mptcp: Handle MP_CAPABLE options for outgoing connections

Add hooks to tcp_output.c to add MP_CAPABLE to an outgoing SYN request,
to capture the MP_CAPABLE in the received SYN-ACK, to add MP_CAPABLE to
the final ACK of the three-way handshake.

Use the .sk_rx_dst_set() handler in the subflow proto to capture when the
responding SYN-ACK is received and notify the MPTCP connection layer.

Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Co-developed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Peter Krystad <peter.krystad@linux.intel.com>
Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 267 insertions, 1 deletions

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index bf8139353653..df3192305967 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -12,9 +12,188 @@
 #include <net/inet_hashtables.h>
 #include <net/protocol.h>
 #include <net/tcp.h>
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+#include <net/ip6_route.h>
+#endif
 #include <net/mptcp.h>
 #include "protocol.h"
 
+static void subflow_init_req(struct request_sock *req,
+			     const struct sock *sk_listener,
+			     struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk_listener);
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct tcp_options_received rx_opt;
+
+	pr_debug("subflow_req=%p, listener=%p", subflow_req, listener);
+
+	memset(&rx_opt.mptcp, 0, sizeof(rx_opt.mptcp));
+	mptcp_get_options(skb, &rx_opt);
+
+	subflow_req->mp_capable = 0;
+
+#ifdef CONFIG_TCP_MD5SIG
+	/* no MPTCP if MD5SIG is enabled on this socket or we may run out of
+	 * TCP option space.
+	 */
+	if (rcu_access_pointer(tcp_sk(sk_listener)->md5sig_info))
+		return;
+#endif
+
+	if (rx_opt.mptcp.mp_capable && listener->request_mptcp) {
+		subflow_req->mp_capable = 1;
+		subflow_req->remote_key = rx_opt.mptcp.sndr_key;
+	}
+}
+
+static void subflow_v4_init_req(struct request_sock *req,
+				const struct sock *sk_listener,
+				struct sk_buff *skb)
+{
+	tcp_rsk(req)->is_mptcp = 1;
+
+	tcp_request_sock_ipv4_ops.init_req(req, sk_listener, skb);
+
+	subflow_init_req(req, sk_listener, skb);
+}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+static void subflow_v6_init_req(struct request_sock *req,
+				const struct sock *sk_listener,
+				struct sk_buff *skb)
+{
+	tcp_rsk(req)->is_mptcp = 1;
+
+	tcp_request_sock_ipv6_ops.init_req(req, sk_listener, skb);
+
+	subflow_init_req(req, sk_listener, skb);
+}
+#endif
+
+static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	subflow->icsk_af_ops->sk_rx_dst_set(sk, skb);
+
+	if (subflow->conn && !subflow->conn_finished) {
+		pr_debug("subflow=%p, remote_key=%llu", mptcp_subflow_ctx(sk),
+			 subflow->remote_key);
+		mptcp_finish_connect(sk);
+		subflow->conn_finished = 1;
+	}
+}
+
+static struct request_sock_ops subflow_request_sock_ops;
+static struct tcp_request_sock_ops subflow_request_sock_ipv4_ops;
+
+static int subflow_v4_conn_request(struct sock *sk, struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	pr_debug("subflow=%p", subflow);
+
+	/* Never answer to SYNs sent to broadcast or multicast */
+	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
+		goto drop;
+
+	return tcp_conn_request(&subflow_request_sock_ops,
+				&subflow_request_sock_ipv4_ops,
+				sk, skb);
+drop:
+	tcp_listendrop(sk);
+	return 0;
+}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+static struct tcp_request_sock_ops subflow_request_sock_ipv6_ops;
+static struct inet_connection_sock_af_ops subflow_v6_specific;
+static struct inet_connection_sock_af_ops subflow_v6m_specific;
+
+static int subflow_v6_conn_request(struct sock *sk, struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	pr_debug("subflow=%p", subflow);
+
+	if (skb->protocol == htons(ETH_P_IP))
+		return subflow_v4_conn_request(sk, skb);
+
+	if (!ipv6_unicast_destination(skb))
+		goto drop;
+
+	return tcp_conn_request(&subflow_request_sock_ops,
+				&subflow_request_sock_ipv6_ops, sk, skb);
+
+drop:
+	tcp_listendrop(sk);
+	return 0; /* don't send reset */
+}
+#endif
+
+static struct sock *subflow_syn_recv_sock(const struct sock *sk,
+					  struct sk_buff *skb,
+					  struct request_sock *req,
+					  struct dst_entry *dst,
+					  struct request_sock *req_unhash,
+					  bool *own_req)
+{
+	struct mptcp_subflow_context *listener = mptcp_subflow_ctx(sk);
+	struct sock *child;
+
+	pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn);
+
+	/* if the sk is MP_CAPABLE, we already received the client key */
+
+	child = listener->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
+						     req_unhash, own_req);
+
+	if (child && *own_req) {
+		if (!mptcp_subflow_ctx(child)) {
+			pr_debug("Closing child socket");
+			inet_sk_set_state(child, TCP_CLOSE);
+			sock_set_flag(child, SOCK_DEAD);
+			inet_csk_destroy_sock(child);
+			child = NULL;
+		}
+	}
+
+	return child;
+}
+
+static struct inet_connection_sock_af_ops subflow_specific;
+
+static struct inet_connection_sock_af_ops *
+subflow_default_af_ops(struct sock *sk)
+{
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (sk->sk_family == AF_INET6)
+		return &subflow_v6_specific;
+#endif
+	return &subflow_specific;
+}
+
+void mptcp_handle_ipv6_mapped(struct sock *sk, bool mapped)
+{
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct inet_connection_sock_af_ops *target;
+
+	target = mapped ? &subflow_v6m_specific : subflow_default_af_ops(sk);
+
+	pr_debug("subflow=%p family=%d ops=%p target=%p mapped=%d",
+	         subflow, sk->sk_family, icsk->icsk_af_ops, target, mapped);
+
+	if (likely(icsk->icsk_af_ops == target))
+		return;
+
+	subflow->icsk_af_ops = icsk->icsk_af_ops;
+	icsk->icsk_af_ops = target;
+#endif
+}
+
 int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 {
 	struct mptcp_subflow_context *subflow;
@@ -22,7 +201,8 @@ int mptcp_subflow_create_socket(struct sock *sk, struct socket **new_sock)
 	struct socket *sf;
 	int err;
 
-	err = sock_create_kern(net, PF_INET, SOCK_STREAM, IPPROTO_TCP, &sf);
+	err = sock_create_kern(net, sk->sk_family, SOCK_STREAM, IPPROTO_TCP,
+			       &sf);
 	if (err)
 		return err;
 
@@ -60,6 +240,7 @@ static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,
 		return NULL;
 
 	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
+	INIT_LIST_HEAD(&ctx->node);
 
 	pr_debug("subflow=%p", ctx);
 
@@ -70,6 +251,7 @@ static struct mptcp_subflow_context *subflow_create_ctx(struct sock *sk,
 
 static int subflow_ulp_init(struct sock *sk)
 {
+	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct mptcp_subflow_context *ctx;
 	struct tcp_sock *tp = tcp_sk(sk);
 	int err = 0;
@@ -91,6 +273,8 @@ static int subflow_ulp_init(struct sock *sk)
 	pr_debug("subflow=%p, family=%d", ctx, sk->sk_family);
 
 	tp->is_mptcp = 1;
+	ctx->icsk_af_ops = icsk->icsk_af_ops;
+	icsk->icsk_af_ops = subflow_default_af_ops(sk);
 out:
 	return err;
 }
@@ -105,15 +289,97 @@ static void subflow_ulp_release(struct sock *sk)
 	kfree_rcu(ctx, rcu);
 }
 
+static void subflow_ulp_fallback(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	icsk->icsk_ulp_ops = NULL;
+	rcu_assign_pointer(icsk->icsk_ulp_data, NULL);
+	tcp_sk(sk)->is_mptcp = 0;
+}
+
+static void subflow_ulp_clone(const struct request_sock *req,
+			      struct sock *newsk,
+			      const gfp_t priority)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct mptcp_subflow_context *old_ctx = mptcp_subflow_ctx(newsk);
+	struct mptcp_subflow_context *new_ctx;
+
+	if (!subflow_req->mp_capable) {
+		subflow_ulp_fallback(newsk);
+		return;
+	}
+
+	new_ctx = subflow_create_ctx(newsk, priority);
+	if (new_ctx == NULL) {
+		subflow_ulp_fallback(newsk);
+		return;
+	}
+
+	new_ctx->conn_finished = 1;
+	new_ctx->icsk_af_ops = old_ctx->icsk_af_ops;
+	new_ctx->mp_capable = 1;
+	new_ctx->fourth_ack = 1;
+	new_ctx->remote_key = subflow_req->remote_key;
+	new_ctx->local_key = subflow_req->local_key;
+}
+
 static struct tcp_ulp_ops subflow_ulp_ops __read_mostly = {
 	.name		= "mptcp",
 	.owner		= THIS_MODULE,
 	.init		= subflow_ulp_init,
 	.release	= subflow_ulp_release,
+	.clone		= subflow_ulp_clone,
 };
 
+static int subflow_ops_init(struct request_sock_ops *subflow_ops)
+{
+	subflow_ops->obj_size = sizeof(struct mptcp_subflow_request_sock);
+	subflow_ops->slab_name = "request_sock_subflow";
+
+	subflow_ops->slab = kmem_cache_create(subflow_ops->slab_name,
+					      subflow_ops->obj_size, 0,
+					      SLAB_ACCOUNT |
+					      SLAB_TYPESAFE_BY_RCU,
+					      NULL);
+	if (!subflow_ops->slab)
+		return -ENOMEM;
+
+	return 0;
+}
+
 void mptcp_subflow_init(void)
 {
+	subflow_request_sock_ops = tcp_request_sock_ops;
+	if (subflow_ops_init(&subflow_request_sock_ops) != 0)
+		panic("MPTCP: failed to init subflow request sock ops\n");
+
+	subflow_request_sock_ipv4_ops = tcp_request_sock_ipv4_ops;
+	subflow_request_sock_ipv4_ops.init_req = subflow_v4_init_req;
+
+	subflow_specific = ipv4_specific;
+	subflow_specific.conn_request = subflow_v4_conn_request;
+	subflow_specific.syn_recv_sock = subflow_syn_recv_sock;
+	subflow_specific.sk_rx_dst_set = subflow_finish_connect;
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	subflow_request_sock_ipv6_ops = tcp_request_sock_ipv6_ops;
+	subflow_request_sock_ipv6_ops.init_req = subflow_v6_init_req;
+
+	subflow_v6_specific = ipv6_specific;
+	subflow_v6_specific.conn_request = subflow_v6_conn_request;
+	subflow_v6_specific.syn_recv_sock = subflow_syn_recv_sock;
+	subflow_v6_specific.sk_rx_dst_set = subflow_finish_connect;
+
+	subflow_v6m_specific = subflow_v6_specific;
+	subflow_v6m_specific.queue_xmit = ipv4_specific.queue_xmit;
+	subflow_v6m_specific.send_check = ipv4_specific.send_check;
+	subflow_v6m_specific.net_header_len = ipv4_specific.net_header_len;
+	subflow_v6m_specific.mtu_reduced = ipv4_specific.mtu_reduced;
+	subflow_v6m_specific.net_frag_header_len = 0;
+#endif
+
 	if (tcp_register_ulp(&subflow_ulp_ops) != 0)
 		panic("MPTCP: failed to register subflows to ULP\n");
 }