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

Sabrina Dubroca
2025-01-17T17:14:38Z

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?

> +
> + 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.

> + 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->//

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

s/sock->//

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

--
Sabrina