// 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>
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
#include <net/ip6_route.h>
#endif
#include <net/mptcp.h>
#include "protocol.h"

static int subflow_rebuild_header(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        int err = 0;

        if (subflow->request_mptcp && !subflow->token) {
                pr_debug("subflow=%p", sk);
                err = mptcp_token_new_connect(sk);
        }

        if (err)
                return err;

        return subflow->icsk_af_ops->rebuild_header(sk);
}

static void subflow_req_destructor(struct request_sock *req)
{
        struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);

        pr_debug("subflow_req=%p", subflow_req);

        if (subflow_req->mp_capable)
                mptcp_token_destroy_request(subflow_req->token);
        tcp_request_sock_ops.destructor(req);
}

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;
        subflow_req->remote_key_valid = 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) {
                int err;

                err = mptcp_token_new_request(req);
                if (err == 0)
                        subflow_req->mp_capable = 1;

                subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
        }
}

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;

                if (skb) {
                        pr_debug("synack seq=%u", TCP_SKB_CB(skb)->seq);
                        subflow->ssn_offset = TCP_SKB_CB(skb)->seq;
                }
        }
}

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 mptcp_subflow_request_sock *subflow_req;
        struct tcp_options_received opt_rx;
        struct sock *child;

        pr_debug("listener=%p, req=%p, conn=%p", listener, req, listener->conn);

        if (tcp_rsk(req)->is_mptcp == 0)
                goto create_child;

        /* if the sk is MP_CAPABLE, we try to fetch the client key */
        subflow_req = mptcp_subflow_rsk(req);
        if (subflow_req->mp_capable) {
                if (TCP_SKB_CB(skb)->seq != subflow_req->ssn_offset + 1) {
                        /* here we can receive and accept an in-window,
                         * out-of-order pkt, which will not carry the MP_CAPABLE
                         * opt even on mptcp enabled paths
                         */
                        goto create_child;
                }

                opt_rx.mptcp.mp_capable = 0;
                mptcp_get_options(skb, &opt_rx);
                if (opt_rx.mptcp.mp_capable) {
                        subflow_req->remote_key = opt_rx.mptcp.sndr_key;
                        subflow_req->remote_key_valid = 1;
                } else {
                        subflow_req->mp_capable = 0;
                }
        }

create_child:
        child = listener->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
                                                     req_unhash, own_req);

        if (child && *own_req) {
                struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(child);

                /* we have null ctx on TCP fallback, not fatal on MPC
                 * handshake
                 */
                if (!ctx)
                        return child;

                if (ctx->mp_capable) {
                        if (mptcp_token_new_accept(ctx->token))
                                goto close_child;
                }
        }

        return child;

close_child:
        pr_debug("closing child socket");
        tcp_send_active_reset(child, GFP_ATOMIC);
        inet_csk_prepare_forced_close(child);
        tcp_done(child);
        return NULL;
}

static struct inet_connection_sock_af_ops subflow_specific;

enum mapping_status {
        MAPPING_OK,
        MAPPING_INVALID,
        MAPPING_EMPTY,
        MAPPING_DATA_FIN
};

static u64 expand_seq(u64 old_seq, u16 old_data_len, u64 seq)
{
        if ((u32)seq == (u32)old_seq)
                return old_seq;

        /* Assume map covers data not mapped yet. */
        return seq | ((old_seq + old_data_len + 1) & GENMASK_ULL(63, 32));
}

static void warn_bad_map(struct mptcp_subflow_context *subflow, u32 ssn)
{
        WARN_ONCE(1, "Bad mapping: ssn=%d map_seq=%d map_data_len=%d",
                  ssn, subflow->map_subflow_seq, subflow->map_data_len);
}

static bool skb_is_fully_mapped(struct sock *ssk, struct sk_buff *skb)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        unsigned int skb_consumed;

        skb_consumed = tcp_sk(ssk)->copied_seq - TCP_SKB_CB(skb)->seq;
        if (WARN_ON_ONCE(skb_consumed >= skb->len))
                return true;

        return skb->len - skb_consumed <= subflow->map_data_len -
                                          mptcp_subflow_get_map_offset(subflow);
}

static bool validate_mapping(struct sock *ssk, struct sk_buff *skb)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        u32 ssn = tcp_sk(ssk)->copied_seq - subflow->ssn_offset;

        if (unlikely(before(ssn, subflow->map_subflow_seq))) {
                /* Mapping covers data later in the subflow stream,
                 * currently unsupported.
                 */
                warn_bad_map(subflow, ssn);
                return false;
        }
        if (unlikely(!before(ssn, subflow->map_subflow_seq +
                                  subflow->map_data_len))) {
                /* Mapping does covers past subflow data, invalid */
                warn_bad_map(subflow, ssn + skb->len);
                return false;
        }
        return true;
}

static enum mapping_status get_mapping_status(struct sock *ssk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct mptcp_ext *mpext;
        struct sk_buff *skb;
        u16 data_len;
        u64 map_seq;

        skb = skb_peek(&ssk->sk_receive_queue);
        if (!skb)
                return MAPPING_EMPTY;

        mpext = mptcp_get_ext(skb);
        if (!mpext || !mpext->use_map) {
                if (!subflow->map_valid && !skb->len) {
                        /* the TCP stack deliver 0 len FIN pkt to the receive
                         * queue, that is the only 0len pkts ever expected here,
                         * and we can admit no mapping only for 0 len pkts
                         */
                        if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
                                WARN_ONCE(1, "0len seq %d:%d flags %x",
                                          TCP_SKB_CB(skb)->seq,
                                          TCP_SKB_CB(skb)->end_seq,
                                          TCP_SKB_CB(skb)->tcp_flags);
                        sk_eat_skb(ssk, skb);
                        return MAPPING_EMPTY;
                }

                if (!subflow->map_valid)
                        return MAPPING_INVALID;

                goto validate_seq;
        }

        pr_debug("seq=%llu is64=%d ssn=%u data_len=%u data_fin=%d",
                 mpext->data_seq, mpext->dsn64, mpext->subflow_seq,
                 mpext->data_len, mpext->data_fin);

        data_len = mpext->data_len;
        if (data_len == 0) {
                pr_err("Infinite mapping not handled");
                return MAPPING_INVALID;
        }

        if (mpext->data_fin == 1) {
                if (data_len == 1) {
                        pr_debug("DATA_FIN with no payload");
                        if (subflow->map_valid) {
                                /* A DATA_FIN might arrive in a DSS
                                 * option before the previous mapping
                                 * has been fully consumed. Continue
                                 * handling the existing mapping.
                                 */
                                skb_ext_del(skb, SKB_EXT_MPTCP);
                                return MAPPING_OK;
                        } else {
                                return MAPPING_DATA_FIN;
                        }
                }

                /* Adjust for DATA_FIN using 1 byte of sequence space */
                data_len--;
        }

        if (!mpext->dsn64) {
                map_seq = expand_seq(subflow->map_seq, subflow->map_data_len,
                                     mpext->data_seq);
                pr_debug("expanded seq=%llu", subflow->map_seq);
        } else {
                map_seq = mpext->data_seq;
        }

        if (subflow->map_valid) {
                /* Allow replacing only with an identical map */
                if (subflow->map_seq == map_seq &&
                    subflow->map_subflow_seq == mpext->subflow_seq &&
                    subflow->map_data_len == data_len) {
                        skb_ext_del(skb, SKB_EXT_MPTCP);
                        return MAPPING_OK;
                }

                /* If this skb data are fully covered by the current mapping,
                 * the new map would need caching, which is not supported
                 */
                if (skb_is_fully_mapped(ssk, skb))
                        return MAPPING_INVALID;

                /* will validate the next map after consuming the current one */
                return MAPPING_OK;
        }

        subflow->map_seq = map_seq;
        subflow->map_subflow_seq = mpext->subflow_seq;
        subflow->map_data_len = data_len;
        subflow->map_valid = 1;
        subflow->mpc_map = mpext->mpc_map;
        pr_debug("new map seq=%llu subflow_seq=%u data_len=%u",
                 subflow->map_seq, subflow->map_subflow_seq,
                 subflow->map_data_len);

validate_seq:
        /* we revalidate valid mapping on new skb, because we must ensure
         * the current skb is completely covered by the available mapping
         */
        if (!validate_mapping(ssk, skb))
                return MAPPING_INVALID;

        skb_ext_del(skb, SKB_EXT_MPTCP);
        return MAPPING_OK;
}

static bool subflow_check_data_avail(struct sock *ssk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        enum mapping_status status;
        struct mptcp_sock *msk;
        struct sk_buff *skb;

        pr_debug("msk=%p ssk=%p data_avail=%d skb=%p", subflow->conn, ssk,
                 subflow->data_avail, skb_peek(&ssk->sk_receive_queue));
        if (subflow->data_avail)
                return true;

        if (!subflow->conn)
                return false;

        msk = mptcp_sk(subflow->conn);
        for (;;) {
                u32 map_remaining;
                size_t delta;
                u64 ack_seq;
                u64 old_ack;

                status = get_mapping_status(ssk);
                pr_debug("msk=%p ssk=%p status=%d", msk, ssk, status);
                if (status == MAPPING_INVALID) {
                        ssk->sk_err = EBADMSG;
                        goto fatal;
                }

                if (status != MAPPING_OK)
                        return false;

                skb = skb_peek(&ssk->sk_receive_queue);
                if (WARN_ON_ONCE(!skb))
                        return false;

                /* if msk lacks the remote key, this subflow must provide an
                 * MP_CAPABLE-based mapping
                 */
                if (unlikely(!READ_ONCE(msk->can_ack))) {
                        if (!subflow->mpc_map) {
                                ssk->sk_err = EBADMSG;
                                goto fatal;
                        }
                        WRITE_ONCE(msk->remote_key, subflow->remote_key);
                        WRITE_ONCE(msk->ack_seq, subflow->map_seq);
                        WRITE_ONCE(msk->can_ack, true);
                }

                old_ack = READ_ONCE(msk->ack_seq);
                ack_seq = mptcp_subflow_get_mapped_dsn(subflow);
                pr_debug("msk ack_seq=%llx subflow ack_seq=%llx", old_ack,
                         ack_seq);
                if (ack_seq == old_ack)
                        break;

                /* only accept in-sequence mapping. Old values are spurious
                 * retransmission; we can hit "future" values on active backup
                 * subflow switch, we relay on retransmissions to get
                 * in-sequence data.
                 * Cuncurrent subflows support will require subflow data
                 * reordering
                 */
                map_remaining = subflow->map_data_len -
                                mptcp_subflow_get_map_offset(subflow);
                if (before64(ack_seq, old_ack))
                        delta = min_t(size_t, old_ack - ack_seq, map_remaining);
                else
                        delta = min_t(size_t, ack_seq - old_ack, map_remaining);

                /* discard mapped data */
                pr_debug("discarding %zu bytes, current map len=%d", delta,
                         map_remaining);
                if (delta) {
                        struct mptcp_read_arg arg = {
                                .msg = NULL,
                        };
                        read_descriptor_t desc = {
                                .count = delta,
                                .arg.data = &arg,
                        };
                        int ret;

                        ret = tcp_read_sock(ssk, &desc, mptcp_read_actor);
                        if (ret < 0) {
                                ssk->sk_err = -ret;
                                goto fatal;
                        }
                        if (ret < delta)
                                return false;
                        if (delta == map_remaining)
                                subflow->map_valid = 0;
                }
        }
        return true;

fatal:
        /* fatal protocol error, close the socket */
        /* This barrier is coupled with smp_rmb() in tcp_poll() */
        smp_wmb();
        ssk->sk_error_report(ssk);
        tcp_set_state(ssk, TCP_CLOSE);
        tcp_send_active_reset(ssk, GFP_ATOMIC);
        return false;
}

bool mptcp_subflow_data_available(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct sk_buff *skb;

        /* check if current mapping is still valid */
        if (subflow->map_valid &&
            mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len) {
                subflow->map_valid = 0;
                subflow->data_avail = 0;

                pr_debug("Done with mapping: seq=%u data_len=%u",
                         subflow->map_subflow_seq,
                         subflow->map_data_len);
        }

        if (!subflow_check_data_avail(sk)) {
                subflow->data_avail = 0;
                return false;
        }

        skb = skb_peek(&sk->sk_receive_queue);
        subflow->data_avail = skb &&
                       before(tcp_sk(sk)->copied_seq, TCP_SKB_CB(skb)->end_seq);
        return subflow->data_avail;
}

static void subflow_data_ready(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct sock *parent = subflow->conn;

        if (!parent || !subflow->mp_capable) {
                subflow->tcp_data_ready(sk);

                if (parent)
                        parent->sk_data_ready(parent);
                return;
        }

        if (mptcp_subflow_data_available(sk)) {
                set_bit(MPTCP_DATA_READY, &mptcp_sk(parent)->flags);

                parent->sk_data_ready(parent);
        }
}

static void subflow_write_space(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct sock *parent = subflow->conn;

        sk_stream_write_space(sk);
        if (parent && sk_stream_is_writeable(sk)) {
                set_bit(MPTCP_SEND_SPACE, &mptcp_sk(parent)->flags);
                smp_mb__after_atomic();
                /* set SEND_SPACE before sk_stream_write_space clears NOSPACE */
                sk_stream_write_space(parent);
        }
}

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;
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
void mptcpv6_handle_mapped(struct sock *sk, bool mapped)
{
        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;
        struct net *net = sock_net(sk);
        struct socket *sf;
        int err;

        err = sock_create_kern(net, sk->sk_family, SOCK_STREAM, IPPROTO_TCP,
                               &sf);
        if (err)
                return err;

        lock_sock(sf->sk);

        /* kernel sockets do not by default acquire net ref, but TCP timer
         * needs it.
         */
        sf->sk->sk_net_refcnt = 1;
        get_net(net);
#ifdef CONFIG_PROC_FS
        this_cpu_add(*net->core.sock_inuse, 1);
#endif
        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;
        sock_hold(sk);
        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);
        INIT_LIST_HEAD(&ctx->node);

        pr_debug("subflow=%p", ctx);

        ctx->tcp_sock = sk;

        return ctx;
}

static void __subflow_state_change(struct sock *sk)
{
        struct socket_wq *wq;

        rcu_read_lock();
        wq = rcu_dereference(sk->sk_wq);
        if (skwq_has_sleeper(wq))
                wake_up_interruptible_all(&wq->wait);
        rcu_read_unlock();
}

static bool subflow_is_done(const struct sock *sk)
{
        return sk->sk_shutdown & RCV_SHUTDOWN || sk->sk_state == TCP_CLOSE;
}

static void subflow_state_change(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct sock *parent = READ_ONCE(subflow->conn);

        __subflow_state_change(sk);

        /* as recvmsg() does not acquire the subflow socket for ssk selection
         * a fin packet carrying a DSS can be unnoticed if we don't trigger
         * the data available machinery here.
         */
        if (parent && subflow->mp_capable && mptcp_subflow_data_available(sk)) {
                set_bit(MPTCP_DATA_READY, &mptcp_sk(parent)->flags);

                parent->sk_data_ready(parent);
        }

        if (parent && !(parent->sk_shutdown & RCV_SHUTDOWN) &&
            !subflow->rx_eof && subflow_is_done(sk)) {
                subflow->rx_eof = 1;
                parent->sk_shutdown |= RCV_SHUTDOWN;
                __subflow_state_change(parent);
        }
}

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;

        /* 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;
        ctx->icsk_af_ops = icsk->icsk_af_ops;
        icsk->icsk_af_ops = subflow_default_af_ops(sk);
        ctx->tcp_data_ready = sk->sk_data_ready;
        ctx->tcp_state_change = sk->sk_state_change;
        ctx->tcp_write_space = sk->sk_write_space;
        sk->sk_data_ready = subflow_data_ready;
        sk->sk_write_space = subflow_write_space;
        sk->sk_state_change = subflow_state_change;
out:
        return err;
}

static void subflow_ulp_release(struct sock *sk)
{
        struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(sk);

        if (!ctx)
                return;

        if (ctx->conn)
                sock_put(ctx->conn);

        kfree_rcu(ctx, rcu);
}

static void subflow_ulp_fallback(struct sock *sk,
                                 struct mptcp_subflow_context *old_ctx)
{
        struct inet_connection_sock *icsk = inet_csk(sk);

        mptcp_subflow_tcp_fallback(sk, old_ctx);
        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 (!tcp_rsk(req)->is_mptcp || !subflow_req->mp_capable) {
                subflow_ulp_fallback(newsk, old_ctx);
                return;
        }

        new_ctx = subflow_create_ctx(newsk, priority);
        if (!new_ctx) {
                subflow_ulp_fallback(newsk, old_ctx);
                return;
        }

        /* see comments in subflow_syn_recv_sock(), MPTCP connection is fully
         * established only after we receive the remote key
         */
        new_ctx->conn_finished = 1;
        new_ctx->icsk_af_ops = old_ctx->icsk_af_ops;
        new_ctx->tcp_data_ready = old_ctx->tcp_data_ready;
        new_ctx->tcp_state_change = old_ctx->tcp_state_change;
        new_ctx->tcp_write_space = old_ctx->tcp_write_space;
        new_ctx->mp_capable = 1;
        new_ctx->fourth_ack = subflow_req->remote_key_valid;
        new_ctx->can_ack = subflow_req->remote_key_valid;
        new_ctx->remote_key = subflow_req->remote_key;
        new_ctx->local_key = subflow_req->local_key;
        new_ctx->token = subflow_req->token;
        new_ctx->ssn_offset = subflow_req->ssn_offset;
        new_ctx->idsn = subflow_req->idsn;
}

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;

        subflow_ops->destructor = subflow_req_destructor;

        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;
        subflow_specific.rebuild_header = subflow_rebuild_header;

#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_v6_specific.rebuild_header = subflow_rebuild_header;

        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");
}