Merge tag 'io_uring-5.7-2020-05-22' of git://git.kernel.dk/linux-block

[thirdparty/linux.git] / net / mptcp / protocol.c

// 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>
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
#include <net/transp_v6.h>
#endif
#include <net/mptcp.h>
#include "protocol.h"
#include "mib.h"

#define MPTCP_SAME_STATE TCP_MAX_STATES

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

struct mptcp_skb_cb {
        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_needs_tcp_fallback(const struct mptcp_sock *msk)
{
        return msk->first && !sk_is_mptcp(msk->first);
}

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

        if (sock->sk != sk)
                return NULL;

        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 sock;
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        } else if (unlikely(sk->sk_prot == &tcpv6_prot)) {
                sock->ops = &inet6_stream_ops;
                return sock;
#endif
        }

        return NULL;
}

static struct socket *__mptcp_tcp_fallback(struct mptcp_sock *msk)
{
        struct socket *sock;

        sock_owned_by_me((const struct sock *)msk);

        sock = mptcp_is_tcpsk((struct sock *)msk);
        if (unlikely(sock))
                return sock;

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

        return msk->subflow;
}

static bool __mptcp_can_create_subflow(const struct mptcp_sock *msk)
{
        return !msk->first;
}

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

        ssock = __mptcp_tcp_fallback(msk);
        if (unlikely(ssock))
                return ssock;

        ssock = __mptcp_nmpc_socket(msk);
        if (ssock)
                goto set_state;

        if (!__mptcp_can_create_subflow(msk))
                return ERR_PTR(-EINVAL);

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

set_state:
        if (state != MPTCP_SAME_STATE)
                inet_sk_state_store(sk, state);
        return ssock;
}

static void __mptcp_move_skb(struct mptcp_sock *msk, struct sock *ssk,
                             struct sk_buff *skb,
                             unsigned int offset, size_t copy_len)
{
        struct sock *sk = (struct sock *)msk;

        __skb_unlink(skb, &ssk->sk_receive_queue);
        skb_set_owner_r(skb, sk);
        __skb_queue_tail(&sk->sk_receive_queue, skb);

        msk->ack_seq += copy_len;
        MPTCP_SKB_CB(skb)->offset = offset;
}

/* both sockets must be locked */
static bool mptcp_subflow_dsn_valid(const struct mptcp_sock *msk,
                                    struct sock *ssk)
{
        struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
        u64 dsn = mptcp_subflow_get_mapped_dsn(subflow);

        /* revalidate data sequence number.
         *
         * mptcp_subflow_data_available() is usually called
         * without msk lock.  Its unlikely (but possible)
         * that msk->ack_seq has been advanced since the last
         * call found in-sequence data.
         */
        if (likely(dsn == msk->ack_seq))
                return true;

        subflow->data_avail = 0;
        return mptcp_subflow_data_available(ssk);
}

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;
        bool done = false;

        if (!mptcp_subflow_dsn_valid(msk, ssk)) {
                *bytes = 0;
                return false;
        }

        if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
                int rcvbuf = max(ssk->sk_rcvbuf, sk->sk_rcvbuf);

                if (rcvbuf > sk->sk_rcvbuf)
                        sk->sk_rcvbuf = rcvbuf;
        }

        tp = tcp_sk(ssk);
        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)
                        break;

                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;

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

        return done;
}

/* 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);

        spin_unlock_bh(&sk->sk_lock.slock);

        return moved > 0;
}

void mptcp_data_ready(struct sock *sk, struct sock *ssk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);

        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:
        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 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 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 (!sk_stream_is_writeable(sk) &&
            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_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 bool mptcp_ext_cache_refill(struct mptcp_sock *msk)
{
        if (!msk->cached_ext)
                msk->cached_ext = __skb_ext_alloc();

        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 void mptcp_clean_una(struct sock *sk)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_data_frag *dtmp, *dfrag;
        u64 snd_una = atomic64_read(&msk->snd_una);
        bool cleaned = false;

        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 = dfrag->data_seq + dfrag->data_len - snd_una;

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

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

        if (cleaned) {
                sk_mem_reclaim_partial(sk);

                /* Only wake up writers if a subflow is ready */
                if (test_bit(MPTCP_SEND_SPACE, &msk->flags))
                        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);
        while ((!retransmission && !mptcp_page_frag_refill(ssk, pfrag)) ||
               !mptcp_ext_cache_refill(msk)) {
                ret = sk_stream_wait_memory(ssk, timeo);
                if (ret)
                        return ret;

                /* if sk_stream_wait_memory() sleeps snd_una can change
                 * significantly, refresh the rtx queue
                 */
                mptcp_clean_una(sk);

                if (unlikely(__mptcp_needs_tcp_fallback(msk)))
                        return 0;
        }
        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))
                        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);
        if (ret <= 0)
                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_seq += ret;
        mptcp_subflow_ctx(ssk)->rel_write_seq += ret;

        return ret;
}

static struct sock *mptcp_subflow_get_send(struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;
        struct sock *backup = NULL;

        sock_owned_by_me((const struct sock *)msk);

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

                if (!sk_stream_memory_free(ssk)) {
                        struct socket *sock = ssk->sk_socket;

                        if (sock) {
                                clear_bit(MPTCP_SEND_SPACE, &msk->flags);
                                smp_mb__after_atomic();

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

                        return NULL;
                }

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

                        continue;
                }

                return ssk;
        }

        return backup;
}

static void ssk_check_wmem(struct mptcp_sock *msk, struct sock *ssk)
{
        struct socket *sock;

        if (likely(sk_stream_is_writeable(ssk)))
                return;

        sock = READ_ONCE(ssk->sk_socket);

        if (sock) {
                clear_bit(MPTCP_SEND_SPACE, &msk->flags);
                smp_mb__after_atomic();
                /* set NOSPACE only after clearing SEND_SPACE flag */
                set_bit(SOCK_NOSPACE, &sock->flags);
        }
}

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 socket *ssock;
        size_t copied = 0;
        struct sock *ssk;
        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;
        }

fallback:
        ssock = __mptcp_tcp_fallback(msk);
        if (unlikely(ssock)) {
                release_sock(sk);
                pr_debug("fallback passthrough");
                ret = sock_sendmsg(ssock, msg);
                return ret >= 0 ? ret + copied : (copied ? copied : ret);
        }

        mptcp_clean_una(sk);

        __mptcp_flush_join_list(msk);
        ssk = mptcp_subflow_get_send(msk);
        while (!sk_stream_memory_free(sk) || !ssk) {
                ret = sk_stream_wait_memory(sk, &timeo);
                if (ret)
                        goto out;

                mptcp_clean_una(sk);

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

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

        lock_sock(ssk);
        while (msg_data_left(msg)) {
                ret = mptcp_sendmsg_frag(sk, ssk, msg, NULL, &timeo, &mss_now,
                                         &size_goal);
                if (ret < 0)
                        break;
                if (ret == 0 && unlikely(__mptcp_needs_tcp_fallback(msk))) {
                        /* Can happen for passive sockets:
                         * 3WHS negotiated MPTCP, but first packet after is
                         * plain TCP (e.g. due to middlebox filtering unknown
                         * options).
                         *
                         * Fall back to TCP.
                         */
                        release_sock(ssk);
                        goto fallback;
                }

                copied += ret;
        }

        mptcp_set_timeout(sk, ssk);
        if (copied) {
                ret = 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);
        }

        ssk_check_wmem(msk, ssk);
        release_sock(ssk);
out:
        release_sock(sk);
        return 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;
}

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

        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);

        return moved > 0;
}

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);
        struct socket *ssock;
        int copied = 0;
        int target;
        long timeo;

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

        lock_sock(sk);
        ssock = __mptcp_tcp_fallback(msk);
        if (unlikely(ssock)) {
fallback:
                release_sock(sk);
                pr_debug("fallback-read subflow=%p",
                         mptcp_subflow_ctx(ssock->sk));
                copied = sock_recvmsg(ssock, msg, flags);
                return copied;
        }

        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 (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 (unlikely(__mptcp_tcp_fallback(msk)))
                        goto fallback;
        }

        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:
        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) == 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);

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

                /* 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.
 */
static 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 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 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, ret, mss_now = 0, size_goal = 0;
        struct mptcp_data_frag *dfrag;
        u64 orig_write_seq;
        size_t copied = 0;
        struct msghdr msg;
        long timeo = 0;

        lock_sock(sk);
        mptcp_clean_una(sk);
        __mptcp_flush_join_list(msk);
        __mptcp_move_skbs(msk);

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

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

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

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

        lock_sock(ssk);

        msg.msg_flags = MSG_DONTWAIT;
        orig_len = dfrag->data_len;
        orig_offset = dfrag->offset;
        orig_write_seq = dfrag->data_seq;
        while (dfrag->data_len > 0) {
                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 (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->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;

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

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

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

        sk_sockets_allocated_inc(sk);
        sk->sk_sndbuf = sock_net(sk)->ipv4.sysctl_tcp_wmem[2];

        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);
}

static void mptcp_subflow_shutdown(struct sock *ssk, int how,
                                   bool data_fin_tx_enable, u64 data_fin_tx_seq)
{
        lock_sock(ssk);

        switch (ssk->sk_state) {
        case TCP_LISTEN:
                if (!(how & RCV_SHUTDOWN))
                        break;
                /* fall through */
        case TCP_SYN_SENT:
                tcp_disconnect(ssk, O_NONBLOCK);
                break;
        default:
                if (data_fin_tx_enable) {
                        struct mptcp_subflow_context *subflow;

                        subflow = mptcp_subflow_ctx(ssk);
                        subflow->data_fin_tx_seq = data_fin_tx_seq;
                        subflow->data_fin_tx_enable = 1;
                }

                ssk->sk_shutdown |= how;
                tcp_shutdown(ssk, how);
                break;
        }

        /* Wake up anyone sleeping in poll. */
        ssk->sk_state_change(ssk);
        release_sock(ssk);
}

/* Called with msk lock held, releases such lock before returning */
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);
        u64 data_fin_tx_seq;

        lock_sock(sk);

        mptcp_token_destroy(msk->token);
        inet_sk_state_store(sk, TCP_CLOSE);

        __mptcp_flush_join_list(msk);

        list_splice_init(&msk->conn_list, &conn_list);

        data_fin_tx_seq = msk->write_seq;

        __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);

                subflow->data_fin_tx_seq = data_fin_tx_seq;
                subflow->data_fin_tx_enable = 1;
                __mptcp_close_ssk(sk, ssk, subflow, timeout);
        }

        mptcp_cancel_work(sk);
        mptcp_pm_close(msk);

        __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;

        if (unlikely(mptcp_token_new_accept(subflow_req->token, nsk))) {
                nsk->sk_state = TCP_CLOSE;
                bh_unlock_sock(nsk);

                /* we can't call into mptcp_close() here - possible BH context
                 * free the sock directly.
                 * sk_clone_lock() sets nsk refcnt to two, hence call sk_free()
                 * too.
                 */
                sk_common_release(nsk);
                sk_free(nsk);
                return NULL;
        }

        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++;
                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;
}

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);
                inet_sk_state_store(newsk, TCP_ESTABLISHED);

                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;
}

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

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

        sk_sockets_allocated_dec(sk);
}

static int mptcp_setsockopt(struct sock *sk, int level, int optname,
                            char __user *optval, unsigned int optlen)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct socket *ssock;

        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 TCP socket options are passed through
         * to the one remaining subflow.
         */
        lock_sock(sk);
        ssock = __mptcp_tcp_fallback(msk);
        release_sock(sk);
        if (ssock)
                return tcp_setsockopt(ssock->sk, level, 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 socket *ssock;

        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);
        ssock = __mptcp_tcp_fallback(msk);
        release_sock(sk);
        if (ssock)
                return tcp_getsockopt(ssock->sk, 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_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);

        if (!subflow->mp_capable) {
                MPTCP_INC_STATS(sock_net(sk),
                                MPTCP_MIB_MPCAPABLEACTIVEFALLBACK);
                return;
        }

        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;
        subflow->rel_write_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->token, subflow->token);
        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);
}

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 (inet_sk_state_load(parent) != TCP_ESTABLISHED)
                return false;

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

        /* passive connection, attach to msk socket */
        parent_sock = READ_ONCE(parent->sk_socket);
        if (parent_sock && !sk->sk_socket)
                mptcp_sock_graft(sk, parent_sock);

        ret = mptcp_pm_allow_new_subflow(msk);
        if (ret) {
                subflow->map_seq = msk->ack_seq;

                /* active connections are already on conn_list */
                spin_lock_bh(&msk->join_list_lock);
                if (!WARN_ON_ONCE(!list_empty(&subflow->node)))
                        list_add_tail(&subflow->node, &msk->join_list);
                spin_unlock_bh(&msk->join_list_lock);
        }
        return ret;
}

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

        return subflow->mp_join == 1;
}

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           = inet_hash,
        .unhash         = inet_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_mem     = sysctl_tcp_mem,
        .obj_size       = sizeof(struct mptcp_sock),
        .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_socket_create(msk, MPTCP_SAME_STATE);
        if (IS_ERR(ssock)) {
                err = PTR_ERR(ssock);
                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 int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
                                int addr_len, int flags)
{
        struct mptcp_sock *msk = mptcp_sk(sock->sk);
        struct socket *ssock;
        int err;

        lock_sock(sock->sk);
        ssock = __mptcp_socket_create(msk, TCP_SYN_SENT);
        if (IS_ERR(ssock)) {
                err = PTR_ERR(ssock);
                goto unlock;
        }

#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_ctx(ssock->sk)->request_mptcp = 0;
#endif

        err = ssock->ops->connect(ssock, uaddr, addr_len, flags);
        inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
        mptcp_copy_inaddrs(sock->sk, ssock->sk);

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

static int mptcp_v4_getname(struct socket *sock, struct sockaddr *uaddr,
                            int peer)
{
        if (sock->sk->sk_prot == &tcp_prot) {
                /* we are being invoked from __sys_accept4, after
                 * mptcp_accept() has just 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 inet_getname(sock, uaddr, peer);
}

#if IS_ENABLED(CONFIG_MPTCP_IPV6)
static int mptcp_v6_getname(struct socket *sock, struct sockaddr *uaddr,
                            int peer)
{
        if (sock->sk->sk_prot == &tcpv6_prot) {
                /* we are being invoked from __sys_accept4 after
                 * mptcp_accept() has accepted a non-mp-capable
                 * subflow: sk is a tcp_sk, not mptcp.
                 *
                 * Hand the socket over to tcp so all further
                 * socket ops bypass mptcp.
                 */
                sock->ops = &inet6_stream_ops;
        }

        return inet6_getname(sock, uaddr, peer);
}
#endif

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_socket_create(msk, TCP_LISTEN);
        if (IS_ERR(ssock)) {
                err = PTR_ERR(ssock);
                goto unlock;
        }

        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 bool is_tcp_proto(const struct proto *p)
{
#if IS_ENABLED(CONFIG_MPTCP_IPV6)
        return p == &tcp_prot || p == &tcpv6_prot;
#else
        return p == &tcp_prot;
#endif
}

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;

        sock_hold(ssock->sk);
        release_sock(sock->sk);

        err = ssock->ops->accept(sock, newsock, flags, kern);
        if (err == 0 && !is_tcp_proto(newsock->sk->sk_prot)) {
                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);
                list_for_each_entry(subflow, &msk->conn_list, node) {
                        struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

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

        sock_put(ssock->sk);
        return err;

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

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;
        struct socket *ssock;
        __poll_t mask = 0;

        msk = mptcp_sk(sk);
        lock_sock(sk);
        ssock = __mptcp_tcp_fallback(msk);
        if (!ssock)
                ssock = __mptcp_nmpc_socket(msk);
        if (ssock) {
                mask = ssock->ops->poll(file, ssock, wait);
                release_sock(sk);
                return mask;
        }

        release_sock(sk);
        sock_poll_wait(file, sock, wait);
        lock_sock(sk);

        if (test_bit(MPTCP_DATA_READY, &msk->flags))
                mask = EPOLLIN | EPOLLRDNORM;
        if (sk_stream_is_writeable(sk) &&
            test_bit(MPTCP_SEND_SPACE, &msk->flags))
                mask |= EPOLLOUT | EPOLLWRNORM;
        if (sk->sk_shutdown & RCV_SHUTDOWN)
                mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;

        release_sock(sk);

        return mask;
}

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

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

        lock_sock(sock->sk);
        ssock = __mptcp_tcp_fallback(msk);
        if (ssock) {
                release_sock(sock->sk);
                return inet_shutdown(ssock, how);
        }

        if (how == SHUT_WR || how == SHUT_RDWR)
                inet_sk_state_store(sock->sk, TCP_FIN_WAIT1);

        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;
        }

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

                mptcp_subflow_shutdown(tcp_sk, how, 1, msk->write_seq);
        }

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           = mptcp_v4_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,
#ifdef CONFIG_COMPAT
        .compat_setsockopt = compat_sock_common_setsockopt,
        .compat_getsockopt = compat_sock_common_getsockopt,
#endif
};

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

void 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();

        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           = mptcp_v6_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_setsockopt = compat_sock_common_setsockopt,
        .compat_getsockopt = compat_sock_common_getsockopt,
#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 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