// SPDX-License-Identifier: GPL-2.0-only
/*
 * Kernel Connection Multiplexor
 *
 * Copyright (c) 2016 Tom Herbert <tom@herbertland.com>
 */

#include <linux/bpf.h>
#include <linux/errno.h>
#include <linux/errqueue.h>
#include <linux/file.h>
#include <linux/filter.h>
#include <linux/in.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/poll.h>
#include <linux/rculist.h>
#include <linux/skbuff.h>
#include <linux/socket.h>
#include <linux/splice.h>
#include <linux/uaccess.h>
#include <linux/workqueue.h>
#include <linux/syscalls.h>
#include <linux/sched/signal.h>

#include <net/kcm.h>
#include <net/netns/generic.h>
#include <net/sock.h>
#include <uapi/linux/kcm.h>
#include <trace/events/sock.h>

unsigned int kcm_net_id;

static struct kmem_cache *kcm_psockp __read_mostly;
static struct kmem_cache *kcm_muxp __read_mostly;
static struct workqueue_struct *kcm_wq;

static inline struct kcm_sock *kcm_sk(const struct sock *sk)
{
        return (struct kcm_sock *)sk;
}

static inline struct kcm_tx_msg *kcm_tx_msg(struct sk_buff *skb)
{
        return (struct kcm_tx_msg *)skb->cb;
}

static void report_csk_error(struct sock *csk, int err)
{
        csk->sk_err = EPIPE;
        sk_error_report(csk);
}

static void kcm_abort_tx_psock(struct kcm_psock *psock, int err,
                               bool wakeup_kcm)
{
        struct sock *csk = psock->sk;
        struct kcm_mux *mux = psock->mux;

        /* Unrecoverable error in transmit */

        spin_lock_bh(&mux->lock);

        if (psock->tx_stopped) {
                spin_unlock_bh(&mux->lock);
                return;
        }

        psock->tx_stopped = 1;
        KCM_STATS_INCR(psock->stats.tx_aborts);

        if (!psock->tx_kcm) {
                /* Take off psocks_avail list */
                list_del(&psock->psock_avail_list);
        } else if (wakeup_kcm) {
                /* In this case psock is being aborted while outside of
                 * write_msgs and psock is reserved. Schedule tx_work
                 * to handle the failure there. Need to commit tx_stopped
                 * before queuing work.
                 */
                smp_mb();

                queue_work(kcm_wq, &psock->tx_kcm->tx_work);
        }

        spin_unlock_bh(&mux->lock);

        /* Report error on lower socket */
        report_csk_error(csk, err);
}

/* RX mux lock held. */
static void kcm_update_rx_mux_stats(struct kcm_mux *mux,
                                    struct kcm_psock *psock)
{
        STRP_STATS_ADD(mux->stats.rx_bytes,
                       psock->strp.stats.bytes -
                       psock->saved_rx_bytes);
        mux->stats.rx_msgs +=
                psock->strp.stats.msgs - psock->saved_rx_msgs;
        psock->saved_rx_msgs = psock->strp.stats.msgs;
        psock->saved_rx_bytes = psock->strp.stats.bytes;
}

static void kcm_update_tx_mux_stats(struct kcm_mux *mux,
                                    struct kcm_psock *psock)
{
        KCM_STATS_ADD(mux->stats.tx_bytes,
                      psock->stats.tx_bytes - psock->saved_tx_bytes);
        mux->stats.tx_msgs +=
                psock->stats.tx_msgs - psock->saved_tx_msgs;
        psock->saved_tx_msgs = psock->stats.tx_msgs;
        psock->saved_tx_bytes = psock->stats.tx_bytes;
}

static int kcm_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);

/* KCM is ready to receive messages on its queue-- either the KCM is new or
 * has become unblocked after being blocked on full socket buffer. Queue any
 * pending ready messages on a psock. RX mux lock held.
 */
static void kcm_rcv_ready(struct kcm_sock *kcm)
{
        struct kcm_mux *mux = kcm->mux;
        struct kcm_psock *psock;
        struct sk_buff *skb;

        if (unlikely(kcm->rx_wait || kcm->rx_psock || kcm->rx_disabled))
                return;

        while (unlikely((skb = __skb_dequeue(&mux->rx_hold_queue)))) {
                if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
                        /* Assuming buffer limit has been reached */
                        skb_queue_head(&mux->rx_hold_queue, skb);
                        WARN_ON(!sk_rmem_alloc_get(&kcm->sk));
                        return;
                }
        }

        while (!list_empty(&mux->psocks_ready)) {
                psock = list_first_entry(&mux->psocks_ready, struct kcm_psock,
                                         psock_ready_list);

                if (kcm_queue_rcv_skb(&kcm->sk, psock->ready_rx_msg)) {
                        /* Assuming buffer limit has been reached */
                        WARN_ON(!sk_rmem_alloc_get(&kcm->sk));
                        return;
                }

                /* Consumed the ready message on the psock. Schedule rx_work to
                 * get more messages.
                 */
                list_del(&psock->psock_ready_list);
                psock->ready_rx_msg = NULL;
                /* Commit clearing of ready_rx_msg for queuing work */
                smp_mb();

                strp_unpause(&psock->strp);
                strp_check_rcv(&psock->strp);
        }

        /* Buffer limit is okay now, add to ready list */
        list_add_tail(&kcm->wait_rx_list,
                      &kcm->mux->kcm_rx_waiters);
        /* paired with lockless reads in kcm_rfree() */
        WRITE_ONCE(kcm->rx_wait, true);
}

static void kcm_rfree(struct sk_buff *skb)
{
        struct sock *sk = skb->sk;
        struct kcm_sock *kcm = kcm_sk(sk);
        struct kcm_mux *mux = kcm->mux;
        unsigned int len = skb->truesize;

        sk_mem_uncharge(sk, len);
        atomic_sub(len, &sk->sk_rmem_alloc);

        /* For reading rx_wait and rx_psock without holding lock */
        smp_mb__after_atomic();

        if (!READ_ONCE(kcm->rx_wait) && !READ_ONCE(kcm->rx_psock) &&
            sk_rmem_alloc_get(sk) < sk->sk_rcvlowat) {
                spin_lock_bh(&mux->rx_lock);
                kcm_rcv_ready(kcm);
                spin_unlock_bh(&mux->rx_lock);
        }
}

static int kcm_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
{
        struct sk_buff_head *list = &sk->sk_receive_queue;

        if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
                return -ENOMEM;

        if (!sk_rmem_schedule(sk, skb, skb->truesize))
                return -ENOBUFS;

        skb->dev = NULL;

        skb_orphan(skb);
        skb->sk = sk;
        skb->destructor = kcm_rfree;
        atomic_add(skb->truesize, &sk->sk_rmem_alloc);
        sk_mem_charge(sk, skb->truesize);

        skb_queue_tail(list, skb);

        if (!sock_flag(sk, SOCK_DEAD))
                sk->sk_data_ready(sk);

        return 0;
}

/* Requeue received messages for a kcm socket to other kcm sockets. This is
 * called with a kcm socket is receive disabled.
 * RX mux lock held.
 */
static void requeue_rx_msgs(struct kcm_mux *mux, struct sk_buff_head *head)
{
        struct sk_buff *skb;
        struct kcm_sock *kcm;

        while ((skb = skb_dequeue(head))) {
                /* Reset destructor to avoid calling kcm_rcv_ready */
                skb->destructor = sock_rfree;
                skb_orphan(skb);
try_again:
                if (list_empty(&mux->kcm_rx_waiters)) {
                        skb_queue_tail(&mux->rx_hold_queue, skb);
                        continue;
                }

                kcm = list_first_entry(&mux->kcm_rx_waiters,
                                       struct kcm_sock, wait_rx_list);

                if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
                        /* Should mean socket buffer full */
                        list_del(&kcm->wait_rx_list);
                        /* paired with lockless reads in kcm_rfree() */
                        WRITE_ONCE(kcm->rx_wait, false);

                        /* Commit rx_wait to read in kcm_free */
                        smp_wmb();

                        goto try_again;
                }
        }
}

/* Lower sock lock held */
static struct kcm_sock *reserve_rx_kcm(struct kcm_psock *psock,
                                       struct sk_buff *head)
{
        struct kcm_mux *mux = psock->mux;
        struct kcm_sock *kcm;

        WARN_ON(psock->ready_rx_msg);

        if (psock->rx_kcm)
                return psock->rx_kcm;

        spin_lock_bh(&mux->rx_lock);

        if (psock->rx_kcm) {
                spin_unlock_bh(&mux->rx_lock);
                return psock->rx_kcm;
        }

        kcm_update_rx_mux_stats(mux, psock);

        if (list_empty(&mux->kcm_rx_waiters)) {
                psock->ready_rx_msg = head;
                strp_pause(&psock->strp);
                list_add_tail(&psock->psock_ready_list,
                              &mux->psocks_ready);
                spin_unlock_bh(&mux->rx_lock);
                return NULL;
        }

        kcm = list_first_entry(&mux->kcm_rx_waiters,
                               struct kcm_sock, wait_rx_list);
        list_del(&kcm->wait_rx_list);
        /* paired with lockless reads in kcm_rfree() */
        WRITE_ONCE(kcm->rx_wait, false);

        psock->rx_kcm = kcm;
        /* paired with lockless reads in kcm_rfree() */
        WRITE_ONCE(kcm->rx_psock, psock);

        spin_unlock_bh(&mux->rx_lock);

        return kcm;
}

static void kcm_done(struct kcm_sock *kcm);

static void kcm_done_work(struct work_struct *w)
{
        kcm_done(container_of(w, struct kcm_sock, done_work));
}

/* Lower sock held */
static void unreserve_rx_kcm(struct kcm_psock *psock,
                             bool rcv_ready)
{
        struct kcm_sock *kcm = psock->rx_kcm;
        struct kcm_mux *mux = psock->mux;

        if (!kcm)
                return;

        spin_lock_bh(&mux->rx_lock);

        psock->rx_kcm = NULL;
        /* paired with lockless reads in kcm_rfree() */
        WRITE_ONCE(kcm->rx_psock, NULL);

        /* Commit kcm->rx_psock before sk_rmem_alloc_get to sync with
         * kcm_rfree
         */
        smp_mb();

        if (unlikely(kcm->done)) {
                spin_unlock_bh(&mux->rx_lock);

                /* Need to run kcm_done in a task since we need to qcquire
                 * callback locks which may already be held here.
                 */
                INIT_WORK(&kcm->done_work, kcm_done_work);
                schedule_work(&kcm->done_work);
                return;
        }

        if (unlikely(kcm->rx_disabled)) {
                requeue_rx_msgs(mux, &kcm->sk.sk_receive_queue);
        } else if (rcv_ready || unlikely(!sk_rmem_alloc_get(&kcm->sk))) {
                /* Check for degenerative race with rx_wait that all
                 * data was dequeued (accounted for in kcm_rfree).
                 */
                kcm_rcv_ready(kcm);
        }
        spin_unlock_bh(&mux->rx_lock);
}

/* Lower sock lock held */
static void psock_data_ready(struct sock *sk)
{
        struct kcm_psock *psock;

        trace_sk_data_ready(sk);

        read_lock_bh(&sk->sk_callback_lock);

        psock = (struct kcm_psock *)sk->sk_user_data;
        if (likely(psock))
                strp_data_ready(&psock->strp);

        read_unlock_bh(&sk->sk_callback_lock);
}

/* Called with lower sock held */
static void kcm_rcv_strparser(struct strparser *strp, struct sk_buff *skb)
{
        struct kcm_psock *psock = container_of(strp, struct kcm_psock, strp);
        struct kcm_sock *kcm;

try_queue:
        kcm = reserve_rx_kcm(psock, skb);
        if (!kcm) {
                 /* Unable to reserve a KCM, message is held in psock and strp
                  * is paused.
                  */
                return;
        }

        if (kcm_queue_rcv_skb(&kcm->sk, skb)) {
                /* Should mean socket buffer full */
                unreserve_rx_kcm(psock, false);
                goto try_queue;
        }
}

static int kcm_parse_func_strparser(struct strparser *strp, struct sk_buff *skb)
{
        struct kcm_psock *psock = container_of(strp, struct kcm_psock, strp);
        struct bpf_prog *prog = psock->bpf_prog;
        int res;

        res = bpf_prog_run_pin_on_cpu(prog, skb);
        return res;
}

static int kcm_read_sock_done(struct strparser *strp, int err)
{
        struct kcm_psock *psock = container_of(strp, struct kcm_psock, strp);

        unreserve_rx_kcm(psock, true);

        return err;
}

static void psock_state_change(struct sock *sk)
{
        /* TCP only does a EPOLLIN for a half close. Do a EPOLLHUP here
         * since application will normally not poll with EPOLLIN
         * on the TCP sockets.
         */

        report_csk_error(sk, EPIPE);
}

static void psock_write_space(struct sock *sk)
{
        struct kcm_psock *psock;
        struct kcm_mux *mux;
        struct kcm_sock *kcm;

        read_lock_bh(&sk->sk_callback_lock);

        psock = (struct kcm_psock *)sk->sk_user_data;
        if (unlikely(!psock))
                goto out;
        mux = psock->mux;

        spin_lock_bh(&mux->lock);

        /* Check if the socket is reserved so someone is waiting for sending. */
        kcm = psock->tx_kcm;
        if (kcm)
                queue_work(kcm_wq, &kcm->tx_work);

        spin_unlock_bh(&mux->lock);
out:
        read_unlock_bh(&sk->sk_callback_lock);
}

static void unreserve_psock(struct kcm_sock *kcm);

/* kcm sock is locked. */
static struct kcm_psock *reserve_psock(struct kcm_sock *kcm)
{
        struct kcm_mux *mux = kcm->mux;
        struct kcm_psock *psock;

        psock = kcm->tx_psock;

        smp_rmb(); /* Must read tx_psock before tx_wait */

        if (psock) {
                WARN_ON(kcm->tx_wait);
                if (unlikely(psock->tx_stopped))
                        unreserve_psock(kcm);
                else
                        return kcm->tx_psock;
        }

        spin_lock_bh(&mux->lock);

        /* Check again under lock to see if psock was reserved for this
         * psock via psock_unreserve.
         */
        psock = kcm->tx_psock;
        if (unlikely(psock)) {
                WARN_ON(kcm->tx_wait);
                spin_unlock_bh(&mux->lock);
                return kcm->tx_psock;
        }

        if (!list_empty(&mux->psocks_avail)) {
                psock = list_first_entry(&mux->psocks_avail,
                                         struct kcm_psock,
                                         psock_avail_list);
                list_del(&psock->psock_avail_list);
                if (kcm->tx_wait) {
                        list_del(&kcm->wait_psock_list);
                        kcm->tx_wait = false;
                }
                kcm->tx_psock = psock;
                psock->tx_kcm = kcm;
                KCM_STATS_INCR(psock->stats.reserved);
        } else if (!kcm->tx_wait) {
                list_add_tail(&kcm->wait_psock_list,
                              &mux->kcm_tx_waiters);
                kcm->tx_wait = true;
        }

        spin_unlock_bh(&mux->lock);

        return psock;
}

/* mux lock held */
static void psock_now_avail(struct kcm_psock *psock)
{
        struct kcm_mux *mux = psock->mux;
        struct kcm_sock *kcm;

        if (list_empty(&mux->kcm_tx_waiters)) {
                list_add_tail(&psock->psock_avail_list,
                              &mux->psocks_avail);
        } else {
                kcm = list_first_entry(&mux->kcm_tx_waiters,
                                       struct kcm_sock,
                                       wait_psock_list);
                list_del(&kcm->wait_psock_list);
                kcm->tx_wait = false;
                psock->tx_kcm = kcm;

                /* Commit before changing tx_psock since that is read in
                 * reserve_psock before queuing work.
                 */
                smp_mb();

                kcm->tx_psock = psock;
                KCM_STATS_INCR(psock->stats.reserved);
                queue_work(kcm_wq, &kcm->tx_work);
        }
}

/* kcm sock is locked. */
static void unreserve_psock(struct kcm_sock *kcm)
{
        struct kcm_psock *psock;
        struct kcm_mux *mux = kcm->mux;

        spin_lock_bh(&mux->lock);

        psock = kcm->tx_psock;

        if (WARN_ON(!psock)) {
                spin_unlock_bh(&mux->lock);
                return;
        }

        smp_rmb(); /* Read tx_psock before tx_wait */

        kcm_update_tx_mux_stats(mux, psock);

        WARN_ON(kcm->tx_wait);

        kcm->tx_psock = NULL;
        psock->tx_kcm = NULL;
        KCM_STATS_INCR(psock->stats.unreserved);

        if (unlikely(psock->tx_stopped)) {
                if (psock->done) {
                        /* Deferred free */
                        list_del(&psock->psock_list);
                        mux->psocks_cnt--;
                        sock_put(psock->sk);
                        fput(psock->sk->sk_socket->file);
                        kmem_cache_free(kcm_psockp, psock);
                }

                /* Don't put back on available list */

                spin_unlock_bh(&mux->lock);

                return;
        }

        psock_now_avail(psock);

        spin_unlock_bh(&mux->lock);
}

static void kcm_report_tx_retry(struct kcm_sock *kcm)
{
        struct kcm_mux *mux = kcm->mux;

        spin_lock_bh(&mux->lock);
        KCM_STATS_INCR(mux->stats.tx_retries);
        spin_unlock_bh(&mux->lock);
}

/* Write any messages ready on the kcm socket.  Called with kcm sock lock
 * held.  Return bytes actually sent or error.
 */
static int kcm_write_msgs(struct kcm_sock *kcm)
{
        unsigned int total_sent = 0;
        struct sock *sk = &kcm->sk;
        struct kcm_psock *psock;
        struct sk_buff *head;
        int ret = 0;

        kcm->tx_wait_more = false;
        psock = kcm->tx_psock;
        if (unlikely(psock && psock->tx_stopped)) {
                /* A reserved psock was aborted asynchronously. Unreserve
                 * it and we'll retry the message.
                 */
                unreserve_psock(kcm);
                kcm_report_tx_retry(kcm);
                if (skb_queue_empty(&sk->sk_write_queue))
                        return 0;

                kcm_tx_msg(skb_peek(&sk->sk_write_queue))->started_tx = false;
        }

retry:
        while ((head = skb_peek(&sk->sk_write_queue))) {
                struct msghdr msg = {
                        .msg_flags = MSG_DONTWAIT | MSG_SPLICE_PAGES,
                };
                struct kcm_tx_msg *txm = kcm_tx_msg(head);
                struct sk_buff *skb;
                unsigned int msize;
                int i;

                if (!txm->started_tx) {
                        psock = reserve_psock(kcm);
                        if (!psock)
                                goto out;
                        skb = head;
                        txm->frag_offset = 0;
                        txm->sent = 0;
                        txm->started_tx = true;
                } else {
                        if (WARN_ON(!psock)) {
                                ret = -EINVAL;
                                goto out;
                        }
                        skb = txm->frag_skb;
                }

                if (WARN_ON_ONCE(!skb_shinfo(skb)->nr_frags) ||
                    WARN_ON_ONCE(!skb_frag_page(&skb_shinfo(skb)->frags[0]))) {
                        ret = -EINVAL;
                        goto out;
                }

                msize = 0;
                for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
                        msize += skb_frag_size(&skb_shinfo(skb)->frags[i]);

                iov_iter_bvec(&msg.msg_iter, ITER_SOURCE,
                              (const struct bio_vec *)skb_shinfo(skb)->frags,
                              skb_shinfo(skb)->nr_frags, msize);
                iov_iter_advance(&msg.msg_iter, txm->frag_offset);

                do {
                        ret = sock_sendmsg(psock->sk->sk_socket, &msg);
                        if (ret <= 0) {
                                if (ret == -EAGAIN) {
                                        /* Save state to try again when there's
                                         * write space on the socket
                                         */
                                        txm->frag_skb = skb;
                                        ret = 0;
                                        goto out;
                                }

                                /* Hard failure in sending message, abort this
                                 * psock since it has lost framing
                                 * synchronization and retry sending the
                                 * message from the beginning.
                                 */
                                kcm_abort_tx_psock(psock, ret ? -ret : EPIPE,
                                                   true);
                                unreserve_psock(kcm);
                                psock = NULL;

                                txm->started_tx = false;
                                kcm_report_tx_retry(kcm);
                                ret = 0;
                                goto retry;
                        }

                        txm->sent += ret;
                        txm->frag_offset += ret;
                        KCM_STATS_ADD(psock->stats.tx_bytes, ret);
                } while (msg.msg_iter.count > 0);

                if (skb == head) {
                        if (skb_has_frag_list(skb)) {
                                txm->frag_skb = skb_shinfo(skb)->frag_list;
                                txm->frag_offset = 0;
                                continue;
                        }
                } else if (skb->next) {
                        txm->frag_skb = skb->next;
                        txm->frag_offset = 0;
                        continue;
                }

                /* Successfully sent the whole packet, account for it. */
                sk->sk_wmem_queued -= txm->sent;
                total_sent += txm->sent;
                skb_dequeue(&sk->sk_write_queue);
                kfree_skb(head);
                KCM_STATS_INCR(psock->stats.tx_msgs);
        }
out:
        if (!head) {
                /* Done with all queued messages. */
                WARN_ON(!skb_queue_empty(&sk->sk_write_queue));
                if (psock)
                        unreserve_psock(kcm);
        }

        /* Check if write space is available */
        sk->sk_write_space(sk);

        return total_sent ? : ret;
}

static void kcm_tx_work(struct work_struct *w)
{
        struct kcm_sock *kcm = container_of(w, struct kcm_sock, tx_work);
        struct sock *sk = &kcm->sk;
        int err;

        lock_sock(sk);

        /* Primarily for SOCK_DGRAM sockets, also handle asynchronous tx
         * aborts
         */
        err = kcm_write_msgs(kcm);
        if (err < 0) {
                /* Hard failure in write, report error on KCM socket */
                pr_warn("KCM: Hard failure on kcm_write_msgs %d\n", err);
                report_csk_error(&kcm->sk, -err);
                goto out;
        }

        /* Primarily for SOCK_SEQPACKET sockets */
        if (likely(sk->sk_socket) &&
            test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
                clear_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
                sk->sk_write_space(sk);
        }

out:
        release_sock(sk);
}

static void kcm_push(struct kcm_sock *kcm)
{
        if (kcm->tx_wait_more)
                kcm_write_msgs(kcm);
}

static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
{
        struct sock *sk = sock->sk;
        struct kcm_sock *kcm = kcm_sk(sk);
        struct sk_buff *skb = NULL, *head = NULL, *frag_prev = NULL;
        size_t copy, copied = 0;
        long timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
        int eor = (sock->type == SOCK_DGRAM) ?
                  !(msg->msg_flags & MSG_MORE) : !!(msg->msg_flags & MSG_EOR);
        int err = -EPIPE;

        mutex_lock(&kcm->tx_mutex);
        lock_sock(sk);

        /* Per tcp_sendmsg this should be in poll */
        sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);

        if (sk->sk_err)
                goto out_error;

        if (kcm->seq_skb) {
                /* Previously opened message */
                head = kcm->seq_skb;
                skb = kcm_tx_msg(head)->last_skb;
                goto start;
        }

        /* Call the sk_stream functions to manage the sndbuf mem. */
        if (!sk_stream_memory_free(sk)) {
                kcm_push(kcm);
                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
                err = sk_stream_wait_memory(sk, &timeo);
                if (err)
                        goto out_error;
        }

        if (msg_data_left(msg)) {
                /* New message, alloc head skb */
                head = alloc_skb(0, sk->sk_allocation);
                while (!head) {
                        kcm_push(kcm);
                        err = sk_stream_wait_memory(sk, &timeo);
                        if (err)
                                goto out_error;

                        head = alloc_skb(0, sk->sk_allocation);
                }

                skb = head;

                /* Set ip_summed to CHECKSUM_UNNECESSARY to avoid calling
                 * csum_and_copy_from_iter from skb_do_copy_data_nocache.
                 */
                skb->ip_summed = CHECKSUM_UNNECESSARY;
        }

start:
        while (msg_data_left(msg)) {
                bool merge = true;
                int i = skb_shinfo(skb)->nr_frags;
                struct page_frag *pfrag = sk_page_frag(sk);

                if (!sk_page_frag_refill(sk, pfrag))
                        goto wait_for_memory;

                if (!skb_can_coalesce(skb, i, pfrag->page,
                                      pfrag->offset)) {
                        if (i == MAX_SKB_FRAGS) {
                                struct sk_buff *tskb;

                                tskb = alloc_skb(0, sk->sk_allocation);
                                if (!tskb)
                                        goto wait_for_memory;

                                if (head == skb)
                                        skb_shinfo(head)->frag_list = tskb;
                                else
                                        skb->next = tskb;

                                frag_prev = skb;
                                skb = tskb;
                                skb->ip_summed = CHECKSUM_UNNECESSARY;
                                continue;
                        }
                        merge = false;
                }

                if (msg->msg_flags & MSG_SPLICE_PAGES) {
                        copy = msg_data_left(msg);
                        if (!sk_wmem_schedule(sk, copy))
                                goto wait_for_memory;

                        err = skb_splice_from_iter(skb, &msg->msg_iter, copy);
                        if (err < 0) {
                                if (err == -EMSGSIZE)
                                        goto wait_for_memory;
                                goto out_error;
                        }

                        copy = err;
                        skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG;
                        sk_wmem_queued_add(sk, copy);
                        sk_mem_charge(sk, copy);

                        if (head != skb)
                                head->truesize += copy;
                } else {
                        copy = min_t(int, msg_data_left(msg),
                                     pfrag->size - pfrag->offset);
                        if (!sk_wmem_schedule(sk, copy))
                                goto wait_for_memory;

                        err = skb_copy_to_page_nocache(sk, &msg->msg_iter, skb,
                                                       pfrag->page,
                                                       pfrag->offset,
                                                       copy);
                        if (err)
                                goto out_error;

                        /* Update the skb. */
                        if (merge) {
                                skb_frag_size_add(
                                        &skb_shinfo(skb)->frags[i - 1], copy);
                        } else {
                                skb_fill_page_desc(skb, i, pfrag->page,
                                                   pfrag->offset, copy);
                                get_page(pfrag->page);
                        }

                        pfrag->offset += copy;
                }

                copied += copy;
                if (head != skb) {
                        head->len += copy;
                        head->data_len += copy;
                }

                continue;

wait_for_memory:
                kcm_push(kcm);
                err = sk_stream_wait_memory(sk, &timeo);
                if (err)
                        goto out_error;
        }

        if (eor) {
                bool not_busy = skb_queue_empty(&sk->sk_write_queue);

                if (head) {
                        /* Message complete, queue it on send buffer */
                        __skb_queue_tail(&sk->sk_write_queue, head);
                        kcm->seq_skb = NULL;
                        KCM_STATS_INCR(kcm->stats.tx_msgs);
                }

                if (msg->msg_flags & MSG_BATCH) {
                        kcm->tx_wait_more = true;
                } else if (kcm->tx_wait_more || not_busy) {
                        err = kcm_write_msgs(kcm);
                        if (err < 0) {
                                /* We got a hard error in write_msgs but have
                                 * already queued this message. Report an error
                                 * in the socket, but don't affect return value
                                 * from sendmsg
                                 */
                                pr_warn("KCM: Hard failure on kcm_write_msgs\n");
                                report_csk_error(&kcm->sk, -err);
                        }
                }
        } else {
                /* Message not complete, save state */
partial_message:
                if (head) {
                        kcm->seq_skb = head;
                        kcm_tx_msg(head)->last_skb = skb;
                }
        }

        KCM_STATS_ADD(kcm->stats.tx_bytes, copied);

        release_sock(sk);
        mutex_unlock(&kcm->tx_mutex);
        return copied;

out_error:
        kcm_push(kcm);

        /* When MAX_SKB_FRAGS was reached, a new skb was allocated and
         * linked into the frag_list before data copy. If the copy
         * subsequently failed, this skb has zero frags. Remove it from
         * the frag_list to prevent kcm_write_msgs from later hitting
         * WARN_ON(!skb_shinfo(skb)->nr_frags).
         */
        if (frag_prev && !skb_shinfo(skb)->nr_frags) {
                if (head == frag_prev)
                        skb_shinfo(head)->frag_list = NULL;
                else
                        frag_prev->next = NULL;
                kfree_skb(skb);
                /* Update skb as it may be saved in partial_message via goto */
                skb = frag_prev;
        }

        if (sock->type == SOCK_SEQPACKET) {
                /* Wrote some bytes before encountering an
                 * error, return partial success.
                 */
                if (copied)
                        goto partial_message;
                if (head != kcm->seq_skb)
                        kfree_skb(head);
        } else {
                kfree_skb(head);
                kcm->seq_skb = NULL;
        }

        err = sk_stream_error(sk, msg->msg_flags, err);

        /* make sure we wake any epoll edge trigger waiter */
        if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN))
                sk->sk_write_space(sk);

        release_sock(sk);
        mutex_unlock(&kcm->tx_mutex);
        return err;
}

static void kcm_splice_eof(struct socket *sock)
{
        struct sock *sk = sock->sk;
        struct kcm_sock *kcm = kcm_sk(sk);

        if (skb_queue_empty_lockless(&sk->sk_write_queue))
                return;

        lock_sock(sk);
        kcm_write_msgs(kcm);
        release_sock(sk);
}

static int kcm_recvmsg(struct socket *sock, struct msghdr *msg,
                       size_t len, int flags)
{
        struct sock *sk = sock->sk;
        struct kcm_sock *kcm = kcm_sk(sk);
        int err = 0;
        struct strp_msg *stm;
        int copied = 0;
        struct sk_buff *skb;

        skb = skb_recv_datagram(sk, flags, &err);
        if (!skb)
                goto out;

        /* Okay, have a message on the receive queue */

        stm = strp_msg(skb);

        if (len > stm->full_len)
                len = stm->full_len;

        err = skb_copy_datagram_msg(skb, stm->offset, msg, len);
        if (err < 0)
                goto out;

        copied = len;
        if (likely(!(flags & MSG_PEEK))) {
                KCM_STATS_ADD(kcm->stats.rx_bytes, copied);
                if (copied < stm->full_len) {
                        if (sock->type == SOCK_DGRAM) {
                                /* Truncated message */
                                msg->msg_flags |= MSG_TRUNC;
                                goto msg_finished;
                        }
                        stm->offset += copied;
                        stm->full_len -= copied;
                } else {
msg_finished:
                        /* Finished with message */
                        msg->msg_flags |= MSG_EOR;
                        KCM_STATS_INCR(kcm->stats.rx_msgs);
                }
        }

out:
        skb_free_datagram(sk, skb);
        return copied ? : err;
}

static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos,
                               struct pipe_inode_info *pipe, size_t len,
                               unsigned int flags)
{
        struct sock *sk = sock->sk;
        struct kcm_sock *kcm = kcm_sk(sk);
        struct strp_msg *stm;
        int err = 0;
        ssize_t copied;
        struct sk_buff *skb;

        if (sock->file->f_flags & O_NONBLOCK || flags & SPLICE_F_NONBLOCK)
                flags = MSG_DONTWAIT;
        else
                flags = 0;

        /* Only support splice for SOCKSEQPACKET */

        skb = skb_recv_datagram(sk, flags, &err);
        if (!skb)
                goto err_out;

        /* Okay, have a message on the receive queue */

        stm = strp_msg(skb);

        if (len > stm->full_len)
                len = stm->full_len;

        copied = skb_splice_bits(skb, sk, stm->offset, pipe, len, flags);
        if (copied < 0) {
                err = copied;
                goto err_out;
        }

        KCM_STATS_ADD(kcm->stats.rx_bytes, copied);

        stm->offset += copied;
        stm->full_len -= copied;

        /* We have no way to return MSG_EOR. If all the bytes have been
         * read we still leave the message in the receive socket buffer.
         * A subsequent recvmsg needs to be done to return MSG_EOR and
         * finish reading the message.
         */

        skb_free_datagram(sk, skb);
        return copied;

err_out:
        skb_free_datagram(sk, skb);
        return err;
}

/* kcm sock lock held */
static void kcm_recv_disable(struct kcm_sock *kcm)
{
        struct kcm_mux *mux = kcm->mux;

        if (kcm->rx_disabled)
                return;

        spin_lock_bh(&mux->rx_lock);

        kcm->rx_disabled = 1;

        /* If a psock is reserved we'll do cleanup in unreserve */
        if (!kcm->rx_psock) {
                if (kcm->rx_wait) {
                        list_del(&kcm->wait_rx_list);
                        /* paired with lockless reads in kcm_rfree() */
                        WRITE_ONCE(kcm->rx_wait, false);
                }

                requeue_rx_msgs(mux, &kcm->sk.sk_receive_queue);
        }

        spin_unlock_bh(&mux->rx_lock);
}

/* kcm sock lock held */
static void kcm_recv_enable(struct kcm_sock *kcm)
{
        struct kcm_mux *mux = kcm->mux;

        if (!kcm->rx_disabled)
                return;

        spin_lock_bh(&mux->rx_lock);

        kcm->rx_disabled = 0;
        kcm_rcv_ready(kcm);

        spin_unlock_bh(&mux->rx_lock);
}

static int kcm_setsockopt(struct socket *sock, int level, int optname,
                          sockptr_t optval, unsigned int optlen)
{
        struct kcm_sock *kcm = kcm_sk(sock->sk);
        int val, valbool;
        int err = 0;

        if (level != SOL_KCM)
                return -ENOPROTOOPT;

        if (optlen < sizeof(int))
                return -EINVAL;

        if (copy_from_sockptr(&val, optval, sizeof(int)))
                return -EFAULT;

        valbool = val ? 1 : 0;

        switch (optname) {
        case KCM_RECV_DISABLE:
                lock_sock(&kcm->sk);
                if (valbool)
                        kcm_recv_disable(kcm);
                else
                        kcm_recv_enable(kcm);
                release_sock(&kcm->sk);
                break;
        default:
                err = -ENOPROTOOPT;
        }

        return err;
}

static int kcm_getsockopt(struct socket *sock, int level, int optname,
                          char __user *optval, int __user *optlen)
{
        struct kcm_sock *kcm = kcm_sk(sock->sk);
        int val, len;

        if (level != SOL_KCM)
                return -ENOPROTOOPT;

        if (get_user(len, optlen))
                return -EFAULT;

        if (len < 0)
                return -EINVAL;

        len = min_t(unsigned int, len, sizeof(int));

        switch (optname) {
        case KCM_RECV_DISABLE:
                val = kcm->rx_disabled;
                break;
        default:
                return -ENOPROTOOPT;
        }

        if (put_user(len, optlen))
                return -EFAULT;
        if (copy_to_user(optval, &val, len))
                return -EFAULT;
        return 0;
}

static void init_kcm_sock(struct kcm_sock *kcm, struct kcm_mux *mux)
{
        struct kcm_sock *tkcm;
        struct list_head *head;
        int index = 0;

        /* For SOCK_SEQPACKET sock type, datagram_poll checks the sk_state, so
         * we set sk_state, otherwise epoll_wait always returns right away with
         * EPOLLHUP
         */
        kcm->sk.sk_state = TCP_ESTABLISHED;

        /* Add to mux's kcm sockets list */
        kcm->mux = mux;
        spin_lock_bh(&mux->lock);

        head = &mux->kcm_socks;
        list_for_each_entry(tkcm, &mux->kcm_socks, kcm_sock_list) {
                if (tkcm->index != index)
                        break;
                head = &tkcm->kcm_sock_list;
                index++;
        }

        list_add(&kcm->kcm_sock_list, head);
        kcm->index = index;

        mux->kcm_socks_cnt++;
        spin_unlock_bh(&mux->lock);

        INIT_WORK(&kcm->tx_work, kcm_tx_work);
        mutex_init(&kcm->tx_mutex);

        spin_lock_bh(&mux->rx_lock);
        kcm_rcv_ready(kcm);
        spin_unlock_bh(&mux->rx_lock);
}

static int kcm_attach(struct socket *sock, struct socket *csock,
                      struct bpf_prog *prog)
{
        struct kcm_sock *kcm = kcm_sk(sock->sk);
        struct kcm_mux *mux = kcm->mux;
        struct sock *csk;
        struct kcm_psock *psock = NULL, *tpsock;
        struct list_head *head;
        int index = 0;
        static const struct strp_callbacks cb = {
                .rcv_msg = kcm_rcv_strparser,
                .parse_msg = kcm_parse_func_strparser,
                .read_sock_done = kcm_read_sock_done,
        };
        int err = 0;

        csk = csock->sk;
        if (!csk)
                return -EINVAL;

        lock_sock(csk);

        /* Only allow TCP sockets to be attached for now */
        if ((csk->sk_family != AF_INET && csk->sk_family != AF_INET6) ||
            csk->sk_protocol != IPPROTO_TCP) {
                err = -EOPNOTSUPP;
                goto out;
        }

        /* Don't allow listeners or closed sockets */
        if (csk->sk_state == TCP_LISTEN || csk->sk_state == TCP_CLOSE) {
                err = -EOPNOTSUPP;
                goto out;
        }

        psock = kmem_cache_zalloc(kcm_psockp, GFP_KERNEL);
        if (!psock) {
                err = -ENOMEM;
                goto out;
        }

        psock->mux = mux;
        psock->sk = csk;
        psock->bpf_prog = prog;

        write_lock_bh(&csk->sk_callback_lock);

        /* Check if sk_user_data is already by KCM or someone else.
         * Must be done under lock to prevent race conditions.
         */
        if (csk->sk_user_data) {
                write_unlock_bh(&csk->sk_callback_lock);
                kmem_cache_free(kcm_psockp, psock);
                err = -EALREADY;
                goto out;
        }

        err = strp_init(&psock->strp, csk, &cb);
        if (err) {
                write_unlock_bh(&csk->sk_callback_lock);
                kmem_cache_free(kcm_psockp, psock);
                goto out;
        }

        psock->save_data_ready = csk->sk_data_ready;
        psock->save_write_space = csk->sk_write_space;
        psock->save_state_change = csk->sk_state_change;
        csk->sk_user_data = psock;
        csk->sk_data_ready = psock_data_ready;
        csk->sk_write_space = psock_write_space;
        csk->sk_state_change = psock_state_change;

        write_unlock_bh(&csk->sk_callback_lock);

        sock_hold(csk);

        /* Finished initialization, now add the psock to the MUX. */
        spin_lock_bh(&mux->lock);
        head = &mux->psocks;
        list_for_each_entry(tpsock, &mux->psocks, psock_list) {
                if (tpsock->index != index)
                        break;
                head = &tpsock->psock_list;
                index++;
        }

        list_add(&psock->psock_list, head);
        psock->index = index;

        KCM_STATS_INCR(mux->stats.psock_attach);
        mux->psocks_cnt++;
        psock_now_avail(psock);
        spin_unlock_bh(&mux->lock);

        /* Schedule RX work in case there are already bytes queued */
        strp_check_rcv(&psock->strp);

out:
        release_sock(csk);

        return err;
}

static int kcm_attach_ioctl(struct socket *sock, struct kcm_attach *info)
{
        struct socket *csock;
        struct bpf_prog *prog;
        int err;

        csock = sockfd_lookup(info->fd, &err);
        if (!csock)
                return -ENOENT;

        prog = bpf_prog_get_type(info->bpf_fd, BPF_PROG_TYPE_SOCKET_FILTER);
        if (IS_ERR(prog)) {
                err = PTR_ERR(prog);
                goto out;
        }

        err = kcm_attach(sock, csock, prog);
        if (err) {
                bpf_prog_put(prog);
                goto out;
        }

        /* Keep reference on file also */

        return 0;
out:
        sockfd_put(csock);
        return err;
}

static void kcm_unattach(struct kcm_psock *psock)
{
        struct sock *csk = psock->sk;
        struct kcm_mux *mux = psock->mux;

        lock_sock(csk);

        /* Stop getting callbacks from TCP socket. After this there should
         * be no way to reserve a kcm for this psock.
         */
        write_lock_bh(&csk->sk_callback_lock);
        csk->sk_user_data = NULL;
        csk->sk_data_ready = psock->save_data_ready;
        csk->sk_write_space = psock->save_write_space;
        csk->sk_state_change = psock->save_state_change;
        strp_stop(&psock->strp);

        if (WARN_ON(psock->rx_kcm)) {
                write_unlock_bh(&csk->sk_callback_lock);
                release_sock(csk);
                return;
        }

        spin_lock_bh(&mux->rx_lock);

        /* Stop receiver activities. After this point psock should not be
         * able to get onto ready list either through callbacks or work.
         */
        if (psock->ready_rx_msg) {
                list_del(&psock->psock_ready_list);
                kfree_skb(psock->ready_rx_msg);
                psock->ready_rx_msg = NULL;
                KCM_STATS_INCR(mux->stats.rx_ready_drops);
        }

        spin_unlock_bh(&mux->rx_lock);

        write_unlock_bh(&csk->sk_callback_lock);

        /* Call strp_done without sock lock */
        release_sock(csk);
        strp_done(&psock->strp);
        lock_sock(csk);

        bpf_prog_put(psock->bpf_prog);

        spin_lock_bh(&mux->lock);

        aggregate_psock_stats(&psock->stats, &mux->aggregate_psock_stats);
        save_strp_stats(&psock->strp, &mux->aggregate_strp_stats);

        KCM_STATS_INCR(mux->stats.psock_unattach);

        if (psock->tx_kcm) {
                /* psock was reserved.  Just mark it finished and we will clean
                 * up in the kcm paths, we need kcm lock which can not be
                 * acquired here.
                 */
                KCM_STATS_INCR(mux->stats.psock_unattach_rsvd);
                spin_unlock_bh(&mux->lock);

                /* We are unattaching a socket that is reserved. Abort the
                 * socket since we may be out of sync in sending on it. We need
                 * to do this without the mux lock.
                 */
                kcm_abort_tx_psock(psock, EPIPE, false);

                spin_lock_bh(&mux->lock);
                if (!psock->tx_kcm) {
                        /* psock now unreserved in window mux was unlocked */
                        goto no_reserved;
                }
                psock->done = 1;

                /* Commit done before queuing work to process it */
                smp_mb();

                /* Queue tx work to make sure psock->done is handled */
                queue_work(kcm_wq, &psock->tx_kcm->tx_work);
                spin_unlock_bh(&mux->lock);
        } else {
no_reserved:
                if (!psock->tx_stopped)
                        list_del(&psock->psock_avail_list);
                list_del(&psock->psock_list);
                mux->psocks_cnt--;
                spin_unlock_bh(&mux->lock);

                sock_put(csk);
                fput(csk->sk_socket->file);
                kmem_cache_free(kcm_psockp, psock);
        }

        release_sock(csk);
}

static int kcm_unattach_ioctl(struct socket *sock, struct kcm_unattach *info)
{
        struct kcm_sock *kcm = kcm_sk(sock->sk);
        struct kcm_mux *mux = kcm->mux;
        struct kcm_psock *psock;
        struct socket *csock;
        struct sock *csk;
        int err;

        csock = sockfd_lookup(info->fd, &err);
        if (!csock)
                return -ENOENT;

        csk = csock->sk;
        if (!csk) {
                err = -EINVAL;
                goto out;
        }

        err = -ENOENT;

        spin_lock_bh(&mux->lock);

        list_for_each_entry(psock, &mux->psocks, psock_list) {
                if (psock->sk != csk)
                        continue;

                /* Found the matching psock */

                if (psock->unattaching || WARN_ON(psock->done)) {
                        err = -EALREADY;
                        break;
                }

                psock->unattaching = 1;

                spin_unlock_bh(&mux->lock);

                /* Lower socket lock should already be held */
                kcm_unattach(psock);

                err = 0;
                goto out;
        }

        spin_unlock_bh(&mux->lock);

out:
        sockfd_put(csock);
        return err;
}

static struct proto kcm_proto = {
        .name   = "KCM",
        .owner  = THIS_MODULE,
        .obj_size = sizeof(struct kcm_sock),
};

/* Clone a kcm socket. */
static struct file *kcm_clone(struct socket *osock)
{
        struct socket *newsock;
        struct sock *newsk;

        newsock = sock_alloc();
        if (!newsock)
                return ERR_PTR(-ENFILE);

        newsock->type = osock->type;
        newsock->ops = osock->ops;

        __module_get(newsock->ops->owner);

        newsk = sk_alloc(sock_net(osock->sk), PF_KCM, GFP_KERNEL,
                         &kcm_proto, false);
        if (!newsk) {
                sock_release(newsock);
                return ERR_PTR(-ENOMEM);
        }
        sock_init_data(newsock, newsk);
        init_kcm_sock(kcm_sk(newsk), kcm_sk(osock->sk)->mux);

        return sock_alloc_file(newsock, 0, osock->sk->sk_prot_creator->name);
}

static int kcm_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
{
        int err;

        switch (cmd) {
        case SIOCKCMATTACH: {
                struct kcm_attach info;

                if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
                        return -EFAULT;

                err = kcm_attach_ioctl(sock, &info);

                break;
        }
        case SIOCKCMUNATTACH: {
                struct kcm_unattach info;

                if (copy_from_user(&info, (void __user *)arg, sizeof(info)))
                        return -EFAULT;

                err = kcm_unattach_ioctl(sock, &info);

                break;
        }
        case SIOCKCMCLONE: {
                struct kcm_clone info;

                FD_PREPARE(fdf, 0, kcm_clone(sock));
                if (fdf.err)
                        return fdf.err;

                info.fd = fd_prepare_fd(fdf);
                if (copy_to_user((void __user *)arg, &info, sizeof(info)))
                        return -EFAULT;

                fd_publish(fdf);
                err = 0;
                break;
        }
        default:
                err = -ENOIOCTLCMD;
                break;
        }

        return err;
}

static void release_mux(struct kcm_mux *mux)
{
        struct kcm_net *knet = mux->knet;
        struct kcm_psock *psock, *tmp_psock;

        /* Release psocks */
        list_for_each_entry_safe(psock, tmp_psock,
                                 &mux->psocks, psock_list) {
                if (!WARN_ON(psock->unattaching))
                        kcm_unattach(psock);
        }

        if (WARN_ON(mux->psocks_cnt))
                return;

        __skb_queue_purge(&mux->rx_hold_queue);

        mutex_lock(&knet->mutex);
        aggregate_mux_stats(&mux->stats, &knet->aggregate_mux_stats);
        aggregate_psock_stats(&mux->aggregate_psock_stats,
                              &knet->aggregate_psock_stats);
        aggregate_strp_stats(&mux->aggregate_strp_stats,
                             &knet->aggregate_strp_stats);
        list_del_rcu(&mux->kcm_mux_list);
        knet->count--;
        mutex_unlock(&knet->mutex);

        kfree_rcu(mux, rcu);
}

static void kcm_done(struct kcm_sock *kcm)
{
        struct kcm_mux *mux = kcm->mux;
        struct sock *sk = &kcm->sk;
        int socks_cnt;

        spin_lock_bh(&mux->rx_lock);
        if (kcm->rx_psock) {
                /* Cleanup in unreserve_rx_kcm */
                WARN_ON(kcm->done);
                kcm->rx_disabled = 1;
                kcm->done = 1;
                spin_unlock_bh(&mux->rx_lock);
                return;
        }

        if (kcm->rx_wait) {
                list_del(&kcm->wait_rx_list);
                /* paired with lockless reads in kcm_rfree() */
                WRITE_ONCE(kcm->rx_wait, false);
        }
        /* Move any pending receive messages to other kcm sockets */
        requeue_rx_msgs(mux, &sk->sk_receive_queue);

        spin_unlock_bh(&mux->rx_lock);

        if (WARN_ON(sk_rmem_alloc_get(sk)))
                return;

        /* Detach from MUX */
        spin_lock_bh(&mux->lock);

        list_del(&kcm->kcm_sock_list);
        mux->kcm_socks_cnt--;
        socks_cnt = mux->kcm_socks_cnt;

        spin_unlock_bh(&mux->lock);

        if (!socks_cnt) {
                /* We are done with the mux now. */
                release_mux(mux);
        }

        WARN_ON(kcm->rx_wait);

        sock_put(&kcm->sk);
}

/* Called by kcm_release to close a KCM socket.
 * If this is the last KCM socket on the MUX, destroy the MUX.
 */
static int kcm_release(struct socket *sock)
{
        struct sock *sk = sock->sk;
        struct kcm_sock *kcm;
        struct kcm_mux *mux;
        struct kcm_psock *psock;

        if (!sk)
                return 0;

        kcm = kcm_sk(sk);
        mux = kcm->mux;

        lock_sock(sk);
        sock_orphan(sk);
        kfree_skb(kcm->seq_skb);

        /* Purge queue under lock to avoid race condition with tx_work trying
         * to act when queue is nonempty. If tx_work runs after this point
         * it will just return.
         */
        __skb_queue_purge(&sk->sk_write_queue);

        release_sock(sk);

        spin_lock_bh(&mux->lock);
        if (kcm->tx_wait) {
                /* Take of tx_wait list, after this point there should be no way
                 * that a psock will be assigned to this kcm.
                 */
                list_del(&kcm->wait_psock_list);
                kcm->tx_wait = false;
        }
        spin_unlock_bh(&mux->lock);

        /* Cancel work. After this point there should be no outside references
         * to the kcm socket.
         */
        disable_work_sync(&kcm->tx_work);

        lock_sock(sk);
        psock = kcm->tx_psock;
        if (psock) {
                /* A psock was reserved, so we need to kill it since it
                 * may already have some bytes queued from a message. We
                 * need to do this after removing kcm from tx_wait list.
                 */
                kcm_abort_tx_psock(psock, EPIPE, false);
                unreserve_psock(kcm);
        }
        release_sock(sk);

        WARN_ON(kcm->tx_wait);
        WARN_ON(kcm->tx_psock);

        sock->sk = NULL;

        kcm_done(kcm);

        return 0;
}

static const struct proto_ops kcm_dgram_ops = {
        .family =       PF_KCM,
        .owner =        THIS_MODULE,
        .release =      kcm_release,
        .bind =         sock_no_bind,
        .connect =      sock_no_connect,
        .socketpair =   sock_no_socketpair,
        .accept =       sock_no_accept,
        .getname =      sock_no_getname,
        .poll =         datagram_poll,
        .ioctl =        kcm_ioctl,
        .listen =       sock_no_listen,
        .shutdown =     sock_no_shutdown,
        .setsockopt =   kcm_setsockopt,
        .getsockopt =   kcm_getsockopt,
        .sendmsg =      kcm_sendmsg,
        .recvmsg =      kcm_recvmsg,
        .mmap =         sock_no_mmap,
        .splice_eof =   kcm_splice_eof,
};

static const struct proto_ops kcm_seqpacket_ops = {
        .family =       PF_KCM,
        .owner =        THIS_MODULE,
        .release =      kcm_release,
        .bind =         sock_no_bind,
        .connect =      sock_no_connect,
        .socketpair =   sock_no_socketpair,
        .accept =       sock_no_accept,
        .getname =      sock_no_getname,
        .poll =         datagram_poll,
        .ioctl =        kcm_ioctl,
        .listen =       sock_no_listen,
        .shutdown =     sock_no_shutdown,
        .setsockopt =   kcm_setsockopt,
        .getsockopt =   kcm_getsockopt,
        .sendmsg =      kcm_sendmsg,
        .recvmsg =      kcm_recvmsg,
        .mmap =         sock_no_mmap,
        .splice_eof =   kcm_splice_eof,
        .splice_read =  kcm_splice_read,
};

/* Create proto operation for kcm sockets */
static int kcm_create(struct net *net, struct socket *sock,
                      int protocol, int kern)
{
        struct kcm_net *knet = net_generic(net, kcm_net_id);
        struct sock *sk;
        struct kcm_mux *mux;

        switch (sock->type) {
        case SOCK_DGRAM:
                sock->ops = &kcm_dgram_ops;
                break;
        case SOCK_SEQPACKET:
                sock->ops = &kcm_seqpacket_ops;
                break;
        default:
                return -ESOCKTNOSUPPORT;
        }

        if (protocol != KCMPROTO_CONNECTED)
                return -EPROTONOSUPPORT;

        sk = sk_alloc(net, PF_KCM, GFP_KERNEL, &kcm_proto, kern);
        if (!sk)
                return -ENOMEM;

        /* Allocate a kcm mux, shared between KCM sockets */
        mux = kmem_cache_zalloc(kcm_muxp, GFP_KERNEL);
        if (!mux) {
                sk_free(sk);
                return -ENOMEM;
        }

        spin_lock_init(&mux->lock);
        spin_lock_init(&mux->rx_lock);
        INIT_LIST_HEAD(&mux->kcm_socks);
        INIT_LIST_HEAD(&mux->kcm_rx_waiters);
        INIT_LIST_HEAD(&mux->kcm_tx_waiters);

        INIT_LIST_HEAD(&mux->psocks);
        INIT_LIST_HEAD(&mux->psocks_ready);
        INIT_LIST_HEAD(&mux->psocks_avail);

        mux->knet = knet;

        /* Add new MUX to list */
        mutex_lock(&knet->mutex);
        list_add_rcu(&mux->kcm_mux_list, &knet->mux_list);
        knet->count++;
        mutex_unlock(&knet->mutex);

        skb_queue_head_init(&mux->rx_hold_queue);

        /* Init KCM socket */
        sock_init_data(sock, sk);
        init_kcm_sock(kcm_sk(sk), mux);

        return 0;
}

static const struct net_proto_family kcm_family_ops = {
        .family = PF_KCM,
        .create = kcm_create,
        .owner  = THIS_MODULE,
};

static __net_init int kcm_init_net(struct net *net)
{
        struct kcm_net *knet = net_generic(net, kcm_net_id);

        INIT_LIST_HEAD_RCU(&knet->mux_list);
        mutex_init(&knet->mutex);

        return 0;
}

static __net_exit void kcm_exit_net(struct net *net)
{
        struct kcm_net *knet = net_generic(net, kcm_net_id);

        /* All KCM sockets should be closed at this point, which should mean
         * that all multiplexors and psocks have been destroyed.
         */
        WARN_ON(!list_empty(&knet->mux_list));

        mutex_destroy(&knet->mutex);
}

static struct pernet_operations kcm_net_ops = {
        .init = kcm_init_net,
        .exit = kcm_exit_net,
        .id   = &kcm_net_id,
        .size = sizeof(struct kcm_net),
};

static int __init kcm_init(void)
{
        int err = -ENOMEM;

        kcm_muxp = KMEM_CACHE(kcm_mux, SLAB_HWCACHE_ALIGN);
        if (!kcm_muxp)
                goto fail;

        kcm_psockp = KMEM_CACHE(kcm_psock, SLAB_HWCACHE_ALIGN);
        if (!kcm_psockp)
                goto fail;

        kcm_wq = create_singlethread_workqueue("kkcmd");
        if (!kcm_wq)
                goto fail;

        err = proto_register(&kcm_proto, 1);
        if (err)
                goto fail;

        err = register_pernet_device(&kcm_net_ops);
        if (err)
                goto net_ops_fail;

        err = sock_register(&kcm_family_ops);
        if (err)
                goto sock_register_fail;

        err = kcm_proc_init();
        if (err)
                goto proc_init_fail;

        return 0;

proc_init_fail:
        sock_unregister(PF_KCM);

sock_register_fail:
        unregister_pernet_device(&kcm_net_ops);

net_ops_fail:
        proto_unregister(&kcm_proto);

fail:
        kmem_cache_destroy(kcm_muxp);
        kmem_cache_destroy(kcm_psockp);

        if (kcm_wq)
                destroy_workqueue(kcm_wq);

        return err;
}

static void __exit kcm_exit(void)
{
        kcm_proc_exit();
        sock_unregister(PF_KCM);
        unregister_pernet_device(&kcm_net_ops);
        proto_unregister(&kcm_proto);
        destroy_workqueue(kcm_wq);

        kmem_cache_destroy(kcm_muxp);
        kmem_cache_destroy(kcm_psockp);
}

module_init(kcm_init);
module_exit(kcm_exit);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("KCM (Kernel Connection Multiplexor) sockets");
MODULE_ALIAS_NETPROTO(PF_KCM);