/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 */

/* A BPF sock_map is used to store sock objects. This is primarly used
 * for doing socket redirect with BPF helper routines.
 *
 * A sock map may have BPF programs attached to it, currently a program
 * used to parse packets and a program to provide a verdict and redirect
 * decision on the packet are supported. Any programs attached to a sock
 * map are inherited by sock objects when they are added to the map. If
 * no BPF programs are attached the sock object may only be used for sock
 * redirect.
 *
 * A sock object may be in multiple maps, but can only inherit a single
 * parse or verdict program. If adding a sock object to a map would result
 * in having multiple parsing programs the update will return an EBUSY error.
 *
 * For reference this program is similar to devmap used in XDP context
 * reviewing these together may be useful. For an example please review
 * ./samples/bpf/sockmap/.
 */
#include <linux/bpf.h>
#include <net/sock.h>
#include <linux/filter.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/kernel.h>
#include <linux/net.h>
#include <linux/skbuff.h>
#include <linux/workqueue.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <net/strparser.h>
#include <net/tcp.h>
#include <linux/ptr_ring.h>
#include <net/inet_common.h>
#include <linux/sched/signal.h>

#define SOCK_CREATE_FLAG_MASK \
        (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)

struct bpf_stab {
        struct bpf_map map;
        struct sock **sock_map;
        struct bpf_prog *bpf_tx_msg;
        struct bpf_prog *bpf_parse;
        struct bpf_prog *bpf_verdict;
};

enum smap_psock_state {
        SMAP_TX_RUNNING,
};

struct smap_psock_map_entry {
        struct list_head list;
        struct sock **entry;
};

struct smap_psock {
        struct rcu_head rcu;
        refcount_t refcnt;

        /* datapath variables */
        struct sk_buff_head rxqueue;
        bool strp_enabled;

        /* datapath error path cache across tx work invocations */
        int save_rem;
        int save_off;
        struct sk_buff *save_skb;

        /* datapath variables for tx_msg ULP */
        struct sock *sk_redir;
        int apply_bytes;
        int cork_bytes;
        int sg_size;
        int eval;
        struct sk_msg_buff *cork;
        struct list_head ingress;

        struct strparser strp;
        struct bpf_prog *bpf_tx_msg;
        struct bpf_prog *bpf_parse;
        struct bpf_prog *bpf_verdict;
        struct list_head maps;

        /* Back reference used when sock callback trigger sockmap operations */
        struct sock *sock;
        unsigned long state;

        struct work_struct tx_work;
        struct work_struct gc_work;

        struct proto *sk_proto;
        void (*save_close)(struct sock *sk, long timeout);
        void (*save_data_ready)(struct sock *sk);
        void (*save_write_space)(struct sock *sk);
};

static void smap_release_sock(struct smap_psock *psock, struct sock *sock);
static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
                           int nonblock, int flags, int *addr_len);
static int bpf_tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
static int bpf_tcp_sendpage(struct sock *sk, struct page *page,
                            int offset, size_t size, int flags);

static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
{
        return rcu_dereference_sk_user_data(sk);
}

static bool bpf_tcp_stream_read(const struct sock *sk)
{
        struct smap_psock *psock;
        bool empty = true;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock))
                goto out;
        empty = list_empty(&psock->ingress);
out:
        rcu_read_unlock();
        return !empty;
}

static struct proto tcp_bpf_proto;
static int bpf_tcp_init(struct sock *sk)
{
        struct smap_psock *psock;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock)) {
                rcu_read_unlock();
                return -EINVAL;
        }

        if (unlikely(psock->sk_proto)) {
                rcu_read_unlock();
                return -EBUSY;
        }

        psock->save_close = sk->sk_prot->close;
        psock->sk_proto = sk->sk_prot;

        if (psock->bpf_tx_msg) {
                tcp_bpf_proto.sendmsg = bpf_tcp_sendmsg;
                tcp_bpf_proto.sendpage = bpf_tcp_sendpage;
                tcp_bpf_proto.recvmsg = bpf_tcp_recvmsg;
                tcp_bpf_proto.stream_memory_read = bpf_tcp_stream_read;
        }

        sk->sk_prot = &tcp_bpf_proto;
        rcu_read_unlock();
        return 0;
}

static void smap_release_sock(struct smap_psock *psock, struct sock *sock);
static int free_start_sg(struct sock *sk, struct sk_msg_buff *md);

static void bpf_tcp_release(struct sock *sk)
{
        struct smap_psock *psock;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock))
                goto out;

        if (psock->cork) {
                free_start_sg(psock->sock, psock->cork);
                kfree(psock->cork);
                psock->cork = NULL;
        }

        if (psock->sk_proto) {
                sk->sk_prot = psock->sk_proto;
                psock->sk_proto = NULL;
        }
out:
        rcu_read_unlock();
}

static void bpf_tcp_close(struct sock *sk, long timeout)
{
        void (*close_fun)(struct sock *sk, long timeout);
        struct smap_psock_map_entry *e, *tmp;
        struct sk_msg_buff *md, *mtmp;
        struct smap_psock *psock;
        struct sock *osk;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock)) {
                rcu_read_unlock();
                return sk->sk_prot->close(sk, timeout);
        }

        /* The psock may be destroyed anytime after exiting the RCU critial
         * section so by the time we use close_fun the psock may no longer
         * be valid. However, bpf_tcp_close is called with the sock lock
         * held so the close hook and sk are still valid.
         */
        close_fun = psock->save_close;

        write_lock_bh(&sk->sk_callback_lock);
        if (psock->cork) {
                free_start_sg(psock->sock, psock->cork);
                kfree(psock->cork);
                psock->cork = NULL;
        }

        list_for_each_entry_safe(md, mtmp, &psock->ingress, list) {
                list_del(&md->list);
                free_start_sg(psock->sock, md);
                kfree(md);
        }

        list_for_each_entry_safe(e, tmp, &psock->maps, list) {
                osk = cmpxchg(e->entry, sk, NULL);
                if (osk == sk) {
                        list_del(&e->list);
                        smap_release_sock(psock, sk);
                }
        }
        write_unlock_bh(&sk->sk_callback_lock);
        rcu_read_unlock();
        close_fun(sk, timeout);
}

enum __sk_action {
        __SK_DROP = 0,
        __SK_PASS,
        __SK_REDIRECT,
        __SK_NONE,
};

static struct tcp_ulp_ops bpf_tcp_ulp_ops __read_mostly = {
        .name           = "bpf_tcp",
        .uid            = TCP_ULP_BPF,
        .user_visible   = false,
        .owner          = NULL,
        .init           = bpf_tcp_init,
        .release        = bpf_tcp_release,
};

static int memcopy_from_iter(struct sock *sk,
                             struct sk_msg_buff *md,
                             struct iov_iter *from, int bytes)
{
        struct scatterlist *sg = md->sg_data;
        int i = md->sg_curr, rc = -ENOSPC;

        do {
                int copy;
                char *to;

                if (md->sg_copybreak >= sg[i].length) {
                        md->sg_copybreak = 0;

                        if (++i == MAX_SKB_FRAGS)
                                i = 0;

                        if (i == md->sg_end)
                                break;
                }

                copy = sg[i].length - md->sg_copybreak;
                to = sg_virt(&sg[i]) + md->sg_copybreak;
                md->sg_copybreak += copy;

                if (sk->sk_route_caps & NETIF_F_NOCACHE_COPY)
                        rc = copy_from_iter_nocache(to, copy, from);
                else
                        rc = copy_from_iter(to, copy, from);

                if (rc != copy) {
                        rc = -EFAULT;
                        goto out;
                }

                bytes -= copy;
                if (!bytes)
                        break;

                md->sg_copybreak = 0;
                if (++i == MAX_SKB_FRAGS)
                        i = 0;
        } while (i != md->sg_end);
out:
        md->sg_curr = i;
        return rc;
}

static int bpf_tcp_push(struct sock *sk, int apply_bytes,
                        struct sk_msg_buff *md,
                        int flags, bool uncharge)
{
        bool apply = apply_bytes;
        struct scatterlist *sg;
        int offset, ret = 0;
        struct page *p;
        size_t size;

        while (1) {
                sg = md->sg_data + md->sg_start;
                size = (apply && apply_bytes < sg->length) ?
                        apply_bytes : sg->length;
                offset = sg->offset;

                tcp_rate_check_app_limited(sk);
                p = sg_page(sg);
retry:
                ret = do_tcp_sendpages(sk, p, offset, size, flags);
                if (ret != size) {
                        if (ret > 0) {
                                if (apply)
                                        apply_bytes -= ret;

                                sg->offset += ret;
                                sg->length -= ret;
                                size -= ret;
                                offset += ret;
                                if (uncharge)
                                        sk_mem_uncharge(sk, ret);
                                goto retry;
                        }

                        return ret;
                }

                if (apply)
                        apply_bytes -= ret;
                sg->offset += ret;
                sg->length -= ret;
                if (uncharge)
                        sk_mem_uncharge(sk, ret);

                if (!sg->length) {
                        put_page(p);
                        md->sg_start++;
                        if (md->sg_start == MAX_SKB_FRAGS)
                                md->sg_start = 0;
                        sg_init_table(sg, 1);

                        if (md->sg_start == md->sg_end)
                                break;
                }

                if (apply && !apply_bytes)
                        break;
        }
        return 0;
}

static inline void bpf_compute_data_pointers_sg(struct sk_msg_buff *md)
{
        struct scatterlist *sg = md->sg_data + md->sg_start;

        if (md->sg_copy[md->sg_start]) {
                md->data = md->data_end = 0;
        } else {
                md->data = sg_virt(sg);
                md->data_end = md->data + sg->length;
        }
}

static void return_mem_sg(struct sock *sk, int bytes, struct sk_msg_buff *md)
{
        struct scatterlist *sg = md->sg_data;
        int i = md->sg_start;

        do {
                int uncharge = (bytes < sg[i].length) ? bytes : sg[i].length;

                sk_mem_uncharge(sk, uncharge);
                bytes -= uncharge;
                if (!bytes)
                        break;
                i++;
                if (i == MAX_SKB_FRAGS)
                        i = 0;
        } while (i != md->sg_end);
}

static void free_bytes_sg(struct sock *sk, int bytes,
                          struct sk_msg_buff *md, bool charge)
{
        struct scatterlist *sg = md->sg_data;
        int i = md->sg_start, free;

        while (bytes && sg[i].length) {
                free = sg[i].length;
                if (bytes < free) {
                        sg[i].length -= bytes;
                        sg[i].offset += bytes;
                        if (charge)
                                sk_mem_uncharge(sk, bytes);
                        break;
                }

                if (charge)
                        sk_mem_uncharge(sk, sg[i].length);
                put_page(sg_page(&sg[i]));
                bytes -= sg[i].length;
                sg[i].length = 0;
                sg[i].page_link = 0;
                sg[i].offset = 0;
                i++;

                if (i == MAX_SKB_FRAGS)
                        i = 0;
        }
        md->sg_start = i;
}

static int free_sg(struct sock *sk, int start, struct sk_msg_buff *md)
{
        struct scatterlist *sg = md->sg_data;
        int i = start, free = 0;

        while (sg[i].length) {
                free += sg[i].length;
                sk_mem_uncharge(sk, sg[i].length);
                put_page(sg_page(&sg[i]));
                sg[i].length = 0;
                sg[i].page_link = 0;
                sg[i].offset = 0;
                i++;

                if (i == MAX_SKB_FRAGS)
                        i = 0;
        }

        return free;
}

static int free_start_sg(struct sock *sk, struct sk_msg_buff *md)
{
        int free = free_sg(sk, md->sg_start, md);

        md->sg_start = md->sg_end;
        return free;
}

static int free_curr_sg(struct sock *sk, struct sk_msg_buff *md)
{
        return free_sg(sk, md->sg_curr, md);
}

static int bpf_map_msg_verdict(int _rc, struct sk_msg_buff *md)
{
        return ((_rc == SK_PASS) ?
               (md->map ? __SK_REDIRECT : __SK_PASS) :
               __SK_DROP);
}

static unsigned int smap_do_tx_msg(struct sock *sk,
                                   struct smap_psock *psock,
                                   struct sk_msg_buff *md)
{
        struct bpf_prog *prog;
        unsigned int rc, _rc;

        preempt_disable();
        rcu_read_lock();

        /* If the policy was removed mid-send then default to 'accept' */
        prog = READ_ONCE(psock->bpf_tx_msg);
        if (unlikely(!prog)) {
                _rc = SK_PASS;
                goto verdict;
        }

        bpf_compute_data_pointers_sg(md);
        rc = (*prog->bpf_func)(md, prog->insnsi);
        psock->apply_bytes = md->apply_bytes;

        /* Moving return codes from UAPI namespace into internal namespace */
        _rc = bpf_map_msg_verdict(rc, md);

        /* The psock has a refcount on the sock but not on the map and because
         * we need to drop rcu read lock here its possible the map could be
         * removed between here and when we need it to execute the sock
         * redirect. So do the map lookup now for future use.
         */
        if (_rc == __SK_REDIRECT) {
                if (psock->sk_redir)
                        sock_put(psock->sk_redir);
                psock->sk_redir = do_msg_redirect_map(md);
                if (!psock->sk_redir) {
                        _rc = __SK_DROP;
                        goto verdict;
                }
                sock_hold(psock->sk_redir);
        }
verdict:
        rcu_read_unlock();
        preempt_enable();

        return _rc;
}

static int bpf_tcp_ingress(struct sock *sk, int apply_bytes,
                           struct smap_psock *psock,
                           struct sk_msg_buff *md, int flags)
{
        bool apply = apply_bytes;
        size_t size, copied = 0;
        struct sk_msg_buff *r;
        int err = 0, i;

        r = kzalloc(sizeof(struct sk_msg_buff), __GFP_NOWARN | GFP_KERNEL);
        if (unlikely(!r))
                return -ENOMEM;

        lock_sock(sk);
        r->sg_start = md->sg_start;
        i = md->sg_start;

        do {
                size = (apply && apply_bytes < md->sg_data[i].length) ?
                        apply_bytes : md->sg_data[i].length;

                if (!sk_wmem_schedule(sk, size)) {
                        if (!copied)
                                err = -ENOMEM;
                        break;
                }

                sk_mem_charge(sk, size);
                r->sg_data[i] = md->sg_data[i];
                r->sg_data[i].length = size;
                md->sg_data[i].length -= size;
                md->sg_data[i].offset += size;
                copied += size;

                if (md->sg_data[i].length) {
                        get_page(sg_page(&r->sg_data[i]));
                        r->sg_end = (i + 1) == MAX_SKB_FRAGS ? 0 : i + 1;
                } else {
                        i++;
                        if (i == MAX_SKB_FRAGS)
                                i = 0;
                        r->sg_end = i;
                }

                if (apply) {
                        apply_bytes -= size;
                        if (!apply_bytes)
                                break;
                }
        } while (i != md->sg_end);

        md->sg_start = i;

        if (!err) {
                list_add_tail(&r->list, &psock->ingress);
                sk->sk_data_ready(sk);
        } else {
                free_start_sg(sk, r);
                kfree(r);
        }

        release_sock(sk);
        return err;
}

static int bpf_tcp_sendmsg_do_redirect(struct sock *sk, int send,
                                       struct sk_msg_buff *md,
                                       int flags)
{
        bool ingress = !!(md->flags & BPF_F_INGRESS);
        struct smap_psock *psock;
        struct scatterlist *sg;
        int err = 0;

        sg = md->sg_data;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock))
                goto out_rcu;

        if (!refcount_inc_not_zero(&psock->refcnt))
                goto out_rcu;

        rcu_read_unlock();

        if (ingress) {
                err = bpf_tcp_ingress(sk, send, psock, md, flags);
        } else {
                lock_sock(sk);
                err = bpf_tcp_push(sk, send, md, flags, false);
                release_sock(sk);
        }
        smap_release_sock(psock, sk);
        if (unlikely(err))
                goto out;
        return 0;
out_rcu:
        rcu_read_unlock();
out:
        free_bytes_sg(NULL, send, md, false);
        return err;
}

static inline void bpf_md_init(struct smap_psock *psock)
{
        if (!psock->apply_bytes) {
                psock->eval =  __SK_NONE;
                if (psock->sk_redir) {
                        sock_put(psock->sk_redir);
                        psock->sk_redir = NULL;
                }
        }
}

static void apply_bytes_dec(struct smap_psock *psock, int i)
{
        if (psock->apply_bytes) {
                if (psock->apply_bytes < i)
                        psock->apply_bytes = 0;
                else
                        psock->apply_bytes -= i;
        }
}

static int bpf_exec_tx_verdict(struct smap_psock *psock,
                               struct sk_msg_buff *m,
                               struct sock *sk,
                               int *copied, int flags)
{
        bool cork = false, enospc = (m->sg_start == m->sg_end);
        struct sock *redir;
        int err = 0;
        int send;

more_data:
        if (psock->eval == __SK_NONE)
                psock->eval = smap_do_tx_msg(sk, psock, m);

        if (m->cork_bytes &&
            m->cork_bytes > psock->sg_size && !enospc) {
                psock->cork_bytes = m->cork_bytes - psock->sg_size;
                if (!psock->cork) {
                        psock->cork = kcalloc(1,
                                        sizeof(struct sk_msg_buff),
                                        GFP_ATOMIC | __GFP_NOWARN);

                        if (!psock->cork) {
                                err = -ENOMEM;
                                goto out_err;
                        }
                }
                memcpy(psock->cork, m, sizeof(*m));
                goto out_err;
        }

        send = psock->sg_size;
        if (psock->apply_bytes && psock->apply_bytes < send)
                send = psock->apply_bytes;

        switch (psock->eval) {
        case __SK_PASS:
                err = bpf_tcp_push(sk, send, m, flags, true);
                if (unlikely(err)) {
                        *copied -= free_start_sg(sk, m);
                        break;
                }

                apply_bytes_dec(psock, send);
                psock->sg_size -= send;
                break;
        case __SK_REDIRECT:
                redir = psock->sk_redir;
                apply_bytes_dec(psock, send);

                if (psock->cork) {
                        cork = true;
                        psock->cork = NULL;
                }

                return_mem_sg(sk, send, m);
                release_sock(sk);

                err = bpf_tcp_sendmsg_do_redirect(redir, send, m, flags);
                lock_sock(sk);

                if (unlikely(err < 0)) {
                        free_start_sg(sk, m);
                        psock->sg_size = 0;
                        if (!cork)
                                *copied -= send;
                } else {
                        psock->sg_size -= send;
                }

                if (cork) {
                        free_start_sg(sk, m);
                        psock->sg_size = 0;
                        kfree(m);
                        m = NULL;
                        err = 0;
                }
                break;
        case __SK_DROP:
        default:
                free_bytes_sg(sk, send, m, true);
                apply_bytes_dec(psock, send);
                *copied -= send;
                psock->sg_size -= send;
                err = -EACCES;
                break;
        }

        if (likely(!err)) {
                bpf_md_init(psock);
                if (m &&
                    m->sg_data[m->sg_start].page_link &&
                    m->sg_data[m->sg_start].length)
                        goto more_data;
        }

out_err:
        return err;
}

static int bpf_wait_data(struct sock *sk,
                         struct smap_psock *psk, int flags,
                         long timeo, int *err)
{
        int rc;

        DEFINE_WAIT_FUNC(wait, woken_wake_function);

        add_wait_queue(sk_sleep(sk), &wait);
        sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
        rc = sk_wait_event(sk, &timeo,
                           !list_empty(&psk->ingress) ||
                           !skb_queue_empty(&sk->sk_receive_queue),
                           &wait);
        sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
        remove_wait_queue(sk_sleep(sk), &wait);

        return rc;
}

static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
                           int nonblock, int flags, int *addr_len)
{
        struct iov_iter *iter = &msg->msg_iter;
        struct smap_psock *psock;
        int copied = 0;

        if (unlikely(flags & MSG_ERRQUEUE))
                return inet_recv_error(sk, msg, len, addr_len);

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock))
                goto out;

        if (unlikely(!refcount_inc_not_zero(&psock->refcnt)))
                goto out;
        rcu_read_unlock();

        if (!skb_queue_empty(&sk->sk_receive_queue))
                return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);

        lock_sock(sk);
bytes_ready:
        while (copied != len) {
                struct scatterlist *sg;
                struct sk_msg_buff *md;
                int i;

                md = list_first_entry_or_null(&psock->ingress,
                                              struct sk_msg_buff, list);
                if (unlikely(!md))
                        break;
                i = md->sg_start;
                do {
                        struct page *page;
                        int n, copy;

                        sg = &md->sg_data[i];
                        copy = sg->length;
                        page = sg_page(sg);

                        if (copied + copy > len)
                                copy = len - copied;

                        n = copy_page_to_iter(page, sg->offset, copy, iter);
                        if (n != copy) {
                                md->sg_start = i;
                                release_sock(sk);
                                smap_release_sock(psock, sk);
                                return -EFAULT;
                        }

                        copied += copy;
                        sg->offset += copy;
                        sg->length -= copy;
                        sk_mem_uncharge(sk, copy);

                        if (!sg->length) {
                                i++;
                                if (i == MAX_SKB_FRAGS)
                                        i = 0;
                                if (!md->skb)
                                        put_page(page);
                        }
                        if (copied == len)
                                break;
                } while (i != md->sg_end);
                md->sg_start = i;

                if (!sg->length && md->sg_start == md->sg_end) {
                        list_del(&md->list);
                        if (md->skb)
                                consume_skb(md->skb);
                        kfree(md);
                }
        }

        if (!copied) {
                long timeo;
                int data;
                int err = 0;

                timeo = sock_rcvtimeo(sk, nonblock);
                data = bpf_wait_data(sk, psock, flags, timeo, &err);

                if (data) {
                        if (!skb_queue_empty(&sk->sk_receive_queue)) {
                                release_sock(sk);
                                smap_release_sock(psock, sk);
                                copied = tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
                                return copied;
                        }
                        goto bytes_ready;
                }

                if (err)
                        copied = err;
        }

        release_sock(sk);
        smap_release_sock(psock, sk);
        return copied;
out:
        rcu_read_unlock();
        return tcp_recvmsg(sk, msg, len, nonblock, flags, addr_len);
}


static int bpf_tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
{
        int flags = msg->msg_flags | MSG_NO_SHARED_FRAGS;
        struct sk_msg_buff md = {0};
        unsigned int sg_copy = 0;
        struct smap_psock *psock;
        int copied = 0, err = 0;
        struct scatterlist *sg;
        long timeo;

        /* Its possible a sock event or user removed the psock _but_ the ops
         * have not been reprogrammed yet so we get here. In this case fallback
         * to tcp_sendmsg. Note this only works because we _only_ ever allow
         * a single ULP there is no hierarchy here.
         */
        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock)) {
                rcu_read_unlock();
                return tcp_sendmsg(sk, msg, size);
        }

        /* Increment the psock refcnt to ensure its not released while sending a
         * message. Required because sk lookup and bpf programs are used in
         * separate rcu critical sections. Its OK if we lose the map entry
         * but we can't lose the sock reference.
         */
        if (!refcount_inc_not_zero(&psock->refcnt)) {
                rcu_read_unlock();
                return tcp_sendmsg(sk, msg, size);
        }

        sg = md.sg_data;
        sg_init_marker(sg, MAX_SKB_FRAGS);
        rcu_read_unlock();

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

        while (msg_data_left(msg)) {
                struct sk_msg_buff *m;
                bool enospc = false;
                int copy;

                if (sk->sk_err) {
                        err = sk->sk_err;
                        goto out_err;
                }

                copy = msg_data_left(msg);
                if (!sk_stream_memory_free(sk))
                        goto wait_for_sndbuf;

                m = psock->cork_bytes ? psock->cork : &md;
                m->sg_curr = m->sg_copybreak ? m->sg_curr : m->sg_end;
                err = sk_alloc_sg(sk, copy, m->sg_data,
                                  m->sg_start, &m->sg_end, &sg_copy,
                                  m->sg_end - 1);
                if (err) {
                        if (err != -ENOSPC)
                                goto wait_for_memory;
                        enospc = true;
                        copy = sg_copy;
                }

                err = memcopy_from_iter(sk, m, &msg->msg_iter, copy);
                if (err < 0) {
                        free_curr_sg(sk, m);
                        goto out_err;
                }

                psock->sg_size += copy;
                copied += copy;
                sg_copy = 0;

                /* When bytes are being corked skip running BPF program and
                 * applying verdict unless there is no more buffer space. In
                 * the ENOSPC case simply run BPF prorgram with currently
                 * accumulated data. We don't have much choice at this point
                 * we could try extending the page frags or chaining complex
                 * frags but even in these cases _eventually_ we will hit an
                 * OOM scenario. More complex recovery schemes may be
                 * implemented in the future, but BPF programs must handle
                 * the case where apply_cork requests are not honored. The
                 * canonical method to verify this is to check data length.
                 */
                if (psock->cork_bytes) {
                        if (copy > psock->cork_bytes)
                                psock->cork_bytes = 0;
                        else
                                psock->cork_bytes -= copy;

                        if (psock->cork_bytes && !enospc)
                                goto out_cork;

                        /* All cork bytes accounted for re-run filter */
                        psock->eval = __SK_NONE;
                        psock->cork_bytes = 0;
                }

                err = bpf_exec_tx_verdict(psock, m, sk, &copied, flags);
                if (unlikely(err < 0))
                        goto out_err;
                continue;
wait_for_sndbuf:
                set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
wait_for_memory:
                err = sk_stream_wait_memory(sk, &timeo);
                if (err)
                        goto out_err;
        }
out_err:
        if (err < 0)
                err = sk_stream_error(sk, msg->msg_flags, err);
out_cork:
        release_sock(sk);
        smap_release_sock(psock, sk);
        return copied ? copied : err;
}

static int bpf_tcp_sendpage(struct sock *sk, struct page *page,
                            int offset, size_t size, int flags)
{
        struct sk_msg_buff md = {0}, *m = NULL;
        int err = 0, copied = 0;
        struct smap_psock *psock;
        struct scatterlist *sg;
        bool enospc = false;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (unlikely(!psock))
                goto accept;

        if (!refcount_inc_not_zero(&psock->refcnt))
                goto accept;
        rcu_read_unlock();

        lock_sock(sk);

        if (psock->cork_bytes) {
                m = psock->cork;
                sg = &m->sg_data[m->sg_end];
        } else {
                m = &md;
                sg = m->sg_data;
                sg_init_marker(sg, MAX_SKB_FRAGS);
        }

        /* Catch case where ring is full and sendpage is stalled. */
        if (unlikely(m->sg_end == m->sg_start &&
            m->sg_data[m->sg_end].length))
                goto out_err;

        psock->sg_size += size;
        sg_set_page(sg, page, size, offset);
        get_page(page);
        m->sg_copy[m->sg_end] = true;
        sk_mem_charge(sk, size);
        m->sg_end++;
        copied = size;

        if (m->sg_end == MAX_SKB_FRAGS)
                m->sg_end = 0;

        if (m->sg_end == m->sg_start)
                enospc = true;

        if (psock->cork_bytes) {
                if (size > psock->cork_bytes)
                        psock->cork_bytes = 0;
                else
                        psock->cork_bytes -= size;

                if (psock->cork_bytes && !enospc)
                        goto out_err;

                /* All cork bytes accounted for re-run filter */
                psock->eval = __SK_NONE;
                psock->cork_bytes = 0;
        }

        err = bpf_exec_tx_verdict(psock, m, sk, &copied, flags);
out_err:
        release_sock(sk);
        smap_release_sock(psock, sk);
        return copied ? copied : err;
accept:
        rcu_read_unlock();
        return tcp_sendpage(sk, page, offset, size, flags);
}

static void bpf_tcp_msg_add(struct smap_psock *psock,
                            struct sock *sk,
                            struct bpf_prog *tx_msg)
{
        struct bpf_prog *orig_tx_msg;

        orig_tx_msg = xchg(&psock->bpf_tx_msg, tx_msg);
        if (orig_tx_msg)
                bpf_prog_put(orig_tx_msg);
}

static int bpf_tcp_ulp_register(void)
{
        tcp_bpf_proto = tcp_prot;
        tcp_bpf_proto.close = bpf_tcp_close;
        /* Once BPF TX ULP is registered it is never unregistered. It
         * will be in the ULP list for the lifetime of the system. Doing
         * duplicate registers is not a problem.
         */
        return tcp_register_ulp(&bpf_tcp_ulp_ops);
}

static int smap_verdict_func(struct smap_psock *psock, struct sk_buff *skb)
{
        struct bpf_prog *prog = READ_ONCE(psock->bpf_verdict);
        int rc;

        if (unlikely(!prog))
                return __SK_DROP;

        skb_orphan(skb);
        /* We need to ensure that BPF metadata for maps is also cleared
         * when we orphan the skb so that we don't have the possibility
         * to reference a stale map.
         */
        TCP_SKB_CB(skb)->bpf.map = NULL;
        skb->sk = psock->sock;
        bpf_compute_data_pointers(skb);
        preempt_disable();
        rc = (*prog->bpf_func)(skb, prog->insnsi);
        preempt_enable();
        skb->sk = NULL;

        /* Moving return codes from UAPI namespace into internal namespace */
        return rc == SK_PASS ?
                (TCP_SKB_CB(skb)->bpf.map ? __SK_REDIRECT : __SK_PASS) :
                __SK_DROP;
}

static int smap_do_ingress(struct smap_psock *psock, struct sk_buff *skb)
{
        struct sock *sk = psock->sock;
        int copied = 0, num_sg;
        struct sk_msg_buff *r;

        r = kzalloc(sizeof(struct sk_msg_buff), __GFP_NOWARN | GFP_ATOMIC);
        if (unlikely(!r))
                return -EAGAIN;

        if (!sk_rmem_schedule(sk, skb, skb->len)) {
                kfree(r);
                return -EAGAIN;
        }

        sg_init_table(r->sg_data, MAX_SKB_FRAGS);
        num_sg = skb_to_sgvec(skb, r->sg_data, 0, skb->len);
        if (unlikely(num_sg < 0)) {
                kfree(r);
                return num_sg;
        }
        sk_mem_charge(sk, skb->len);
        copied = skb->len;
        r->sg_start = 0;
        r->sg_end = num_sg == MAX_SKB_FRAGS ? 0 : num_sg;
        r->skb = skb;
        list_add_tail(&r->list, &psock->ingress);
        sk->sk_data_ready(sk);
        return copied;
}

static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
{
        struct smap_psock *peer;
        struct sock *sk;
        __u32 in;
        int rc;

        rc = smap_verdict_func(psock, skb);
        switch (rc) {
        case __SK_REDIRECT:
                sk = do_sk_redirect_map(skb);
                if (!sk) {
                        kfree_skb(skb);
                        break;
                }

                peer = smap_psock_sk(sk);
                in = (TCP_SKB_CB(skb)->bpf.flags) & BPF_F_INGRESS;

                if (unlikely(!peer || sock_flag(sk, SOCK_DEAD) ||
                             !test_bit(SMAP_TX_RUNNING, &peer->state))) {
                        kfree_skb(skb);
                        break;
                }

                if (!in && sock_writeable(sk)) {
                        skb_set_owner_w(skb, sk);
                        skb_queue_tail(&peer->rxqueue, skb);
                        schedule_work(&peer->tx_work);
                        break;
                } else if (in &&
                           atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) {
                        skb_queue_tail(&peer->rxqueue, skb);
                        schedule_work(&peer->tx_work);
                        break;
                }
        /* Fall through and free skb otherwise */
        case __SK_DROP:
        default:
                kfree_skb(skb);
        }
}

static void smap_report_sk_error(struct smap_psock *psock, int err)
{
        struct sock *sk = psock->sock;

        sk->sk_err = err;
        sk->sk_error_report(sk);
}

static void smap_read_sock_strparser(struct strparser *strp,
                                     struct sk_buff *skb)
{
        struct smap_psock *psock;

        rcu_read_lock();
        psock = container_of(strp, struct smap_psock, strp);
        smap_do_verdict(psock, skb);
        rcu_read_unlock();
}

/* Called with lock held on socket */
static void smap_data_ready(struct sock *sk)
{
        struct smap_psock *psock;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (likely(psock)) {
                write_lock_bh(&sk->sk_callback_lock);
                strp_data_ready(&psock->strp);
                write_unlock_bh(&sk->sk_callback_lock);
        }
        rcu_read_unlock();
}

static void smap_tx_work(struct work_struct *w)
{
        struct smap_psock *psock;
        struct sk_buff *skb;
        int rem, off, n;

        psock = container_of(w, struct smap_psock, tx_work);

        /* lock sock to avoid losing sk_socket at some point during loop */
        lock_sock(psock->sock);
        if (psock->save_skb) {
                skb = psock->save_skb;
                rem = psock->save_rem;
                off = psock->save_off;
                psock->save_skb = NULL;
                goto start;
        }

        while ((skb = skb_dequeue(&psock->rxqueue))) {
                __u32 flags;

                rem = skb->len;
                off = 0;
start:
                flags = (TCP_SKB_CB(skb)->bpf.flags) & BPF_F_INGRESS;
                do {
                        if (likely(psock->sock->sk_socket)) {
                                if (flags)
                                        n = smap_do_ingress(psock, skb);
                                else
                                        n = skb_send_sock_locked(psock->sock,
                                                                 skb, off, rem);
                        } else {
                                n = -EINVAL;
                        }

                        if (n <= 0) {
                                if (n == -EAGAIN) {
                                        /* Retry when space is available */
                                        psock->save_skb = skb;
                                        psock->save_rem = rem;
                                        psock->save_off = off;
                                        goto out;
                                }
                                /* Hard errors break pipe and stop xmit */
                                smap_report_sk_error(psock, n ? -n : EPIPE);
                                clear_bit(SMAP_TX_RUNNING, &psock->state);
                                kfree_skb(skb);
                                goto out;
                        }
                        rem -= n;
                        off += n;
                } while (rem);

                if (!flags)
                        kfree_skb(skb);
        }
out:
        release_sock(psock->sock);
}

static void smap_write_space(struct sock *sk)
{
        struct smap_psock *psock;

        rcu_read_lock();
        psock = smap_psock_sk(sk);
        if (likely(psock && test_bit(SMAP_TX_RUNNING, &psock->state)))
                schedule_work(&psock->tx_work);
        rcu_read_unlock();
}

static void smap_stop_sock(struct smap_psock *psock, struct sock *sk)
{
        if (!psock->strp_enabled)
                return;
        sk->sk_data_ready = psock->save_data_ready;
        sk->sk_write_space = psock->save_write_space;
        psock->save_data_ready = NULL;
        psock->save_write_space = NULL;
        strp_stop(&psock->strp);
        psock->strp_enabled = false;
}

static void smap_destroy_psock(struct rcu_head *rcu)
{
        struct smap_psock *psock = container_of(rcu,
                                                  struct smap_psock, rcu);

        /* Now that a grace period has passed there is no longer
         * any reference to this sock in the sockmap so we can
         * destroy the psock, strparser, and bpf programs. But,
         * because we use workqueue sync operations we can not
         * do it in rcu context
         */
        schedule_work(&psock->gc_work);
}

static void smap_release_sock(struct smap_psock *psock, struct sock *sock)
{
        if (refcount_dec_and_test(&psock->refcnt)) {
                tcp_cleanup_ulp(sock);
                smap_stop_sock(psock, sock);
                clear_bit(SMAP_TX_RUNNING, &psock->state);
                rcu_assign_sk_user_data(sock, NULL);
                call_rcu_sched(&psock->rcu, smap_destroy_psock);
        }
}

static int smap_parse_func_strparser(struct strparser *strp,
                                       struct sk_buff *skb)
{
        struct smap_psock *psock;
        struct bpf_prog *prog;
        int rc;

        rcu_read_lock();
        psock = container_of(strp, struct smap_psock, strp);
        prog = READ_ONCE(psock->bpf_parse);

        if (unlikely(!prog)) {
                rcu_read_unlock();
                return skb->len;
        }

        /* Attach socket for bpf program to use if needed we can do this
         * because strparser clones the skb before handing it to a upper
         * layer, meaning skb_orphan has been called. We NULL sk on the
         * way out to ensure we don't trigger a BUG_ON in skb/sk operations
         * later and because we are not charging the memory of this skb to
         * any socket yet.
         */
        skb->sk = psock->sock;
        bpf_compute_data_pointers(skb);
        rc = (*prog->bpf_func)(skb, prog->insnsi);
        skb->sk = NULL;
        rcu_read_unlock();
        return rc;
}

static int smap_read_sock_done(struct strparser *strp, int err)
{
        return err;
}

static int smap_init_sock(struct smap_psock *psock,
                          struct sock *sk)
{
        static const struct strp_callbacks cb = {
                .rcv_msg = smap_read_sock_strparser,
                .parse_msg = smap_parse_func_strparser,
                .read_sock_done = smap_read_sock_done,
        };

        return strp_init(&psock->strp, sk, &cb);
}

static void smap_init_progs(struct smap_psock *psock,
                            struct bpf_stab *stab,
                            struct bpf_prog *verdict,
                            struct bpf_prog *parse)
{
        struct bpf_prog *orig_parse, *orig_verdict;

        orig_parse = xchg(&psock->bpf_parse, parse);
        orig_verdict = xchg(&psock->bpf_verdict, verdict);

        if (orig_verdict)
                bpf_prog_put(orig_verdict);
        if (orig_parse)
                bpf_prog_put(orig_parse);
}

static void smap_start_sock(struct smap_psock *psock, struct sock *sk)
{
        if (sk->sk_data_ready == smap_data_ready)
                return;
        psock->save_data_ready = sk->sk_data_ready;
        psock->save_write_space = sk->sk_write_space;
        sk->sk_data_ready = smap_data_ready;
        sk->sk_write_space = smap_write_space;
        psock->strp_enabled = true;
}

static void sock_map_remove_complete(struct bpf_stab *stab)
{
        bpf_map_area_free(stab->sock_map);
        kfree(stab);
}

static void smap_gc_work(struct work_struct *w)
{
        struct smap_psock_map_entry *e, *tmp;
        struct sk_msg_buff *md, *mtmp;
        struct smap_psock *psock;

        psock = container_of(w, struct smap_psock, gc_work);

        /* no callback lock needed because we already detached sockmap ops */
        if (psock->strp_enabled)
                strp_done(&psock->strp);

        cancel_work_sync(&psock->tx_work);
        __skb_queue_purge(&psock->rxqueue);

        /* At this point all strparser and xmit work must be complete */
        if (psock->bpf_parse)
                bpf_prog_put(psock->bpf_parse);
        if (psock->bpf_verdict)
                bpf_prog_put(psock->bpf_verdict);
        if (psock->bpf_tx_msg)
                bpf_prog_put(psock->bpf_tx_msg);

        if (psock->cork) {
                free_start_sg(psock->sock, psock->cork);
                kfree(psock->cork);
        }

        list_for_each_entry_safe(md, mtmp, &psock->ingress, list) {
                list_del(&md->list);
                free_start_sg(psock->sock, md);
                kfree(md);
        }

        list_for_each_entry_safe(e, tmp, &psock->maps, list) {
                list_del(&e->list);
                kfree(e);
        }

        if (psock->sk_redir)
                sock_put(psock->sk_redir);

        sock_put(psock->sock);
        kfree(psock);
}

static struct smap_psock *smap_init_psock(struct sock *sock,
                                          struct bpf_stab *stab)
{
        struct smap_psock *psock;

        psock = kzalloc_node(sizeof(struct smap_psock),
                             GFP_ATOMIC | __GFP_NOWARN,
                             stab->map.numa_node);
        if (!psock)
                return ERR_PTR(-ENOMEM);

        psock->eval =  __SK_NONE;
        psock->sock = sock;
        skb_queue_head_init(&psock->rxqueue);
        INIT_WORK(&psock->tx_work, smap_tx_work);
        INIT_WORK(&psock->gc_work, smap_gc_work);
        INIT_LIST_HEAD(&psock->maps);
        INIT_LIST_HEAD(&psock->ingress);
        refcount_set(&psock->refcnt, 1);

        rcu_assign_sk_user_data(sock, psock);
        sock_hold(sock);
        return psock;
}

static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
{
        struct bpf_stab *stab;
        u64 cost;
        int err;

        if (!capable(CAP_NET_ADMIN))
                return ERR_PTR(-EPERM);

        /* check sanity of attributes */
        if (attr->max_entries == 0 || attr->key_size != 4 ||
            attr->value_size != 4 || attr->map_flags & ~SOCK_CREATE_FLAG_MASK)
                return ERR_PTR(-EINVAL);

        err = bpf_tcp_ulp_register();
        if (err && err != -EEXIST)
                return ERR_PTR(err);

        stab = kzalloc(sizeof(*stab), GFP_USER);
        if (!stab)
                return ERR_PTR(-ENOMEM);

        bpf_map_init_from_attr(&stab->map, attr);

        /* make sure page count doesn't overflow */
        cost = (u64) stab->map.max_entries * sizeof(struct sock *);
        err = -EINVAL;
        if (cost >= U32_MAX - PAGE_SIZE)
                goto free_stab;

        stab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

        /* if map size is larger than memlock limit, reject it early */
        err = bpf_map_precharge_memlock(stab->map.pages);
        if (err)
                goto free_stab;

        err = -ENOMEM;
        stab->sock_map = bpf_map_area_alloc(stab->map.max_entries *
                                            sizeof(struct sock *),
                                            stab->map.numa_node);
        if (!stab->sock_map)
                goto free_stab;

        return &stab->map;
free_stab:
        kfree(stab);
        return ERR_PTR(err);
}

static void smap_list_remove(struct smap_psock *psock, struct sock **entry)
{
        struct smap_psock_map_entry *e, *tmp;

        list_for_each_entry_safe(e, tmp, &psock->maps, list) {
                if (e->entry == entry) {
                        list_del(&e->list);
                        break;
                }
        }
}

static void sock_map_free(struct bpf_map *map)
{
        struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
        int i;

        synchronize_rcu();

        /* At this point no update, lookup or delete operations can happen.
         * However, be aware we can still get a socket state event updates,
         * and data ready callabacks that reference the psock from sk_user_data
         * Also psock worker threads are still in-flight. So smap_release_sock
         * will only free the psock after cancel_sync on the worker threads
         * and a grace period expire to ensure psock is really safe to remove.
         */
        rcu_read_lock();
        for (i = 0; i < stab->map.max_entries; i++) {
                struct smap_psock *psock;
                struct sock *sock;

                sock = xchg(&stab->sock_map[i], NULL);
                if (!sock)
                        continue;

                write_lock_bh(&sock->sk_callback_lock);
                psock = smap_psock_sk(sock);
                /* This check handles a racing sock event that can get the
                 * sk_callback_lock before this case but after xchg happens
                 * causing the refcnt to hit zero and sock user data (psock)
                 * to be null and queued for garbage collection.
                 */
                if (likely(psock)) {
                        smap_list_remove(psock, &stab->sock_map[i]);
                        smap_release_sock(psock, sock);
                }
                write_unlock_bh(&sock->sk_callback_lock);
        }
        rcu_read_unlock();

        sock_map_remove_complete(stab);
}

static int sock_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
        struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
        u32 i = key ? *(u32 *)key : U32_MAX;
        u32 *next = (u32 *)next_key;

        if (i >= stab->map.max_entries) {
                *next = 0;
                return 0;
        }

        if (i == stab->map.max_entries - 1)
                return -ENOENT;

        *next = i + 1;
        return 0;
}

struct sock  *__sock_map_lookup_elem(struct bpf_map *map, u32 key)
{
        struct bpf_stab *stab = container_of(map, struct bpf_stab, map);

        if (key >= map->max_entries)
                return NULL;

        return READ_ONCE(stab->sock_map[key]);
}

static int sock_map_delete_elem(struct bpf_map *map, void *key)
{
        struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
        struct smap_psock *psock;
        int k = *(u32 *)key;
        struct sock *sock;

        if (k >= map->max_entries)
                return -EINVAL;

        sock = xchg(&stab->sock_map[k], NULL);
        if (!sock)
                return -EINVAL;

        write_lock_bh(&sock->sk_callback_lock);
        psock = smap_psock_sk(sock);
        if (!psock)
                goto out;

        if (psock->bpf_parse)
                smap_stop_sock(psock, sock);
        smap_list_remove(psock, &stab->sock_map[k]);
        smap_release_sock(psock, sock);
out:
        write_unlock_bh(&sock->sk_callback_lock);
        return 0;
}

/* Locking notes: Concurrent updates, deletes, and lookups are allowed and are
 * done inside rcu critical sections. This ensures on updates that the psock
 * will not be released via smap_release_sock() until concurrent updates/deletes
 * complete. All operations operate on sock_map using cmpxchg and xchg
 * operations to ensure we do not get stale references. Any reads into the
 * map must be done with READ_ONCE() because of this.
 *
 * A psock is destroyed via call_rcu and after any worker threads are cancelled
 * and syncd so we are certain all references from the update/lookup/delete
 * operations as well as references in the data path are no longer in use.
 *
 * Psocks may exist in multiple maps, but only a single set of parse/verdict
 * programs may be inherited from the maps it belongs to. A reference count
 * is kept with the total number of references to the psock from all maps. The
 * psock will not be released until this reaches zero. The psock and sock
 * user data data use the sk_callback_lock to protect critical data structures
 * from concurrent access. This allows us to avoid two updates from modifying
 * the user data in sock and the lock is required anyways for modifying
 * callbacks, we simply increase its scope slightly.
 *
 * Rules to follow,
 *  - psock must always be read inside RCU critical section
 *  - sk_user_data must only be modified inside sk_callback_lock and read
 *    inside RCU critical section.
 *  - psock->maps list must only be read & modified inside sk_callback_lock
 *  - sock_map must use READ_ONCE and (cmp)xchg operations
 *  - BPF verdict/parse programs must use READ_ONCE and xchg operations
 */
static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops,
                                    struct bpf_map *map,
                                    void *key, u64 flags)
{
        struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
        struct smap_psock_map_entry *e = NULL;
        struct bpf_prog *verdict, *parse, *tx_msg;
        struct sock *osock, *sock;
        struct smap_psock *psock;
        u32 i = *(u32 *)key;
        bool new = false;
        int err;

        if (unlikely(flags > BPF_EXIST))
                return -EINVAL;

        if (unlikely(i >= stab->map.max_entries))
                return -E2BIG;

        sock = READ_ONCE(stab->sock_map[i]);
        if (flags == BPF_EXIST && !sock)
                return -ENOENT;
        else if (flags == BPF_NOEXIST && sock)
                return -EEXIST;

        sock = skops->sk;

        /* 1. If sock map has BPF programs those will be inherited by the
         * sock being added. If the sock is already attached to BPF programs
         * this results in an error.
         */
        verdict = READ_ONCE(stab->bpf_verdict);
        parse = READ_ONCE(stab->bpf_parse);
        tx_msg = READ_ONCE(stab->bpf_tx_msg);

        if (parse && verdict) {
                /* bpf prog refcnt may be zero if a concurrent attach operation
                 * removes the program after the above READ_ONCE() but before
                 * we increment the refcnt. If this is the case abort with an
                 * error.
                 */
                verdict = bpf_prog_inc_not_zero(verdict);
                if (IS_ERR(verdict))
                        return PTR_ERR(verdict);

                parse = bpf_prog_inc_not_zero(parse);
                if (IS_ERR(parse)) {
                        bpf_prog_put(verdict);
                        return PTR_ERR(parse);
                }
        }

        if (tx_msg) {
                tx_msg = bpf_prog_inc_not_zero(tx_msg);
                if (IS_ERR(tx_msg)) {
                        if (parse && verdict) {
                                bpf_prog_put(parse);
                                bpf_prog_put(verdict);
                        }
                        return PTR_ERR(tx_msg);
                }
        }

        write_lock_bh(&sock->sk_callback_lock);
        psock = smap_psock_sk(sock);

        /* 2. Do not allow inheriting programs if psock exists and has
         * already inherited programs. This would create confusion on
         * which parser/verdict program is running. If no psock exists
         * create one. Inside sk_callback_lock to ensure concurrent create
         * doesn't update user data.
         */
        if (psock) {
                if (READ_ONCE(psock->bpf_parse) && parse) {
                        err = -EBUSY;
                        goto out_progs;
                }
                if (READ_ONCE(psock->bpf_tx_msg) && tx_msg) {
                        err = -EBUSY;
                        goto out_progs;
                }
                if (!refcount_inc_not_zero(&psock->refcnt)) {
                        err = -EAGAIN;
                        goto out_progs;
                }
        } else {
                psock = smap_init_psock(sock, stab);
                if (IS_ERR(psock)) {
                        err = PTR_ERR(psock);
                        goto out_progs;
                }

                set_bit(SMAP_TX_RUNNING, &psock->state);
                new = true;
        }

        e = kzalloc(sizeof(*e), GFP_ATOMIC | __GFP_NOWARN);
        if (!e) {
                err = -ENOMEM;
                goto out_progs;
        }
        e->entry = &stab->sock_map[i];

        /* 3. At this point we have a reference to a valid psock that is
         * running. Attach any BPF programs needed.
         */
        if (tx_msg)
                bpf_tcp_msg_add(psock, sock, tx_msg);
        if (new) {
                err = tcp_set_ulp_id(sock, TCP_ULP_BPF);
                if (err)
                        goto out_free;
        }

        if (parse && verdict && !psock->strp_enabled) {
                err = smap_init_sock(psock, sock);
                if (err)
                        goto out_free;
                smap_init_progs(psock, stab, verdict, parse);
                smap_start_sock(psock, sock);
        }

        /* 4. Place psock in sockmap for use and stop any programs on
         * the old sock assuming its not the same sock we are replacing
         * it with. Because we can only have a single set of programs if
         * old_sock has a strp we can stop it.
         */
        list_add_tail(&e->list, &psock->maps);
        write_unlock_bh(&sock->sk_callback_lock);

        osock = xchg(&stab->sock_map[i], sock);
        if (osock) {
                struct smap_psock *opsock = smap_psock_sk(osock);

                write_lock_bh(&osock->sk_callback_lock);
                smap_list_remove(opsock, &stab->sock_map[i]);
                smap_release_sock(opsock, osock);
                write_unlock_bh(&osock->sk_callback_lock);
        }
        return 0;
out_free:
        smap_release_sock(psock, sock);
out_progs:
        if (parse && verdict) {
                bpf_prog_put(parse);
                bpf_prog_put(verdict);
        }
        if (tx_msg)
                bpf_prog_put(tx_msg);
        write_unlock_bh(&sock->sk_callback_lock);
        kfree(e);
        return err;
}

int sock_map_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type)
{
        struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
        struct bpf_prog *orig;

        if (unlikely(map->map_type != BPF_MAP_TYPE_SOCKMAP))
                return -EINVAL;

        switch (type) {
        case BPF_SK_MSG_VERDICT:
                orig = xchg(&stab->bpf_tx_msg, prog);
                break;
        case BPF_SK_SKB_STREAM_PARSER:
                orig = xchg(&stab->bpf_parse, prog);
                break;
        case BPF_SK_SKB_STREAM_VERDICT:
                orig = xchg(&stab->bpf_verdict, prog);
                break;
        default:
                return -EOPNOTSUPP;
        }

        if (orig)
                bpf_prog_put(orig);

        return 0;
}

static void *sock_map_lookup(struct bpf_map *map, void *key)
{
        return NULL;
}

static int sock_map_update_elem(struct bpf_map *map,
                                void *key, void *value, u64 flags)
{
        struct bpf_sock_ops_kern skops;
        u32 fd = *(u32 *)value;
        struct socket *socket;
        int err;

        socket = sockfd_lookup(fd, &err);
        if (!socket)
                return err;

        skops.sk = socket->sk;
        if (!skops.sk) {
                fput(socket->file);
                return -EINVAL;
        }

        if (skops.sk->sk_type != SOCK_STREAM ||
            skops.sk->sk_protocol != IPPROTO_TCP) {
                fput(socket->file);
                return -EOPNOTSUPP;
        }

        err = sock_map_ctx_update_elem(&skops, map, key, flags);
        fput(socket->file);
        return err;
}

static void sock_map_release(struct bpf_map *map)
{
        struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
        struct bpf_prog *orig;

        orig = xchg(&stab->bpf_parse, NULL);
        if (orig)
                bpf_prog_put(orig);
        orig = xchg(&stab->bpf_verdict, NULL);
        if (orig)
                bpf_prog_put(orig);

        orig = xchg(&stab->bpf_tx_msg, NULL);
        if (orig)
                bpf_prog_put(orig);
}

const struct bpf_map_ops sock_map_ops = {
        .map_alloc = sock_map_alloc,
        .map_free = sock_map_free,
        .map_lookup_elem = sock_map_lookup,
        .map_get_next_key = sock_map_get_next_key,
        .map_update_elem = sock_map_update_elem,
        .map_delete_elem = sock_map_delete_elem,
        .map_release_uref = sock_map_release,
};

BPF_CALL_4(bpf_sock_map_update, struct bpf_sock_ops_kern *, bpf_sock,
           struct bpf_map *, map, void *, key, u64, flags)
{
        WARN_ON_ONCE(!rcu_read_lock_held());
        return sock_map_ctx_update_elem(bpf_sock, map, key, flags);
}

const struct bpf_func_proto bpf_sock_map_update_proto = {
        .func           = bpf_sock_map_update,
        .gpl_only       = false,
        .pkt_access     = true,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_PTR_TO_CTX,
        .arg2_type      = ARG_CONST_MAP_PTR,
        .arg3_type      = ARG_PTR_TO_MAP_KEY,
        .arg4_type      = ARG_ANYTHING,
};