// 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"

#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

/* 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_tcp_fallback(struct mptcp_sock *msk)
{
        sock_owned_by_me((const struct sock *)msk);

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

        if (msk->subflow) {
                release_sock((struct sock *)msk);
                return msk->subflow;
        }

        return NULL;
}

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_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 struct sock *mptcp_subflow_get(const struct mptcp_sock *msk)
{
        struct mptcp_subflow_context *subflow;

        sock_owned_by_me((const struct sock *)msk);

        mptcp_for_each_subflow(msk, subflow) {
                return mptcp_subflow_tcp_sock(subflow);
        }

        return NULL;
}

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 inline bool mptcp_skb_can_collapse_to(const struct mptcp_sock *msk,
                                             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 == msk->write_seq;
}

static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
                              struct msghdr *msg, long *timeo, int *pmss_now,
                              int *ps_goal)
{
        int mss_now, avail_size, size_goal, ret;
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_ext *mpext = NULL;
        struct sk_buff *skb, *tail;
        bool can_collapse = false;
        struct page_frag *pfrag;
        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
         */
        pfrag = sk_page_frag(sk);
        while (!sk_page_frag_refill(ssk, pfrag) ||
               !mptcp_ext_cache_refill(msk)) {
                ret = sk_stream_wait_memory(ssk, timeo);
                if (ret)
                        return ret;
                if (unlikely(__mptcp_needs_tcp_fallback(msk)))
                        return 0;
        }

        /* 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(msk, skb, mpext);
                if (!can_collapse)
                        TCP_SKB_CB(skb)->eor = 1;
                else
                        avail_size = size_goal - skb->len;
        }
        psize = min_t(size_t, pfrag->size - pfrag->offset, avail_size);

        /* Copy to page */
        pr_debug("left=%zu", msg_data_left(msg));
        psize = copy_page_from_iter(pfrag->page, pfrag->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;

        /* 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, pfrag->page, pfrag->offset, psize,
                               msg->msg_flags | MSG_SENDPAGE_NOTLAST);
        if (ret <= 0)
                return ret;
        if (unlikely(ret < psize))
                iov_iter_revert(&msg->msg_iter, psize - ret);

        /* 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 = msk->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:
        pfrag->offset += ret;
        msk->write_seq += ret;
        mptcp_subflow_ctx(ssk)->rel_write_seq += ret;

        return ret;
}

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

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

        ssk = mptcp_subflow_get(msk);
        if (!ssk) {
                release_sock(sk);
                return -ENOTCONN;
        }

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

        lock_sock(ssk);
        while (msg_data_left(msg)) {
                ret = mptcp_sendmsg_frag(sk, ssk, msg, &timeo, &mss_now,
                                         &size_goal);
                if (ret < 0)
                        break;
                if (ret == 0 && unlikely(__mptcp_needs_tcp_fallback(msk))) {
                        release_sock(ssk);
                        ssock = __mptcp_tcp_fallback(msk);
                        goto fallback;
                }

                copied += ret;
        }

        if (copied) {
                ret = copied;
                tcp_push(ssk, msg->msg_flags, mss_now, tcp_sk(ssk)->nonagle,
                         size_goal);
        }

        ssk_check_wmem(msk, ssk);
        release_sock(ssk);
        release_sock(sk);
        return ret;
}

int mptcp_read_actor(read_descriptor_t *desc, struct sk_buff *skb,
                     unsigned int offset, size_t len)
{
        struct mptcp_read_arg *arg = desc->arg.data;
        size_t copy_len;

        copy_len = min(desc->count, len);

        if (likely(arg->msg)) {
                int err;

                err = skb_copy_datagram_msg(skb, offset, arg->msg, copy_len);
                if (err) {
                        pr_debug("error path");
                        desc->error = err;
                        return err;
                }
        } else {
                pr_debug("Flushing skb payload");
        }

        desc->count -= copy_len;

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

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(struct sock *sk, struct msghdr *msg, size_t len,
                         int nonblock, int flags, int *addr_len)
{
        struct mptcp_sock *msk = mptcp_sk(sk);
        struct mptcp_subflow_context *subflow;
        bool more_data_avail = false;
        struct mptcp_read_arg arg;
        read_descriptor_t desc;
        bool wait_data = false;
        struct socket *ssock;
        struct tcp_sock *tp;
        bool done = false;
        struct sock *ssk;
        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:
                pr_debug("fallback-read subflow=%p",
                         mptcp_subflow_ctx(ssock->sk));
                copied = sock_recvmsg(ssock, msg, flags);
                return copied;
        }

        arg.msg = msg;
        desc.arg.data = &arg;
        desc.error = 0;

        timeo = sock_rcvtimeo(sk, nonblock);

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

        while (!done) {
                u32 map_remaining;
                int bytes_read;

                ssk = mptcp_subflow_recv_lookup(msk);
                pr_debug("msk=%p ssk=%p", msk, ssk);
                if (!ssk)
                        goto wait_for_data;

                subflow = mptcp_subflow_ctx(ssk);
                tp = tcp_sk(ssk);

                lock_sock(ssk);
                do {
                        /* try to read as much data as available */
                        map_remaining = subflow->map_data_len -
                                        mptcp_subflow_get_map_offset(subflow);
                        desc.count = min_t(size_t, len - copied, map_remaining);
                        pr_debug("reading %zu bytes, copied %d", desc.count,
                                 copied);
                        bytes_read = tcp_read_sock(ssk, &desc,
                                                   mptcp_read_actor);
                        if (bytes_read < 0) {
                                if (!copied)
                                        copied = bytes_read;
                                done = true;
                                goto next;
                        }

                        pr_debug("msk ack_seq=%llx -> %llx", msk->ack_seq,
                                 msk->ack_seq + bytes_read);
                        msk->ack_seq += bytes_read;
                        copied += bytes_read;
                        if (copied >= len) {
                                done = true;
                                goto next;
                        }
                        if (tp->urg_data && tp->urg_seq == tp->copied_seq) {
                                pr_err("Urgent data present, cannot proceed");
                                done = true;
                                goto next;
                        }
next:
                        more_data_avail = mptcp_subflow_data_available(ssk);
                } while (more_data_avail && !done);
                release_sock(ssk);
                continue;

wait_for_data:
                more_data_avail = false;

                /* 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);
                wait_data = true;
                mptcp_wait_data(sk, &timeo);
                if (unlikely(__mptcp_tcp_fallback(msk)))
                        goto fallback;
        }

        if (more_data_avail) {
                if (!test_bit(MPTCP_DATA_READY, &msk->flags))
                        set_bit(MPTCP_DATA_READY, &msk->flags);
        } else if (!wait_data) {
                clear_bit(MPTCP_DATA_READY, &msk->flags);

                /* .. race-breaker: ssk might get new data after last
                 * data_available() returns false.
                 */
                ssk = mptcp_subflow_recv_lookup(msk);
                if (unlikely(ssk))
                        set_bit(MPTCP_DATA_READY, &msk->flags);
        }

        release_sock(sk);
        return copied;
}

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

        INIT_LIST_HEAD(&msk->conn_list);
        __set_bit(MPTCP_SEND_SPACE, &msk->flags);

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

        return 0;
}

static int mptcp_init_sock(struct sock *sk)
{
        if (!mptcp_is_enabled(sock_net(sk)))
                return -ENOPROTOOPT;

        return __mptcp_init_sock(sk);
}

static void mptcp_subflow_shutdown(struct sock *ssk, int how)
{
        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:
                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);

        lock_sock(sk);

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

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

        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);
        }

        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;
}

#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

static struct sock *mptcp_sk_clone_lock(const struct sock *sk)
{
        struct sock *nsk = sk_clone_lock(sk, GFP_ATOMIC);

        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

        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;
                u64 ack_seq;

                subflow = mptcp_subflow_ctx(newsk);
                lock_sock(sk);

                local_bh_disable();
                new_mptcp_sock = mptcp_sk_clone_lock(sk);
                if (!new_mptcp_sock) {
                        *err = -ENOBUFS;
                        local_bh_enable();
                        release_sock(sk);
                        mptcp_subflow_shutdown(newsk, SHUT_RDWR + 1);
                        tcp_close(newsk, 0);
                        return NULL;
                }

                __mptcp_init_sock(new_mptcp_sock);

                msk = mptcp_sk(new_mptcp_sock);
                msk->local_key = subflow->local_key;
                msk->token = subflow->token;
                msk->subflow = NULL;
                msk->first = newsk;

                mptcp_token_update_accept(newsk, new_mptcp_sock);

                msk->write_seq = subflow->idsn + 1;
                if (subflow->can_ack) {
                        msk->can_ack = true;
                        msk->remote_key = subflow->remote_key;
                        mptcp_crypto_key_sha(msk->remote_key, NULL, &ack_seq);
                        ack_seq++;
                        msk->ack_seq = ack_seq;
                }
                newsk = new_mptcp_sock;
                mptcp_copy_inaddrs(newsk, ssk);
                list_add(&subflow->node, &msk->conn_list);

                /* will be fully established at mptcp_stream_accept()
                 * completion.
                 */
                inet_sk_state_store(new_mptcp_sock, TCP_SYN_RECV);
                bh_unlock_sock(new_mptcp_sock);
                local_bh_enable();
                release_sock(sk);

                /* the subflow can already receive packet, avoid racing with
                 * the receive path and process the pending ones
                 */
                lock_sock(ssk);
                subflow->rel_write_seq = 1;
                subflow->tcp_sock = ssk;
                subflow->conn = new_mptcp_sock;
                if (unlikely(!skb_queue_empty(&ssk->sk_receive_queue)))
                        mptcp_subflow_data_available(ssk);
                release_sock(ssk);
        }

        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);
}

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);
        if (ssock)
                return tcp_setsockopt(ssock->sk, level, optname, optval,
                                      optlen);

        release_sock(sk);

        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);
        if (ssock)
                return tcp_getsockopt(ssock->sk, level, optname, optval,
                                      option);

        release_sock(sk);

        return -EOPNOTSUPP;
}

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);

        if (!subflow->mp_capable)
                return;

        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;
        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);
}

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);
}

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,
        .close          = mptcp_close,
        .accept         = mptcp_accept,
        .setsockopt     = mptcp_setsockopt,
        .getsockopt     = mptcp_getsockopt,
        .shutdown       = tcp_shutdown,
        .destroy        = mptcp_destroy,
        .sendmsg        = mptcp_sendmsg,
        .recvmsg        = mptcp_recvmsg,
        .hash           = inet_hash,
        .unhash         = inet_unhash,
        .get_port       = mptcp_get_port,
        .stream_memory_free     = mptcp_memory_free,
        .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;
        }

        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.
                 */
                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);
                }

                inet_sk_state_store(newsock->sk, TCP_ESTABLISHED);
        }

        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_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);
        ssock = __mptcp_tcp_fallback(msk);
        if (unlikely(ssock))
                return ssock->ops->poll(file, ssock, NULL);

        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;
        int ret = 0;

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

        lock_sock(sock->sk);

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

                mptcp_subflow_shutdown(tcp_sk, how);
        }

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;

        mptcp_subflow_init();

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

        inet_register_protosw(&mptcp_protosw);
}

#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