// 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 <crypto/algapi.h>
#include <crypto/sha2.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>
#include <net/transp_v6.h>
#endif
#include <net/mptcp.h>
#include <uapi/linux/mptcp.h>
#include "protocol.h"
#include "mib.h"

#include <trace/events/mptcp.h>

static void mptcp_subflow_ops_undo_override(struct sock *ssk);

static void SUBFLOW_REQ_INC_STATS(struct request_sock *req,
                                  enum linux_mptcp_mib_field field)
{
        MPTCP_INC_STATS(sock_net(req_to_sk(req)), field);
}

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->msk)
                sock_put((struct sock *)subflow_req->msk);

        mptcp_token_destroy_request(req);
        tcp_request_sock_ops.destructor(req);
}

static void subflow_generate_hmac(u64 key1, u64 key2, u32 nonce1, u32 nonce2,
                                  void *hmac)
{
        u8 msg[8];

        put_unaligned_be32(nonce1, &msg[0]);
        put_unaligned_be32(nonce2, &msg[4]);

        mptcp_crypto_hmac_sha(key1, key2, msg, 8, hmac);
}

static bool mptcp_can_accept_new_subflow(const struct mptcp_sock *msk)
{
        return mptcp_is_fully_established((void *)msk) &&
               READ_ONCE(msk->pm.accept_subflow);
}

/* validate received token and create truncated hmac and nonce for SYN-ACK */
static void subflow_req_create_thmac(struct mptcp_subflow_request_sock *subflow_req)
{
        struct mptcp_sock *msk = subflow_req->msk;
        u8 hmac[SHA256_DIGEST_SIZE];

        get_random_bytes(&subflow_req->local_nonce, sizeof(u32));

        subflow_generate_hmac(msk->local_key, msk->remote_key,
                              subflow_req->local_nonce,
                              subflow_req->remote_nonce, hmac);

        subflow_req->thmac = get_unaligned_be64(hmac);
}

static struct mptcp_sock *subflow_token_join_request(struct request_sock *req)
{
        struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
        struct mptcp_sock *msk;
        int local_id;

        msk = mptcp_token_get_sock(sock_net(req_to_sk(req)), subflow_req->token);
        if (!msk) {
                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINNOTOKEN);
                return NULL;
        }

        local_id = mptcp_pm_get_local_id(msk, (struct sock_common *)req);
        if (local_id < 0) {
                sock_put((struct sock *)msk);
                return NULL;
        }
        subflow_req->local_id = local_id;

        return msk;
}

static void subflow_init_req(struct request_sock *req, const struct sock *sk_listener)
{
        struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);

        subflow_req->mp_capable = 0;
        subflow_req->mp_join = 0;
        subflow_req->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk_listener));
        subflow_req->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk_listener));
        subflow_req->msk = NULL;
        mptcp_token_init_request(req);
}

static bool subflow_use_different_sport(struct mptcp_sock *msk, const struct sock *sk)
{
        return inet_sk(sk)->inet_sport != inet_sk((struct sock *)msk)->inet_sport;
}

static void subflow_add_reset_reason(struct sk_buff *skb, u8 reason)
{
        struct mptcp_ext *mpext = skb_ext_add(skb, SKB_EXT_MPTCP);

        if (mpext) {
                memset(mpext, 0, sizeof(*mpext));
                mpext->reset_reason = reason;
        }
}

/* Init mptcp request socket.
 *
 * Returns an error code if a JOIN has failed and a TCP reset
 * should be sent.
 */
static int subflow_check_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 mptcp_options_received mp_opt;
        bool opt_mp_capable, opt_mp_join;

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

#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 -EINVAL;
#endif

        mptcp_get_options(skb, &mp_opt);

        opt_mp_capable = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPC);
        opt_mp_join = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ);
        if (opt_mp_capable) {
                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVE);

                if (opt_mp_join)
                        return 0;
        } else if (opt_mp_join) {
                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINSYNRX);
        }

        if (opt_mp_capable && listener->request_mptcp) {
                int err, retries = MPTCP_TOKEN_MAX_RETRIES;

                subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
again:
                do {
                        get_random_bytes(&subflow_req->local_key, sizeof(subflow_req->local_key));
                } while (subflow_req->local_key == 0);

                if (unlikely(req->syncookie)) {
                        mptcp_crypto_key_sha(subflow_req->local_key,
                                             &subflow_req->token,
                                             &subflow_req->idsn);
                        if (mptcp_token_exists(subflow_req->token)) {
                                if (retries-- > 0)
                                        goto again;
                                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_TOKENFALLBACKINIT);
                        } else {
                                subflow_req->mp_capable = 1;
                        }
                        return 0;
                }

                err = mptcp_token_new_request(req);
                if (err == 0)
                        subflow_req->mp_capable = 1;
                else if (retries-- > 0)
                        goto again;
                else
                        SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_TOKENFALLBACKINIT);

        } else if (opt_mp_join && listener->request_mptcp) {
                subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq;
                subflow_req->mp_join = 1;
                subflow_req->backup = mp_opt.backup;
                subflow_req->remote_id = mp_opt.join_id;
                subflow_req->token = mp_opt.token;
                subflow_req->remote_nonce = mp_opt.nonce;
                subflow_req->msk = subflow_token_join_request(req);

                /* Can't fall back to TCP in this case. */
                if (!subflow_req->msk) {
                        subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
                        return -EPERM;
                }

                if (subflow_use_different_sport(subflow_req->msk, sk_listener)) {
                        pr_debug("syn inet_sport=%d %d",
                                 ntohs(inet_sk(sk_listener)->inet_sport),
                                 ntohs(inet_sk((struct sock *)subflow_req->msk)->inet_sport));
                        if (!mptcp_pm_sport_in_anno_list(subflow_req->msk, sk_listener)) {
                                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MISMATCHPORTSYNRX);
                                return -EPERM;
                        }
                        SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINPORTSYNRX);
                }

                subflow_req_create_thmac(subflow_req);

                if (unlikely(req->syncookie)) {
                        if (mptcp_can_accept_new_subflow(subflow_req->msk))
                                subflow_init_req_cookie_join_save(subflow_req, skb);
                        else
                                return -EPERM;
                }

                pr_debug("token=%u, remote_nonce=%u msk=%p", subflow_req->token,
                         subflow_req->remote_nonce, subflow_req->msk);
        }

        return 0;
}

int mptcp_subflow_init_cookie_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 mptcp_options_received mp_opt;
        bool opt_mp_capable, opt_mp_join;
        int err;

        subflow_init_req(req, sk_listener);
        mptcp_get_options(skb, &mp_opt);

        opt_mp_capable = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPC);
        opt_mp_join = !!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ);
        if (opt_mp_capable && opt_mp_join)
                return -EINVAL;

        if (opt_mp_capable && listener->request_mptcp) {
                if (mp_opt.sndr_key == 0)
                        return -EINVAL;

                subflow_req->local_key = mp_opt.rcvr_key;
                err = mptcp_token_new_request(req);
                if (err)
                        return err;

                subflow_req->mp_capable = 1;
                subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
        } else if (opt_mp_join && listener->request_mptcp) {
                if (!mptcp_token_join_cookie_init_state(subflow_req, skb))
                        return -EINVAL;

                subflow_req->mp_join = 1;
                subflow_req->ssn_offset = TCP_SKB_CB(skb)->seq - 1;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(mptcp_subflow_init_cookie_req);

static struct dst_entry *subflow_v4_route_req(const struct sock *sk,
                                              struct sk_buff *skb,
                                              struct flowi *fl,
                                              struct request_sock *req)
{
        struct dst_entry *dst;
        int err;

        tcp_rsk(req)->is_mptcp = 1;
        subflow_init_req(req, sk);

        dst = tcp_request_sock_ipv4_ops.route_req(sk, skb, fl, req);
        if (!dst)
                return NULL;

        err = subflow_check_req(req, sk, skb);
        if (err == 0)
                return dst;

        dst_release(dst);
        if (!req->syncookie)
                tcp_request_sock_ops.send_reset(sk, skb);
        return NULL;
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static struct dst_entry *subflow_v6_route_req(const struct sock *sk,
                                              struct sk_buff *skb,
                                              struct flowi *fl,
                                              struct request_sock *req)
{
        struct dst_entry *dst;
        int err;

        tcp_rsk(req)->is_mptcp = 1;
        subflow_init_req(req, sk);

        dst = tcp_request_sock_ipv6_ops.route_req(sk, skb, fl, req);
        if (!dst)
                return NULL;

        err = subflow_check_req(req, sk, skb);
        if (err == 0)
                return dst;

        dst_release(dst);
        if (!req->syncookie)
                tcp6_request_sock_ops.send_reset(sk, skb);
        return NULL;
}
#endif

/* validate received truncated hmac and create hmac for third ACK */
static bool subflow_thmac_valid(struct mptcp_subflow_context *subflow)
{
        u8 hmac[SHA256_DIGEST_SIZE];
        u64 thmac;

        subflow_generate_hmac(subflow->remote_key, subflow->local_key,
                              subflow->remote_nonce, subflow->local_nonce,
                              hmac);

        thmac = get_unaligned_be64(hmac);
        pr_debug("subflow=%p, token=%u, thmac=%llu, subflow->thmac=%llu\n",
                 subflow, subflow->token, thmac, subflow->thmac);

        return thmac == subflow->thmac;
}

void mptcp_subflow_reset(struct sock *ssk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct sock *sk = subflow->conn;

        /* must hold: tcp_done() could drop last reference on parent */
        sock_hold(sk);

        tcp_set_state(ssk, TCP_CLOSE);
        tcp_send_active_reset(ssk, GFP_ATOMIC);
        tcp_done(ssk);
        if (!test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &mptcp_sk(sk)->flags) &&
            schedule_work(&mptcp_sk(sk)->work))
                return; /* worker will put sk for us */

        sock_put(sk);
}

static bool subflow_use_different_dport(struct mptcp_sock *msk, const struct sock *sk)
{
        return inet_sk(sk)->inet_dport != inet_sk((struct sock *)msk)->inet_dport;
}

void __mptcp_set_connected(struct sock *sk)
{
        if (sk->sk_state == TCP_SYN_SENT) {
                inet_sk_state_store(sk, TCP_ESTABLISHED);
                sk->sk_state_change(sk);
        }
}

static void mptcp_set_connected(struct sock *sk)
{
        mptcp_data_lock(sk);
        if (!sock_owned_by_user(sk))
                __mptcp_set_connected(sk);
        else
                __set_bit(MPTCP_CONNECTED, &mptcp_sk(sk)->cb_flags);
        mptcp_data_unlock(sk);
}

static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_options_received mp_opt;
        struct sock *parent = subflow->conn;

        subflow->icsk_af_ops->sk_rx_dst_set(sk, skb);

        /* be sure no special action on any packet other than syn-ack */
        if (subflow->conn_finished)
                return;

        mptcp_propagate_sndbuf(parent, sk);
        subflow->rel_write_seq = 1;
        subflow->conn_finished = 1;
        subflow->ssn_offset = TCP_SKB_CB(skb)->seq;
        pr_debug("subflow=%p synack seq=%x", subflow, subflow->ssn_offset);

        mptcp_get_options(skb, &mp_opt);
        if (subflow->request_mptcp) {
                if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPC)) {
                        MPTCP_INC_STATS(sock_net(sk),
                                        MPTCP_MIB_MPCAPABLEACTIVEFALLBACK);
                        mptcp_do_fallback(sk);
                        pr_fallback(mptcp_sk(subflow->conn));
                        goto fallback;
                }

                if (mp_opt.suboptions & OPTION_MPTCP_CSUMREQD)
                        WRITE_ONCE(mptcp_sk(parent)->csum_enabled, true);
                if (mp_opt.deny_join_id0)
                        WRITE_ONCE(mptcp_sk(parent)->pm.remote_deny_join_id0, true);
                subflow->mp_capable = 1;
                subflow->can_ack = 1;
                subflow->remote_key = mp_opt.sndr_key;
                pr_debug("subflow=%p, remote_key=%llu", subflow,
                         subflow->remote_key);
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEACTIVEACK);
                mptcp_finish_connect(sk);
                mptcp_set_connected(parent);
        } else if (subflow->request_join) {
                u8 hmac[SHA256_DIGEST_SIZE];

                if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ)) {
                        subflow->reset_reason = MPTCP_RST_EMPTCP;
                        goto do_reset;
                }

                subflow->backup = mp_opt.backup;
                subflow->thmac = mp_opt.thmac;
                subflow->remote_nonce = mp_opt.nonce;
                pr_debug("subflow=%p, thmac=%llu, remote_nonce=%u backup=%d",
                         subflow, subflow->thmac, subflow->remote_nonce,
                         subflow->backup);

                if (!subflow_thmac_valid(subflow)) {
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINACKMAC);
                        subflow->reset_reason = MPTCP_RST_EMPTCP;
                        goto do_reset;
                }

                if (!mptcp_finish_join(sk))
                        goto do_reset;

                subflow_generate_hmac(subflow->local_key, subflow->remote_key,
                                      subflow->local_nonce,
                                      subflow->remote_nonce,
                                      hmac);
                memcpy(subflow->hmac, hmac, MPTCPOPT_HMAC_LEN);

                subflow->mp_join = 1;
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINSYNACKRX);

                if (subflow_use_different_dport(mptcp_sk(parent), sk)) {
                        pr_debug("synack inet_dport=%d %d",
                                 ntohs(inet_sk(sk)->inet_dport),
                                 ntohs(inet_sk(parent)->inet_dport));
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINPORTSYNACKRX);
                }
        } else if (mptcp_check_fallback(sk)) {
fallback:
                mptcp_rcv_space_init(mptcp_sk(parent), sk);
                mptcp_set_connected(parent);
        }
        return;

do_reset:
        subflow->reset_transient = 0;
        mptcp_subflow_reset(sk);
}

static void subflow_set_local_id(struct mptcp_subflow_context *subflow, int local_id)
{
        subflow->local_id = local_id;
        subflow->local_id_valid = 1;
}

static int subflow_chk_local_id(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        int err;

        if (likely(subflow->local_id_valid))
                return 0;

        err = mptcp_pm_get_local_id(msk, (struct sock_common *)sk);
        if (err < 0)
                return err;

        subflow_set_local_id(subflow, err);
        return 0;
}

static int subflow_rebuild_header(struct sock *sk)
{
        int err = subflow_chk_local_id(sk);

        if (unlikely(err < 0))
                return err;

        return inet_sk_rebuild_header(sk);
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static int subflow_v6_rebuild_header(struct sock *sk)
{
        int err = subflow_chk_local_id(sk);

        if (unlikely(err < 0))
                return err;

        return inet6_sk_rebuild_header(sk);
}
#endif

struct request_sock_ops mptcp_subflow_request_sock_ops;
static struct tcp_request_sock_ops subflow_request_sock_ipv4_ops __ro_after_init;

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(&mptcp_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 __ro_after_init;
static struct inet_connection_sock_af_ops subflow_v6_specific __ro_after_init;
static struct inet_connection_sock_af_ops subflow_v6m_specific __ro_after_init;
static struct proto tcpv6_prot_override;

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;

        if (ipv6_addr_v4mapped(&ipv6_hdr(skb)->saddr)) {
                __IP6_INC_STATS(sock_net(sk), NULL, IPSTATS_MIB_INHDRERRORS);
                return 0;
        }

        return tcp_conn_request(&mptcp_subflow_request_sock_ops,
                                &subflow_request_sock_ipv6_ops, sk, skb);

drop:
        tcp_listendrop(sk);
        return 0; /* don't send reset */
}
#endif

/* validate hmac received in third ACK */
static bool subflow_hmac_valid(const struct request_sock *req,
                               const struct mptcp_options_received *mp_opt)
{
        const struct mptcp_subflow_request_sock *subflow_req;
        u8 hmac[SHA256_DIGEST_SIZE];
        struct mptcp_sock *msk;

        subflow_req = mptcp_subflow_rsk(req);
        msk = subflow_req->msk;
        if (!msk)
                return false;

        subflow_generate_hmac(msk->remote_key, msk->local_key,
                              subflow_req->remote_nonce,
                              subflow_req->local_nonce, hmac);

        return !crypto_memneq(hmac, mp_opt->hmac, MPTCPOPT_HMAC_LEN);
}

static void mptcp_sock_destruct(struct sock *sk)
{
        /* if new mptcp socket isn't accepted, it is free'd
         * from the tcp listener sockets request queue, linked
         * from req->sk.  The tcp socket is released.
         * This calls the ULP release function which will
         * also remove the mptcp socket, via
         * sock_put(ctx->conn).
         *
         * Problem is that the mptcp socket will be in
         * ESTABLISHED state and will not have the SOCK_DEAD flag.
         * Both result in warnings from inet_sock_destruct.
         */
        if ((1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
                sk->sk_state = TCP_CLOSE;
                WARN_ON_ONCE(sk->sk_socket);
                sock_orphan(sk);
        }

        mptcp_destroy_common(mptcp_sk(sk));
        inet_sock_destruct(sk);
}

static void mptcp_force_close(struct sock *sk)
{
        /* the msk is not yet exposed to user-space */
        inet_sk_state_store(sk, TCP_CLOSE);
        sk_common_release(sk);
}

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;

        mptcp_subflow_ops_undo_override(sk);
}

static void subflow_drop_ctx(struct sock *ssk)
{
        struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(ssk);

        if (!ctx)
                return;

        subflow_ulp_fallback(ssk, ctx);
        if (ctx->conn)
                sock_put(ctx->conn);

        kfree_rcu(ctx, rcu);
}

void mptcp_subflow_fully_established(struct mptcp_subflow_context *subflow,
                                     struct mptcp_options_received *mp_opt)
{
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);

        subflow->remote_key = mp_opt->sndr_key;
        subflow->fully_established = 1;
        subflow->can_ack = 1;
        WRITE_ONCE(msk->fully_established, true);
}

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 mptcp_options_received mp_opt;
        bool fallback, fallback_is_fatal;
        struct sock *new_msk = NULL;
        struct sock *child;

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

        /* After child creation we must look for MPC even when options
         * are not parsed
         */
        mp_opt.suboptions = 0;

        /* hopefully temporary handling for MP_JOIN+syncookie */
        subflow_req = mptcp_subflow_rsk(req);
        fallback_is_fatal = tcp_rsk(req)->is_mptcp && subflow_req->mp_join;
        fallback = !tcp_rsk(req)->is_mptcp;
        if (fallback)
                goto create_child;

        /* if the sk is MP_CAPABLE, we try to fetch the client key */
        if (subflow_req->mp_capable) {
                /* we can receive and accept an in-window, out-of-order pkt,
                 * which may not carry the MP_CAPABLE opt even on mptcp enabled
                 * paths: always try to extract the peer key, and fallback
                 * for packets missing it.
                 * Even OoO DSS packets coming legitly after dropped or
                 * reordered MPC will cause fallback, but we don't have other
                 * options.
                 */
                mptcp_get_options(skb, &mp_opt);
                if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPC)) {
                        fallback = true;
                        goto create_child;
                }

                new_msk = mptcp_sk_clone(listener->conn, &mp_opt, req);
                if (!new_msk)
                        fallback = true;
        } else if (subflow_req->mp_join) {
                mptcp_get_options(skb, &mp_opt);
                if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ) ||
                    !subflow_hmac_valid(req, &mp_opt) ||
                    !mptcp_can_accept_new_subflow(subflow_req->msk)) {
                        SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC);
                        fallback = true;
                }
        }

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);

                tcp_rsk(req)->drop_req = false;

                /* we need to fallback on ctx allocation failure and on pre-reqs
                 * checking above. In the latter scenario we additionally need
                 * to reset the context to non MPTCP status.
                 */
                if (!ctx || fallback) {
                        if (fallback_is_fatal) {
                                subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
                                goto dispose_child;
                        }

                        subflow_drop_ctx(child);
                        goto out;
                }

                /* ssk inherits options of listener sk */
                ctx->setsockopt_seq = listener->setsockopt_seq;

                if (ctx->mp_capable) {
                        /* this can't race with mptcp_close(), as the msk is
                         * not yet exposted to user-space
                         */
                        inet_sk_state_store((void *)new_msk, TCP_ESTABLISHED);

                        /* record the newly created socket as the first msk
                         * subflow, but don't link it yet into conn_list
                         */
                        WRITE_ONCE(mptcp_sk(new_msk)->first, child);

                        /* new mpc subflow takes ownership of the newly
                         * created mptcp socket
                         */
                        new_msk->sk_destruct = mptcp_sock_destruct;
                        mptcp_sk(new_msk)->setsockopt_seq = ctx->setsockopt_seq;
                        mptcp_pm_new_connection(mptcp_sk(new_msk), child, 1);
                        mptcp_token_accept(subflow_req, mptcp_sk(new_msk));
                        ctx->conn = new_msk;
                        new_msk = NULL;

                        /* with OoO packets we can reach here without ingress
                         * mpc option
                         */
                        if (mp_opt.suboptions & OPTIONS_MPTCP_MPC)
                                mptcp_subflow_fully_established(ctx, &mp_opt);
                } else if (ctx->mp_join) {
                        struct mptcp_sock *owner;

                        owner = subflow_req->msk;
                        if (!owner) {
                                subflow_add_reset_reason(skb, MPTCP_RST_EPROHIBIT);
                                goto dispose_child;
                        }

                        /* move the msk reference ownership to the subflow */
                        subflow_req->msk = NULL;
                        ctx->conn = (struct sock *)owner;

                        if (subflow_use_different_sport(owner, sk)) {
                                pr_debug("ack inet_sport=%d %d",
                                         ntohs(inet_sk(sk)->inet_sport),
                                         ntohs(inet_sk((struct sock *)owner)->inet_sport));
                                if (!mptcp_pm_sport_in_anno_list(owner, sk)) {
                                        SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MISMATCHPORTACKRX);
                                        goto dispose_child;
                                }
                                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINPORTACKRX);
                        }

                        if (!mptcp_finish_join(child))
                                goto dispose_child;

                        SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKRX);
                        tcp_rsk(req)->drop_req = true;
                }
        }

out:
        /* dispose of the left over mptcp master, if any */
        if (unlikely(new_msk))
                mptcp_force_close(new_msk);

        /* check for expected invariant - should never trigger, just help
         * catching eariler subtle bugs
         */
        WARN_ON_ONCE(child && *own_req && tcp_sk(child)->is_mptcp &&
                     (!mptcp_subflow_ctx(child) ||
                      !mptcp_subflow_ctx(child)->conn));
        return child;

dispose_child:
        subflow_drop_ctx(child);
        tcp_rsk(req)->drop_req = true;
        inet_csk_prepare_for_destroy_sock(child);
        tcp_done(child);
        req->rsk_ops->send_reset(sk, skb);

        /* The last child reference will be released by the caller */
        return child;
}

static struct inet_connection_sock_af_ops subflow_specific __ro_after_init;
static struct proto tcp_prot_override;

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

static void dbg_bad_map(struct mptcp_subflow_context *subflow, u32 ssn)
{
        pr_debug("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.
                 */
                dbg_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 */
                dbg_bad_map(subflow, ssn);
                return false;
        }
        return true;
}

static enum mapping_status validate_data_csum(struct sock *ssk, struct sk_buff *skb,
                                              bool csum_reqd)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        u32 offset, seq, delta;
        __sum16 csum;
        int len;

        if (!csum_reqd)
                return MAPPING_OK;

        /* mapping already validated on previous traversal */
        if (subflow->map_csum_len == subflow->map_data_len)
                return MAPPING_OK;

        /* traverse the receive queue, ensuring it contains a full
         * DSS mapping and accumulating the related csum.
         * Preserve the accoumlate csum across multiple calls, to compute
         * the csum only once
         */
        delta = subflow->map_data_len - subflow->map_csum_len;
        for (;;) {
                seq = tcp_sk(ssk)->copied_seq + subflow->map_csum_len;
                offset = seq - TCP_SKB_CB(skb)->seq;

                /* if the current skb has not been accounted yet, csum its contents
                 * up to the amount covered by the current DSS
                 */
                if (offset < skb->len) {
                        __wsum csum;

                        len = min(skb->len - offset, delta);
                        csum = skb_checksum(skb, offset, len, 0);
                        subflow->map_data_csum = csum_block_add(subflow->map_data_csum, csum,
                                                                subflow->map_csum_len);

                        delta -= len;
                        subflow->map_csum_len += len;
                }
                if (delta == 0)
                        break;

                if (skb_queue_is_last(&ssk->sk_receive_queue, skb)) {
                        /* if this subflow is closed, the partial mapping
                         * will be never completed; flush the pending skbs, so
                         * that subflow_sched_work_if_closed() can kick in
                         */
                        if (unlikely(ssk->sk_state == TCP_CLOSE))
                                while ((skb = skb_peek(&ssk->sk_receive_queue)))
                                        sk_eat_skb(ssk, skb);

                        /* not enough data to validate the csum */
                        return MAPPING_EMPTY;
                }

                /* the DSS mapping for next skbs will be validated later,
                 * when a get_mapping_status call will process such skb
                 */
                skb = skb->next;
        }

        /* note that 'map_data_len' accounts only for the carried data, does
         * not include the eventual seq increment due to the data fin,
         * while the pseudo header requires the original DSS data len,
         * including that
         */
        csum = __mptcp_make_csum(subflow->map_seq,
                                 subflow->map_subflow_seq,
                                 subflow->map_data_len + subflow->map_data_fin,
                                 subflow->map_data_csum);
        if (unlikely(csum)) {
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DATACSUMERR);
                if (subflow->mp_join || subflow->valid_csum_seen) {
                        subflow->send_mp_fail = 1;
                        MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_MPFAILTX);
                }
                return subflow->mp_join ? MAPPING_INVALID : MAPPING_DUMMY;
        }

        subflow->valid_csum_seen = 1;
        return MAPPING_OK;
}

static enum mapping_status get_mapping_status(struct sock *ssk,
                                              struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        bool csum_reqd = READ_ONCE(msk->csum_enabled);
        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;

        if (mptcp_check_fallback(ssk))
                return MAPPING_DUMMY;

        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;
        }

        trace_get_mapping_status(mpext);

        data_len = mpext->data_len;
        if (data_len == 0) {
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_INFINITEMAPRX);
                return MAPPING_INVALID;
        }

        if (mpext->data_fin == 1) {
                if (data_len == 1) {
                        bool updated = mptcp_update_rcv_data_fin(msk, mpext->data_seq,
                                                                 mpext->dsn64);
                        pr_debug("DATA_FIN with no payload seq=%llu", mpext->data_seq);
                        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 {
                                if (updated && schedule_work(&msk->work))
                                        sock_hold((struct sock *)msk);

                                return MAPPING_DATA_FIN;
                        }
                } else {
                        u64 data_fin_seq = mpext->data_seq + data_len - 1;

                        /* If mpext->data_seq is a 32-bit value, data_fin_seq
                         * must also be limited to 32 bits.
                         */
                        if (!mpext->dsn64)
                                data_fin_seq &= GENMASK_ULL(31, 0);

                        mptcp_update_rcv_data_fin(msk, data_fin_seq, mpext->dsn64);
                        pr_debug("DATA_FIN with mapping seq=%llu dsn64=%d",
                                 data_fin_seq, mpext->dsn64);
                }

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

        map_seq = mptcp_expand_seq(READ_ONCE(msk->ack_seq), mpext->data_seq, mpext->dsn64);
        WRITE_ONCE(mptcp_sk(subflow->conn)->use_64bit_ack, !!mpext->dsn64);

        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 &&
                    subflow->map_csum_reqd == mpext->csum_reqd) {
                        skb_ext_del(skb, SKB_EXT_MPTCP);
                        goto validate_csum;
                }

                /* 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)) {
                        MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSNOMATCH);
                        return MAPPING_INVALID;
                }

                /* will validate the next map after consuming the current one */
                goto validate_csum;
        }

        subflow->map_seq = map_seq;
        subflow->map_subflow_seq = mpext->subflow_seq;
        subflow->map_data_len = data_len;
        subflow->map_valid = 1;
        subflow->map_data_fin = mpext->data_fin;
        subflow->mpc_map = mpext->mpc_map;
        subflow->map_csum_reqd = mpext->csum_reqd;
        subflow->map_csum_len = 0;
        subflow->map_data_csum = csum_unfold(mpext->csum);

        /* Cfr RFC 8684 Section 3.3.0 */
        if (unlikely(subflow->map_csum_reqd != csum_reqd))
                return MAPPING_INVALID;

        pr_debug("new map seq=%llu subflow_seq=%u data_len=%u csum=%d:%u",
                 subflow->map_seq, subflow->map_subflow_seq,
                 subflow->map_data_len, subflow->map_csum_reqd,
                 subflow->map_data_csum);

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)) {
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSTCPMISMATCH);
                return MAPPING_INVALID;
        }

        skb_ext_del(skb, SKB_EXT_MPTCP);

validate_csum:
        return validate_data_csum(ssk, skb, csum_reqd);
}

static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
                                       u64 limit)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        bool fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
        u32 incr;

        incr = limit >= skb->len ? skb->len + fin : limit;

        pr_debug("discarding=%d len=%d seq=%d", incr, skb->len,
                 subflow->map_subflow_seq);
        MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DUPDATA);
        tcp_sk(ssk)->copied_seq += incr;
        if (!before(tcp_sk(ssk)->copied_seq, TCP_SKB_CB(skb)->end_seq))
                sk_eat_skb(ssk, skb);
        if (mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len)
                subflow->map_valid = 0;
}

/* sched mptcp worker to remove the subflow if no more data is pending */
static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ssk)
{
        struct sock *sk = (struct sock *)msk;

        if (likely(ssk->sk_state != TCP_CLOSE))
                return;

        if (skb_queue_empty(&ssk->sk_receive_queue) &&
            !test_and_set_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags)) {
                sock_hold(sk);
                if (!schedule_work(&msk->work))
                        sock_put(sk);
        }
}

static bool subflow_can_fallback(struct mptcp_subflow_context *subflow)
{
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);

        if (subflow->mp_join)
                return false;
        else if (READ_ONCE(msk->csum_enabled))
                return !subflow->valid_csum_seen;
        else
                return !subflow->fully_established;
}

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;

        if (!skb_peek(&ssk->sk_receive_queue))
                WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
        if (subflow->data_avail)
                return true;

        msk = mptcp_sk(subflow->conn);
        for (;;) {
                u64 ack_seq;
                u64 old_ack;

                status = get_mapping_status(ssk, msk);
                trace_subflow_check_data_avail(status, skb_peek(&ssk->sk_receive_queue));
                if (unlikely(status == MAPPING_INVALID))
                        goto fallback;

                if (unlikely(status == MAPPING_DUMMY))
                        goto fallback;

                if (status != MAPPING_OK)
                        goto no_data;

                skb = skb_peek(&ssk->sk_receive_queue);
                if (WARN_ON_ONCE(!skb))
                        goto no_data;

                /* 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)
                                goto fallback;
                        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 (unlikely(before64(ack_seq, old_ack))) {
                        mptcp_subflow_discard_data(ssk, skb, old_ack - ack_seq);
                        continue;
                }

                WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_DATA_AVAIL);
                break;
        }
        return true;

no_data:
        subflow_sched_work_if_closed(msk, ssk);
        return false;

fallback:
        /* RFC 8684 section 3.7. */
        if (subflow->send_mp_fail) {
                if (mptcp_has_another_subflow(ssk)) {
                        while ((skb = skb_peek(&ssk->sk_receive_queue)))
                                sk_eat_skb(ssk, skb);
                }
                ssk->sk_err = EBADMSG;
                tcp_set_state(ssk, TCP_CLOSE);
                subflow->reset_transient = 0;
                subflow->reset_reason = MPTCP_RST_EMIDDLEBOX;
                tcp_send_active_reset(ssk, GFP_ATOMIC);
                WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
                return true;
        }

        if (!subflow_can_fallback(subflow)) {
                /* fatal protocol error, close the socket.
                 * subflow_error_report() will introduce the appropriate barriers
                 */
                ssk->sk_err = EBADMSG;
                tcp_set_state(ssk, TCP_CLOSE);
                subflow->reset_transient = 0;
                subflow->reset_reason = MPTCP_RST_EMPTCP;
                tcp_send_active_reset(ssk, GFP_ATOMIC);
                WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
                return false;
        }

        __mptcp_do_fallback(msk);
        skb = skb_peek(&ssk->sk_receive_queue);
        subflow->map_valid = 1;
        subflow->map_seq = READ_ONCE(msk->ack_seq);
        subflow->map_data_len = skb->len;
        subflow->map_subflow_seq = tcp_sk(ssk)->copied_seq - subflow->ssn_offset;
        WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_DATA_AVAIL);
        return true;
}

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

        /* 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;
                WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);

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

        return subflow_check_data_avail(sk);
}

/* If ssk has an mptcp parent socket, use the mptcp rcvbuf occupancy,
 * not the ssk one.
 *
 * In mptcp, rwin is about the mptcp-level connection data.
 *
 * Data that is still on the ssk rx queue can thus be ignored,
 * as far as mptcp peer is concerned that data is still inflight.
 * DSS ACK is updated when skb is moved to the mptcp rx queue.
 */
void mptcp_space(const struct sock *ssk, int *space, int *full_space)
{
        const struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        const struct sock *sk = subflow->conn;

        *space = __mptcp_space(sk);
        *full_space = tcp_full_space(sk);
}

void __mptcp_error_report(struct sock *sk)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk = mptcp_sk(sk);

        mptcp_for_each_subflow(msk, subflow) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
                int err = sock_error(ssk);

                if (!err)
                        continue;

                /* only propagate errors on fallen-back sockets or
                 * on MPC connect
                 */
                if (sk->sk_state != TCP_SYN_SENT && !__mptcp_check_fallback(msk))
                        continue;

                inet_sk_state_store(sk, inet_sk_state_load(ssk));
                sk->sk_err = -err;

                /* This barrier is coupled with smp_rmb() in mptcp_poll() */
                smp_wmb();
                sk_error_report(sk);
                break;
        }
}

static void subflow_error_report(struct sock *ssk)
{
        struct sock *sk = mptcp_subflow_ctx(ssk)->conn;

        mptcp_data_lock(sk);
        if (!sock_owned_by_user(sk))
                __mptcp_error_report(sk);
        else
                __set_bit(MPTCP_ERROR_REPORT,  &mptcp_sk(sk)->cb_flags);
        mptcp_data_unlock(sk);
}

static void subflow_data_ready(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        u16 state = 1 << inet_sk_state_load(sk);
        struct sock *parent = subflow->conn;
        struct mptcp_sock *msk;

        msk = mptcp_sk(parent);
        if (state & TCPF_LISTEN) {
                /* MPJ subflow are removed from accept queue before reaching here,
                 * avoid stray wakeups
                 */
                if (reqsk_queue_empty(&inet_csk(sk)->icsk_accept_queue))
                        return;

                parent->sk_data_ready(parent);
                return;
        }

        WARN_ON_ONCE(!__mptcp_check_fallback(msk) && !subflow->mp_capable &&
                     !subflow->mp_join && !(state & TCPF_CLOSE));

        if (mptcp_subflow_data_available(sk))
                mptcp_data_ready(parent, sk);
        else if (unlikely(sk->sk_err))
                subflow_error_report(sk);
}

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

        mptcp_propagate_sndbuf(sk, ssk);
        mptcp_write_space(sk);
}

static const 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);
        const 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

void mptcp_info2sockaddr(const struct mptcp_addr_info *info,
                         struct sockaddr_storage *addr,
                         unsigned short family)
{
        memset(addr, 0, sizeof(*addr));
        addr->ss_family = family;
        if (addr->ss_family == AF_INET) {
                struct sockaddr_in *in_addr = (struct sockaddr_in *)addr;

                if (info->family == AF_INET)
                        in_addr->sin_addr = info->addr;
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
                else if (ipv6_addr_v4mapped(&info->addr6))
                        in_addr->sin_addr.s_addr = info->addr6.s6_addr32[3];
#endif
                in_addr->sin_port = info->port;
        }
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        else if (addr->ss_family == AF_INET6) {
                struct sockaddr_in6 *in6_addr = (struct sockaddr_in6 *)addr;

                if (info->family == AF_INET)
                        ipv6_addr_set_v4mapped(info->addr.s_addr,
                                               &in6_addr->sin6_addr);
                else
                        in6_addr->sin6_addr = info->addr6;
                in6_addr->sin6_port = info->port;
        }
#endif
}

int __mptcp_subflow_connect(struct sock *sk, const struct mptcp_addr_info *loc,
                            const struct mptcp_addr_info *remote)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_subflow_context *subflow;
        struct sockaddr_storage addr;
        int remote_id = remote->id;
        int local_id = loc->id;
        int err = -ENOTCONN;
        struct socket *sf;
        struct sock *ssk;
        u32 remote_token;
        int addrlen;
        int ifindex;
        u8 flags;

        if (!mptcp_is_fully_established(sk))
                goto err_out;

        err = mptcp_subflow_create_socket(sk, &sf);
        if (err)
                goto err_out;

        ssk = sf->sk;
        subflow = mptcp_subflow_ctx(ssk);
        do {
                get_random_bytes(&subflow->local_nonce, sizeof(u32));
        } while (!subflow->local_nonce);

        if (local_id)
                subflow_set_local_id(subflow, local_id);

        mptcp_pm_get_flags_and_ifindex_by_id(sock_net(sk), local_id,
                                             &flags, &ifindex);
        subflow->remote_key = msk->remote_key;
        subflow->local_key = msk->local_key;
        subflow->token = msk->token;
        mptcp_info2sockaddr(loc, &addr, ssk->sk_family);

        addrlen = sizeof(struct sockaddr_in);
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        if (addr.ss_family == AF_INET6)
                addrlen = sizeof(struct sockaddr_in6);
#endif
        mptcp_sockopt_sync(msk, ssk);

        ssk->sk_bound_dev_if = ifindex;
        err = kernel_bind(sf, (struct sockaddr *)&addr, addrlen);
        if (err)
                goto failed;

        mptcp_crypto_key_sha(subflow->remote_key, &remote_token, NULL);
        pr_debug("msk=%p remote_token=%u local_id=%d remote_id=%d", msk,
                 remote_token, local_id, remote_id);
        subflow->remote_token = remote_token;
        subflow->remote_id = remote_id;
        subflow->request_join = 1;
        subflow->request_bkup = !!(flags & MPTCP_PM_ADDR_FLAG_BACKUP);
        mptcp_info2sockaddr(remote, &addr, ssk->sk_family);

        sock_hold(ssk);
        list_add_tail(&subflow->node, &msk->conn_list);
        err = kernel_connect(sf, (struct sockaddr *)&addr, addrlen, O_NONBLOCK);
        if (err && err != -EINPROGRESS)
                goto failed_unlink;

        /* discard the subflow socket */
        mptcp_sock_graft(ssk, sk->sk_socket);
        iput(SOCK_INODE(sf));
        return err;

failed_unlink:
        list_del(&subflow->node);
        sock_put(mptcp_subflow_tcp_sock(subflow));

failed:
        subflow->disposable = 1;
        sock_release(sf);

err_out:
        /* we account subflows before the creation, and this failures will not
         * be caught by sk_state_change()
         */
        mptcp_pm_close_subflow(msk);
        return err;
}

static void mptcp_attach_cgroup(struct sock *parent, struct sock *child)
{
#ifdef CONFIG_SOCK_CGROUP_DATA
        struct sock_cgroup_data *parent_skcd = &parent->sk_cgrp_data,
                                *child_skcd = &child->sk_cgrp_data;

        /* only the additional subflows created by kworkers have to be modified */
        if (cgroup_id(sock_cgroup_ptr(parent_skcd)) !=
            cgroup_id(sock_cgroup_ptr(child_skcd))) {
#ifdef CONFIG_MEMCG
                struct mem_cgroup *memcg = parent->sk_memcg;

                mem_cgroup_sk_free(child);
                if (memcg && css_tryget(&memcg->css))
                        child->sk_memcg = memcg;
#endif /* CONFIG_MEMCG */

                cgroup_sk_free(child_skcd);
                *child_skcd = *parent_skcd;
                cgroup_sk_clone(child_skcd);
        }
#endif /* CONFIG_SOCK_CGROUP_DATA */
}

static void mptcp_subflow_ops_override(struct sock *ssk)
{
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        if (ssk->sk_prot == &tcpv6_prot)
                ssk->sk_prot = &tcpv6_prot_override;
        else
#endif
                ssk->sk_prot = &tcp_prot_override;
}

static void mptcp_subflow_ops_undo_override(struct sock *ssk)
{
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        if (ssk->sk_prot == &tcpv6_prot_override)
                ssk->sk_prot = &tcpv6_prot;
        else
#endif
                ssk->sk_prot = &tcp_prot;
}
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;

        /* un-accepted server sockets can reach here - on bad configuration
         * bail early to avoid greater trouble later
         */
        if (unlikely(!sk->sk_socket))
                return -EINVAL;

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

        lock_sock(sf->sk);

        /* the newly created socket has to be in the same cgroup as its parent */
        mptcp_attach_cgroup(sk, sf->sk);

        /* kernel sockets do not by default acquire net ref, but TCP timer
         * needs it.
         */
        sf->sk->sk_net_refcnt = 1;
        get_net_track(net, &sf->sk->ns_tracker, GFP_KERNEL);
        sock_inuse_add(net, 1);
        err = tcp_set_ulp(sf->sk, "mptcp");
        release_sock(sf->sk);

        if (err) {
                sock_release(sf);
                return err;
        }

        /* the newly created socket really belongs to the owning MPTCP master
         * socket, even if for additional subflows the allocation is performed
         * by a kernel workqueue. Adjust inode references, so that the
         * procfs/diag interaces really show this one belonging to the correct
         * user.
         */
        SOCK_INODE(sf)->i_ino = SOCK_INODE(sk->sk_socket)->i_ino;
        SOCK_INODE(sf)->i_uid = SOCK_INODE(sk->sk_socket)->i_uid;
        SOCK_INODE(sf)->i_gid = SOCK_INODE(sk->sk_socket)->i_gid;

        subflow = mptcp_subflow_ctx(sf->sk);
        pr_debug("subflow=%p", subflow);

        *new_sock = sf;
        sock_hold(sk);
        subflow->conn = sk;
        mptcp_subflow_ops_override(sf->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);
        INIT_LIST_HEAD(&ctx->delegated_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 = subflow->conn;

        __subflow_state_change(sk);

        if (subflow_simultaneous_connect(sk)) {
                mptcp_propagate_sndbuf(parent, sk);
                mptcp_do_fallback(sk);
                mptcp_rcv_space_init(mptcp_sk(parent), sk);
                pr_fallback(mptcp_sk(parent));
                subflow->conn_finished = 1;
                mptcp_set_connected(parent);
        }

        /* 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 (mptcp_subflow_data_available(sk))
                mptcp_data_ready(parent, sk);
        else if (unlikely(sk->sk_err))
                subflow_error_report(sk);

        subflow_sched_work_if_closed(mptcp_sk(parent), sk);

        if (__mptcp_check_fallback(mptcp_sk(parent)) &&
            !subflow->rx_eof && subflow_is_done(sk)) {
                subflow->rx_eof = 1;
                mptcp_subflow_eof(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_state_change = sk->sk_state_change;
        ctx->tcp_error_report = sk->sk_error_report;

        WARN_ON_ONCE(sk->sk_data_ready != sock_def_readable);
        WARN_ON_ONCE(sk->sk_write_space != sk_stream_write_space);

        sk->sk_data_ready = subflow_data_ready;
        sk->sk_write_space = subflow_write_space;
        sk->sk_state_change = subflow_state_change;
        sk->sk_error_report = subflow_error_report;
out:
        return err;
}

static void subflow_ulp_release(struct sock *ssk)
{
        struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(ssk);
        bool release = true;
        struct sock *sk;

        if (!ctx)
                return;

        sk = ctx->conn;
        if (sk) {
                /* if the msk has been orphaned, keep the ctx
                 * alive, will be freed by __mptcp_close_ssk(),
                 * when the subflow is still unaccepted
                 */
                release = ctx->disposable || list_empty(&ctx->node);
                sock_put(sk);
        }

        mptcp_subflow_ops_undo_override(ssk);
        if (release)
                kfree_rcu(ctx, rcu);
}

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_req->mp_join)) {
                subflow_ulp_fallback(newsk, old_ctx);
                return;
        }

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

        new_ctx->conn_finished = 1;
        new_ctx->icsk_af_ops = old_ctx->icsk_af_ops;
        new_ctx->tcp_state_change = old_ctx->tcp_state_change;
        new_ctx->tcp_error_report = old_ctx->tcp_error_report;
        new_ctx->rel_write_seq = 1;
        new_ctx->tcp_sock = newsk;

        if (subflow_req->mp_capable) {
                /* see comments in subflow_syn_recv_sock(), MPTCP connection
                 * is fully established only after we receive the remote key
                 */
                new_ctx->mp_capable = 1;
                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;

                /* this is the first subflow, id is always 0 */
                new_ctx->local_id_valid = 1;
        } else if (subflow_req->mp_join) {
                new_ctx->ssn_offset = subflow_req->ssn_offset;
                new_ctx->mp_join = 1;
                new_ctx->fully_established = 1;
                new_ctx->backup = subflow_req->backup;
                new_ctx->remote_id = subflow_req->remote_id;
                new_ctx->token = subflow_req->token;
                new_ctx->thmac = subflow_req->thmac;

                /* the subflow req id is valid, fetched via subflow_check_req()
                 * and subflow_token_join_request()
                 */
                subflow_set_local_id(new_ctx, subflow_req->local_id);
        }
}

static void tcp_release_cb_override(struct sock *ssk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);

        if (mptcp_subflow_has_delegated_action(subflow))
                mptcp_subflow_process_delegated(ssk);

        tcp_release_cb(ssk);
}

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 __init mptcp_subflow_init(void)
{
        mptcp_subflow_request_sock_ops = tcp_request_sock_ops;
        if (subflow_ops_init(&mptcp_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.route_req = subflow_v4_route_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;

        tcp_prot_override = tcp_prot;
        tcp_prot_override.release_cb = tcp_release_cb_override;

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        subflow_request_sock_ipv6_ops = tcp_request_sock_ipv6_ops;
        subflow_request_sock_ipv6_ops.route_req = subflow_v6_route_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_v6_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;
        subflow_v6m_specific.rebuild_header = subflow_rebuild_header;

        tcpv6_prot_override = tcpv6_prot;
        tcpv6_prot_override.release_cb = tcp_release_cb_override;
#endif

        mptcp_diag_subflow_init(&subflow_ulp_ops);

        if (tcp_register_ulp(&subflow_ulp_ops) != 0)
                panic("MPTCP: failed to register subflows to ULP\n");
}