// 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/sha.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"
#include "mib.h"

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

        if (subflow->request_mptcp && !subflow->token) {
                pr_debug("subflow=%p", sk);
                err = mptcp_token_new_connect(sk);
        } else if (subflow->request_join && !subflow->local_nonce) {
                struct mptcp_sock *msk = (struct mptcp_sock *)subflow->conn;

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

                do {
                        get_random_bytes(&subflow->local_nonce, sizeof(u32));
                } while (!subflow->local_nonce);

                if (subflow->local_id)
                        goto out;

                local_id = mptcp_pm_get_local_id(msk, (struct sock_common *)sk);
                if (local_id < 0)
                        return -EINVAL;

                subflow->local_id = local_id;
        }

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

        if (subflow_req->mp_capable)
                mptcp_token_destroy_request(subflow_req->token);
        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);
}

/* validate received token and create truncated hmac and nonce for SYN-ACK */
static struct mptcp_sock *subflow_token_join_request(struct request_sock *req,
                                                     const struct sk_buff *skb)
{
        struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
        u8 hmac[SHA256_DIGEST_SIZE];
        struct mptcp_sock *msk;
        int local_id;

        msk = mptcp_token_get_sock(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;

        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);
        return msk;
}

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 mptcp_options_received mp_opt;

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

        mptcp_get_options(skb, &mp_opt);

        subflow_req->mp_capable = 0;
        subflow_req->mp_join = 0;
        subflow_req->msk = NULL;

#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 (mp_opt.mp_capable) {
                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVE);

                if (mp_opt.mp_join)
                        return;
        } else if (mp_opt.mp_join) {
                SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINSYNRX);
        }

        if (mp_opt.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;
        } else if (mp_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, skb);
                pr_debug("token=%u, remote_nonce=%u msk=%p", subflow_req->token,
                         subflow_req->remote_nonce, subflow_req->msk);
        }
}

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

/* 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,
                 (unsigned long long)thmac,
                 (unsigned long long)subflow->thmac);

        return thmac == subflow->thmac;
}

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);

        if (inet_sk_state_load(parent) == TCP_SYN_SENT) {
                inet_sk_state_store(parent, TCP_ESTABLISHED);
                parent->sk_state_change(parent);
        }

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

        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 && mp_opt.mp_capable) {
                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);
        } else if (subflow->request_join && mp_opt.mp_join) {
                subflow->mp_join = 1;
                subflow->thmac = mp_opt.thmac;
                subflow->remote_nonce = mp_opt.nonce;
                pr_debug("subflow=%p, thmac=%llu, remote_nonce=%u", subflow,
                         subflow->thmac, subflow->remote_nonce);
        } else {
                if (subflow->request_mptcp)
                        MPTCP_INC_STATS(sock_net(sk),
                                        MPTCP_MIB_MPCAPABLEACTIVEFALLBACK);
                mptcp_do_fallback(sk);
                pr_fallback(mptcp_sk(subflow->conn));
        }

        if (mptcp_check_fallback(sk)) {
                mptcp_rcv_space_init(mptcp_sk(parent), sk);
                return;
        }

        if (subflow->mp_capable) {
                pr_debug("subflow=%p, remote_key=%llu", mptcp_subflow_ctx(sk),
                         subflow->remote_key);
                mptcp_finish_connect(sk);
        } else if (subflow->mp_join) {
                u8 hmac[SHA256_DIGEST_SIZE];

                pr_debug("subflow=%p, thmac=%llu, remote_nonce=%u",
                         subflow, subflow->thmac,
                         subflow->remote_nonce);
                if (!subflow_thmac_valid(subflow)) {
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINACKMAC);
                        subflow->mp_join = 0;
                        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);

                if (!mptcp_finish_join(sk))
                        goto do_reset;

                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINSYNACKRX);
        } else {
do_reset:
                tcp_send_active_reset(sk, GFP_ATOMIC);
                tcp_done(sk);
        }
}

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

/* 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 not be in
         * SYN_RECV state and doesn't have SOCK_DEAD flag.
         * Both result in warnings from inet_sock_destruct.
         */

        if (sk->sk_state == TCP_SYN_RECV) {
                sk->sk_state = TCP_CLOSE;
                WARN_ON_ONCE(sk->sk_socket);
                sock_orphan(sk);
        }

        mptcp_token_destroy(mptcp_sk(sk)->token);
        inet_sock_destruct(sk);
}

static void mptcp_force_close(struct sock *sk)
{
        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;
}

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);
}

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 'mp_capable' even when options
         * are not parsed
         */
        mp_opt.mp_capable = 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) {
                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_msk;
                }

                mptcp_get_options(skb, &mp_opt);
                if (!mp_opt.mp_capable) {
                        fallback = true;
                        goto create_child;
                }

create_msk:
                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.mp_join ||
                    !subflow_hmac_valid(req, &mp_opt)) {
                        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)
                                goto dispose_child;

                        subflow_drop_ctx(child);
                        goto out;
                }

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

                        /* with OoO packets we can reach here without ingress
                         * mpc option
                         */
                        ctx->remote_key = mp_opt.sndr_key;
                        ctx->fully_established = mp_opt.mp_capable;
                        ctx->can_ack = mp_opt.mp_capable;
                } else if (ctx->mp_join) {
                        struct mptcp_sock *owner;

                        owner = subflow_req->msk;
                        if (!owner)
                                goto dispose_child;

                        /* move the msk reference ownership to the subflow */
                        subflow_req->msk = NULL;
                        ctx->conn = (struct sock *)owner;
                        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;
        tcp_send_active_reset(child, GFP_ATOMIC);
        inet_csk_prepare_for_destroy_sock(child);
        tcp_done(child);

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

static struct inet_connection_sock_af_ops subflow_specific;

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

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;

        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;
        }

        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");
                MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_INFINITEMAPRX);
                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)) {
                        MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSNOMATCH);
                        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 int subflow_read_actor(read_descriptor_t *desc,
                              struct sk_buff *skb,
                              unsigned int offset, size_t len)
{
        size_t copy_len = min(desc->count, len);

        desc->count -= copy_len;

        pr_debug("flushed %zu bytes, %zu left", copy_len, desc->count);
        return copy_len;
}

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;

        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_DUMMY) {
                        __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;
                        return true;
                }

                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) {
                        read_descriptor_t desc = {
                                .count = delta,
                        };
                        int ret;

                        ret = tcp_read_sock(ssk, &desc, subflow_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;
}

/* 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 concerened 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 = tcp_space(sk);
        *full_space = tcp_full_space(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) {
                set_bit(MPTCP_DATA_READY, &msk->flags);
                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);
}

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 (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

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

                in_addr->sin_addr = info->addr;
                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;

                in6_addr->sin6_addr = info->addr6;
                in6_addr->sin6_port = info->port;
        }
#endif
}

int __mptcp_subflow_connect(struct sock *sk, int ifindex,
                            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;
        struct socket *sf;
        u32 remote_token;
        int addrlen;
        int err;

        if (sk->sk_state != TCP_ESTABLISHED)
                return -ENOTCONN;

        err = mptcp_subflow_create_socket(sk, &sf);
        if (err)
                return err;

        subflow = mptcp_subflow_ctx(sf->sk);
        subflow->remote_key = msk->remote_key;
        subflow->local_key = msk->local_key;
        subflow->token = msk->token;
        mptcp_info2sockaddr(loc, &addr);

        addrlen = sizeof(struct sockaddr_in);
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        if (loc->family == AF_INET6)
                addrlen = sizeof(struct sockaddr_in6);
#endif
        sf->sk->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", msk, remote_token);
        subflow->remote_token = remote_token;
        subflow->local_id = loc->id;
        subflow->request_join = 1;
        subflow->request_bkup = 1;
        mptcp_info2sockaddr(remote, &addr);

        err = kernel_connect(sf, (struct sockaddr *)&addr, addrlen, O_NONBLOCK);
        if (err && err != -EINPROGRESS)
                goto failed;

        spin_lock_bh(&msk->join_list_lock);
        list_add_tail(&subflow->node, &msk->join_list);
        spin_unlock_bh(&msk->join_list_lock);

        return err;

failed:
        sock_release(sf);
        return err;
}

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);

        /* 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) {
                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;

        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 = subflow->conn;

        __subflow_state_change(sk);

        if (subflow_simultaneous_connect(sk)) {
                mptcp_do_fallback(sk);
                mptcp_rcv_space_init(mptcp_sk(parent), sk);
                pr_fallback(mptcp_sk(parent));
                subflow->conn_finished = 1;
                if (inet_sk_state_load(parent) == TCP_SYN_SENT) {
                        inet_sk_state_store(parent, TCP_ESTABLISHED);
                        parent->sk_state_change(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);

        if (!(parent->sk_shutdown & RCV_SHUTDOWN) &&
            !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_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_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_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->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;
        } 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->local_id = subflow_req->local_id;
                new_ctx->token = subflow_req->token;
                new_ctx->thmac = subflow_req->thmac;
        }
}

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

        mptcp_diag_subflow_init(&subflow_ulp_ops);

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