// 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 <crypto/sha2.h>
#include <net/tcp.h>
#include <net/mptcp.h>
#include "protocol.h"
#include "mib.h"

static bool mptcp_cap_flag_sha256(u8 flags)
{
        return (flags & MPTCP_CAP_FLAG_MASK) == MPTCP_CAP_HMAC_SHA256;
}

static void mptcp_parse_option(const struct sk_buff *skb,
                               const unsigned char *ptr, int opsize,
                               struct mptcp_options_received *mp_opt)
{
        u8 subtype = *ptr >> 4;
        int expected_opsize;
        u8 version;
        u8 flags;

        switch (subtype) {
        case MPTCPOPT_MP_CAPABLE:
                /* strict size checking */
                if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
                        if (skb->len > tcp_hdr(skb)->doff << 2)
                                expected_opsize = TCPOLEN_MPTCP_MPC_ACK_DATA;
                        else
                                expected_opsize = TCPOLEN_MPTCP_MPC_ACK;
                } else {
                        if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)
                                expected_opsize = TCPOLEN_MPTCP_MPC_SYNACK;
                        else
                                expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
                }
                if (opsize != expected_opsize)
                        break;

                /* try to be gentle vs future versions on the initial syn */
                version = *ptr++ & MPTCP_VERSION_MASK;
                if (opsize != TCPOLEN_MPTCP_MPC_SYN) {
                        if (version != MPTCP_SUPPORTED_VERSION)
                                break;
                } else if (version < MPTCP_SUPPORTED_VERSION) {
                        break;
                }

                flags = *ptr++;
                if (!mptcp_cap_flag_sha256(flags) ||
                    (flags & MPTCP_CAP_EXTENSIBILITY))
                        break;

                /* RFC 6824, Section 3.1:
                 * "For the Checksum Required bit (labeled "A"), if either
                 * host requires the use of checksums, checksums MUST be used.
                 * In other words, the only way for checksums not to be used
                 * is if both hosts in their SYNs set A=0."
                 *
                 * Section 3.3.0:
                 * "If a checksum is not present when its use has been
                 * negotiated, the receiver MUST close the subflow with a RST as
                 * it is considered broken."
                 *
                 * We don't implement DSS checksum - fall back to TCP.
                 */
                if (flags & MPTCP_CAP_CHECKSUM_REQD)
                        break;

                mp_opt->mp_capable = 1;
                if (opsize >= TCPOLEN_MPTCP_MPC_SYNACK) {
                        mp_opt->sndr_key = get_unaligned_be64(ptr);
                        ptr += 8;
                }
                if (opsize >= TCPOLEN_MPTCP_MPC_ACK) {
                        mp_opt->rcvr_key = get_unaligned_be64(ptr);
                        ptr += 8;
                }
                if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA) {
                        /* Section 3.1.:
                         * "the data parameters in a MP_CAPABLE are semantically
                         * equivalent to those in a DSS option and can be used
                         * interchangeably."
                         */
                        mp_opt->dss = 1;
                        mp_opt->use_map = 1;
                        mp_opt->mpc_map = 1;
                        mp_opt->data_len = get_unaligned_be16(ptr);
                        ptr += 2;
                }
                pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d",
                         version, flags, opsize, mp_opt->sndr_key,
                         mp_opt->rcvr_key, mp_opt->data_len);
                break;

        case MPTCPOPT_MP_JOIN:
                mp_opt->mp_join = 1;
                if (opsize == TCPOLEN_MPTCP_MPJ_SYN) {
                        mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
                        mp_opt->join_id = *ptr++;
                        mp_opt->token = get_unaligned_be32(ptr);
                        ptr += 4;
                        mp_opt->nonce = get_unaligned_be32(ptr);
                        ptr += 4;
                        pr_debug("MP_JOIN bkup=%u, id=%u, token=%u, nonce=%u",
                                 mp_opt->backup, mp_opt->join_id,
                                 mp_opt->token, mp_opt->nonce);
                } else if (opsize == TCPOLEN_MPTCP_MPJ_SYNACK) {
                        mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
                        mp_opt->join_id = *ptr++;
                        mp_opt->thmac = get_unaligned_be64(ptr);
                        ptr += 8;
                        mp_opt->nonce = get_unaligned_be32(ptr);
                        ptr += 4;
                        pr_debug("MP_JOIN bkup=%u, id=%u, thmac=%llu, nonce=%u",
                                 mp_opt->backup, mp_opt->join_id,
                                 mp_opt->thmac, mp_opt->nonce);
                } else if (opsize == TCPOLEN_MPTCP_MPJ_ACK) {
                        ptr += 2;
                        memcpy(mp_opt->hmac, ptr, MPTCPOPT_HMAC_LEN);
                        pr_debug("MP_JOIN hmac");
                } else {
                        pr_warn("MP_JOIN bad option size");
                        mp_opt->mp_join = 0;
                }
                break;

        case MPTCPOPT_DSS:
                pr_debug("DSS");
                ptr++;

                /* we must clear 'mpc_map' be able to detect MP_CAPABLE
                 * map vs DSS map in mptcp_incoming_options(), and reconstruct
                 * map info accordingly
                 */
                mp_opt->mpc_map = 0;
                flags = (*ptr++) & MPTCP_DSS_FLAG_MASK;
                mp_opt->data_fin = (flags & MPTCP_DSS_DATA_FIN) != 0;
                mp_opt->dsn64 = (flags & MPTCP_DSS_DSN64) != 0;
                mp_opt->use_map = (flags & MPTCP_DSS_HAS_MAP) != 0;
                mp_opt->ack64 = (flags & MPTCP_DSS_ACK64) != 0;
                mp_opt->use_ack = (flags & MPTCP_DSS_HAS_ACK);

                pr_debug("data_fin=%d dsn64=%d use_map=%d ack64=%d use_ack=%d",
                         mp_opt->data_fin, mp_opt->dsn64,
                         mp_opt->use_map, mp_opt->ack64,
                         mp_opt->use_ack);

                expected_opsize = TCPOLEN_MPTCP_DSS_BASE;

                if (mp_opt->use_ack) {
                        if (mp_opt->ack64)
                                expected_opsize += TCPOLEN_MPTCP_DSS_ACK64;
                        else
                                expected_opsize += TCPOLEN_MPTCP_DSS_ACK32;
                }

                if (mp_opt->use_map) {
                        if (mp_opt->dsn64)
                                expected_opsize += TCPOLEN_MPTCP_DSS_MAP64;
                        else
                                expected_opsize += TCPOLEN_MPTCP_DSS_MAP32;
                }

                /* RFC 6824, Section 3.3:
                 * If a checksum is present, but its use had
                 * not been negotiated in the MP_CAPABLE handshake,
                 * the checksum field MUST be ignored.
                 */
                if (opsize != expected_opsize &&
                    opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM)
                        break;

                mp_opt->dss = 1;

                if (mp_opt->use_ack) {
                        if (mp_opt->ack64) {
                                mp_opt->data_ack = get_unaligned_be64(ptr);
                                ptr += 8;
                        } else {
                                mp_opt->data_ack = get_unaligned_be32(ptr);
                                ptr += 4;
                        }

                        pr_debug("data_ack=%llu", mp_opt->data_ack);
                }

                if (mp_opt->use_map) {
                        if (mp_opt->dsn64) {
                                mp_opt->data_seq = get_unaligned_be64(ptr);
                                ptr += 8;
                        } else {
                                mp_opt->data_seq = get_unaligned_be32(ptr);
                                ptr += 4;
                        }

                        mp_opt->subflow_seq = get_unaligned_be32(ptr);
                        ptr += 4;

                        mp_opt->data_len = get_unaligned_be16(ptr);
                        ptr += 2;

                        pr_debug("data_seq=%llu subflow_seq=%u data_len=%u",
                                 mp_opt->data_seq, mp_opt->subflow_seq,
                                 mp_opt->data_len);
                }

                break;

        case MPTCPOPT_ADD_ADDR:
                mp_opt->echo = (*ptr++) & MPTCP_ADDR_ECHO;
                if (!mp_opt->echo) {
                        if (opsize == TCPOLEN_MPTCP_ADD_ADDR ||
                            opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT)
                                mp_opt->family = MPTCP_ADDR_IPVERSION_4;
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
                        else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6 ||
                                 opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT)
                                mp_opt->family = MPTCP_ADDR_IPVERSION_6;
#endif
                        else
                                break;
                } else {
                        if (opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE ||
                            opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT)
                                mp_opt->family = MPTCP_ADDR_IPVERSION_4;
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
                        else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE ||
                                 opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT)
                                mp_opt->family = MPTCP_ADDR_IPVERSION_6;
#endif
                        else
                                break;
                }

                mp_opt->add_addr = 1;
                mp_opt->addr_id = *ptr++;
                if (mp_opt->family == MPTCP_ADDR_IPVERSION_4) {
                        memcpy((u8 *)&mp_opt->addr.s_addr, (u8 *)ptr, 4);
                        ptr += 4;
                        if (opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT ||
                            opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT) {
                                mp_opt->port = get_unaligned_be16(ptr);
                                ptr += 2;
                        }
                }
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
                else {
                        memcpy(mp_opt->addr6.s6_addr, (u8 *)ptr, 16);
                        ptr += 16;
                        if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT ||
                            opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT) {
                                mp_opt->port = get_unaligned_be16(ptr);
                                ptr += 2;
                        }
                }
#endif
                if (!mp_opt->echo) {
                        mp_opt->ahmac = get_unaligned_be64(ptr);
                        ptr += 8;
                }
                pr_debug("ADD_ADDR%s: id=%d, ahmac=%llu, echo=%d, port=%d",
                         (mp_opt->family == MPTCP_ADDR_IPVERSION_6) ? "6" : "",
                         mp_opt->addr_id, mp_opt->ahmac, mp_opt->echo, mp_opt->port);
                break;

        case MPTCPOPT_RM_ADDR:
                if (opsize != TCPOLEN_MPTCP_RM_ADDR_BASE)
                        break;

                ptr++;

                mp_opt->rm_addr = 1;
                mp_opt->rm_id = *ptr++;
                pr_debug("RM_ADDR: id=%d", mp_opt->rm_id);
                break;

        case MPTCPOPT_MP_PRIO:
                if (opsize != TCPOLEN_MPTCP_PRIO)
                        break;

                mp_opt->mp_prio = 1;
                mp_opt->backup = *ptr++ & MPTCP_PRIO_BKUP;
                pr_debug("MP_PRIO: prio=%d", mp_opt->backup);
                break;

        case MPTCPOPT_MP_FASTCLOSE:
                if (opsize != TCPOLEN_MPTCP_FASTCLOSE)
                        break;

                ptr += 2;
                mp_opt->rcvr_key = get_unaligned_be64(ptr);
                ptr += 8;
                mp_opt->fastclose = 1;
                break;

        default:
                break;
        }
}

void mptcp_get_options(const struct sk_buff *skb,
                       struct mptcp_options_received *mp_opt)
{
        const struct tcphdr *th = tcp_hdr(skb);
        const unsigned char *ptr;
        int length;

        /* initialize option status */
        mp_opt->mp_capable = 0;
        mp_opt->mp_join = 0;
        mp_opt->add_addr = 0;
        mp_opt->ahmac = 0;
        mp_opt->fastclose = 0;
        mp_opt->port = 0;
        mp_opt->rm_addr = 0;
        mp_opt->dss = 0;
        mp_opt->mp_prio = 0;

        length = (th->doff * 4) - sizeof(struct tcphdr);
        ptr = (const unsigned char *)(th + 1);

        while (length > 0) {
                int opcode = *ptr++;
                int opsize;

                switch (opcode) {
                case TCPOPT_EOL:
                        return;
                case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
                        length--;
                        continue;
                default:
                        opsize = *ptr++;
                        if (opsize < 2) /* "silly options" */
                                return;
                        if (opsize > length)
                                return; /* don't parse partial options */
                        if (opcode == TCPOPT_MPTCP)
                                mptcp_parse_option(skb, ptr, opsize, mp_opt);
                        ptr += opsize - 2;
                        length -= opsize;
                }
        }
}

bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
                       unsigned int *size, struct mptcp_out_options *opts)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);

        /* we will use snd_isn to detect first pkt [re]transmission
         * in mptcp_established_options_mp()
         */
        subflow->snd_isn = TCP_SKB_CB(skb)->end_seq;
        if (subflow->request_mptcp) {
                opts->suboptions = OPTION_MPTCP_MPC_SYN;
                *size = TCPOLEN_MPTCP_MPC_SYN;
                return true;
        } else if (subflow->request_join) {
                pr_debug("remote_token=%u, nonce=%u", subflow->remote_token,
                         subflow->local_nonce);
                opts->suboptions = OPTION_MPTCP_MPJ_SYN;
                opts->join_id = subflow->local_id;
                opts->token = subflow->remote_token;
                opts->nonce = subflow->local_nonce;
                opts->backup = subflow->request_bkup;
                *size = TCPOLEN_MPTCP_MPJ_SYN;
                return true;
        }
        return false;
}

/* MP_JOIN client subflow must wait for 4th ack before sending any data:
 * TCP can't schedule delack timer before the subflow is fully established.
 * MPTCP uses the delack timer to do 3rd ack retransmissions
 */
static void schedule_3rdack_retransmission(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        struct tcp_sock *tp = tcp_sk(sk);
        unsigned long timeout;

        /* reschedule with a timeout above RTT, as we must look only for drop */
        if (tp->srtt_us)
                timeout = tp->srtt_us << 1;
        else
                timeout = TCP_TIMEOUT_INIT;

        WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER);
        icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
        icsk->icsk_ack.timeout = timeout;
        sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
}

static void clear_3rdack_retransmission(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);

        sk_stop_timer(sk, &icsk->icsk_delack_timer);
        icsk->icsk_ack.timeout = 0;
        icsk->icsk_ack.ato = 0;
        icsk->icsk_ack.pending &= ~(ICSK_ACK_SCHED | ICSK_ACK_TIMER);
}

static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
                                         bool snd_data_fin_enable,
                                         unsigned int *size,
                                         unsigned int remaining,
                                         struct mptcp_out_options *opts)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_ext *mpext;
        unsigned int data_len;

        /* When skb is not available, we better over-estimate the emitted
         * options len. A full DSS option (28 bytes) is longer than
         * TCPOLEN_MPTCP_MPC_ACK_DATA(22) or TCPOLEN_MPTCP_MPJ_ACK(24), so
         * tell the caller to defer the estimate to
         * mptcp_established_options_dss(), which will reserve enough space.
         */
        if (!skb)
                return false;

        /* MPC/MPJ needed only on 3rd ack packet, DATA_FIN and TCP shutdown take precedence */
        if (subflow->fully_established || snd_data_fin_enable ||
            subflow->snd_isn != TCP_SKB_CB(skb)->seq ||
            sk->sk_state != TCP_ESTABLISHED)
                return false;

        if (subflow->mp_capable) {
                mpext = mptcp_get_ext(skb);
                data_len = mpext ? mpext->data_len : 0;

                /* we will check ext_copy.data_len in mptcp_write_options() to
                 * discriminate between TCPOLEN_MPTCP_MPC_ACK_DATA and
                 * TCPOLEN_MPTCP_MPC_ACK
                 */
                opts->ext_copy.data_len = data_len;
                opts->suboptions = OPTION_MPTCP_MPC_ACK;
                opts->sndr_key = subflow->local_key;
                opts->rcvr_key = subflow->remote_key;

                /* Section 3.1.
                 * The MP_CAPABLE option is carried on the SYN, SYN/ACK, and ACK
                 * packets that start the first subflow of an MPTCP connection,
                 * as well as the first packet that carries data
                 */
                if (data_len > 0)
                        *size = ALIGN(TCPOLEN_MPTCP_MPC_ACK_DATA, 4);
                else
                        *size = TCPOLEN_MPTCP_MPC_ACK;

                pr_debug("subflow=%p, local_key=%llu, remote_key=%llu map_len=%d",
                         subflow, subflow->local_key, subflow->remote_key,
                         data_len);

                return true;
        } else if (subflow->mp_join) {
                opts->suboptions = OPTION_MPTCP_MPJ_ACK;
                memcpy(opts->hmac, subflow->hmac, MPTCPOPT_HMAC_LEN);
                *size = TCPOLEN_MPTCP_MPJ_ACK;
                pr_debug("subflow=%p", subflow);

                schedule_3rdack_retransmission(sk);
                return true;
        }
        return false;
}

static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
                                 struct sk_buff *skb, struct mptcp_ext *ext)
{
        /* The write_seq value has already been incremented, so the actual
         * sequence number for the DATA_FIN is one less.
         */
        u64 data_fin_tx_seq = READ_ONCE(mptcp_sk(subflow->conn)->write_seq) - 1;

        if (!ext->use_map || !skb->len) {
                /* RFC6824 requires a DSS mapping with specific values
                 * if DATA_FIN is set but no data payload is mapped
                 */
                ext->data_fin = 1;
                ext->use_map = 1;
                ext->dsn64 = 1;
                ext->data_seq = data_fin_tx_seq;
                ext->subflow_seq = 0;
                ext->data_len = 1;
        } else if (ext->data_seq + ext->data_len == data_fin_tx_seq) {
                /* If there's an existing DSS mapping and it is the
                 * final mapping, DATA_FIN consumes 1 additional byte of
                 * mapping space.
                 */
                ext->data_fin = 1;
                ext->data_len++;
        }
}

static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
                                          bool snd_data_fin_enable,
                                          unsigned int *size,
                                          unsigned int remaining,
                                          struct mptcp_out_options *opts)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        unsigned int dss_size = 0;
        struct mptcp_ext *mpext;
        unsigned int ack_size;
        bool ret = false;
        u64 ack_seq;

        mpext = skb ? mptcp_get_ext(skb) : NULL;

        if (!skb || (mpext && mpext->use_map) || snd_data_fin_enable) {
                unsigned int map_size;

                map_size = TCPOLEN_MPTCP_DSS_BASE + TCPOLEN_MPTCP_DSS_MAP64;

                remaining -= map_size;
                dss_size = map_size;
                if (mpext)
                        opts->ext_copy = *mpext;

                if (skb && snd_data_fin_enable)
                        mptcp_write_data_fin(subflow, skb, &opts->ext_copy);
                ret = true;
        }

        /* passive sockets msk will set the 'can_ack' after accept(), even
         * if the first subflow may have the already the remote key handy
         */
        opts->ext_copy.use_ack = 0;
        if (!READ_ONCE(msk->can_ack)) {
                *size = ALIGN(dss_size, 4);
                return ret;
        }

        ack_seq = READ_ONCE(msk->ack_seq);
        if (READ_ONCE(msk->use_64bit_ack)) {
                ack_size = TCPOLEN_MPTCP_DSS_ACK64;
                opts->ext_copy.data_ack = ack_seq;
                opts->ext_copy.ack64 = 1;
        } else {
                ack_size = TCPOLEN_MPTCP_DSS_ACK32;
                opts->ext_copy.data_ack32 = (uint32_t)ack_seq;
                opts->ext_copy.ack64 = 0;
        }
        opts->ext_copy.use_ack = 1;
        WRITE_ONCE(msk->old_wspace, __mptcp_space((struct sock *)msk));

        /* Add kind/length/subtype/flag overhead if mapping is not populated */
        if (dss_size == 0)
                ack_size += TCPOLEN_MPTCP_DSS_BASE;

        dss_size += ack_size;

        *size = ALIGN(dss_size, 4);
        return true;
}

static u64 add_addr_generate_hmac(u64 key1, u64 key2, u8 addr_id,
                                  struct in_addr *addr, u16 port)
{
        u8 hmac[SHA256_DIGEST_SIZE];
        u8 msg[7];

        msg[0] = addr_id;
        memcpy(&msg[1], &addr->s_addr, 4);
        msg[5] = port >> 8;
        msg[6] = port & 0xFF;

        mptcp_crypto_hmac_sha(key1, key2, msg, 7, hmac);

        return get_unaligned_be64(&hmac[SHA256_DIGEST_SIZE - sizeof(u64)]);
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static u64 add_addr6_generate_hmac(u64 key1, u64 key2, u8 addr_id,
                                   struct in6_addr *addr, u16 port)
{
        u8 hmac[SHA256_DIGEST_SIZE];
        u8 msg[19];

        msg[0] = addr_id;
        memcpy(&msg[1], &addr->s6_addr, 16);
        msg[17] = port >> 8;
        msg[18] = port & 0xFF;

        mptcp_crypto_hmac_sha(key1, key2, msg, 19, hmac);

        return get_unaligned_be64(&hmac[SHA256_DIGEST_SIZE - sizeof(u64)]);
}
#endif

static bool mptcp_established_options_add_addr(struct sock *sk, struct sk_buff *skb,
                                               unsigned int *size,
                                               unsigned int remaining,
                                               struct mptcp_out_options *opts)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        bool drop_other_suboptions = false;
        unsigned int opt_size = *size;
        struct mptcp_addr_info saddr;
        bool echo;
        bool port;
        int len;

        if ((mptcp_pm_should_add_signal_ipv6(msk) ||
             mptcp_pm_should_add_signal_port(msk)) &&
            skb && skb_is_tcp_pure_ack(skb)) {
                pr_debug("drop other suboptions");
                opts->suboptions = 0;
                opts->ext_copy.use_ack = 0;
                opts->ext_copy.use_map = 0;
                remaining += opt_size;
                drop_other_suboptions = true;
        }

        if (!mptcp_pm_should_add_signal(msk) ||
            !(mptcp_pm_add_addr_signal(msk, remaining, &saddr, &echo, &port)))
                return false;

        len = mptcp_add_addr_len(saddr.family, echo, port);
        if (remaining < len)
                return false;

        *size = len;
        if (drop_other_suboptions)
                *size -= opt_size;
        opts->addr_id = saddr.id;
        if (port)
                opts->port = ntohs(saddr.port);
        if (saddr.family == AF_INET) {
                opts->suboptions |= OPTION_MPTCP_ADD_ADDR;
                opts->addr = saddr.addr;
                if (!echo) {
                        opts->ahmac = add_addr_generate_hmac(msk->local_key,
                                                             msk->remote_key,
                                                             opts->addr_id,
                                                             &opts->addr,
                                                             opts->port);
                }
        }
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        else if (saddr.family == AF_INET6) {
                opts->suboptions |= OPTION_MPTCP_ADD_ADDR6;
                opts->addr6 = saddr.addr6;
                if (!echo) {
                        opts->ahmac = add_addr6_generate_hmac(msk->local_key,
                                                              msk->remote_key,
                                                              opts->addr_id,
                                                              &opts->addr6,
                                                              opts->port);
                }
        }
#endif
        pr_debug("addr_id=%d, ahmac=%llu, echo=%d, port=%d",
                 opts->addr_id, opts->ahmac, echo, opts->port);

        return true;
}

static bool mptcp_established_options_rm_addr(struct sock *sk,
                                              unsigned int *size,
                                              unsigned int remaining,
                                              struct mptcp_out_options *opts)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        u8 rm_id;

        if (!mptcp_pm_should_rm_signal(msk) ||
            !(mptcp_pm_rm_addr_signal(msk, remaining, &rm_id)))
                return false;

        if (remaining < TCPOLEN_MPTCP_RM_ADDR_BASE)
                return false;

        *size = TCPOLEN_MPTCP_RM_ADDR_BASE;
        opts->suboptions |= OPTION_MPTCP_RM_ADDR;
        opts->rm_id = rm_id;

        pr_debug("rm_id=%d", opts->rm_id);

        return true;
}

static bool mptcp_established_options_mp_prio(struct sock *sk,
                                              unsigned int *size,
                                              unsigned int remaining,
                                              struct mptcp_out_options *opts)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);

        if (!subflow->send_mp_prio)
                return false;

        /* account for the trailing 'nop' option */
        if (remaining < TCPOLEN_MPTCP_PRIO_ALIGN)
                return false;

        *size = TCPOLEN_MPTCP_PRIO_ALIGN;
        opts->suboptions |= OPTION_MPTCP_PRIO;
        opts->backup = subflow->request_bkup;

        pr_debug("prio=%d", opts->backup);

        return true;
}

bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
                               unsigned int *size, unsigned int remaining,
                               struct mptcp_out_options *opts)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        unsigned int opt_size = 0;
        bool snd_data_fin;
        bool ret = false;

        opts->suboptions = 0;

        if (unlikely(__mptcp_check_fallback(msk)))
                return false;

        /* prevent adding of any MPTCP related options on reset packet
         * until we support MP_TCPRST/MP_FASTCLOSE
         */
        if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST))
                return false;

        snd_data_fin = mptcp_data_fin_enabled(msk);
        if (mptcp_established_options_mp(sk, skb, snd_data_fin, &opt_size, remaining, opts))
                ret = true;
        else if (mptcp_established_options_dss(sk, skb, snd_data_fin, &opt_size, remaining, opts))
                ret = true;

        /* we reserved enough space for the above options, and exceeding the
         * TCP option space would be fatal
         */
        if (WARN_ON_ONCE(opt_size > remaining))
                return false;

        *size += opt_size;
        remaining -= opt_size;
        if (mptcp_established_options_add_addr(sk, skb, &opt_size, remaining, opts)) {
                *size += opt_size;
                remaining -= opt_size;
                ret = true;
        } else if (mptcp_established_options_rm_addr(sk, &opt_size, remaining, opts)) {
                *size += opt_size;
                remaining -= opt_size;
                ret = true;
        }

        if (mptcp_established_options_mp_prio(sk, &opt_size, remaining, opts)) {
                *size += opt_size;
                remaining -= opt_size;
                ret = true;
        }

        return ret;
}

bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
                          struct mptcp_out_options *opts)
{
        struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);

        if (subflow_req->mp_capable) {
                opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
                opts->sndr_key = subflow_req->local_key;
                *size = TCPOLEN_MPTCP_MPC_SYNACK;
                pr_debug("subflow_req=%p, local_key=%llu",
                         subflow_req, subflow_req->local_key);
                return true;
        } else if (subflow_req->mp_join) {
                opts->suboptions = OPTION_MPTCP_MPJ_SYNACK;
                opts->backup = subflow_req->backup;
                opts->join_id = subflow_req->local_id;
                opts->thmac = subflow_req->thmac;
                opts->nonce = subflow_req->local_nonce;
                pr_debug("req=%p, bkup=%u, id=%u, thmac=%llu, nonce=%u",
                         subflow_req, opts->backup, opts->join_id,
                         opts->thmac, opts->nonce);
                *size = TCPOLEN_MPTCP_MPJ_SYNACK;
                return true;
        }
        return false;
}

static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
                                    struct mptcp_subflow_context *subflow,
                                    struct sk_buff *skb,
                                    struct mptcp_options_received *mp_opt)
{
        /* here we can process OoO, in-window pkts, only in-sequence 4th ack
         * will make the subflow fully established
         */
        if (likely(subflow->fully_established)) {
                /* on passive sockets, check for 3rd ack retransmission
                 * note that msk is always set by subflow_syn_recv_sock()
                 * for mp_join subflows
                 */
                if (TCP_SKB_CB(skb)->seq == subflow->ssn_offset + 1 &&
                    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq &&
                    subflow->mp_join && mp_opt->mp_join &&
                    READ_ONCE(msk->pm.server_side))
                        tcp_send_ack(ssk);
                goto fully_established;
        }

        /* we must process OoO packets before the first subflow is fully
         * established. OoO packets are instead a protocol violation
         * for MP_JOIN subflows as the peer must not send any data
         * before receiving the forth ack - cfr. RFC 8684 section 3.2.
         */
        if (TCP_SKB_CB(skb)->seq != subflow->ssn_offset + 1) {
                if (subflow->mp_join)
                        goto reset;
                return subflow->mp_capable;
        }

        if (mp_opt->dss && mp_opt->use_ack) {
                /* subflows are fully established as soon as we get any
                 * additional ack.
                 */
                subflow->fully_established = 1;
                WRITE_ONCE(msk->fully_established, true);
                goto fully_established;
        }

        if (mp_opt->add_addr) {
                WRITE_ONCE(msk->fully_established, true);
                return true;
        }

        /* If the first established packet does not contain MP_CAPABLE + data
         * then fallback to TCP. Fallback scenarios requires a reset for
         * MP_JOIN subflows.
         */
        if (!mp_opt->mp_capable) {
                if (subflow->mp_join)
                        goto reset;
                subflow->mp_capable = 0;
                pr_fallback(msk);
                __mptcp_do_fallback(msk);
                return false;
        }

        if (unlikely(!READ_ONCE(msk->pm.server_side)))
                pr_warn_once("bogus mpc option on established client sk");
        mptcp_subflow_fully_established(subflow, mp_opt);

fully_established:
        /* if the subflow is not already linked into the conn_list, we can't
         * notify the PM: this subflow is still on the listener queue
         * and the PM possibly acquiring the subflow lock could race with
         * the listener close
         */
        if (likely(subflow->pm_notified) || list_empty(&subflow->node))
                return true;

        subflow->pm_notified = 1;
        if (subflow->mp_join) {
                clear_3rdack_retransmission(ssk);
                mptcp_pm_subflow_established(msk, subflow);
        } else {
                mptcp_pm_fully_established(msk, ssk, GFP_ATOMIC);
        }
        return true;

reset:
        mptcp_subflow_reset(ssk);
        return false;
}

static u64 expand_ack(u64 old_ack, u64 cur_ack, bool use_64bit)
{
        u32 old_ack32, cur_ack32;

        if (use_64bit)
                return cur_ack;

        old_ack32 = (u32)old_ack;
        cur_ack32 = (u32)cur_ack;
        cur_ack = (old_ack & GENMASK_ULL(63, 32)) + cur_ack32;
        if (unlikely(before(cur_ack32, old_ack32)))
                return cur_ack + (1LL << 32);
        return cur_ack;
}

static void ack_update_msk(struct mptcp_sock *msk,
                           struct sock *ssk,
                           struct mptcp_options_received *mp_opt)
{
        u64 new_wnd_end, new_snd_una, snd_nxt = READ_ONCE(msk->snd_nxt);
        struct sock *sk = (struct sock *)msk;
        u64 old_snd_una;

        mptcp_data_lock(sk);

        /* avoid ack expansion on update conflict, to reduce the risk of
         * wrongly expanding to a future ack sequence number, which is way
         * more dangerous than missing an ack
         */
        old_snd_una = msk->snd_una;
        new_snd_una = expand_ack(old_snd_una, mp_opt->data_ack, mp_opt->ack64);

        /* ACK for data not even sent yet? Ignore. */
        if (after64(new_snd_una, snd_nxt))
                new_snd_una = old_snd_una;

        new_wnd_end = new_snd_una + tcp_sk(ssk)->snd_wnd;

        if (after64(new_wnd_end, msk->wnd_end))
                msk->wnd_end = new_wnd_end;

        /* this assumes mptcp_incoming_options() is invoked after tcp_ack() */
        if (after64(msk->wnd_end, READ_ONCE(msk->snd_nxt)))
                __mptcp_check_push(sk, ssk);

        if (after64(new_snd_una, old_snd_una)) {
                msk->snd_una = new_snd_una;
                __mptcp_data_acked(sk);
        }
        mptcp_data_unlock(sk);
}

bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit)
{
        /* Skip if DATA_FIN was already received.
         * If updating simultaneously with the recvmsg loop, values
         * should match. If they mismatch, the peer is misbehaving and
         * we will prefer the most recent information.
         */
        if (READ_ONCE(msk->rcv_data_fin) || !READ_ONCE(msk->first))
                return false;

        WRITE_ONCE(msk->rcv_data_fin_seq,
                   expand_ack(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
        WRITE_ONCE(msk->rcv_data_fin, 1);

        return true;
}

static bool add_addr_hmac_valid(struct mptcp_sock *msk,
                                struct mptcp_options_received *mp_opt)
{
        u64 hmac = 0;

        if (mp_opt->echo)
                return true;

        if (mp_opt->family == MPTCP_ADDR_IPVERSION_4)
                hmac = add_addr_generate_hmac(msk->remote_key,
                                              msk->local_key,
                                              mp_opt->addr_id, &mp_opt->addr,
                                              mp_opt->port);
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        else
                hmac = add_addr6_generate_hmac(msk->remote_key,
                                               msk->local_key,
                                               mp_opt->addr_id, &mp_opt->addr6,
                                               mp_opt->port);
#endif

        pr_debug("msk=%p, ahmac=%llu, mp_opt->ahmac=%llu\n",
                 msk, (unsigned long long)hmac,
                 (unsigned long long)mp_opt->ahmac);

        return hmac == mp_opt->ahmac;
}

void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        struct mptcp_options_received mp_opt;
        struct mptcp_ext *mpext;

        if (__mptcp_check_fallback(msk)) {
                /* Keep it simple and unconditionally trigger send data cleanup and
                 * pending queue spooling. We will need to acquire the data lock
                 * for more accurate checks, and once the lock is acquired, such
                 * helpers are cheap.
                 */
                mptcp_data_lock(subflow->conn);
                if (sk_stream_memory_free(sk))
                        __mptcp_check_push(subflow->conn, sk);
                __mptcp_data_acked(subflow->conn);

                mptcp_data_unlock(subflow->conn);
                return;
        }

        mptcp_get_options(skb, &mp_opt);
        if (!check_fully_established(msk, sk, subflow, skb, &mp_opt))
                return;

        if (mp_opt.fastclose &&
            msk->local_key == mp_opt.rcvr_key) {
                WRITE_ONCE(msk->rcv_fastclose, true);
                mptcp_schedule_work((struct sock *)msk);
        }

        if (mp_opt.add_addr && add_addr_hmac_valid(msk, &mp_opt)) {
                struct mptcp_addr_info addr;

                addr.port = htons(mp_opt.port);
                addr.id = mp_opt.addr_id;
                if (mp_opt.family == MPTCP_ADDR_IPVERSION_4) {
                        addr.family = AF_INET;
                        addr.addr = mp_opt.addr;
                }
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
                else if (mp_opt.family == MPTCP_ADDR_IPVERSION_6) {
                        addr.family = AF_INET6;
                        addr.addr6 = mp_opt.addr6;
                }
#endif
                if (!mp_opt.echo) {
                        mptcp_pm_add_addr_received(msk, &addr);
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDR);
                } else {
                        mptcp_pm_del_add_timer(msk, &addr);
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ECHOADD);
                }

                if (mp_opt.port)
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_PORTADD);

                mp_opt.add_addr = 0;
        }

        if (mp_opt.rm_addr) {
                mptcp_pm_rm_addr_received(msk, mp_opt.rm_id);
                mp_opt.rm_addr = 0;
        }

        if (mp_opt.mp_prio) {
                mptcp_pm_mp_prio_received(sk, mp_opt.backup);
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPPRIORX);
                mp_opt.mp_prio = 0;
        }

        if (!mp_opt.dss)
                return;

        /* we can't wait for recvmsg() to update the ack_seq, otherwise
         * monodirectional flows will stuck
         */
        if (mp_opt.use_ack)
                ack_update_msk(msk, sk, &mp_opt);

        /* Zero-data-length packets are dropped by the caller and not
         * propagated to the MPTCP layer, so the skb extension does not
         * need to be allocated or populated. DATA_FIN information, if
         * present, needs to be updated here before the skb is freed.
         */
        if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
                if (mp_opt.data_fin && mp_opt.data_len == 1 &&
                    mptcp_update_rcv_data_fin(msk, mp_opt.data_seq, mp_opt.dsn64) &&
                    schedule_work(&msk->work))
                        sock_hold(subflow->conn);

                return;
        }

        mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
        if (!mpext)
                return;

        memset(mpext, 0, sizeof(*mpext));

        if (mp_opt.use_map) {
                if (mp_opt.mpc_map) {
                        /* this is an MP_CAPABLE carrying MPTCP data
                         * we know this map the first chunk of data
                         */
                        mptcp_crypto_key_sha(subflow->remote_key, NULL,
                                             &mpext->data_seq);
                        mpext->data_seq++;
                        mpext->subflow_seq = 1;
                        mpext->dsn64 = 1;
                        mpext->mpc_map = 1;
                        mpext->data_fin = 0;
                } else {
                        mpext->data_seq = mp_opt.data_seq;
                        mpext->subflow_seq = mp_opt.subflow_seq;
                        mpext->dsn64 = mp_opt.dsn64;
                        mpext->data_fin = mp_opt.data_fin;
                }
                mpext->data_len = mp_opt.data_len;
                mpext->use_map = 1;
        }
}

static void mptcp_set_rwin(const struct tcp_sock *tp)
{
        const struct sock *ssk = (const struct sock *)tp;
        const struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk;
        u64 ack_seq;

        subflow = mptcp_subflow_ctx(ssk);
        msk = mptcp_sk(subflow->conn);

        ack_seq = READ_ONCE(msk->ack_seq) + tp->rcv_wnd;

        if (after64(ack_seq, READ_ONCE(msk->rcv_wnd_sent)))
                WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);
}

void mptcp_write_options(__be32 *ptr, const struct tcp_sock *tp,
                         struct mptcp_out_options *opts)
{
        if ((OPTION_MPTCP_MPC_SYN | OPTION_MPTCP_MPC_SYNACK |
             OPTION_MPTCP_MPC_ACK) & opts->suboptions) {
                u8 len;

                if (OPTION_MPTCP_MPC_SYN & opts->suboptions)
                        len = TCPOLEN_MPTCP_MPC_SYN;
                else if (OPTION_MPTCP_MPC_SYNACK & opts->suboptions)
                        len = TCPOLEN_MPTCP_MPC_SYNACK;
                else if (opts->ext_copy.data_len)
                        len = TCPOLEN_MPTCP_MPC_ACK_DATA;
                else
                        len = TCPOLEN_MPTCP_MPC_ACK;

                *ptr++ = mptcp_option(MPTCPOPT_MP_CAPABLE, len,
                                      MPTCP_SUPPORTED_VERSION,
                                      MPTCP_CAP_HMAC_SHA256);

                if (!((OPTION_MPTCP_MPC_SYNACK | OPTION_MPTCP_MPC_ACK) &
                    opts->suboptions))
                        goto mp_capable_done;

                put_unaligned_be64(opts->sndr_key, ptr);
                ptr += 2;
                if (!((OPTION_MPTCP_MPC_ACK) & opts->suboptions))
                        goto mp_capable_done;

                put_unaligned_be64(opts->rcvr_key, ptr);
                ptr += 2;
                if (!opts->ext_copy.data_len)
                        goto mp_capable_done;

                put_unaligned_be32(opts->ext_copy.data_len << 16 |
                                   TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
                ptr += 1;
        }

mp_capable_done:
        if ((OPTION_MPTCP_ADD_ADDR
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
             | OPTION_MPTCP_ADD_ADDR6
#endif
            ) & opts->suboptions) {
                u8 len = TCPOLEN_MPTCP_ADD_ADDR_BASE;
                u8 echo = MPTCP_ADDR_ECHO;

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
                if (OPTION_MPTCP_ADD_ADDR6 & opts->suboptions)
                        len = TCPOLEN_MPTCP_ADD_ADDR6_BASE;
#endif

                if (opts->port)
                        len += TCPOLEN_MPTCP_PORT_LEN;

                if (opts->ahmac) {
                        len += sizeof(opts->ahmac);
                        echo = 0;
                }

                *ptr++ = mptcp_option(MPTCPOPT_ADD_ADDR,
                                      len, echo, opts->addr_id);
                if (OPTION_MPTCP_ADD_ADDR & opts->suboptions) {
                        memcpy((u8 *)ptr, (u8 *)&opts->addr.s_addr, 4);
                        ptr += 1;
                }
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
                else if (OPTION_MPTCP_ADD_ADDR6 & opts->suboptions) {
                        memcpy((u8 *)ptr, opts->addr6.s6_addr, 16);
                        ptr += 4;
                }
#endif

                if (!opts->port) {
                        if (opts->ahmac) {
                                put_unaligned_be64(opts->ahmac, ptr);
                                ptr += 2;
                        }
                } else {
                        if (opts->ahmac) {
                                u8 *bptr = (u8 *)ptr;

                                put_unaligned_be16(opts->port, bptr);
                                bptr += 2;
                                put_unaligned_be64(opts->ahmac, bptr);
                                bptr += 8;
                                put_unaligned_be16(TCPOPT_NOP << 8 |
                                                   TCPOPT_NOP, bptr);

                                ptr += 3;
                        } else {
                                put_unaligned_be32(opts->port << 16 |
                                                   TCPOPT_NOP << 8 |
                                                   TCPOPT_NOP, ptr);
                                ptr += 1;
                        }
                }
        }

        if (OPTION_MPTCP_RM_ADDR & opts->suboptions) {
                *ptr++ = mptcp_option(MPTCPOPT_RM_ADDR,
                                      TCPOLEN_MPTCP_RM_ADDR_BASE,
                                      0, opts->rm_id);
        }

        if (OPTION_MPTCP_PRIO & opts->suboptions) {
                const struct sock *ssk = (const struct sock *)tp;
                struct mptcp_subflow_context *subflow;

                subflow = mptcp_subflow_ctx(ssk);
                subflow->send_mp_prio = 0;

                *ptr++ = mptcp_option(MPTCPOPT_MP_PRIO,
                                      TCPOLEN_MPTCP_PRIO,
                                      opts->backup, TCPOPT_NOP);
        }

        if (OPTION_MPTCP_MPJ_SYN & opts->suboptions) {
                *ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
                                      TCPOLEN_MPTCP_MPJ_SYN,
                                      opts->backup, opts->join_id);
                put_unaligned_be32(opts->token, ptr);
                ptr += 1;
                put_unaligned_be32(opts->nonce, ptr);
                ptr += 1;
        }

        if (OPTION_MPTCP_MPJ_SYNACK & opts->suboptions) {
                *ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
                                      TCPOLEN_MPTCP_MPJ_SYNACK,
                                      opts->backup, opts->join_id);
                put_unaligned_be64(opts->thmac, ptr);
                ptr += 2;
                put_unaligned_be32(opts->nonce, ptr);
                ptr += 1;
        }

        if (OPTION_MPTCP_MPJ_ACK & opts->suboptions) {
                *ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
                                      TCPOLEN_MPTCP_MPJ_ACK, 0, 0);
                memcpy(ptr, opts->hmac, MPTCPOPT_HMAC_LEN);
                ptr += 5;
        }

        if (opts->ext_copy.use_ack || opts->ext_copy.use_map) {
                struct mptcp_ext *mpext = &opts->ext_copy;
                u8 len = TCPOLEN_MPTCP_DSS_BASE;
                u8 flags = 0;

                if (mpext->use_ack) {
                        flags = MPTCP_DSS_HAS_ACK;
                        if (mpext->ack64) {
                                len += TCPOLEN_MPTCP_DSS_ACK64;
                                flags |= MPTCP_DSS_ACK64;
                        } else {
                                len += TCPOLEN_MPTCP_DSS_ACK32;
                        }
                }

                if (mpext->use_map) {
                        len += TCPOLEN_MPTCP_DSS_MAP64;

                        /* Use only 64-bit mapping flags for now, add
                         * support for optional 32-bit mappings later.
                         */
                        flags |= MPTCP_DSS_HAS_MAP | MPTCP_DSS_DSN64;
                        if (mpext->data_fin)
                                flags |= MPTCP_DSS_DATA_FIN;
                }

                *ptr++ = mptcp_option(MPTCPOPT_DSS, len, 0, flags);

                if (mpext->use_ack) {
                        if (mpext->ack64) {
                                put_unaligned_be64(mpext->data_ack, ptr);
                                ptr += 2;
                        } else {
                                put_unaligned_be32(mpext->data_ack32, ptr);
                                ptr += 1;
                        }
                }

                if (mpext->use_map) {
                        put_unaligned_be64(mpext->data_seq, ptr);
                        ptr += 2;
                        put_unaligned_be32(mpext->subflow_seq, ptr);
                        ptr += 1;
                        put_unaligned_be32(mpext->data_len << 16 |
                                           TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
                }
        }

        if (tp)
                mptcp_set_rwin(tp);
}