pointer to the
> +	 * beginning of the packet

There's no update to skb->data being done in ovpn_tcp_parse AFAICT.

[...]
> +static void ovpn_tcp_rcv(struct strparser *strp, struct sk_buff *skb)
> +{
> +	struct ovpn_peer *peer = container_of(strp, struct ovpn_peer, tcp.strp);
> +	struct strp_msg *msg = strp_msg(skb);
> +	size_t pkt_len = msg->full_len - 2;
> +	size_t off = msg->offset + 2;
> +	u8 opcode;
> +
> +	/* ensure skb->data points to the beginning of the openvpn packet */
> +	if (!pskb_pull(skb, off)) {

Is that the one you mean in the previous comment?

> +		net_warn_ratelimited("%s: packet too small for peer %u\n",
> +				     netdev_name(peer->ovpn->dev), peer->id);
> +		goto err;
> +	}
[some checks]
> +	/* DATA_V2 packets are handled in kernel, the rest goes to user space */
> +	opcode = ovpn_opcode_from_skb(skb, 0);
> +	if (unlikely(opcode != OVPN_DATA_V2)) {
> +		if (opcode == OVPN_DATA_V1) {
> +			net_warn_ratelimited("%s: DATA_V1 detected on the TCP stream\n",
> +					     netdev_name(peer->ovpn->dev));
> +			goto err;

In TCP encap, receiving OVPN_DATA_V1 packets is going to kill the peer:

> +err:
> +	dev_core_stats_rx_dropped_inc(peer->ovpn->dev);
> +	kfree_skb(skb);
> +	ovpn_peer_del(peer, OVPN_DEL_PEER_REASON_TRANSPORT_ERROR);
> +}
> +

but that's not the case with the UDP encap (ovpn_udp_encap_recv simply
drops those packets). Should the TCP/UDP behavior be consistent?




> +void ovpn_tcp_send_skb(struct ovpn_peer *peer, struct socket *sock,
> +		       struct sk_buff *skb)
> +{
> +	u16 len = skb->len;
> +
> +	*(__be16 *)__skb_push(skb, sizeof(u16)) = htons(len);
> +
> +	spin_lock_nested(&sock->sk->sk_lock.slock, OVPN_TCP_DEPTH_NESTING);

With this, lockdep is still going to complain in the unlikely case
that ovpn-TCP traffic is carried over another ovpn-TCP socket, right?
(probably fine to leave it like that)


[...]
> +static int ovpn_tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
> +{
> +	struct ovpn_socket *sock;
> +	int ret, linear = PAGE_SIZE;
> +	struct ovpn_peer *peer;
> +	struct sk_buff *skb;
> +
> +	lock_sock(sk);
> +	rcu_read_lock();
> +	sock = rcu_dereference_sk_user_data(sk);
> +	if (unlikely(!sock || !sock->peer || !ovpn_peer_hold(sock->peer))) {
> +		rcu_read_unlock();
> +		release_sock(sk);
> +		return -EIO;
> +	}
> +	rcu_read_unlock();
> +	peer = sock->peer;

This used to be done under RCU in previous versions of the series. Why
is it after rcu_read_unlock now? (likely safe since we're under
lock_sock so detach can't happen)

> +
> +	if (msg->msg_flags & ~MSG_DONTWAIT) {
> +		ret = -EOPNOTSUPP;
> +		goto peer_free;
> +	}


-- 
Sabrina