Re: [PATCH net-next v15 11/22] ovpn: implement TCP transport

[Sabrina Dubroca <sd@xxxxxxxxxxxxxxx>]

2024-12-11, 22:15:15 +0100, Antonio Quartulli wrote:
> @@ -42,6 +56,31 @@ struct ovpn_peer {
>  		struct in6_addr ipv6;
>  	} vpn_addrs;
>  	struct ovpn_socket *sock;
> +
> +	/* state of the TCP reading. Needed to keep track of how much of a
> +	 * single packet has already been read from the stream and how much is
> +	 * missing
> +	 */

nit: not so accurate since the switch to strp, can probably be dropped
since @tcp has a kdoc entry

> +	struct {
> +		struct strparser strp;
> +		struct work_struct tx_work;
> +		struct sk_buff_head user_queue;
> +		struct sk_buff_head out_queue;
> +		bool tx_in_progress;
> +
> +		struct {
> +			struct sk_buff *skb;
> +			int offset;
> +			int len;
> +		} out_msg;
> +
> +		struct {
> +			void (*sk_data_ready)(struct sock *sk);
> +			void (*sk_write_space)(struct sock *sk);
> +			struct proto *prot;
> +			const struct proto_ops *ops;
> +		} sk_cb;
> +	} tcp;

[...]
> +static void ovpn_tcp_send_sock_skb(struct ovpn_peer *peer, struct sk_buff *skb)
> +{
> +	if (peer->tcp.out_msg.skb)
> +		ovpn_tcp_send_sock(peer);
> +
> +	if (peer->tcp.out_msg.skb) {
> +		dev_core_stats_rx_dropped_inc(peer->ovpn->dev);

tx_dropped?

> +		kfree_skb(skb);
> +		return;
> +	}
> +
> +	peer->tcp.out_msg.skb = skb;
> +	peer->tcp.out_msg.len = skb->len;
> +	peer->tcp.out_msg.offset = 0;
> +	ovpn_tcp_send_sock(peer);
> +}
> +
> +void ovpn_tcp_send_skb(struct ovpn_peer *peer, struct sk_buff *skb)
> +{
> +	u16 len = skb->len;
> +
> +	*(__be16 *)__skb_push(skb, sizeof(u16)) = htons(len);
> +
> +	bh_lock_sock(peer->sock->sock->sk);
> +	if (sock_owned_by_user(peer->sock->sock->sk)) {
> +		if (skb_queue_len(&peer->tcp.out_queue) >=
> +		    READ_ONCE(net_hotdata.max_backlog)) {
> +			dev_core_stats_rx_dropped_inc(peer->ovpn->dev);

tx_dropped?

> +			kfree_skb(skb);
> +			goto unlock;
> +		}
> +		__skb_queue_tail(&peer->tcp.out_queue, skb);
> +	} else {
> +		ovpn_tcp_send_sock_skb(peer, skb);
> +	}
> +unlock:
> +	bh_unlock_sock(peer->sock->sock->sk);
> +}

[...]
> +static void ovpn_tcp_close(struct sock *sk, long timeout)
> +{
> +	struct ovpn_socket *sock;
> +
> +	rcu_read_lock();

[can't sleep until unlock]

> +	sock = rcu_dereference_sk_user_data(sk);
> +
> +	strp_stop(&sock->peer->tcp.strp);
> +
> +	tcp_close(sk, timeout);


    void tcp_close(struct sock *sk, long timeout)
    {
    	lock_sock(sk);

but this can sleep.

Is there anything that prevents delaying tcp_close until after
ovpn_peer_del and rcu_read_unlock?

> +	ovpn_peer_del(sock->peer, OVPN_DEL_PEER_REASON_TRANSPORT_ERROR);
> +	rcu_read_unlock();
> +}

[...]
> +void __init ovpn_tcp_init(void)
> +{
> +	ovpn_tcp_build_protos(&ovpn_tcp_prot, &ovpn_tcp_ops, &tcp_prot,
> +			      &inet_stream_ops);
> +
> +#if IS_ENABLED(CONFIG_IPV6)
> +	ovpn_tcp_build_protos(&ovpn_tcp6_prot, &ovpn_tcp6_ops, &tcpv6_prot,
> +			      &inet6_stream_ops);

I don't think that works for CONFIG_OVPN=y and CONFIG_IPV6=m. You can
either go back to the ugly thing espintcp and tls do, or use the
traditional Kconfig hack:

	depends on IPV6 || !IPV6

(you can find it sprinkled in various places of drivers/net/Kconfig
and net/)

-- 
Sabrina