mptcp: Add MPTCP socket stubs

Implements the infrastructure for MPTCP sockets.

MPTCP sockets open one in-kernel TCP socket per subflow. These subflow
sockets are only managed by the MPTCP socket that owns them and are not
visible from userspace. This commit allows a userspace program to open
an MPTCP socket with:

  sock = socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP);

The resulting socket is simply a wrapper around a single regular TCP
socket, without any of the MPTCP protocol implemented over the wire.

Co-developed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Co-developed-by: Peter Krystad <peter.krystad@linux.intel.com>
Signed-off-by: Peter Krystad <peter.krystad@linux.intel.com>
Co-developed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 184 insertions, 0 deletions

diff --git a/net/mptcp/Kconfig b/net/mptcp/Kconfig
new file mode 100644
index 000000000000..c1a99f07a4cd
--- /dev/null
+++ b/net/mptcp/Kconfig
@@ -0,0 +1,16 @@
+
+config MPTCP
+	bool "MPTCP: Multipath TCP"
+	depends on INET
+	select SKB_EXTENSIONS
+	help
+	  Multipath TCP (MPTCP) connections send and receive data over multiple
+	  subflows in order to utilize multiple network paths. Each subflow
+	  uses the TCP protocol, and TCP options carry header information for
+	  MPTCP.
+
+config MPTCP_IPV6
+	bool "MPTCP: IPv6 support for Multipath TCP"
+	depends on MPTCP
+	select IPV6
+	default y
diff --git a/net/mptcp/Makefile b/net/mptcp/Makefile
new file mode 100644
index 000000000000..659129d1fcbf
--- /dev/null
+++ b/net/mptcp/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_MPTCP) += mptcp.o
+
+mptcp-y := protocol.o
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
new file mode 100644
index 000000000000..5e24e7cf7d70
--- /dev/null
+++ b/net/mptcp/protocol.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Multipath TCP
+ *
+ * Copyright (c) 2017 - 2019, Intel Corporation.
+ */
+
+#define pr_fmt(fmt) "MPTCP: " fmt
+
+#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"
+
+static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct socket *subflow = msk->subflow;
+
+	if (msg->msg_flags & ~(MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL))
+		return -EOPNOTSUPP;
+
+	return sock_sendmsg(subflow, msg);
+}
+
+static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
+			 int nonblock, int flags, int *addr_len)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	struct socket *subflow = msk->subflow;
+
+	if (msg->msg_flags & ~(MSG_WAITALL | MSG_DONTWAIT))
+		return -EOPNOTSUPP;
+
+	return sock_recvmsg(subflow, msg, flags);
+}
+
+static int mptcp_init_sock(struct sock *sk)
+{
+	return 0;
+}
+
+static void mptcp_close(struct sock *sk, long timeout)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+
+	inet_sk_state_store(sk, TCP_CLOSE);
+
+	if (msk->subflow) {
+		pr_debug("subflow=%p", msk->subflow->sk);
+		sock_release(msk->subflow);
+	}
+
+	sock_orphan(sk);
+	sock_put(sk);
+}
+
+static int mptcp_connect(struct sock *sk, struct sockaddr *saddr, int len)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+	int err;
+
+	saddr->sa_family = AF_INET;
+
+	pr_debug("msk=%p, subflow=%p", msk, msk->subflow->sk);
+
+	err = kernel_connect(msk->subflow, saddr, len, 0);
+
+	sk->sk_state = TCP_ESTABLISHED;
+
+	return err;
+}
+
+static struct proto mptcp_prot = {
+	.name		= "MPTCP",
+	.owner		= THIS_MODULE,
+	.init		= mptcp_init_sock,
+	.close		= mptcp_close,
+	.accept		= inet_csk_accept,
+	.connect	= mptcp_connect,
+	.shutdown	= tcp_shutdown,
+	.sendmsg	= mptcp_sendmsg,
+	.recvmsg	= mptcp_recvmsg,
+	.hash		= inet_hash,
+	.unhash		= inet_unhash,
+	.get_port	= inet_csk_get_port,
+	.obj_size	= sizeof(struct mptcp_sock),
+	.no_autobind	= true,
+};
+
+static struct inet_protosw mptcp_protosw = {
+	.type		= SOCK_STREAM,
+	.protocol	= IPPROTO_MPTCP,
+	.prot		= &mptcp_prot,
+	.ops		= &inet_stream_ops,
+};
+
+void __init mptcp_init(void)
+{
+	if (proto_register(&mptcp_prot, 1) != 0)
+		panic("Failed to register MPTCP proto.\n");
+
+	inet_register_protosw(&mptcp_protosw);
+}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+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,
+	.flags		= INET_PROTOSW_ICSK,
+};
+
+int mptcpv6_init(void)
+{
+	int err;
+
+	mptcp_v6_prot = mptcp_prot;
+	strcpy(mptcp_v6_prot.name, "MPTCPv6");
+	mptcp_v6_prot.slab = NULL;
+	mptcp_v6_prot.obj_size = sizeof(struct mptcp_sock) +
+				 sizeof(struct ipv6_pinfo);
+
+	err = proto_register(&mptcp_v6_prot, 1);
+	if (err)
+		return err;
+
+	err = inet6_register_protosw(&mptcp_v6_protosw);
+	if (err)
+		proto_unregister(&mptcp_v6_prot);
+
+	return err;
+}
+#endif
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
new file mode 100644
index 000000000000..ee04a01bffd3
--- /dev/null
+++ b/net/mptcp/protocol.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Multipath TCP
+ *
+ * Copyright (c) 2017 - 2019, Intel Corporation.
+ */
+
+#ifndef __MPTCP_PROTOCOL_H
+#define __MPTCP_PROTOCOL_H
+
+/* MPTCP connection sock */
+struct mptcp_sock {
+	/* inet_connection_sock must be the first member */
+	struct inet_connection_sock sk;
+	struct socket	*subflow; /* outgoing connect/listener/!mp_capable */
+};
+
+static inline struct mptcp_sock *mptcp_sk(const struct sock *sk)
+{
+	return (struct mptcp_sock *)sk;
+}
+
+#endif /* __MPTCP_PROTOCOL_H */