netdev - [PATCH net-next v1] net: mptcp, Fast Open Mechanism

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Date:   Fri, 22 Oct 2021 07:15:22 +0200
From:   Dmytro Shytyi <dmytro@...tyi.net>
To:     "mathewjmartineau" <mathew.j.martineau@...ux.intel.com>,
        "" matthieubaerts " <" <matthieu.baerts@...sares.net>
Cc:     "Davem" <davem@...emloft.net>, "Kuba" <kuba@...nel.org>,
        "mptcp" <mptcp@...ts.linux.dev>, "netdev" <netdev@...r.kernel.org>
Subject: [PATCH net-next v1] net: mptcp, Fast Open Mechanism

This set of patches will bring "Fast Open" Option support to MPTCP.
The aim of Fast Open Mechanism is to eliminate one round trip 
time from a TCP conversation by allowing data to be included as 
part of the SYN segment that initiates the connection. 

IETF RFC 8684: Appendix B.  TCP Fast Open and MPTCP.

[PATCH v1] includes "client" partial support for :
1. send request for cookie;
2. send syn+data+cookie.

Signed-off-by: Dmytro Shytyi <dmytro@...tyi.net>
---
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index cd6b11c9b54d..1f9ef060e980 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1686,6 +1686,68 @@ static void mptcp_set_nospace(struct sock *sk)
        set_bit(MPTCP_NOSPACE, &mptcp_sk(sk)->flags);
 }

+static int mptcp_sendmsg_fastopen_cookie_req(struct sock *sk, struct msghdr *msg,
+                                            size_t *copied, size_t size,
+                                            struct ubuf_info *uarg)
+{
+       struct mptcp_sock *msk = mptcp_sk(sk);
+       struct socket *ssk = __mptcp_nmpc_socket(msk);
+       struct tcp_sock *tp = tcp_sk(ssk->sk);
+       struct sockaddr *uaddr = msg->msg_name;
+       struct tcp_fastopen_context *ctx;
+       const struct iphdr *iph;
+       struct sk_buff *skb;
+       int err;
+
+       skb = sk_stream_alloc_skb(ssk->sk, 0, ssk->sk->sk_allocation, true);
+       iph = ip_hdr(skb);
+       tcp_fastopen_init_key_once(sock_net(ssk->sk));
+       ctx = tcp_fastopen_get_ctx(ssk->sk);
+       tp->fastopen_req = kzalloc(sizeof(*tp->fatopen_req),
+                                  ssk->sk->sk_allocation);
+       tp->fastopen_req->data = msg;
+       tp->fastopen_req->size = size;
+       tp->fastopen_req->uarg = uarg;
+       err = mptcp_stream_connect(sk->sk_socket, uaddr, msg->msg_namelen, msg->msg_flags);
+       return err;
+}
+
+static int mptcp_sendmsg_fastopen_cookie_send(struct sock *sk, struct msghdr *msg,
+                                             size_t *copied, size_t size,
+                                             struct ubuf_info *uarg)
+{
+       struct tcp_fastopen_cookie *fastopen_cookie = kmalloc(sizeof(*fastopen_cookie),
+                                                             GFP_KERNEL);
+       struct mptcp_sock *msk = mptcp_sk(sk);
+       struct socket *ssk = __mptcp_nmpc_socket(msk);
+       struct tcp_sock *tp = tcp_sk(ssk->sk);
+       struct sockaddr *uaddr = msg->msg_name;
+       struct tcp_fastopen_context *ctx;
+       const struct iphdr *iph;
+       struct sk_buff *skb;
+       int err;
+
+       skb = sk_stream_alloc_skb(ssk->sk, 0, ssk->sk->sk_allocation, true);
+       iph = ip_hdr(skb);
+       tcp_fastopen_init_key_once(sock_net(ssk->sk));
+       ctx = tcp_fastopen_get_ctx(ssk->sk);
+
+       fastopen_cookie->val[0] = cpu_to_le64(siphash(&iph->saddr,
+                                             sizeof(iph->saddr) +
+                                             sizeof(iph->daddr),
+                                             &ctx->key[0]));
+       fastopen_cookie->len = TCP_FASTOPEN_COOKIE_SIZE;
+
+       tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
+                                  ssk->sk->sk_allocation);
+       tp->fastopen_req->data = msg;
+       tp->fastopen_req->size = size;
+       tp->fastopen_req->uarg = uarg;
+       memcpy(&tp->fastopen_req->cookie, fastopen_cookie, sizeof(tp->fastopen_req->cookie));
+       err = mptcp_stream_connect(sk->sk_socket, uaddr, msg->msg_namelen, msg->msg_flags);
+       return err;
+}
+
 static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
        struct mptcp_sock *msk = mptcp_sk(sk);
@@ -1694,9 +1756,22 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
        int ret = 0;
        long timeo;

-       /* we don't support FASTOPEN yet */
-       if (msg->msg_flags & MSG_FASTOPEN)
-               return -EOPNOTSUPP;
+       /* we don't fully support FASTOPEN yet */
+
+       if (msg->msg_flags & MSG_FASTOPEN) {
+               struct socket *ssk = __mptcp_nmpc_socket(msk);
+               struct tcp_sock *tp = tcp_sk(ssk->sk);
+
+               if (tp && tp->fastopen_req && tp->fastopen_req->cookie.len != 0) {
+                       // send cookie
+                       ret = mptcp_sendmsg_fastopen_cookie_send(sk, msg, &copied, len, uarg);
+               } else {
+                       struct tcp_fastopen_request *fastopen = tp->fastopen_req;
+                       //requests a cookie
+                       ret = mptcp_sendmsg_fastopen_cookie_req(sk, msg, &copied, len, uarg);
+               }
+       return ret;
+       }

        /* silently ignore everything else */
        msg->msg_flags &= MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL;