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

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.n... ovpn_peer_release -> ovpn_socket_put

v12: - https://lore.kernel.org/netdev/20241202-b4-ovpn-v12-9-239ff733bf97@openvpn.n... ovpn_peer_release doesn't do ovpn_socket_put

- https://lore.kernel.org/netdev/20241202-b4-ovpn-v12-7-239ff733bf97@openvpn.n... 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;

+}