Re: [PATCH net-next v18 12/25] ovpn: implement TCP transport

[Antonio Quartulli <antonio@openvpn.net>]

On 17/01/2025 18:14, Sabrina Dubroca wrote:
> 2025-01-13, 10:31:31 +0100, Antonio Quartulli wrote:
>> +static int ovpn_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
>> +			    int flags, int *addr_len)
>> +{
>> +	int err = 0, off, copied = 0, ret;
>> +	struct ovpn_socket *sock;
>> +	struct ovpn_peer *peer;
>> +	struct sk_buff *skb;
>> +
>> +	rcu_read_lock();
>> +	sock = rcu_dereference_sk_user_data(sk);
>> +	if (!sock || !sock->peer) {
>> +		rcu_read_unlock();
>> +		return -EBADF;
>> +	}
>> +	/* we take a reference to the peer linked to this TCP socket, because
>> +	 * in turn the peer holds a reference to the socket itself.
> 
> Not anymore since v12? [*]
> 
> I think it's ok here because we're only using peer and sk (not
> anything from ovpn_socket), but it is relevant in _sendmsg, which has
> the same peer_hold pattern without this comment.
> 
> [*]
> v11:
>   - https://lore.kernel.org/netdev/20241029-b4-ovpn-v11-8-de4698c73a25@openvpn.net/
>     ovpn_peer_release -> ovpn_socket_put
> 
> v12:
>   - https://lore.kernel.org/netdev/20241202-b4-ovpn-v12-9-239ff733bf97@openvpn.net/
>     ovpn_peer_release doesn't do ovpn_socket_put
> 
>   - https://lore.kernel.org/netdev/20241202-b4-ovpn-v12-7-239ff733bf97@openvpn.net/
>     ovpn_socket_put is done directly at ovpn_peer_remove time, before the final peer_put
> 
>> +	 * By doing so we also ensure that the peer stays alive along with
>> +	 * the socket while executing this function
>> +	 */
>> +	ovpn_peer_hold(sock->peer);
>> +	peer = sock->peer;
>> +	rcu_read_unlock();
>> +
>> +	skb = __skb_recv_datagram(sk, &peer->tcp.user_queue, flags, &off, &err);
>> +	if (!skb) {
>> +		if (err == -EAGAIN && sk->sk_shutdown & RCV_SHUTDOWN) {
>> +			ret = 0;
>> +			goto out;
>> +		}
>> +		ret = err;
>> +		goto out;
>> +	}
>> +
>> +	copied = len;
>> +	if (copied > skb->len)
>> +		copied = skb->len;
>> +	else if (copied < skb->len)
>> +		msg->msg_flags |= MSG_TRUNC;
>> +
>> +	err = skb_copy_datagram_msg(skb, 0, msg, copied);
>> +	if (unlikely(err)) {
>> +		kfree_skb(skb);
>> +		ret = err;
>> +		goto out;
>> +	}
>> +
>> +	if (flags & MSG_TRUNC)
>> +		copied = skb->len;
>> +	kfree_skb(skb);
>> +	ret = copied;
>> +out:
>> +	ovpn_peer_put(peer);
>> +	return ret;
>> +}
> 
> [...]
>> +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;
>> +
>> +	rcu_read_lock();
>> +	sock = rcu_dereference_sk_user_data(sk);
>> +	if (unlikely(!sock || !sock->peer || !ovpn_peer_hold(sock->peer))) {
>> +		rcu_read_unlock();
>> +		return -EIO;
>> +	}
>> +	peer = sock->peer;
>> +	rcu_read_unlock();
>> +
>> +	lock_sock(peer->sock->sock->sk);
> 
> Isn't that just sk?

Right - it's the same object at this point. I'll use sk.

> 
>> +
>> +	if (msg->msg_flags & ~MSG_DONTWAIT) {
>> +		ret = -EOPNOTSUPP;
>> +		goto peer_free;
>> +	}
>> +
>> +	if (peer->tcp.out_msg.skb) {
>> +		ret = -EAGAIN;
>> +		goto peer_free;
>> +	}
>> +
>> +	if (size < linear)
>> +		linear = size;
>> +
>> +	skb = sock_alloc_send_pskb(sk, linear, size - linear,
>> +				   msg->msg_flags & MSG_DONTWAIT, &ret, 0);
>> +	if (!skb) {
>> +		net_err_ratelimited("%s: skb alloc failed: %d\n",
>> +				    netdev_name(sock->peer->ovpn->dev), ret);
> 
> Since we only have a ref on peer (but not on sock), I'd use
> peer->... directly instead of sock->peer.

ACK

> 
>> +		goto peer_free;
>> +	}
>> +
>> +	skb_put(skb, linear);
>> +	skb->len = size;
>> +	skb->data_len = size - linear;
>> +
>> +	ret = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
>> +	if (ret) {
>> +		kfree_skb(skb);
>> +		net_err_ratelimited("%s: skb copy from iter failed: %d\n",
>> +				    netdev_name(sock->peer->ovpn->dev), ret);
> 
> s/sock->//

ACK

> 
>> +		goto peer_free;
>> +	}
>> +
>> +	ovpn_tcp_send_sock_skb(sock->peer, skb);
> 
> s/sock->//

ACK

> 
>> +	ret = size;
>> +peer_free:
>> +	release_sock(peer->sock->sock->sk);
>> +	ovpn_peer_put(peer);
>> +	return ret;
>> +}
> 

-- 
Antonio Quartulli
OpenVPN Inc.