Linux 4.15.6

[linux/fpc-iii.git] / kernel / bpf / sockmap.c

/* 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 <net/strparser.h>
#include <net/tcp.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_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;
        /* refcnt is used inside sk_callback_lock */
        u32 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;

        struct strparser strp;
        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;

        void (*save_data_ready)(struct sock *sk);
        void (*save_write_space)(struct sock *sk);
        void (*save_state_change)(struct sock *sk);
};

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

/* compute the linear packet data range [data, data_end) for skb when
 * sk_skb type programs are in use.
 */
static inline void bpf_compute_data_end_sk_skb(struct sk_buff *skb)
{
        TCP_SKB_CB(skb)->bpf.data_end = skb->data + skb_headlen(skb);
}

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

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

        rc = smap_verdict_func(psock, skb);
        switch (rc) {
        case __SK_REDIRECT:
                sk = do_sk_redirect_map(skb);
                if (likely(sk)) {
                        struct smap_psock *peer = smap_psock_sk(sk);

                        if (likely(peer &&
                                   test_bit(SMAP_TX_RUNNING, &peer->state) &&
                                   !sock_flag(sk, SOCK_DEAD) &&
                                   sock_writeable(sk))) {
                                skb_set_owner_w(skb, sk);
                                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_release_sock(struct smap_psock *psock, struct sock *sock);

/* Called with lock_sock(sk) held */
static void smap_state_change(struct sock *sk)
{
        struct smap_psock_map_entry *e, *tmp;
        struct smap_psock *psock;
        struct socket_wq *wq;
        struct sock *osk;

        rcu_read_lock();

        /* Allowing transitions into an established syn_recv states allows
         * for early binding sockets to a smap object before the connection
         * is established.
         */
        switch (sk->sk_state) {
        case TCP_SYN_SENT:
        case TCP_SYN_RECV:
        case TCP_ESTABLISHED:
                break;
        case TCP_CLOSE_WAIT:
        case TCP_CLOSING:
        case TCP_LAST_ACK:
        case TCP_FIN_WAIT1:
        case TCP_FIN_WAIT2:
        case TCP_LISTEN:
                break;
        case TCP_CLOSE:
                /* Only release if the map entry is in fact the sock in
                 * question. There is a case where the operator deletes
                 * the sock from the map, but the TCP sock is closed before
                 * the psock is detached. Use cmpxchg to verify correct
                 * sock is removed.
                 */
                psock = smap_psock_sk(sk);
                if (unlikely(!psock))
                        break;
                write_lock_bh(&sk->sk_callback_lock);
                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);
                break;
        default:
                psock = smap_psock_sk(sk);
                if (unlikely(!psock))
                        break;
                smap_report_sk_error(psock, EPIPE);
                break;
        }

        wq = rcu_dereference(sk->sk_wq);
        if (skwq_has_sleeper(wq))
                wake_up_interruptible_all(&wq->wait);
        rcu_read_unlock();
}

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))) {
                rem = skb->len;
                off = 0;
start:
                do {
                        if (likely(psock->sock->sk_socket))
                                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);
                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;
        sk->sk_state_change = psock->save_state_change;
        psock->save_data_ready = NULL;
        psock->save_write_space = NULL;
        psock->save_state_change = 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)
{
        psock->refcnt--;
        if (psock->refcnt)
                return;

        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;
        psock->save_state_change = sk->sk_state_change;
        sk->sk_data_ready = smap_data_ready;
        sk->sk_write_space = smap_write_space;
        sk->sk_state_change = smap_state_change;
        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 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);

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

        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->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);
        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;
        int err = -EINVAL;
        u64 cost;

        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);

        if (attr->value_size > KMALLOC_MAX_SIZE)
                return ERR_PTR(-E2BIG);

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

        /* mandatory map attributes */
        stab->map.map_type = attr->map_type;
        stab->map.key_size = attr->key_size;
        stab->map.value_size = attr->value_size;
        stab->map.max_entries = attr->max_entries;
        stab->map.map_flags = attr->map_flags;
        stab->map.numa_node = bpf_map_attr_numa_node(attr);

        /* make sure page count doesn't overflow */
        cost = (u64) stab->map.max_entries * sizeof(struct sock *);
        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();

        if (stab->bpf_verdict)
                bpf_prog_put(stab->bpf_verdict);
        if (stab->bpf_parse)
                bpf_prog_put(stab->bpf_parse);

        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;
        struct sock *osock, *sock;
        struct smap_psock *psock;
        u32 i = *(u32 *)key;
        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);

        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(stab->bpf_verdict);
                if (IS_ERR(verdict))
                        return PTR_ERR(verdict);

                parse = bpf_prog_inc_not_zero(stab->bpf_parse);
                if (IS_ERR(parse)) {
                        bpf_prog_put(verdict);
                        return PTR_ERR(parse);
                }
        }

        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;
                }
                psock->refcnt++;
        } 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);
        }

        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 (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);
                if (osock != sock && parse)
                        smap_stop_sock(opsock, osock);
                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 (verdict)
                bpf_prog_put(verdict);
        if (parse)
                bpf_prog_put(parse);
        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_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;
}

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,
};

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,
};