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

Antonio Quartulli
2025-01-19T20:05:53Z

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.