[net-next,03/15] mptcp: Associate MPTCP context with TCP socket

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 52798ab00394..877947475814 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -397,6 +397,9 @@  struct tcp_sock {
 	u32	mtu_info; /* We received an ICMP_FRAG_NEEDED / ICMPV6_PKT_TOOBIG
 			   * while socket was owned by user.
 			   */
+#if IS_ENABLED(CONFIG_MPTCP)
+	bool	is_mptcp;
+#endif
 
 #ifdef CONFIG_TCP_MD5SIG
 /* TCP AF-Specific parts; only used by MD5 Signature support so far */
diff --git a/net/mptcp/Makefile b/net/mptcp/Makefile
index 27a846263f08..e1ee5aade8b0 100644
--- a/net/mptcp/Makefile
+++ b/net/mptcp/Makefile
@@ -1,4 +1,4 @@ 
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_MPTCP) += mptcp.o
 
-mptcp-y := protocol.o options.o
+mptcp-y := protocol.o subflow.o options.o
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 2e0a3266725a..1f8c66c9f828 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -17,6 +17,54 @@ 
 #include <net/mptcp.h>
 #include "protocol.h"
 
+#define MPTCP_SAME_STATE TCP_MAX_STATES
+
+/* if msk has a single subflow socket, and the mp_capable handshake is not
+ * completed yet or has failed - that is, the socket is Not MP Capable,
+ * returns it.
+ * Otherwise returns NULL
+ */
+static struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk)
+{
+	if (!msk->subflow)
+		return NULL;
+
+	return msk->subflow;
+}
+
+static bool __mptcp_can_create_subflow(const struct mptcp_sock *msk)
+{
+	return ((struct sock *)msk)->sk_state == TCP_CLOSE;
+}
+
+static struct socket *__mptcp_socket_create(struct mptcp_sock *msk, int state)
+{
+	struct mptcp_subflow_context *subflow;
+	struct sock *sk = (struct sock *)msk;
+	struct socket *ssock;
+	int err;
+
+	ssock = __mptcp_nmpc_socket(msk);
+	if (ssock)
+		goto set_state;
+
+	if (!__mptcp_can_create_subflow(msk))
+		return ERR_PTR(-EINVAL);
+
+	err = mptcp_subflow_create_socket(sk, &ssock);
+	if (err)
+		return ERR_PTR(err);
+
+	msk->subflow = ssock;
+	subflow = mptcp_subflow_ctx(ssock->sk);
+	subflow->request_mptcp = 1; /* @@ if MPTCP enabled */
+
+set_state:
+	if (state != MPTCP_SAME_STATE)
+		inet_sk_state_store(sk, state);
+	return ssock;
+}
+
 static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
@@ -45,12 +93,14 @@  static int mptcp_init_sock(struct sock *sk)
 static void mptcp_close(struct sock *sk, long timeout)
 {
 	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct socket *ssock;
 
 	inet_sk_state_store(sk, TCP_CLOSE);
 
-	if (msk->subflow) {
-		pr_debug("subflow=%p", msk->subflow->sk);
-		sock_release(msk->subflow);
+	ssock = __mptcp_nmpc_socket(msk);
+	if (ssock) {
+		pr_debug("subflow=%p", mptcp_subflow_ctx(ssock->sk));
+		sock_release(ssock);
 	}
 
 	sock_orphan(sk);
@@ -64,7 +114,8 @@  static int mptcp_connect(struct sock *sk, struct sockaddr *saddr, int len)
 
 	saddr->sa_family = AF_INET;
 
-	pr_debug("msk=%p, subflow=%p", msk, msk->subflow->sk);
+	pr_debug("msk=%p, subflow=%p", msk,
+		 mptcp_subflow_ctx(msk->subflow->sk));
 
 	err = kernel_connect(msk->subflow, saddr, len, 0);
 
@@ -90,15 +141,79 @@  static struct proto mptcp_prot = {
 	.no_autobind	= true,
 };
 
+static int mptcp_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
+{
+	struct mptcp_sock *msk = mptcp_sk(sock->sk);
+	struct socket *ssock;
+	int err = -ENOTSUPP;
+
+	if (uaddr->sa_family != AF_INET) // @@ allow only IPv4 for now
+		return err;
+
+	lock_sock(sock->sk);
+	ssock = __mptcp_socket_create(msk, MPTCP_SAME_STATE);
+	if (IS_ERR(ssock)) {
+		err = PTR_ERR(ssock);
+		goto unlock;
+	}
+
+	err = ssock->ops->bind(ssock, uaddr, addr_len);
+
+unlock:
+	release_sock(sock->sk);
+	return err;
+}
+
+static int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
+				int addr_len, int flags)
+{
+	struct mptcp_sock *msk = mptcp_sk(sock->sk);
+	struct socket *ssock;
+	int err;
+
+	lock_sock(sock->sk);
+	ssock = __mptcp_socket_create(msk, TCP_SYN_SENT);
+	if (IS_ERR(ssock)) {
+		err = PTR_ERR(ssock);
+		goto unlock;
+	}
+
+	err = ssock->ops->connect(ssock, uaddr, addr_len, flags);
+	inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
+
+unlock:
+	release_sock(sock->sk);
+	return err;
+}
+
+static __poll_t mptcp_poll(struct file *file, struct socket *sock,
+			   struct poll_table_struct *wait)
+{
+	__poll_t mask = 0;
+
+	return mask;
+}
+
+static struct proto_ops mptcp_stream_ops;
+
 static struct inet_protosw mptcp_protosw = {
 	.type		= SOCK_STREAM,
 	.protocol	= IPPROTO_MPTCP,
 	.prot		= &mptcp_prot,
-	.ops		= &inet_stream_ops,
+	.ops		= &mptcp_stream_ops,
+	.flags		= INET_PROTOSW_ICSK,
 };
 
 void __init mptcp_init(void)
 {
+	mptcp_prot.h.hashinfo = tcp_prot.h.hashinfo;
+	mptcp_stream_ops = inet_stream_ops;
+	mptcp_stream_ops.bind = mptcp_bind;
+	mptcp_stream_ops.connect = mptcp_stream_connect;
+	mptcp_stream_ops.poll = mptcp_poll;
+
+	mptcp_subflow_init();
+
 	if (proto_register(&mptcp_prot, 1) != 0)
 		panic("Failed to register MPTCP proto.\n");
 
@@ -106,13 +221,14 @@  void __init mptcp_init(void)
 }
 
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
+static struct proto_ops mptcp_v6_stream_ops;
 static struct proto mptcp_v6_prot;
 
 static struct inet_protosw mptcp_v6_protosw = {
 	.type		= SOCK_STREAM,
 	.protocol	= IPPROTO_MPTCP,
 	.prot		= &mptcp_v6_prot,
-	.ops		= &inet6_stream_ops,
+	.ops		= &mptcp_v6_stream_ops,
 	.flags		= INET_PROTOSW_ICSK,
 };
 
@@ -130,6 +246,11 @@  int mptcpv6_init(void)
 	if (err)
 		return err;
 
+	mptcp_v6_stream_ops = inet6_stream_ops;
+	mptcp_v6_stream_ops.bind = mptcp_bind;
+	mptcp_v6_stream_ops.connect = mptcp_stream_connect;
+	mptcp_v6_stream_ops.poll = mptcp_poll;
+
 	err = inet6_register_protosw(&mptcp_v6_protosw);
 	if (err)
 		proto_unregister(&mptcp_v6_prot);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index c59cf8b220b0..543d4d5d8985 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -48,4 +48,30 @@  static inline struct mptcp_sock *mptcp_sk(const struct sock *sk)
 	return (struct mptcp_sock *)sk;
 }
 
+/* MPTCP subflow context */
+struct mptcp_subflow_context {
+	u32	request_mptcp : 1;  /* send MP_CAPABLE */
+	struct	sock *tcp_sock;	    /* tcp sk backpointer */
+	struct	sock *conn;	    /* parent mptcp_sock */
+	struct	rcu_head rcu;
+};
+
+static inline struct mptcp_subflow_context *
+mptcp_subflow_ctx(const struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	/* Use RCU on icsk_ulp_data only for sock diag code */
+	return (__force struct mptcp_subflow_context *)icsk->icsk_ulp_data;
+}
+
+static inline struct sock *
+mptcp_subflow_tcp_sock(const struct mptcp_subflow_context *subflow)
+{
+	return subflow->tcp_sock;
+}
+
+void mptcp_subflow_init(void);
+int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock);
+
 #endif /* __MPTCP_PROTOCOL_H */
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
new file mode 100644
index 000000000000..9e2ff5b40d13
--- /dev/null
+++ b/net/mptcp/subflow.c
@@ -0,0 +1,111 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/* Multipath TCP
+ *
+ * Copyright (c) 2017 - 2019, Intel Corporation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <net/sock.h>
+#include <net/inet_common.h>
+#include <net/inet_hashtables.h>
+#include <net/protocol.h>
+#include <net/tcp.h>
+#include <net/mptcp.h>
+#include "protocol.h"
+
+int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
+{
+	struct mptcp_subflow_context *subflow;
+	struct net *net = sock_net(sk);
+	struct socket *sf;
+	int err;
+
+	err = sock_create_kern(net, PF_INET, SOCK_STREAM, IPPROTO_TCP, &sf);
+	if (err)
+		return err;
+
+	lock_sock(sf->sk);
+	err = tcp_set_ulp(sf->sk, "mptcp");
+	release_sock(sf->sk);
+
+	if (err)
+		return err;
+
+	subflow = mptcp_subflow_ctx(sf->sk);
+	pr_debug("subflow=%p", subflow);
+
+	*new_sock = sf;
+	subflow->conn = sk;
+
+	return 0;
+}
+
+static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,
+							gfp_t priority)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct mptcp_subflow_context *ctx;
+
+	ctx = kzalloc(sizeof(*ctx), priority);
+	if (!ctx)
+		return NULL;
+	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
+
+	pr_debug("subflow=%p", ctx);
+
+	ctx->tcp_sock = sk;
+
+	return ctx;
+}
+
+static int subflow_ulp_init(struct sock *sk)
+{
+	struct mptcp_subflow_context *ctx;
+	struct tcp_sock *tp = tcp_sk(sk);
+	int err = 0;
+
+	/* disallow attaching ULP to a socket unless it has been
+	 * created with sock_create_kern()
+	 */
+	if (!sk->sk_kern_sock) {
+		err = -EOPNOTSUPP;
+		goto out;
+	}
+
+	ctx = subflow_create_ctx(sk, GFP_KERNEL);
+	if (!ctx) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	pr_debug("subflow=%p, family=%d", ctx, sk->sk_family);
+
+	tp->is_mptcp = 1;
+out:
+	return err;
+}
+
+static void subflow_ulp_release(struct sock *sk)
+{
+	struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(sk);
+
+	if (!ctx)
+		return;
+
+	kfree_rcu(ctx, rcu);
+}
+
+static struct tcp_ulp_ops subflow_ulp_ops __read_mostly = {
+	.name		= "mptcp",
+	.owner		= THIS_MODULE,
+	.init		= subflow_ulp_init,
+	.release	= subflow_ulp_release,
+};
+
+void mptcp_subflow_init(void)
+{
+	if (tcp_register_ulp(&subflow_ulp_ops) != 0)
+		panic("MPTCP: failed to register subflows to ULP\n");
+}