// 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 <linux/sched/signal.h>
#include <linux/atomic.h>
#include <net/sock.h>
#include <net/inet_common.h>
#include <net/inet_hashtables.h>
#include <net/protocol.h>
#include <net/tcp.h>
#include <net/tcp_states.h>
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
#include <net/transp_v6.h>
#endif
#include <net/mptcp.h>
#include "protocol.h"
#include "mib.h"

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
struct mptcp6_sock {
        struct mptcp_sock msk;
        struct ipv6_pinfo np;
};
#endif

struct mptcp_skb_cb {
        u64 map_seq;
        u64 end_seq;
        u32 offset;
};

#define MPTCP_SKB_CB(__skb)     ((struct mptcp_skb_cb *)&((__skb)->cb[0]))

static struct percpu_counter mptcp_sockets_allocated;

/* If msk has an initial subflow socket, and the MP_CAPABLE handshake has not
 * completed yet or has failed, return the subflow socket.
 * Otherwise return NULL.
 */
static struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk)
{
        if (!msk->subflow || READ_ONCE(msk->can_ack))
                return NULL;

        return msk->subflow;
}

static bool mptcp_is_tcpsk(struct sock *sk)
{
        struct socket *sock = sk->sk_socket;

        if (unlikely(sk->sk_prot == &tcp_prot)) {
                /* we are being invoked after mptcp_accept() has
                 * accepted a non-mp-capable flow: sk is a tcp_sk,
                 * not an mptcp one.
                 *
                 * Hand the socket over to tcp so all further socket ops
                 * bypass mptcp.
                 */
                sock->ops = &inet_stream_ops;
                return true;
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        } else if (unlikely(sk->sk_prot == &tcpv6_prot)) {
                sock->ops = &inet6_stream_ops;
                return true;
#endif
        }

        return false;
}

static struct sock *__mptcp_tcp_fallback(struct mptcp_sock *msk)
{
        sock_owned_by_me((const struct sock *)msk);

        if (likely(!__mptcp_check_fallback(msk)))
                return NULL;

        return msk->first;
}

static int __mptcp_socket_create(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;
        struct sock *sk = (struct sock *)msk;
        struct socket *ssock;
        int err;

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

        msk->first = ssock->sk;
        msk->subflow = ssock;
        subflow = mptcp_subflow_ctx(ssock->sk);
        list_add(&subflow->node, &msk->conn_list);
        subflow->request_mptcp = 1;

        /* accept() will wait on first subflow sk_wq, and we always wakes up
         * via msk->sk_socket
         */
        RCU_INIT_POINTER(msk->first->sk_wq, &sk->sk_socket->wq);

        return 0;
}

static void mptcp_drop(struct sock *sk, struct sk_buff *skb)
{
        sk_drops_add(sk, skb);
        __kfree_skb(skb);
}

static bool mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
                               struct sk_buff *from)
{
        bool fragstolen;
        int delta;

        if (MPTCP_SKB_CB(from)->offset ||
            !skb_try_coalesce(to, from, &fragstolen, &delta))
                return false;

        pr_debug("colesced seq %llx into %llx new len %d new end seq %llx",
                 MPTCP_SKB_CB(from)->map_seq, MPTCP_SKB_CB(to)->map_seq,
                 to->len, MPTCP_SKB_CB(from)->end_seq);
        MPTCP_SKB_CB(to)->end_seq = MPTCP_SKB_CB(from)->end_seq;
        kfree_skb_partial(from, fragstolen);
        atomic_add(delta, &sk->sk_rmem_alloc);
        sk_mem_charge(sk, delta);
        return true;
}

static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to,
                                   struct sk_buff *from)
{
        if (MPTCP_SKB_CB(from)->map_seq != MPTCP_SKB_CB(to)->end_seq)
                return false;

        return mptcp_try_coalesce((struct sock *)msk, to, from);
}

/* "inspired" by tcp_data_queue_ofo(), main differences:
 * - use mptcp seqs
 * - don't cope with sacks
 */
static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb)
{
        struct sock *sk = (struct sock *)msk;
        struct rb_node **p, *parent;
        u64 seq, end_seq, max_seq;
        struct sk_buff *skb1;
        int space;

        seq = MPTCP_SKB_CB(skb)->map_seq;
        end_seq = MPTCP_SKB_CB(skb)->end_seq;
        space = tcp_space(sk);
        max_seq = space > 0 ? space + msk->ack_seq : msk->ack_seq;

        pr_debug("msk=%p seq=%llx limit=%llx empty=%d", msk, seq, max_seq,
                 RB_EMPTY_ROOT(&msk->out_of_order_queue));
        if (after64(seq, max_seq)) {
                /* out of window */
                mptcp_drop(sk, skb);
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_NODSSWINDOW);
                return;
        }

        p = &msk->out_of_order_queue.rb_node;
        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUE);
        if (RB_EMPTY_ROOT(&msk->out_of_order_queue)) {
                rb_link_node(&skb->rbnode, NULL, p);
                rb_insert_color(&skb->rbnode, &msk->out_of_order_queue);
                msk->ooo_last_skb = skb;
                goto end;
        }

        /* with 2 subflows, adding at end of ooo queue is quite likely
         * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
         */
        if (mptcp_ooo_try_coalesce(msk, msk->ooo_last_skb, skb)) {
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOMERGE);
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUETAIL);
                return;
        }

        /* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
        if (!before64(seq, MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq)) {
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOQUEUETAIL);
                parent = &msk->ooo_last_skb->rbnode;
                p = &parent->rb_right;
                goto insert;
        }

        /* Find place to insert this segment. Handle overlaps on the way. */
        parent = NULL;
        while (*p) {
                parent = *p;
                skb1 = rb_to_skb(parent);
                if (before64(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
                        p = &parent->rb_left;
                        continue;
                }
                if (before64(seq, MPTCP_SKB_CB(skb1)->end_seq)) {
                        if (!after64(end_seq, MPTCP_SKB_CB(skb1)->end_seq)) {
                                /* All the bits are present. Drop. */
                                mptcp_drop(sk, skb);
                                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
                                return;
                        }
                        if (after64(seq, MPTCP_SKB_CB(skb1)->map_seq)) {
                                /* partial overlap:
                                 *     |     skb      |
                                 *  |     skb1    |
                                 * continue traversing
                                 */
                        } else {
                                /* skb's seq == skb1's seq and skb covers skb1.
                                 * Replace skb1 with skb.
                                 */
                                rb_replace_node(&skb1->rbnode, &skb->rbnode,
                                                &msk->out_of_order_queue);
                                mptcp_drop(sk, skb1);
                                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
                                goto merge_right;
                        }
                } else if (mptcp_ooo_try_coalesce(msk, skb1, skb)) {
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOMERGE);
                        return;
                }
                p = &parent->rb_right;
        }

insert:
        /* Insert segment into RB tree. */
        rb_link_node(&skb->rbnode, parent, p);
        rb_insert_color(&skb->rbnode, &msk->out_of_order_queue);

merge_right:
        /* Remove other segments covered by skb. */
        while ((skb1 = skb_rb_next(skb)) != NULL) {
                if (before64(end_seq, MPTCP_SKB_CB(skb1)->end_seq))
                        break;
                rb_erase(&skb1->rbnode, &msk->out_of_order_queue);
                mptcp_drop(sk, skb1);
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
        }
        /* If there is no skb after us, we are the last_skb ! */
        if (!skb1)
                msk->ooo_last_skb = skb;

end:
        skb_condense(skb);
        skb_set_owner_r(skb, sk);
}

static bool __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
                             struct sk_buff *skb, unsigned int offset,
                             size_t copy_len)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct sock *sk = (struct sock *)msk;
        struct sk_buff *tail;

        __skb_unlink(skb, &ssk->sk_receive_queue);

        skb_ext_reset(skb);
        skb_orphan(skb);

        /* try to fetch required memory from subflow */
        if (!sk_rmem_schedule(sk, skb, skb->truesize)) {
                if (ssk->sk_forward_alloc < skb->truesize)
                        goto drop;
                __sk_mem_reclaim(ssk, skb->truesize);
                if (!sk_rmem_schedule(sk, skb, skb->truesize))
                        goto drop;
        }

        /* the skb map_seq accounts for the skb offset:
         * mptcp_subflow_get_mapped_dsn() is based on the current tp->copied_seq
         * value
         */
        MPTCP_SKB_CB(skb)->map_seq = mptcp_subflow_get_mapped_dsn(subflow);
        MPTCP_SKB_CB(skb)->end_seq = MPTCP_SKB_CB(skb)->map_seq + copy_len;
        MPTCP_SKB_CB(skb)->offset = offset;

        if (MPTCP_SKB_CB(skb)->map_seq == msk->ack_seq) {
                /* in sequence */
                WRITE_ONCE(msk->ack_seq, msk->ack_seq + copy_len);
                tail = skb_peek_tail(&sk->sk_receive_queue);
                if (tail && mptcp_try_coalesce(sk, tail, skb))
                        return true;

                skb_set_owner_r(skb, sk);
                __skb_queue_tail(&sk->sk_receive_queue, skb);
                return true;
        } else if (after64(MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq)) {
                mptcp_data_queue_ofo(msk, skb);
                return false;
        }

        /* old data, keep it simple and drop the whole pkt, sender
         * will retransmit as needed, if needed.
         */
        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
drop:
        mptcp_drop(sk, skb);
        return false;
}

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

        sk_stop_timer(sk, &icsk->icsk_retransmit_timer);
        mptcp_sk(sk)->timer_ival = 0;
}

static void mptcp_check_data_fin_ack(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (__mptcp_check_fallback(msk))
                return;

        /* Look for an acknowledged DATA_FIN */
        if (((1 << sk->sk_state) &
             (TCPF_FIN_WAIT1 | TCPF_CLOSING | TCPF_LAST_ACK)) &&
            msk->write_seq == atomic64_read(&msk->snd_una)) {
                mptcp_stop_timer(sk);

                WRITE_ONCE(msk->snd_data_fin_enable, 0);

                switch (sk->sk_state) {
                case TCP_FIN_WAIT1:
                        inet_sk_state_store(sk, TCP_FIN_WAIT2);
                        sk->sk_state_change(sk);
                        break;
                case TCP_CLOSING:
                case TCP_LAST_ACK:
                        inet_sk_state_store(sk, TCP_CLOSE);
                        sk->sk_state_change(sk);
                        break;
                }

                if (sk->sk_shutdown == SHUTDOWN_MASK ||
                    sk->sk_state == TCP_CLOSE)
                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
                else
                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
        }
}

static bool mptcp_pending_data_fin(struct sock *sk, u64 *seq)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (READ_ONCE(msk->rcv_data_fin) &&
            ((1 << sk->sk_state) &
             (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_FIN_WAIT2))) {
                u64 rcv_data_fin_seq = READ_ONCE(msk->rcv_data_fin_seq);

                if (msk->ack_seq == rcv_data_fin_seq) {
                        if (seq)
                                *seq = rcv_data_fin_seq;

                        return true;
                }
        }

        return false;
}

static void mptcp_set_timeout(const struct sock *sk, const struct sock *ssk)
{
        long tout = ssk && inet_csk(ssk)->icsk_pending ?
                                      inet_csk(ssk)->icsk_timeout - jiffies : 0;

        if (tout <= 0)
                tout = mptcp_sk(sk)->timer_ival;
        mptcp_sk(sk)->timer_ival = tout > 0 ? tout : TCP_RTO_MIN;
}

static void mptcp_check_data_fin(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        u64 rcv_data_fin_seq;

        if (__mptcp_check_fallback(msk) || !msk->first)
                return;

        /* Need to ack a DATA_FIN received from a peer while this side
         * of the connection is in ESTABLISHED, FIN_WAIT1, or FIN_WAIT2.
         * msk->rcv_data_fin was set when parsing the incoming options
         * at the subflow level and the msk lock was not held, so this
         * is the first opportunity to act on the DATA_FIN and change
         * the msk state.
         *
         * If we are caught up to the sequence number of the incoming
         * DATA_FIN, send the DATA_ACK now and do state transition.  If
         * not caught up, do nothing and let the recv code send DATA_ACK
         * when catching up.
         */

        if (mptcp_pending_data_fin(sk, &rcv_data_fin_seq)) {
                struct mptcp_subflow_context *subflow;

                WRITE_ONCE(msk->ack_seq, msk->ack_seq + 1);
                WRITE_ONCE(msk->rcv_data_fin, 0);

                sk->sk_shutdown |= RCV_SHUTDOWN;
                smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
                set_bit(MPTCP_DATA_READY, &msk->flags);

                switch (sk->sk_state) {
                case TCP_ESTABLISHED:
                        inet_sk_state_store(sk, TCP_CLOSE_WAIT);
                        break;
                case TCP_FIN_WAIT1:
                        inet_sk_state_store(sk, TCP_CLOSING);
                        break;
                case TCP_FIN_WAIT2:
                        inet_sk_state_store(sk, TCP_CLOSE);
                        // @@ Close subflows now?
                        break;
                default:
                        /* Other states not expected */
                        WARN_ON_ONCE(1);
                        break;
                }

                mptcp_set_timeout(sk, NULL);
                mptcp_for_each_subflow(msk, subflow) {
                        struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

                        lock_sock(ssk);
                        tcp_send_ack(ssk);
                        release_sock(ssk);
                }

                sk->sk_state_change(sk);

                if (sk->sk_shutdown == SHUTDOWN_MASK ||
                    sk->sk_state == TCP_CLOSE)
                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
                else
                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
        }
}

static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
                                           struct sock *ssk,
                                           unsigned int *bytes)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct sock *sk = (struct sock *)msk;
        unsigned int moved = 0;
        bool more_data_avail;
        struct tcp_sock *tp;
        u32 old_copied_seq;
        bool done = false;

        pr_debug("msk=%p ssk=%p", msk, ssk);
        tp = tcp_sk(ssk);
        old_copied_seq = tp->copied_seq;
        do {
                u32 map_remaining, offset;
                u32 seq = tp->copied_seq;
                struct sk_buff *skb;
                bool fin;

                /* try to move as much data as available */
                map_remaining = subflow->map_data_len -
                                mptcp_subflow_get_map_offset(subflow);

                skb = skb_peek(&ssk->sk_receive_queue);
                if (!skb) {
                        /* if no data is found, a racing workqueue/recvmsg
                         * already processed the new data, stop here or we
                         * can enter an infinite loop
                         */
                        if (!moved)
                                done = true;
                        break;
                }

                if (__mptcp_check_fallback(msk)) {
                        /* if we are running under the workqueue, TCP could have
                         * collapsed skbs between dummy map creation and now
                         * be sure to adjust the size
                         */
                        map_remaining = skb->len;
                        subflow->map_data_len = skb->len;
                }

                offset = seq - TCP_SKB_CB(skb)->seq;
                fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
                if (fin) {
                        done = true;
                        seq++;
                }

                if (offset < skb->len) {
                        size_t len = skb->len - offset;

                        if (tp->urg_data)
                                done = true;

                        if (__mptcp_move_skb(msk, ssk, skb, offset, len))
                                moved += len;
                        seq += len;

                        if (WARN_ON_ONCE(map_remaining < len))
                                break;
                } else {
                        WARN_ON_ONCE(!fin);
                        sk_eat_skb(ssk, skb);
                        done = true;
                }

                WRITE_ONCE(tp->copied_seq, seq);
                more_data_avail = mptcp_subflow_data_available(ssk);

                if (atomic_read(&sk->sk_rmem_alloc) > READ_ONCE(sk->sk_rcvbuf)) {
                        done = true;
                        break;
                }
        } while (more_data_avail);

        *bytes += moved;
        if (tp->copied_seq != old_copied_seq)
                tcp_cleanup_rbuf(ssk, 1);

        return done;
}

static bool mptcp_ofo_queue(struct mptcp_sock *msk)
{
        struct sock *sk = (struct sock *)msk;
        struct sk_buff *skb, *tail;
        bool moved = false;
        struct rb_node *p;
        u64 end_seq;

        p = rb_first(&msk->out_of_order_queue);
        pr_debug("msk=%p empty=%d", msk, RB_EMPTY_ROOT(&msk->out_of_order_queue));
        while (p) {
                skb = rb_to_skb(p);
                if (after64(MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq))
                        break;

                p = rb_next(p);
                rb_erase(&skb->rbnode, &msk->out_of_order_queue);

                if (unlikely(!after64(MPTCP_SKB_CB(skb)->end_seq,
                                      msk->ack_seq))) {
                        mptcp_drop(sk, skb);
                        MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_DUPDATA);
                        continue;
                }

                end_seq = MPTCP_SKB_CB(skb)->end_seq;
                tail = skb_peek_tail(&sk->sk_receive_queue);
                if (!tail || !mptcp_ooo_try_coalesce(msk, tail, skb)) {
                        int delta = msk->ack_seq - MPTCP_SKB_CB(skb)->map_seq;

                        /* skip overlapping data, if any */
                        pr_debug("uncoalesced seq=%llx ack seq=%llx delta=%d",
                                 MPTCP_SKB_CB(skb)->map_seq, msk->ack_seq,
                                 delta);
                        MPTCP_SKB_CB(skb)->offset += delta;
                        __skb_queue_tail(&sk->sk_receive_queue, skb);
                }
                msk->ack_seq = end_seq;
                moved = true;
        }
        return moved;
}

/* In most cases we will be able to lock the mptcp socket.  If its already
 * owned, we need to defer to the work queue to avoid ABBA deadlock.
 */
static bool move_skbs_to_msk(struct mptcp_sock *msk, struct sock *ssk)
{
        struct sock *sk = (struct sock *)msk;
        unsigned int moved = 0;

        if (READ_ONCE(sk->sk_lock.owned))
                return false;

        if (unlikely(!spin_trylock_bh(&sk->sk_lock.slock)))
                return false;

        /* must re-check after taking the lock */
        if (!READ_ONCE(sk->sk_lock.owned)) {
                __mptcp_move_skbs_from_subflow(msk, ssk, &moved);
                mptcp_ofo_queue(msk);

                /* If the moves have caught up with the DATA_FIN sequence number
                 * it's time to ack the DATA_FIN and change socket state, but
                 * this is not a good place to change state. Let the workqueue
                 * do it.
                 */
                if (mptcp_pending_data_fin(sk, NULL) &&
                    schedule_work(&msk->work))
                        sock_hold(sk);
        }

        spin_unlock_bh(&sk->sk_lock.slock);

        return moved > 0;
}

void mptcp_data_ready(struct sock *sk, struct sock *ssk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        struct mptcp_sock *msk = mptcp_sk(sk);
        bool wake;

        /* move_skbs_to_msk below can legitly clear the data_avail flag,
         * but we will need later to properly woke the reader, cache its
         * value
         */
        wake = subflow->data_avail == MPTCP_SUBFLOW_DATA_AVAIL;
        if (wake)
                set_bit(MPTCP_DATA_READY, &msk->flags);

        if (atomic_read(&sk->sk_rmem_alloc) < READ_ONCE(sk->sk_rcvbuf) &&
            move_skbs_to_msk(msk, ssk))
                goto wake;

        /* don't schedule if mptcp sk is (still) over limit */
        if (atomic_read(&sk->sk_rmem_alloc) > READ_ONCE(sk->sk_rcvbuf))
                goto wake;

        /* mptcp socket is owned, release_cb should retry */
        if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED,
                              &sk->sk_tsq_flags)) {
                sock_hold(sk);

                /* need to try again, its possible release_cb() has already
                 * been called after the test_and_set_bit() above.
                 */
                move_skbs_to_msk(msk, ssk);
        }
wake:
        if (wake)
                sk->sk_data_ready(sk);
}

static void __mptcp_flush_join_list(struct mptcp_sock *msk)
{
        if (likely(list_empty(&msk->join_list)))
                return;

        spin_lock_bh(&msk->join_list_lock);
        list_splice_tail_init(&msk->join_list, &msk->conn_list);
        spin_unlock_bh(&msk->join_list_lock);
}

static bool mptcp_timer_pending(struct sock *sk)
{
        return timer_pending(&inet_csk(sk)->icsk_retransmit_timer);
}

static void mptcp_reset_timer(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        unsigned long tout;

        /* should never be called with mptcp level timer cleared */
        tout = READ_ONCE(mptcp_sk(sk)->timer_ival);
        if (WARN_ON_ONCE(!tout))
                tout = TCP_RTO_MIN;
        sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + tout);
}

void mptcp_data_acked(struct sock *sk)
{
        mptcp_reset_timer(sk);

        if ((!test_bit(MPTCP_SEND_SPACE, &mptcp_sk(sk)->flags) ||
             (inet_sk_state_load(sk) != TCP_ESTABLISHED)) &&
            schedule_work(&mptcp_sk(sk)->work))
                sock_hold(sk);
}

void mptcp_subflow_eof(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (!test_and_set_bit(MPTCP_WORK_EOF, &msk->flags) &&
            schedule_work(&msk->work))
                sock_hold(sk);
}

static void mptcp_check_for_eof(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;
        struct sock *sk = (struct sock *)msk;
        int receivers = 0;

        mptcp_for_each_subflow(msk, subflow)
                receivers += !subflow->rx_eof;

        if (!receivers && !(sk->sk_shutdown & RCV_SHUTDOWN)) {
                /* hopefully temporary hack: propagate shutdown status
                 * to msk, when all subflows agree on it
                 */
                sk->sk_shutdown |= RCV_SHUTDOWN;

                smp_mb__before_atomic(); /* SHUTDOWN must be visible first */
                set_bit(MPTCP_DATA_READY, &msk->flags);
                sk->sk_data_ready(sk);
        }
}

static bool mptcp_ext_cache_refill(struct mptcp_sock *msk)
{
        const struct sock *sk = (const struct sock *)msk;

        if (!msk->cached_ext)
                msk->cached_ext = __skb_ext_alloc(sk->sk_allocation);

        return !!msk->cached_ext;
}

static struct sock *mptcp_subflow_recv_lookup(const struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;
        struct sock *sk = (struct sock *)msk;

        sock_owned_by_me(sk);

        mptcp_for_each_subflow(msk, subflow) {
                if (subflow->data_avail)
                        return mptcp_subflow_tcp_sock(subflow);
        }

        return NULL;
}

static bool mptcp_skb_can_collapse_to(u64 write_seq,
                                      const struct sk_buff *skb,
                                      const struct mptcp_ext *mpext)
{
        if (!tcp_skb_can_collapse_to(skb))
                return false;

        /* can collapse only if MPTCP level sequence is in order */
        return mpext && mpext->data_seq + mpext->data_len == write_seq;
}

static bool mptcp_frag_can_collapse_to(const struct mptcp_sock *msk,
                                       const struct page_frag *pfrag,
                                       const struct mptcp_data_frag *df)
{
        return df && pfrag->page == df->page &&
                df->data_seq + df->data_len == msk->write_seq;
}

static void dfrag_uncharge(struct sock *sk, int len)
{
        sk_mem_uncharge(sk, len);
        sk_wmem_queued_add(sk, -len);
}

static void dfrag_clear(struct sock *sk, struct mptcp_data_frag *dfrag)
{
        int len = dfrag->data_len + dfrag->overhead;

        list_del(&dfrag->list);
        dfrag_uncharge(sk, len);
        put_page(dfrag->page);
}

static bool mptcp_is_writeable(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;

        if (!sk_stream_is_writeable((struct sock *)msk))
                return false;

        mptcp_for_each_subflow(msk, subflow) {
                if (sk_stream_is_writeable(subflow->tcp_sock))
                        return true;
        }
        return false;
}

static void mptcp_clean_una(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_data_frag *dtmp, *dfrag;
        bool cleaned = false;
        u64 snd_una;

        /* on fallback we just need to ignore snd_una, as this is really
         * plain TCP
         */
        if (__mptcp_check_fallback(msk))
                atomic64_set(&msk->snd_una, msk->write_seq);
        snd_una = atomic64_read(&msk->snd_una);

        list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list) {
                if (after64(dfrag->data_seq + dfrag->data_len, snd_una))
                        break;

                dfrag_clear(sk, dfrag);
                cleaned = true;
        }

        dfrag = mptcp_rtx_head(sk);
        if (dfrag && after64(snd_una, dfrag->data_seq)) {
                u64 delta = snd_una - dfrag->data_seq;

                if (WARN_ON_ONCE(delta > dfrag->data_len))
                        goto out;

                dfrag->data_seq += delta;
                dfrag->offset += delta;
                dfrag->data_len -= delta;

                dfrag_uncharge(sk, delta);
                cleaned = true;
        }

out:
        if (cleaned) {
                sk_mem_reclaim_partial(sk);

                /* Only wake up writers if a subflow is ready */
                if (mptcp_is_writeable(msk)) {
                        set_bit(MPTCP_SEND_SPACE, &mptcp_sk(sk)->flags);
                        smp_mb__after_atomic();

                        /* set SEND_SPACE before sk_stream_write_space clears
                         * NOSPACE
                         */
                        sk_stream_write_space(sk);
                }
        }
}

/* ensure we get enough memory for the frag hdr, beyond some minimal amount of
 * data
 */
static bool mptcp_page_frag_refill(struct sock *sk, struct page_frag *pfrag)
{
        if (likely(skb_page_frag_refill(32U + sizeof(struct mptcp_data_frag),
                                        pfrag, sk->sk_allocation)))
                return true;

        sk->sk_prot->enter_memory_pressure(sk);
        sk_stream_moderate_sndbuf(sk);
        return false;
}

static struct mptcp_data_frag *
mptcp_carve_data_frag(const struct mptcp_sock *msk, struct page_frag *pfrag,
                      int orig_offset)
{
        int offset = ALIGN(orig_offset, sizeof(long));
        struct mptcp_data_frag *dfrag;

        dfrag = (struct mptcp_data_frag *)(page_to_virt(pfrag->page) + offset);
        dfrag->data_len = 0;
        dfrag->data_seq = msk->write_seq;
        dfrag->overhead = offset - orig_offset + sizeof(struct mptcp_data_frag);
        dfrag->offset = offset + sizeof(struct mptcp_data_frag);
        dfrag->page = pfrag->page;

        return dfrag;
}

static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
                              struct msghdr *msg, struct mptcp_data_frag *dfrag,
                              long *timeo, int *pmss_now,
                              int *ps_goal)
{
        int mss_now, avail_size, size_goal, offset, ret, frag_truesize = 0;
        bool dfrag_collapsed, can_collapse = false;
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_ext *mpext = NULL;
        bool retransmission = !!dfrag;
        struct sk_buff *skb, *tail;
        struct page_frag *pfrag;
        struct page *page;
        u64 *write_seq;
        size_t psize;

        /* use the mptcp page cache so that we can easily move the data
         * from one substream to another, but do per subflow memory accounting
         * Note: pfrag is used only !retransmission, but the compiler if
         * fooled into a warning if we don't init here
         */
        pfrag = sk_page_frag(sk);
        if (!retransmission) {
                write_seq = &msk->write_seq;
                page = pfrag->page;
        } else {
                write_seq = &dfrag->data_seq;
                page = dfrag->page;
        }

        /* compute copy limit */
        mss_now = tcp_send_mss(ssk, &size_goal, msg->msg_flags);
        *pmss_now = mss_now;
        *ps_goal = size_goal;
        avail_size = size_goal;
        skb = tcp_write_queue_tail(ssk);
        if (skb) {
                mpext = skb_ext_find(skb, SKB_EXT_MPTCP);

                /* Limit the write to the size available in the
                 * current skb, if any, so that we create at most a new skb.
                 * Explicitly tells TCP internals to avoid collapsing on later
                 * queue management operation, to avoid breaking the ext <->
                 * SSN association set here
                 */
                can_collapse = (size_goal - skb->len > 0) &&
                              mptcp_skb_can_collapse_to(*write_seq, skb, mpext);
                if (!can_collapse)
                        TCP_SKB_CB(skb)->eor = 1;
                else
                        avail_size = size_goal - skb->len;
        }

        if (!retransmission) {
                /* reuse tail pfrag, if possible, or carve a new one from the
                 * page allocator
                 */
                dfrag = mptcp_rtx_tail(sk);
                offset = pfrag->offset;
                dfrag_collapsed = mptcp_frag_can_collapse_to(msk, pfrag, dfrag);
                if (!dfrag_collapsed) {
                        dfrag = mptcp_carve_data_frag(msk, pfrag, offset);
                        offset = dfrag->offset;
                        frag_truesize = dfrag->overhead;
                }
                psize = min_t(size_t, pfrag->size - offset, avail_size);

                /* Copy to page */
                pr_debug("left=%zu", msg_data_left(msg));
                psize = copy_page_from_iter(pfrag->page, offset,
                                            min_t(size_t, msg_data_left(msg),
                                                  psize),
                                            &msg->msg_iter);
                pr_debug("left=%zu", msg_data_left(msg));
                if (!psize)
                        return -EINVAL;

                if (!sk_wmem_schedule(sk, psize + dfrag->overhead)) {
                        iov_iter_revert(&msg->msg_iter, psize);
                        return -ENOMEM;
                }
        } else {
                offset = dfrag->offset;
                psize = min_t(size_t, dfrag->data_len, avail_size);
        }

        /* tell the TCP stack to delay the push so that we can safely
         * access the skb after the sendpages call
         */
        ret = do_tcp_sendpages(ssk, page, offset, psize,
                               msg->msg_flags | MSG_SENDPAGE_NOTLAST | MSG_DONTWAIT);
        if (ret <= 0) {
                if (!retransmission)
                        iov_iter_revert(&msg->msg_iter, psize);
                return ret;
        }

        frag_truesize += ret;
        if (!retransmission) {
                if (unlikely(ret < psize))
                        iov_iter_revert(&msg->msg_iter, psize - ret);

                /* send successful, keep track of sent data for mptcp-level
                 * retransmission
                 */
                dfrag->data_len += ret;
                if (!dfrag_collapsed) {
                        get_page(dfrag->page);
                        list_add_tail(&dfrag->list, &msk->rtx_queue);
                        sk_wmem_queued_add(sk, frag_truesize);
                } else {
                        sk_wmem_queued_add(sk, ret);
                }

                /* charge data on mptcp rtx queue to the master socket
                 * Note: we charge such data both to sk and ssk
                 */
                sk->sk_forward_alloc -= frag_truesize;

        }

        /* if the tail skb extension is still the cached one, collapsing
         * really happened. Note: we can't check for 'same skb' as the sk_buff
         * hdr on tail can be transmitted, freed and re-allocated by the
         * do_tcp_sendpages() call
         */
        tail = tcp_write_queue_tail(ssk);
        if (mpext && tail && mpext == skb_ext_find(tail, SKB_EXT_MPTCP)) {
                WARN_ON_ONCE(!can_collapse);
                mpext->data_len += ret;
                goto out;
        }

        skb = tcp_write_queue_tail(ssk);
        mpext = __skb_ext_set(skb, SKB_EXT_MPTCP, msk->cached_ext);
        msk->cached_ext = NULL;

        memset(mpext, 0, sizeof(*mpext));
        mpext->data_seq = *write_seq;
        mpext->subflow_seq = mptcp_subflow_ctx(ssk)->rel_write_seq;
        mpext->data_len = ret;
        mpext->use_map = 1;
        mpext->dsn64 = 1;

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

out:
        if (!retransmission)
                pfrag->offset += frag_truesize;
        WRITE_ONCE(*write_seq, *write_seq + ret);
        mptcp_subflow_ctx(ssk)->rel_write_seq += ret;

        return ret;
}

static void mptcp_nospace(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;

        clear_bit(MPTCP_SEND_SPACE, &msk->flags);
        smp_mb__after_atomic(); /* msk->flags is changed by write_space cb */

        mptcp_for_each_subflow(msk, subflow) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
                struct socket *sock = READ_ONCE(ssk->sk_socket);

                /* enables ssk->write_space() callbacks */
                if (sock)
                        set_bit(SOCK_NOSPACE, &sock->flags);
        }
}

static bool mptcp_subflow_active(struct mptcp_subflow_context *subflow)
{
        struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

        /* can't send if JOIN hasn't completed yet (i.e. is usable for mptcp) */
        if (subflow->request_join && !subflow->fully_established)
                return false;

        /* only send if our side has not closed yet */
        return ((1 << ssk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT));
}

#define MPTCP_SEND_BURST_SIZE           ((1 << 16) - \
                                         sizeof(struct tcphdr) - \
                                         MAX_TCP_OPTION_SPACE - \
                                         sizeof(struct ipv6hdr) - \
                                         sizeof(struct frag_hdr))

struct subflow_send_info {
        struct sock *ssk;
        u64 ratio;
};

static struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk,
                                           u32 *sndbuf)
{
        struct subflow_send_info send_info[2];
        struct mptcp_subflow_context *subflow;
        int i, nr_active = 0;
        struct sock *ssk;
        u64 ratio;
        u32 pace;

        sock_owned_by_me((struct sock *)msk);

        *sndbuf = 0;
        if (!mptcp_ext_cache_refill(msk))
                return NULL;

        if (__mptcp_check_fallback(msk)) {
                if (!msk->first)
                        return NULL;
                *sndbuf = msk->first->sk_sndbuf;
                return sk_stream_memory_free(msk->first) ? msk->first : NULL;
        }

        /* re-use last subflow, if the burst allow that */
        if (msk->last_snd && msk->snd_burst > 0 &&
            sk_stream_memory_free(msk->last_snd) &&
            mptcp_subflow_active(mptcp_subflow_ctx(msk->last_snd))) {
                mptcp_for_each_subflow(msk, subflow) {
                        ssk =  mptcp_subflow_tcp_sock(subflow);
                        *sndbuf = max(tcp_sk(ssk)->snd_wnd, *sndbuf);
                }
                return msk->last_snd;
        }

        /* pick the subflow with the lower wmem/wspace ratio */
        for (i = 0; i < 2; ++i) {
                send_info[i].ssk = NULL;
                send_info[i].ratio = -1;
        }
        mptcp_for_each_subflow(msk, subflow) {
                ssk =  mptcp_subflow_tcp_sock(subflow);
                if (!mptcp_subflow_active(subflow))
                        continue;

                nr_active += !subflow->backup;
                *sndbuf = max(tcp_sk(ssk)->snd_wnd, *sndbuf);
                if (!sk_stream_memory_free(subflow->tcp_sock))
                        continue;

                pace = READ_ONCE(ssk->sk_pacing_rate);
                if (!pace)
                        continue;

                ratio = div_u64((u64)READ_ONCE(ssk->sk_wmem_queued) << 32,
                                pace);
                if (ratio < send_info[subflow->backup].ratio) {
                        send_info[subflow->backup].ssk = ssk;
                        send_info[subflow->backup].ratio = ratio;
                }
        }

        pr_debug("msk=%p nr_active=%d ssk=%p:%lld backup=%p:%lld",
                 msk, nr_active, send_info[0].ssk, send_info[0].ratio,
                 send_info[1].ssk, send_info[1].ratio);

        /* pick the best backup if no other subflow is active */
        if (!nr_active)
                send_info[0].ssk = send_info[1].ssk;

        if (send_info[0].ssk) {
                msk->last_snd = send_info[0].ssk;
                msk->snd_burst = min_t(int, MPTCP_SEND_BURST_SIZE,
                                       sk_stream_wspace(msk->last_snd));
                return msk->last_snd;
        }
        return NULL;
}

static void ssk_check_wmem(struct mptcp_sock *msk)
{
        if (unlikely(!mptcp_is_writeable(msk)))
                mptcp_nospace(msk);
}

static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
        int mss_now = 0, size_goal = 0, ret = 0;
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct page_frag *pfrag;
        size_t copied = 0;
        struct sock *ssk;
        u32 sndbuf;
        bool tx_ok;
        long timeo;

        if (msg->msg_flags & ~(MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL))
                return -EOPNOTSUPP;

        lock_sock(sk);

        timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);

        if ((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
                ret = sk_stream_wait_connect(sk, &timeo);
                if (ret)
                        goto out;
        }

        pfrag = sk_page_frag(sk);
restart:
        mptcp_clean_una(sk);

        if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN)) {
                ret = -EPIPE;
                goto out;
        }

        __mptcp_flush_join_list(msk);
        ssk = mptcp_subflow_get_send(msk, &sndbuf);
        while (!sk_stream_memory_free(sk) ||
               !ssk ||
               !mptcp_page_frag_refill(ssk, pfrag)) {
                if (ssk) {
                        /* make sure retransmit timer is
                         * running before we wait for memory.
                         *
                         * The retransmit timer might be needed
                         * to make the peer send an up-to-date
                         * MPTCP Ack.
                         */
                        mptcp_set_timeout(sk, ssk);
                        if (!mptcp_timer_pending(sk))
                                mptcp_reset_timer(sk);
                }

                mptcp_nospace(msk);
                ret = sk_stream_wait_memory(sk, &timeo);
                if (ret)
                        goto out;

                mptcp_clean_una(sk);

                ssk = mptcp_subflow_get_send(msk, &sndbuf);
                if (list_empty(&msk->conn_list)) {
                        ret = -ENOTCONN;
                        goto out;
                }
        }

        /* do auto tuning */
        if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK) &&
            sndbuf > READ_ONCE(sk->sk_sndbuf))
                WRITE_ONCE(sk->sk_sndbuf, sndbuf);

        pr_debug("conn_list->subflow=%p", ssk);

        lock_sock(ssk);
        tx_ok = msg_data_left(msg);
        while (tx_ok) {
                ret = mptcp_sendmsg_frag(sk, ssk, msg, NULL, &timeo, &mss_now,
                                         &size_goal);
                if (ret < 0) {
                        if (ret == -EAGAIN && timeo > 0) {
                                mptcp_set_timeout(sk, ssk);
                                release_sock(ssk);
                                goto restart;
                        }
                        break;
                }

                /* burst can be negative, we will try move to the next subflow
                 * at selection time, if possible.
                 */
                msk->snd_burst -= ret;
                copied += ret;

                tx_ok = msg_data_left(msg);
                if (!tx_ok)
                        break;

                if (!sk_stream_memory_free(ssk) ||
                    !mptcp_page_frag_refill(ssk, pfrag) ||
                    !mptcp_ext_cache_refill(msk)) {
                        tcp_push(ssk, msg->msg_flags, mss_now,
                                 tcp_sk(ssk)->nonagle, size_goal);
                        mptcp_set_timeout(sk, ssk);
                        release_sock(ssk);
                        goto restart;
                }

                /* memory is charged to mptcp level socket as well, i.e.
                 * if msg is very large, mptcp socket may run out of buffer
                 * space.  mptcp_clean_una() will release data that has
                 * been acked at mptcp level in the mean time, so there is
                 * a good chance we can continue sending data right away.
                 *
                 * Normally, when the tcp subflow can accept more data, then
                 * so can the MPTCP socket.  However, we need to cope with
                 * peers that might lag behind in their MPTCP-level
                 * acknowledgements, i.e.  data might have been acked at
                 * tcp level only.  So, we must also check the MPTCP socket
                 * limits before we send more data.
                 */
                if (unlikely(!sk_stream_memory_free(sk))) {
                        tcp_push(ssk, msg->msg_flags, mss_now,
                                 tcp_sk(ssk)->nonagle, size_goal);
                        mptcp_clean_una(sk);
                        if (!sk_stream_memory_free(sk)) {
                                /* can't send more for now, need to wait for
                                 * MPTCP-level ACKs from peer.
                                 *
                                 * Wakeup will happen via mptcp_clean_una().
                                 */
                                mptcp_set_timeout(sk, ssk);
                                release_sock(ssk);
                                goto restart;
                        }
                }
        }

        mptcp_set_timeout(sk, ssk);
        if (copied) {
                tcp_push(ssk, msg->msg_flags, mss_now, tcp_sk(ssk)->nonagle,
                         size_goal);

                /* start the timer, if it's not pending */
                if (!mptcp_timer_pending(sk))
                        mptcp_reset_timer(sk);
        }

        release_sock(ssk);
out:
        ssk_check_wmem(msk);
        release_sock(sk);
        return copied ? : ret;
}

static void mptcp_wait_data(struct sock *sk, long *timeo)
{
        DEFINE_WAIT_FUNC(wait, woken_wake_function);
        struct mptcp_sock *msk = mptcp_sk(sk);

        add_wait_queue(sk_sleep(sk), &wait);
        sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);

        sk_wait_event(sk, timeo,
                      test_and_clear_bit(MPTCP_DATA_READY, &msk->flags), &wait);

        sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
        remove_wait_queue(sk_sleep(sk), &wait);
}

static int __mptcp_recvmsg_mskq(struct mptcp_sock *msk,
                                struct msghdr *msg,
                                size_t len)
{
        struct sock *sk = (struct sock *)msk;
        struct sk_buff *skb;
        int copied = 0;

        while ((skb = skb_peek(&sk->sk_receive_queue)) != NULL) {
                u32 offset = MPTCP_SKB_CB(skb)->offset;
                u32 data_len = skb->len - offset;
                u32 count = min_t(size_t, len - copied, data_len);
                int err;

                err = skb_copy_datagram_msg(skb, offset, msg, count);
                if (unlikely(err < 0)) {
                        if (!copied)
                                return err;
                        break;
                }

                copied += count;

                if (count < data_len) {
                        MPTCP_SKB_CB(skb)->offset += count;
                        break;
                }

                __skb_unlink(skb, &sk->sk_receive_queue);
                __kfree_skb(skb);

                if (copied >= len)
                        break;
        }

        return copied;
}

/* receive buffer autotuning.  See tcp_rcv_space_adjust for more information.
 *
 * Only difference: Use highest rtt estimate of the subflows in use.
 */
static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
{
        struct mptcp_subflow_context *subflow;
        struct sock *sk = (struct sock *)msk;
        u32 time, advmss = 1;
        u64 rtt_us, mstamp;

        sock_owned_by_me(sk);

        if (copied <= 0)
                return;

        msk->rcvq_space.copied += copied;

        mstamp = div_u64(tcp_clock_ns(), NSEC_PER_USEC);
        time = tcp_stamp_us_delta(mstamp, msk->rcvq_space.time);

        rtt_us = msk->rcvq_space.rtt_us;
        if (rtt_us && time < (rtt_us >> 3))
                return;

        rtt_us = 0;
        mptcp_for_each_subflow(msk, subflow) {
                const struct tcp_sock *tp;
                u64 sf_rtt_us;
                u32 sf_advmss;

                tp = tcp_sk(mptcp_subflow_tcp_sock(subflow));

                sf_rtt_us = READ_ONCE(tp->rcv_rtt_est.rtt_us);
                sf_advmss = READ_ONCE(tp->advmss);

                rtt_us = max(sf_rtt_us, rtt_us);
                advmss = max(sf_advmss, advmss);
        }

        msk->rcvq_space.rtt_us = rtt_us;
        if (time < (rtt_us >> 3) || rtt_us == 0)
                return;

        if (msk->rcvq_space.copied <= msk->rcvq_space.space)
                goto new_measure;

        if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
            !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
                int rcvmem, rcvbuf;
                u64 rcvwin, grow;

                rcvwin = ((u64)msk->rcvq_space.copied << 1) + 16 * advmss;

                grow = rcvwin * (msk->rcvq_space.copied - msk->rcvq_space.space);

                do_div(grow, msk->rcvq_space.space);
                rcvwin += (grow << 1);

                rcvmem = SKB_TRUESIZE(advmss + MAX_TCP_HEADER);
                while (tcp_win_from_space(sk, rcvmem) < advmss)
                        rcvmem += 128;

                do_div(rcvwin, advmss);
                rcvbuf = min_t(u64, rcvwin * rcvmem,
                               sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);

                if (rcvbuf > sk->sk_rcvbuf) {
                        u32 window_clamp;

                        window_clamp = tcp_win_from_space(sk, rcvbuf);
                        WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);

                        /* Make subflows follow along.  If we do not do this, we
                         * get drops at subflow level if skbs can't be moved to
                         * the mptcp rx queue fast enough (announced rcv_win can
                         * exceed ssk->sk_rcvbuf).
                         */
                        mptcp_for_each_subflow(msk, subflow) {
                                struct sock *ssk;
                                bool slow;

                                ssk = mptcp_subflow_tcp_sock(subflow);
                                slow = lock_sock_fast(ssk);
                                WRITE_ONCE(ssk->sk_rcvbuf, rcvbuf);
                                tcp_sk(ssk)->window_clamp = window_clamp;
                                tcp_cleanup_rbuf(ssk, 1);
                                unlock_sock_fast(ssk, slow);
                        }
                }
        }

        msk->rcvq_space.space = msk->rcvq_space.copied;
new_measure:
        msk->rcvq_space.copied = 0;
        msk->rcvq_space.time = mstamp;
}

static bool __mptcp_move_skbs(struct mptcp_sock *msk)
{
        unsigned int moved = 0;
        bool done;

        /* avoid looping forever below on racing close */
        if (((struct sock *)msk)->sk_state == TCP_CLOSE)
                return false;

        __mptcp_flush_join_list(msk);
        do {
                struct sock *ssk = mptcp_subflow_recv_lookup(msk);

                if (!ssk)
                        break;

                lock_sock(ssk);
                done = __mptcp_move_skbs_from_subflow(msk, ssk, &moved);
                release_sock(ssk);
        } while (!done);

        if (mptcp_ofo_queue(msk) || moved > 0) {
                mptcp_check_data_fin((struct sock *)msk);
                return true;
        }
        return false;
}

static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
                         int nonblock, int flags, int *addr_len)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        int copied = 0;
        int target;
        long timeo;

        if (msg->msg_flags & ~(MSG_WAITALL | MSG_DONTWAIT))
                return -EOPNOTSUPP;

        lock_sock(sk);
        timeo = sock_rcvtimeo(sk, nonblock);

        len = min_t(size_t, len, INT_MAX);
        target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);
        __mptcp_flush_join_list(msk);

        while (len > (size_t)copied) {
                int bytes_read;

                bytes_read = __mptcp_recvmsg_mskq(msk, msg, len - copied);
                if (unlikely(bytes_read < 0)) {
                        if (!copied)
                                copied = bytes_read;
                        goto out_err;
                }

                copied += bytes_read;

                if (skb_queue_empty(&sk->sk_receive_queue) &&
                    __mptcp_move_skbs(msk))
                        continue;

                /* only the master socket status is relevant here. The exit
                 * conditions mirror closely tcp_recvmsg()
                 */
                if (copied >= target)
                        break;

                if (copied) {
                        if (sk->sk_err ||
                            sk->sk_state == TCP_CLOSE ||
                            (sk->sk_shutdown & RCV_SHUTDOWN) ||
                            !timeo ||
                            signal_pending(current))
                                break;
                } else {
                        if (sk->sk_err) {
                                copied = sock_error(sk);
                                break;
                        }

                        if (test_and_clear_bit(MPTCP_WORK_EOF, &msk->flags))
                                mptcp_check_for_eof(msk);

                        if (sk->sk_shutdown & RCV_SHUTDOWN)
                                break;

                        if (sk->sk_state == TCP_CLOSE) {
                                copied = -ENOTCONN;
                                break;
                        }

                        if (!timeo) {
                                copied = -EAGAIN;
                                break;
                        }

                        if (signal_pending(current)) {
                                copied = sock_intr_errno(timeo);
                                break;
                        }
                }

                pr_debug("block timeout %ld", timeo);
                mptcp_wait_data(sk, &timeo);
        }

        if (skb_queue_empty(&sk->sk_receive_queue)) {
                /* entire backlog drained, clear DATA_READY. */
                clear_bit(MPTCP_DATA_READY, &msk->flags);

                /* .. race-breaker: ssk might have gotten new data
                 * after last __mptcp_move_skbs() returned false.
                 */
                if (unlikely(__mptcp_move_skbs(msk)))
                        set_bit(MPTCP_DATA_READY, &msk->flags);
        } else if (unlikely(!test_bit(MPTCP_DATA_READY, &msk->flags))) {
                /* data to read but mptcp_wait_data() cleared DATA_READY */
                set_bit(MPTCP_DATA_READY, &msk->flags);
        }
out_err:
        pr_debug("msk=%p data_ready=%d rx queue empty=%d copied=%d",
                 msk, test_bit(MPTCP_DATA_READY, &msk->flags),
                 skb_queue_empty(&sk->sk_receive_queue), copied);
        mptcp_rcv_space_adjust(msk, copied);

        release_sock(sk);
        return copied;
}

static void mptcp_retransmit_handler(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (atomic64_read(&msk->snd_una) == READ_ONCE(msk->write_seq)) {
                mptcp_stop_timer(sk);
        } else {
                set_bit(MPTCP_WORK_RTX, &msk->flags);
                if (schedule_work(&msk->work))
                        sock_hold(sk);
        }
}

static void mptcp_retransmit_timer(struct timer_list *t)
{
        struct inet_connection_sock *icsk = from_timer(icsk, t,
                                                       icsk_retransmit_timer);
        struct sock *sk = &icsk->icsk_inet.sk;

        bh_lock_sock(sk);
        if (!sock_owned_by_user(sk)) {
                mptcp_retransmit_handler(sk);
        } else {
                /* delegate our work to tcp_release_cb() */
                if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED,
                                      &sk->sk_tsq_flags))
                        sock_hold(sk);
        }
        bh_unlock_sock(sk);
        sock_put(sk);
}

/* Find an idle subflow.  Return NULL if there is unacked data at tcp
 * level.
 *
 * A backup subflow is returned only if that is the only kind available.
 */
static struct sock *mptcp_subflow_get_retrans(const struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;
        struct sock *backup = NULL;

        sock_owned_by_me((const struct sock *)msk);

        if (__mptcp_check_fallback(msk))
                return msk->first;

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

                if (!mptcp_subflow_active(subflow))
                        continue;

                /* still data outstanding at TCP level?  Don't retransmit. */
                if (!tcp_write_queue_empty(ssk))
                        return NULL;

                if (subflow->backup) {
                        if (!backup)
                                backup = ssk;
                        continue;
                }

                return ssk;
        }

        return backup;
}

/* subflow sockets can be either outgoing (connect) or incoming
 * (accept).
 *
 * Outgoing subflows use in-kernel sockets.
 * Incoming subflows do not have their own 'struct socket' allocated,
 * so we need to use tcp_close() after detaching them from the mptcp
 * parent socket.
 */
void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
                       struct mptcp_subflow_context *subflow,
                       long timeout)
{
        struct socket *sock = READ_ONCE(ssk->sk_socket);

        list_del(&subflow->node);

        if (sock && sock != sk->sk_socket) {
                /* outgoing subflow */
                sock_release(sock);
        } else {
                /* incoming subflow */
                tcp_close(ssk, timeout);
        }
}

static unsigned int mptcp_sync_mss(struct sock *sk, u32 pmtu)
{
        return 0;
}

static void pm_work(struct mptcp_sock *msk)
{
        struct mptcp_pm_data *pm = &msk->pm;

        spin_lock_bh(&msk->pm.lock);

        pr_debug("msk=%p status=%x", msk, pm->status);
        if (pm->status & BIT(MPTCP_PM_ADD_ADDR_RECEIVED)) {
                pm->status &= ~BIT(MPTCP_PM_ADD_ADDR_RECEIVED);
                mptcp_pm_nl_add_addr_received(msk);
        }
        if (pm->status & BIT(MPTCP_PM_RM_ADDR_RECEIVED)) {
                pm->status &= ~BIT(MPTCP_PM_RM_ADDR_RECEIVED);
                mptcp_pm_nl_rm_addr_received(msk);
        }
        if (pm->status & BIT(MPTCP_PM_ESTABLISHED)) {
                pm->status &= ~BIT(MPTCP_PM_ESTABLISHED);
                mptcp_pm_nl_fully_established(msk);
        }
        if (pm->status & BIT(MPTCP_PM_SUBFLOW_ESTABLISHED)) {
                pm->status &= ~BIT(MPTCP_PM_SUBFLOW_ESTABLISHED);
                mptcp_pm_nl_subflow_established(msk);
        }

        spin_unlock_bh(&msk->pm.lock);
}

static void __mptcp_close_subflow(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow, *tmp;

        list_for_each_entry_safe(subflow, tmp, &msk->conn_list, node) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

                if (inet_sk_state_load(ssk) != TCP_CLOSE)
                        continue;

                __mptcp_close_ssk((struct sock *)msk, ssk, subflow, 0);
        }
}

static void mptcp_worker(struct work_struct *work)
{
        struct mptcp_sock *msk = container_of(work, struct mptcp_sock, work);
        struct sock *ssk, *sk = &msk->sk.icsk_inet.sk;
        int orig_len, orig_offset, mss_now = 0, size_goal = 0;
        struct mptcp_data_frag *dfrag;
        u64 orig_write_seq;
        size_t copied = 0;
        struct msghdr msg = {
                .msg_flags = MSG_DONTWAIT,
        };
        long timeo = 0;

        lock_sock(sk);
        mptcp_clean_una(sk);
        mptcp_check_data_fin_ack(sk);
        __mptcp_flush_join_list(msk);
        if (test_and_clear_bit(MPTCP_WORK_CLOSE_SUBFLOW, &msk->flags))
                __mptcp_close_subflow(msk);

        __mptcp_move_skbs(msk);

        if (msk->pm.status)
                pm_work(msk);

        if (test_and_clear_bit(MPTCP_WORK_EOF, &msk->flags))
                mptcp_check_for_eof(msk);

        mptcp_check_data_fin(sk);

        if (!test_and_clear_bit(MPTCP_WORK_RTX, &msk->flags))
                goto unlock;

        dfrag = mptcp_rtx_head(sk);
        if (!dfrag)
                goto unlock;

        if (!mptcp_ext_cache_refill(msk))
                goto reset_unlock;

        ssk = mptcp_subflow_get_retrans(msk);
        if (!ssk)
                goto reset_unlock;

        lock_sock(ssk);

        orig_len = dfrag->data_len;
        orig_offset = dfrag->offset;
        orig_write_seq = dfrag->data_seq;
        while (dfrag->data_len > 0) {
                int ret = mptcp_sendmsg_frag(sk, ssk, &msg, dfrag, &timeo,
                                             &mss_now, &size_goal);
                if (ret < 0)
                        break;

                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RETRANSSEGS);
                copied += ret;
                dfrag->data_len -= ret;
                dfrag->offset += ret;

                if (!mptcp_ext_cache_refill(msk))
                        break;
        }
        if (copied)
                tcp_push(ssk, msg.msg_flags, mss_now, tcp_sk(ssk)->nonagle,
                         size_goal);

        dfrag->data_seq = orig_write_seq;
        dfrag->offset = orig_offset;
        dfrag->data_len = orig_len;

        mptcp_set_timeout(sk, ssk);
        release_sock(ssk);

reset_unlock:
        if (!mptcp_timer_pending(sk))
                mptcp_reset_timer(sk);

unlock:
        release_sock(sk);
        sock_put(sk);
}

static int __mptcp_init_sock(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        spin_lock_init(&msk->join_list_lock);

        INIT_LIST_HEAD(&msk->conn_list);
        INIT_LIST_HEAD(&msk->join_list);
        INIT_LIST_HEAD(&msk->rtx_queue);
        __set_bit(MPTCP_SEND_SPACE, &msk->flags);
        INIT_WORK(&msk->work, mptcp_worker);
        msk->out_of_order_queue = RB_ROOT;

        msk->first = NULL;
        inet_csk(sk)->icsk_sync_mss = mptcp_sync_mss;

        mptcp_pm_data_init(msk);

        /* re-use the csk retrans timer for MPTCP-level retrans */
        timer_setup(&msk->sk.icsk_retransmit_timer, mptcp_retransmit_timer, 0);

        return 0;
}

static int mptcp_init_sock(struct sock *sk)
{
        struct net *net = sock_net(sk);
        int ret;

        ret = __mptcp_init_sock(sk);
        if (ret)
                return ret;

        if (!mptcp_is_enabled(net))
                return -ENOPROTOOPT;

        if (unlikely(!net->mib.mptcp_statistics) && !mptcp_mib_alloc(net))
                return -ENOMEM;

        ret = __mptcp_socket_create(mptcp_sk(sk));
        if (ret)
                return ret;

        sk_sockets_allocated_inc(sk);
        sk->sk_rcvbuf = sock_net(sk)->ipv4.sysctl_tcp_rmem[1];
        sk->sk_sndbuf = sock_net(sk)->ipv4.sysctl_tcp_wmem[1];

        return 0;
}

static void __mptcp_clear_xmit(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_data_frag *dtmp, *dfrag;

        sk_stop_timer(sk, &msk->sk.icsk_retransmit_timer);

        list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list)
                dfrag_clear(sk, dfrag);
}

static void mptcp_cancel_work(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (cancel_work_sync(&msk->work))
                sock_put(sk);
}

void mptcp_subflow_shutdown(struct sock *sk, struct sock *ssk, int how)
{
        lock_sock(ssk);

        switch (ssk->sk_state) {
        case TCP_LISTEN:
                if (!(how & RCV_SHUTDOWN))
                        break;
                fallthrough;
        case TCP_SYN_SENT:
                tcp_disconnect(ssk, O_NONBLOCK);
                break;
        default:
                if (__mptcp_check_fallback(mptcp_sk(sk))) {
                        pr_debug("Fallback");
                        ssk->sk_shutdown |= how;
                        tcp_shutdown(ssk, how);
                } else {
                        pr_debug("Sending DATA_FIN on subflow %p", ssk);
                        mptcp_set_timeout(sk, ssk);
                        tcp_send_ack(ssk);
                }
                break;
        }

        release_sock(ssk);
}

static const unsigned char new_state[16] = {
        /* current state:     new state:      action:   */
        [0 /* (Invalid) */] = TCP_CLOSE,
        [TCP_ESTABLISHED]   = TCP_FIN_WAIT1 | TCP_ACTION_FIN,
        [TCP_SYN_SENT]      = TCP_CLOSE,
        [TCP_SYN_RECV]      = TCP_FIN_WAIT1 | TCP_ACTION_FIN,
        [TCP_FIN_WAIT1]     = TCP_FIN_WAIT1,
        [TCP_FIN_WAIT2]     = TCP_FIN_WAIT2,
        [TCP_TIME_WAIT]     = TCP_CLOSE,        /* should not happen ! */
        [TCP_CLOSE]         = TCP_CLOSE,
        [TCP_CLOSE_WAIT]    = TCP_LAST_ACK  | TCP_ACTION_FIN,
        [TCP_LAST_ACK]      = TCP_LAST_ACK,
        [TCP_LISTEN]        = TCP_CLOSE,
        [TCP_CLOSING]       = TCP_CLOSING,
        [TCP_NEW_SYN_RECV]  = TCP_CLOSE,        /* should not happen ! */
};

static int mptcp_close_state(struct sock *sk)
{
        int next = (int)new_state[sk->sk_state];
        int ns = next & TCP_STATE_MASK;

        inet_sk_state_store(sk, ns);

        return next & TCP_ACTION_FIN;
}

static void mptcp_close(struct sock *sk, long timeout)
{
        struct mptcp_subflow_context *subflow, *tmp;
        struct mptcp_sock *msk = mptcp_sk(sk);
        LIST_HEAD(conn_list);

        lock_sock(sk);
        sk->sk_shutdown = SHUTDOWN_MASK;

        if (sk->sk_state == TCP_LISTEN) {
                inet_sk_state_store(sk, TCP_CLOSE);
                goto cleanup;
        } else if (sk->sk_state == TCP_CLOSE) {
                goto cleanup;
        }

        if (__mptcp_check_fallback(msk)) {
                goto update_state;
        } else if (mptcp_close_state(sk)) {
                pr_debug("Sending DATA_FIN sk=%p", sk);
                WRITE_ONCE(msk->write_seq, msk->write_seq + 1);
                WRITE_ONCE(msk->snd_data_fin_enable, 1);

                mptcp_for_each_subflow(msk, subflow) {
                        struct sock *tcp_sk = mptcp_subflow_tcp_sock(subflow);

                        mptcp_subflow_shutdown(sk, tcp_sk, SHUTDOWN_MASK);
                }
        }

        sk_stream_wait_close(sk, timeout);

update_state:
        inet_sk_state_store(sk, TCP_CLOSE);

cleanup:
        /* be sure to always acquire the join list lock, to sync vs
         * mptcp_finish_join().
         */
        spin_lock_bh(&msk->join_list_lock);
        list_splice_tail_init(&msk->join_list, &msk->conn_list);
        spin_unlock_bh(&msk->join_list_lock);
        list_splice_init(&msk->conn_list, &conn_list);

        __mptcp_clear_xmit(sk);

        release_sock(sk);

        list_for_each_entry_safe(subflow, tmp, &conn_list, node) {
                struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
                __mptcp_close_ssk(sk, ssk, subflow, timeout);
        }

        mptcp_cancel_work(sk);

        __skb_queue_purge(&sk->sk_receive_queue);

        sk_common_release(sk);
}

static void mptcp_copy_inaddrs(struct sock *msk, const struct sock *ssk)
{
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        const struct ipv6_pinfo *ssk6 = inet6_sk(ssk);
        struct ipv6_pinfo *msk6 = inet6_sk(msk);

        msk->sk_v6_daddr = ssk->sk_v6_daddr;
        msk->sk_v6_rcv_saddr = ssk->sk_v6_rcv_saddr;

        if (msk6 && ssk6) {
                msk6->saddr = ssk6->saddr;
                msk6->flow_label = ssk6->flow_label;
        }
#endif

        inet_sk(msk)->inet_num = inet_sk(ssk)->inet_num;
        inet_sk(msk)->inet_dport = inet_sk(ssk)->inet_dport;
        inet_sk(msk)->inet_sport = inet_sk(ssk)->inet_sport;
        inet_sk(msk)->inet_daddr = inet_sk(ssk)->inet_daddr;
        inet_sk(msk)->inet_saddr = inet_sk(ssk)->inet_saddr;
        inet_sk(msk)->inet_rcv_saddr = inet_sk(ssk)->inet_rcv_saddr;
}

static int mptcp_disconnect(struct sock *sk, int flags)
{
        /* Should never be called.
         * inet_stream_connect() calls ->disconnect, but that
         * refers to the subflow socket, not the mptcp one.
         */
        WARN_ON_ONCE(1);
        return 0;
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static struct ipv6_pinfo *mptcp_inet6_sk(const struct sock *sk)
{
        unsigned int offset = sizeof(struct mptcp6_sock) - sizeof(struct ipv6_pinfo);

        return (struct ipv6_pinfo *)(((u8 *)sk) + offset);
}
#endif

struct sock *mptcp_sk_clone(const struct sock *sk,
                            const struct mptcp_options_received *mp_opt,
                            struct request_sock *req)
{
        struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
        struct sock *nsk = sk_clone_lock(sk, GFP_ATOMIC);
        struct mptcp_sock *msk;
        u64 ack_seq;

        if (!nsk)
                return NULL;

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        if (nsk->sk_family == AF_INET6)
                inet_sk(nsk)->pinet6 = mptcp_inet6_sk(nsk);
#endif

        __mptcp_init_sock(nsk);

        msk = mptcp_sk(nsk);
        msk->local_key = subflow_req->local_key;
        msk->token = subflow_req->token;
        msk->subflow = NULL;
        WRITE_ONCE(msk->fully_established, false);

        msk->write_seq = subflow_req->idsn + 1;
        atomic64_set(&msk->snd_una, msk->write_seq);
        if (mp_opt->mp_capable) {
                msk->can_ack = true;
                msk->remote_key = mp_opt->sndr_key;
                mptcp_crypto_key_sha(msk->remote_key, NULL, &ack_seq);
                ack_seq++;
                WRITE_ONCE(msk->ack_seq, ack_seq);
        }

        sock_reset_flag(nsk, SOCK_RCU_FREE);
        /* will be fully established after successful MPC subflow creation */
        inet_sk_state_store(nsk, TCP_SYN_RECV);
        bh_unlock_sock(nsk);

        /* keep a single reference */
        __sock_put(nsk);
        return nsk;
}

void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk)
{
        const struct tcp_sock *tp = tcp_sk(ssk);

        msk->rcvq_space.copied = 0;
        msk->rcvq_space.rtt_us = 0;

        msk->rcvq_space.time = tp->tcp_mstamp;

        /* initial rcv_space offering made to peer */
        msk->rcvq_space.space = min_t(u32, tp->rcv_wnd,
                                      TCP_INIT_CWND * tp->advmss);
        if (msk->rcvq_space.space == 0)
                msk->rcvq_space.space = TCP_INIT_CWND * TCP_MSS_DEFAULT;
}

static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
                                 bool kern)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct socket *listener;
        struct sock *newsk;

        listener = __mptcp_nmpc_socket(msk);
        if (WARN_ON_ONCE(!listener)) {
                *err = -EINVAL;
                return NULL;
        }

        pr_debug("msk=%p, listener=%p", msk, mptcp_subflow_ctx(listener->sk));
        newsk = inet_csk_accept(listener->sk, flags, err, kern);
        if (!newsk)
                return NULL;

        pr_debug("msk=%p, subflow is mptcp=%d", msk, sk_is_mptcp(newsk));
        if (sk_is_mptcp(newsk)) {
                struct mptcp_subflow_context *subflow;
                struct sock *new_mptcp_sock;
                struct sock *ssk = newsk;

                subflow = mptcp_subflow_ctx(newsk);
                new_mptcp_sock = subflow->conn;

                /* is_mptcp should be false if subflow->conn is missing, see
                 * subflow_syn_recv_sock()
                 */
                if (WARN_ON_ONCE(!new_mptcp_sock)) {
                        tcp_sk(newsk)->is_mptcp = 0;
                        return newsk;
                }

                /* acquire the 2nd reference for the owning socket */
                sock_hold(new_mptcp_sock);

                local_bh_disable();
                bh_lock_sock(new_mptcp_sock);
                msk = mptcp_sk(new_mptcp_sock);
                msk->first = newsk;

                newsk = new_mptcp_sock;
                mptcp_copy_inaddrs(newsk, ssk);
                list_add(&subflow->node, &msk->conn_list);

                mptcp_rcv_space_init(msk, ssk);
                bh_unlock_sock(new_mptcp_sock);

                __MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEPASSIVEACK);
                local_bh_enable();
        } else {
                MPTCP_INC_STATS(sock_net(sk),
                                MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
        }

        return newsk;
}

void mptcp_destroy_common(struct mptcp_sock *msk)
{
        skb_rbtree_purge(&msk->out_of_order_queue);
        mptcp_token_destroy(msk);
        mptcp_pm_free_anno_list(msk);
}

static void mptcp_destroy(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        if (msk->cached_ext)
                __skb_ext_put(msk->cached_ext);

        mptcp_destroy_common(msk);
        sk_sockets_allocated_dec(sk);
}

static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
                                       sockptr_t optval, unsigned int optlen)
{
        struct sock *sk = (struct sock *)msk;
        struct socket *ssock;
        int ret;

        switch (optname) {
        case SO_REUSEPORT:
        case SO_REUSEADDR:
                lock_sock(sk);
                ssock = __mptcp_nmpc_socket(msk);
                if (!ssock) {
                        release_sock(sk);
                        return -EINVAL;
                }

                ret = sock_setsockopt(ssock, SOL_SOCKET, optname, optval, optlen);
                if (ret == 0) {
                        if (optname == SO_REUSEPORT)
                                sk->sk_reuseport = ssock->sk->sk_reuseport;
                        else if (optname == SO_REUSEADDR)
                                sk->sk_reuse = ssock->sk->sk_reuse;
                }
                release_sock(sk);
                return ret;
        }

        return sock_setsockopt(sk->sk_socket, SOL_SOCKET, optname, optval, optlen);
}

static int mptcp_setsockopt_v6(struct mptcp_sock *msk, int optname,
                               sockptr_t optval, unsigned int optlen)
{
        struct sock *sk = (struct sock *)msk;
        int ret = -EOPNOTSUPP;
        struct socket *ssock;

        switch (optname) {
        case IPV6_V6ONLY:
                lock_sock(sk);
                ssock = __mptcp_nmpc_socket(msk);
                if (!ssock) {
                        release_sock(sk);
                        return -EINVAL;
                }

                ret = tcp_setsockopt(ssock->sk, SOL_IPV6, optname, optval, optlen);
                if (ret == 0)
                        sk->sk_ipv6only = ssock->sk->sk_ipv6only;

                release_sock(sk);
                break;
        }

        return ret;
}

static int mptcp_setsockopt(struct sock *sk, int level, int optname,
                            sockptr_t optval, unsigned int optlen)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sock *ssk;

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

        if (level == SOL_SOCKET)
                return mptcp_setsockopt_sol_socket(msk, optname, optval, optlen);

        /* @@ the meaning of setsockopt() when the socket is connected and
         * there are multiple subflows is not yet defined. It is up to the
         * MPTCP-level socket to configure the subflows until the subflow
         * is in TCP fallback, when TCP socket options are passed through
         * to the one remaining subflow.
         */
        lock_sock(sk);
        ssk = __mptcp_tcp_fallback(msk);
        release_sock(sk);
        if (ssk)
                return tcp_setsockopt(ssk, level, optname, optval, optlen);

        if (level == SOL_IPV6)
                return mptcp_setsockopt_v6(msk, optname, optval, optlen);

        return -EOPNOTSUPP;
}

static int mptcp_getsockopt(struct sock *sk, int level, int optname,
                            char __user *optval, int __user *option)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct sock *ssk;

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

        /* @@ the meaning of setsockopt() when the socket is connected and
         * there are multiple subflows is not yet defined. It is up to the
         * MPTCP-level socket to configure the subflows until the subflow
         * is in TCP fallback, when socket options are passed through
         * to the one remaining subflow.
         */
        lock_sock(sk);
        ssk = __mptcp_tcp_fallback(msk);
        release_sock(sk);
        if (ssk)
                return tcp_getsockopt(ssk, level, optname, optval, option);

        return -EOPNOTSUPP;
}

#define MPTCP_DEFERRED_ALL (TCPF_DELACK_TIMER_DEFERRED | \
                            TCPF_WRITE_TIMER_DEFERRED)

/* this is very alike tcp_release_cb() but we must handle differently a
 * different set of events
 */
static void mptcp_release_cb(struct sock *sk)
{
        unsigned long flags, nflags;

        do {
                flags = sk->sk_tsq_flags;
                if (!(flags & MPTCP_DEFERRED_ALL))
                        return;
                nflags = flags & ~MPTCP_DEFERRED_ALL;
        } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags);

        sock_release_ownership(sk);

        if (flags & TCPF_DELACK_TIMER_DEFERRED) {
                struct mptcp_sock *msk = mptcp_sk(sk);
                struct sock *ssk;

                ssk = mptcp_subflow_recv_lookup(msk);
                if (!ssk || !schedule_work(&msk->work))
                        __sock_put(sk);
        }

        if (flags & TCPF_WRITE_TIMER_DEFERRED) {
                mptcp_retransmit_handler(sk);
                __sock_put(sk);
        }
}

static int mptcp_hash(struct sock *sk)
{
        /* should never be called,
         * we hash the TCP subflows not the master socket
         */
        WARN_ON_ONCE(1);
        return 0;
}

static void mptcp_unhash(struct sock *sk)
{
        /* called from sk_common_release(), but nothing to do here */
}

static int mptcp_get_port(struct sock *sk, unsigned short snum)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct socket *ssock;

        ssock = __mptcp_nmpc_socket(msk);
        pr_debug("msk=%p, subflow=%p", msk, ssock);
        if (WARN_ON_ONCE(!ssock))
                return -EINVAL;

        return inet_csk_get_port(ssock->sk, snum);
}

void mptcp_finish_connect(struct sock *ssk)
{
        struct mptcp_subflow_context *subflow;
        struct mptcp_sock *msk;
        struct sock *sk;
        u64 ack_seq;

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

        pr_debug("msk=%p, token=%u", sk, subflow->token);

        mptcp_crypto_key_sha(subflow->remote_key, NULL, &ack_seq);
        ack_seq++;
        subflow->map_seq = ack_seq;
        subflow->map_subflow_seq = 1;

        /* the socket is not connected yet, no msk/subflow ops can access/race
         * accessing the field below
         */
        WRITE_ONCE(msk->remote_key, subflow->remote_key);
        WRITE_ONCE(msk->local_key, subflow->local_key);
        WRITE_ONCE(msk->write_seq, subflow->idsn + 1);
        WRITE_ONCE(msk->ack_seq, ack_seq);
        WRITE_ONCE(msk->can_ack, 1);
        atomic64_set(&msk->snd_una, msk->write_seq);

        mptcp_pm_new_connection(msk, 0);

        mptcp_rcv_space_init(msk, ssk);
}

static void mptcp_sock_graft(struct sock *sk, struct socket *parent)
{
        write_lock_bh(&sk->sk_callback_lock);
        rcu_assign_pointer(sk->sk_wq, &parent->wq);
        sk_set_socket(sk, parent);
        sk->sk_uid = SOCK_INODE(parent)->i_uid;
        write_unlock_bh(&sk->sk_callback_lock);
}

bool mptcp_finish_join(struct sock *sk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
        struct mptcp_sock *msk = mptcp_sk(subflow->conn);
        struct sock *parent = (void *)msk;
        struct socket *parent_sock;
        bool ret;

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

        /* mptcp socket already closing? */
        if (!mptcp_is_fully_established(parent))
                return false;

        if (!msk->pm.server_side)
                return true;

        if (!mptcp_pm_allow_new_subflow(msk))
                return false;

        /* active connections are already on conn_list, and we can't acquire
         * msk lock here.
         * use the join list lock as synchronization point and double-check
         * msk status to avoid racing with mptcp_close()
         */
        spin_lock_bh(&msk->join_list_lock);
        ret = inet_sk_state_load(parent) == TCP_ESTABLISHED;
        if (ret && !WARN_ON_ONCE(!list_empty(&subflow->node)))
                list_add_tail(&subflow->node, &msk->join_list);
        spin_unlock_bh(&msk->join_list_lock);
        if (!ret)
                return false;

        /* attach to msk socket only after we are sure he will deal with us
         * at close time
         */
        parent_sock = READ_ONCE(parent->sk_socket);
        if (parent_sock && !sk->sk_socket)
                mptcp_sock_graft(sk, parent_sock);
        subflow->map_seq = READ_ONCE(msk->ack_seq);
        return true;
}

static bool mptcp_memory_free(const struct sock *sk, int wake)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        return wake ? test_bit(MPTCP_SEND_SPACE, &msk->flags) : true;
}

static struct proto mptcp_prot = {
        .name           = "MPTCP",
        .owner          = THIS_MODULE,
        .init           = mptcp_init_sock,
        .disconnect     = mptcp_disconnect,
        .close          = mptcp_close,
        .accept         = mptcp_accept,
        .setsockopt     = mptcp_setsockopt,
        .getsockopt     = mptcp_getsockopt,
        .shutdown       = tcp_shutdown,
        .destroy        = mptcp_destroy,
        .sendmsg        = mptcp_sendmsg,
        .recvmsg        = mptcp_recvmsg,
        .release_cb     = mptcp_release_cb,
        .hash           = mptcp_hash,
        .unhash         = mptcp_unhash,
        .get_port       = mptcp_get_port,
        .sockets_allocated      = &mptcp_sockets_allocated,
        .memory_allocated       = &tcp_memory_allocated,
        .memory_pressure        = &tcp_memory_pressure,
        .stream_memory_free     = mptcp_memory_free,
        .sysctl_wmem_offset     = offsetof(struct net, ipv4.sysctl_tcp_wmem),
        .sysctl_rmem_offset     = offsetof(struct net, ipv4.sysctl_tcp_rmem),
        .sysctl_mem     = sysctl_tcp_mem,
        .obj_size       = sizeof(struct mptcp_sock),
        .slab_flags     = SLAB_TYPESAFE_BY_RCU,
        .no_autobind    = true,
};

static int mptcp_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct socket *ssock;
        int err;

        lock_sock(sock->sk);
        ssock = __mptcp_nmpc_socket(msk);
        if (!ssock) {
                err = -EINVAL;
                goto unlock;
        }

        err = ssock->ops->bind(ssock, uaddr, addr_len);
        if (!err)
                mptcp_copy_inaddrs(sock->sk, ssock->sk);

unlock:
        release_sock(sock->sk);
        return err;
}

static void mptcp_subflow_early_fallback(struct mptcp_sock *msk,
                                         struct mptcp_subflow_context *subflow)
{
        subflow->request_mptcp = 0;
        __mptcp_do_fallback(msk);
}

static int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
                                int addr_len, int flags)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct mptcp_subflow_context *subflow;
        struct socket *ssock;
        int err;

        lock_sock(sock->sk);
        if (sock->state != SS_UNCONNECTED && msk->subflow) {
                /* pending connection or invalid state, let existing subflow
                 * cope with that
                 */
                ssock = msk->subflow;
                goto do_connect;
        }

        ssock = __mptcp_nmpc_socket(msk);
        if (!ssock) {
                err = -EINVAL;
                goto unlock;
        }

        mptcp_token_destroy(msk);
        inet_sk_state_store(sock->sk, TCP_SYN_SENT);
        subflow = mptcp_subflow_ctx(ssock->sk);
#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(ssock->sk)->md5sig_info))
                mptcp_subflow_early_fallback(msk, subflow);
#endif
        if (subflow->request_mptcp && mptcp_token_new_connect(ssock->sk))
                mptcp_subflow_early_fallback(msk, subflow);

do_connect:
        err = ssock->ops->connect(ssock, uaddr, addr_len, flags);
        sock->state = ssock->state;

        /* on successful connect, the msk state will be moved to established by
         * subflow_finish_connect()
         */
        if (!err || err == -EINPROGRESS)
                mptcp_copy_inaddrs(sock->sk, ssock->sk);
        else
                inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));

unlock:
        release_sock(sock->sk);
        return err;
}

static int mptcp_listen(struct socket *sock, int backlog)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct socket *ssock;
        int err;

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

        lock_sock(sock->sk);
        ssock = __mptcp_nmpc_socket(msk);
        if (!ssock) {
                err = -EINVAL;
                goto unlock;
        }

        mptcp_token_destroy(msk);
        inet_sk_state_store(sock->sk, TCP_LISTEN);
        sock_set_flag(sock->sk, SOCK_RCU_FREE);

        err = ssock->ops->listen(ssock, backlog);
        inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
        if (!err)
                mptcp_copy_inaddrs(sock->sk, ssock->sk);

unlock:
        release_sock(sock->sk);
        return err;
}

static int mptcp_stream_accept(struct socket *sock, struct socket *newsock,
                               int flags, bool kern)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct socket *ssock;
        int err;

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

        lock_sock(sock->sk);
        if (sock->sk->sk_state != TCP_LISTEN)
                goto unlock_fail;

        ssock = __mptcp_nmpc_socket(msk);
        if (!ssock)
                goto unlock_fail;

        clear_bit(MPTCP_DATA_READY, &msk->flags);
        sock_hold(ssock->sk);
        release_sock(sock->sk);

        err = ssock->ops->accept(sock, newsock, flags, kern);
        if (err == 0 && !mptcp_is_tcpsk(newsock->sk)) {
                struct mptcp_sock *msk = mptcp_sk(newsock->sk);
                struct mptcp_subflow_context *subflow;

                /* set ssk->sk_socket of accept()ed flows to mptcp socket.
                 * This is needed so NOSPACE flag can be set from tcp stack.
                 */
                __mptcp_flush_join_list(msk);
                mptcp_for_each_subflow(msk, subflow) {
                        struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

                        if (!ssk->sk_socket)
                                mptcp_sock_graft(ssk, newsock);
                }
        }

        if (inet_csk_listen_poll(ssock->sk))
                set_bit(MPTCP_DATA_READY, &msk->flags);
        sock_put(ssock->sk);
        return err;

unlock_fail:
        release_sock(sock->sk);
        return -EINVAL;
}

static __poll_t mptcp_check_readable(struct mptcp_sock *msk)
{
        return test_bit(MPTCP_DATA_READY, &msk->flags) ? EPOLLIN | EPOLLRDNORM :
               0;
}

static __poll_t mptcp_poll(struct file *file, struct socket *sock,
                           struct poll_table_struct *wait)
{
        struct sock *sk = sock->sk;
        struct mptcp_sock *msk;
        __poll_t mask = 0;
        int state;

        msk = mptcp_sk(sk);
        sock_poll_wait(file, sock, wait);

        state = inet_sk_state_load(sk);
        pr_debug("msk=%p state=%d flags=%lx", msk, state, msk->flags);
        if (state == TCP_LISTEN)
                return mptcp_check_readable(msk);

        if (state != TCP_SYN_SENT && state != TCP_SYN_RECV) {
                mask |= mptcp_check_readable(msk);
                if (test_bit(MPTCP_SEND_SPACE, &msk->flags))
                        mask |= EPOLLOUT | EPOLLWRNORM;
        }
        if (sk->sk_shutdown & RCV_SHUTDOWN)
                mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;

        return mask;
}

static int mptcp_shutdown(struct socket *sock, int how)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct mptcp_subflow_context *subflow;
        int ret = 0;

        pr_debug("sk=%p, how=%d", msk, how);

        lock_sock(sock->sk);

        how++;
        if ((how & ~SHUTDOWN_MASK) || !how) {
                ret = -EINVAL;
                goto out_unlock;
        }

        if (sock->state == SS_CONNECTING) {
                if ((1 << sock->sk->sk_state) &
                    (TCPF_SYN_SENT | TCPF_SYN_RECV | TCPF_CLOSE))
                        sock->state = SS_DISCONNECTING;
                else
                        sock->state = SS_CONNECTED;
        }

        /* If we've already sent a FIN, or it's a closed state, skip this. */
        if (__mptcp_check_fallback(msk)) {
                if (how == SHUT_WR || how == SHUT_RDWR)
                        inet_sk_state_store(sock->sk, TCP_FIN_WAIT1);

                mptcp_for_each_subflow(msk, subflow) {
                        struct sock *tcp_sk = mptcp_subflow_tcp_sock(subflow);

                        mptcp_subflow_shutdown(sock->sk, tcp_sk, how);
                }
        } else if ((how & SEND_SHUTDOWN) &&
                   ((1 << sock->sk->sk_state) &
                    (TCPF_ESTABLISHED | TCPF_SYN_SENT |
                     TCPF_SYN_RECV | TCPF_CLOSE_WAIT)) &&
                   mptcp_close_state(sock->sk)) {
                __mptcp_flush_join_list(msk);

                WRITE_ONCE(msk->write_seq, msk->write_seq + 1);
                WRITE_ONCE(msk->snd_data_fin_enable, 1);

                mptcp_for_each_subflow(msk, subflow) {
                        struct sock *tcp_sk = mptcp_subflow_tcp_sock(subflow);

                        mptcp_subflow_shutdown(sock->sk, tcp_sk, how);
                }
        }

        /* Wake up anyone sleeping in poll. */
        sock->sk->sk_state_change(sock->sk);

out_unlock:
        release_sock(sock->sk);

        return ret;
}

static const struct proto_ops mptcp_stream_ops = {
        .family            = PF_INET,
        .owner             = THIS_MODULE,
        .release           = inet_release,
        .bind              = mptcp_bind,
        .connect           = mptcp_stream_connect,
        .socketpair        = sock_no_socketpair,
        .accept            = mptcp_stream_accept,
        .getname           = inet_getname,
        .poll              = mptcp_poll,
        .ioctl             = inet_ioctl,
        .gettstamp         = sock_gettstamp,
        .listen            = mptcp_listen,
        .shutdown          = mptcp_shutdown,
        .setsockopt        = sock_common_setsockopt,
        .getsockopt        = sock_common_getsockopt,
        .sendmsg           = inet_sendmsg,
        .recvmsg           = inet_recvmsg,
        .mmap              = sock_no_mmap,
        .sendpage          = inet_sendpage,
};

static struct inet_protosw mptcp_protosw = {
        .type           = SOCK_STREAM,
        .protocol       = IPPROTO_MPTCP,
        .prot           = &mptcp_prot,
        .ops            = &mptcp_stream_ops,
        .flags          = INET_PROTOSW_ICSK,
};

void __init mptcp_proto_init(void)
{
        mptcp_prot.h.hashinfo = tcp_prot.h.hashinfo;

        if (percpu_counter_init(&mptcp_sockets_allocated, 0, GFP_KERNEL))
                panic("Failed to allocate MPTCP pcpu counter\n");

        mptcp_subflow_init();
        mptcp_pm_init();
        mptcp_token_init();

        if (proto_register(&mptcp_prot, 1) != 0)
                panic("Failed to register MPTCP proto.\n");

        inet_register_protosw(&mptcp_protosw);

        BUILD_BUG_ON(sizeof(struct mptcp_skb_cb) > sizeof_field(struct sk_buff, cb));
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static const struct proto_ops mptcp_v6_stream_ops = {
        .family            = PF_INET6,
        .owner             = THIS_MODULE,
        .release           = inet6_release,
        .bind              = mptcp_bind,
        .connect           = mptcp_stream_connect,
        .socketpair        = sock_no_socketpair,
        .accept            = mptcp_stream_accept,
        .getname           = inet6_getname,
        .poll              = mptcp_poll,
        .ioctl             = inet6_ioctl,
        .gettstamp         = sock_gettstamp,
        .listen            = mptcp_listen,
        .shutdown          = mptcp_shutdown,
        .setsockopt        = sock_common_setsockopt,
        .getsockopt        = sock_common_getsockopt,
        .sendmsg           = inet6_sendmsg,
        .recvmsg           = inet6_recvmsg,
        .mmap              = sock_no_mmap,
        .sendpage          = inet_sendpage,
#ifdef CONFIG_COMPAT
        .compat_ioctl      = inet6_compat_ioctl,
#endif
};

static struct proto mptcp_v6_prot;

static void mptcp_v6_destroy(struct sock *sk)
{
        mptcp_destroy(sk);
        inet6_destroy_sock(sk);
}

static struct inet_protosw mptcp_v6_protosw = {
        .type           = SOCK_STREAM,
        .protocol       = IPPROTO_MPTCP,
        .prot           = &mptcp_v6_prot,
        .ops            = &mptcp_v6_stream_ops,
        .flags          = INET_PROTOSW_ICSK,
};

int __init mptcp_proto_v6_init(void)
{
        int err;

        mptcp_v6_prot = mptcp_prot;
        strcpy(mptcp_v6_prot.name, "MPTCPv6");
        mptcp_v6_prot.slab = NULL;
        mptcp_v6_prot.destroy = mptcp_v6_destroy;
        mptcp_v6_prot.obj_size = sizeof(struct mptcp6_sock);

        err = proto_register(&mptcp_v6_prot, 1);
        if (err)
                return err;

        err = inet6_register_protosw(&mptcp_v6_protosw);
        if (err)
                proto_unregister(&mptcp_v6_prot);

        return err;
}
#endif