WIP FPC-III support

[linux/fpc-iii.git] / net / core / bpf_sk_storage.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019 Facebook  */
#include <linux/rculist.h>
#include <linux/list.h>
#include <linux/hash.h>
#include <linux/types.h>
#include <linux/spinlock.h>
#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/btf_ids.h>
#include <linux/bpf_local_storage.h>
#include <net/bpf_sk_storage.h>
#include <net/sock.h>
#include <uapi/linux/sock_diag.h>
#include <uapi/linux/btf.h>

DEFINE_BPF_STORAGE_CACHE(sk_cache);

static struct bpf_local_storage_data *
bpf_sk_storage_lookup(struct sock *sk, struct bpf_map *map, bool cacheit_lockit)
{
        struct bpf_local_storage *sk_storage;
        struct bpf_local_storage_map *smap;

        sk_storage = rcu_dereference(sk->sk_bpf_storage);
        if (!sk_storage)
                return NULL;

        smap = (struct bpf_local_storage_map *)map;
        return bpf_local_storage_lookup(sk_storage, smap, cacheit_lockit);
}

static int bpf_sk_storage_del(struct sock *sk, struct bpf_map *map)
{
        struct bpf_local_storage_data *sdata;

        sdata = bpf_sk_storage_lookup(sk, map, false);
        if (!sdata)
                return -ENOENT;

        bpf_selem_unlink(SELEM(sdata));

        return 0;
}

/* Called by __sk_destruct() & bpf_sk_storage_clone() */
void bpf_sk_storage_free(struct sock *sk)
{
        struct bpf_local_storage_elem *selem;
        struct bpf_local_storage *sk_storage;
        bool free_sk_storage = false;
        struct hlist_node *n;

        rcu_read_lock();
        sk_storage = rcu_dereference(sk->sk_bpf_storage);
        if (!sk_storage) {
                rcu_read_unlock();
                return;
        }

        /* Netiher the bpf_prog nor the bpf-map's syscall
         * could be modifying the sk_storage->list now.
         * Thus, no elem can be added-to or deleted-from the
         * sk_storage->list by the bpf_prog or by the bpf-map's syscall.
         *
         * It is racing with bpf_local_storage_map_free() alone
         * when unlinking elem from the sk_storage->list and
         * the map's bucket->list.
         */
        raw_spin_lock_bh(&sk_storage->lock);
        hlist_for_each_entry_safe(selem, n, &sk_storage->list, snode) {
                /* Always unlink from map before unlinking from
                 * sk_storage.
                 */
                bpf_selem_unlink_map(selem);
                free_sk_storage = bpf_selem_unlink_storage_nolock(sk_storage,
                                                                  selem, true);
        }
        raw_spin_unlock_bh(&sk_storage->lock);
        rcu_read_unlock();

        if (free_sk_storage)
                kfree_rcu(sk_storage, rcu);
}

static void bpf_sk_storage_map_free(struct bpf_map *map)
{
        struct bpf_local_storage_map *smap;

        smap = (struct bpf_local_storage_map *)map;
        bpf_local_storage_cache_idx_free(&sk_cache, smap->cache_idx);
        bpf_local_storage_map_free(smap);
}

static struct bpf_map *bpf_sk_storage_map_alloc(union bpf_attr *attr)
{
        struct bpf_local_storage_map *smap;

        smap = bpf_local_storage_map_alloc(attr);
        if (IS_ERR(smap))
                return ERR_CAST(smap);

        smap->cache_idx = bpf_local_storage_cache_idx_get(&sk_cache);
        return &smap->map;
}

static int notsupp_get_next_key(struct bpf_map *map, void *key,
                                void *next_key)
{
        return -ENOTSUPP;
}

static void *bpf_fd_sk_storage_lookup_elem(struct bpf_map *map, void *key)
{
        struct bpf_local_storage_data *sdata;
        struct socket *sock;
        int fd, err;

        fd = *(int *)key;
        sock = sockfd_lookup(fd, &err);
        if (sock) {
                sdata = bpf_sk_storage_lookup(sock->sk, map, true);
                sockfd_put(sock);
                return sdata ? sdata->data : NULL;
        }

        return ERR_PTR(err);
}

static int bpf_fd_sk_storage_update_elem(struct bpf_map *map, void *key,
                                         void *value, u64 map_flags)
{
        struct bpf_local_storage_data *sdata;
        struct socket *sock;
        int fd, err;

        fd = *(int *)key;
        sock = sockfd_lookup(fd, &err);
        if (sock) {
                sdata = bpf_local_storage_update(
                        sock->sk, (struct bpf_local_storage_map *)map, value,
                        map_flags);
                sockfd_put(sock);
                return PTR_ERR_OR_ZERO(sdata);
        }

        return err;
}

static int bpf_fd_sk_storage_delete_elem(struct bpf_map *map, void *key)
{
        struct socket *sock;
        int fd, err;

        fd = *(int *)key;
        sock = sockfd_lookup(fd, &err);
        if (sock) {
                err = bpf_sk_storage_del(sock->sk, map);
                sockfd_put(sock);
                return err;
        }

        return err;
}

static struct bpf_local_storage_elem *
bpf_sk_storage_clone_elem(struct sock *newsk,
                          struct bpf_local_storage_map *smap,
                          struct bpf_local_storage_elem *selem)
{
        struct bpf_local_storage_elem *copy_selem;

        copy_selem = bpf_selem_alloc(smap, newsk, NULL, true);
        if (!copy_selem)
                return NULL;

        if (map_value_has_spin_lock(&smap->map))
                copy_map_value_locked(&smap->map, SDATA(copy_selem)->data,
                                      SDATA(selem)->data, true);
        else
                copy_map_value(&smap->map, SDATA(copy_selem)->data,
                               SDATA(selem)->data);

        return copy_selem;
}

int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk)
{
        struct bpf_local_storage *new_sk_storage = NULL;
        struct bpf_local_storage *sk_storage;
        struct bpf_local_storage_elem *selem;
        int ret = 0;

        RCU_INIT_POINTER(newsk->sk_bpf_storage, NULL);

        rcu_read_lock();
        sk_storage = rcu_dereference(sk->sk_bpf_storage);

        if (!sk_storage || hlist_empty(&sk_storage->list))
                goto out;

        hlist_for_each_entry_rcu(selem, &sk_storage->list, snode) {
                struct bpf_local_storage_elem *copy_selem;
                struct bpf_local_storage_map *smap;
                struct bpf_map *map;

                smap = rcu_dereference(SDATA(selem)->smap);
                if (!(smap->map.map_flags & BPF_F_CLONE))
                        continue;

                /* Note that for lockless listeners adding new element
                 * here can race with cleanup in bpf_local_storage_map_free.
                 * Try to grab map refcnt to make sure that it's still
                 * alive and prevent concurrent removal.
                 */
                map = bpf_map_inc_not_zero(&smap->map);
                if (IS_ERR(map))
                        continue;

                copy_selem = bpf_sk_storage_clone_elem(newsk, smap, selem);
                if (!copy_selem) {
                        ret = -ENOMEM;
                        bpf_map_put(map);
                        goto out;
                }

                if (new_sk_storage) {
                        bpf_selem_link_map(smap, copy_selem);
                        bpf_selem_link_storage_nolock(new_sk_storage, copy_selem);
                } else {
                        ret = bpf_local_storage_alloc(newsk, smap, copy_selem);
                        if (ret) {
                                kfree(copy_selem);
                                atomic_sub(smap->elem_size,
                                           &newsk->sk_omem_alloc);
                                bpf_map_put(map);
                                goto out;
                        }

                        new_sk_storage =
                                rcu_dereference(copy_selem->local_storage);
                }
                bpf_map_put(map);
        }

out:
        rcu_read_unlock();

        /* In case of an error, don't free anything explicitly here, the
         * caller is responsible to call bpf_sk_storage_free.
         */

        return ret;
}

BPF_CALL_4(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
           void *, value, u64, flags)
{
        struct bpf_local_storage_data *sdata;

        if (!sk || !sk_fullsock(sk) || flags > BPF_SK_STORAGE_GET_F_CREATE)
                return (unsigned long)NULL;

        sdata = bpf_sk_storage_lookup(sk, map, true);
        if (sdata)
                return (unsigned long)sdata->data;

        if (flags == BPF_SK_STORAGE_GET_F_CREATE &&
            /* Cannot add new elem to a going away sk.
             * Otherwise, the new elem may become a leak
             * (and also other memory issues during map
             *  destruction).
             */
            refcount_inc_not_zero(&sk->sk_refcnt)) {
                sdata = bpf_local_storage_update(
                        sk, (struct bpf_local_storage_map *)map, value,
                        BPF_NOEXIST);
                /* sk must be a fullsock (guaranteed by verifier),
                 * so sock_gen_put() is unnecessary.
                 */
                sock_put(sk);
                return IS_ERR(sdata) ?
                        (unsigned long)NULL : (unsigned long)sdata->data;
        }

        return (unsigned long)NULL;
}

BPF_CALL_2(bpf_sk_storage_delete, struct bpf_map *, map, struct sock *, sk)
{
        if (!sk || !sk_fullsock(sk))
                return -EINVAL;

        if (refcount_inc_not_zero(&sk->sk_refcnt)) {
                int err;

                err = bpf_sk_storage_del(sk, map);
                sock_put(sk);
                return err;
        }

        return -ENOENT;
}

static int bpf_sk_storage_charge(struct bpf_local_storage_map *smap,
                                 void *owner, u32 size)
{
        struct sock *sk = (struct sock *)owner;

        /* same check as in sock_kmalloc() */
        if (size <= sysctl_optmem_max &&
            atomic_read(&sk->sk_omem_alloc) + size < sysctl_optmem_max) {
                atomic_add(size, &sk->sk_omem_alloc);
                return 0;
        }

        return -ENOMEM;
}

static void bpf_sk_storage_uncharge(struct bpf_local_storage_map *smap,
                                    void *owner, u32 size)
{
        struct sock *sk = owner;

        atomic_sub(size, &sk->sk_omem_alloc);
}

static struct bpf_local_storage __rcu **
bpf_sk_storage_ptr(void *owner)
{
        struct sock *sk = owner;

        return &sk->sk_bpf_storage;
}

static int sk_storage_map_btf_id;
const struct bpf_map_ops sk_storage_map_ops = {
        .map_meta_equal = bpf_map_meta_equal,
        .map_alloc_check = bpf_local_storage_map_alloc_check,
        .map_alloc = bpf_sk_storage_map_alloc,
        .map_free = bpf_sk_storage_map_free,
        .map_get_next_key = notsupp_get_next_key,
        .map_lookup_elem = bpf_fd_sk_storage_lookup_elem,
        .map_update_elem = bpf_fd_sk_storage_update_elem,
        .map_delete_elem = bpf_fd_sk_storage_delete_elem,
        .map_check_btf = bpf_local_storage_map_check_btf,
        .map_btf_name = "bpf_local_storage_map",
        .map_btf_id = &sk_storage_map_btf_id,
        .map_local_storage_charge = bpf_sk_storage_charge,
        .map_local_storage_uncharge = bpf_sk_storage_uncharge,
        .map_owner_storage_ptr = bpf_sk_storage_ptr,
};

const struct bpf_func_proto bpf_sk_storage_get_proto = {
        .func           = bpf_sk_storage_get,
        .gpl_only       = false,
        .ret_type       = RET_PTR_TO_MAP_VALUE_OR_NULL,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
        .arg3_type      = ARG_PTR_TO_MAP_VALUE_OR_NULL,
        .arg4_type      = ARG_ANYTHING,
};

const struct bpf_func_proto bpf_sk_storage_get_cg_sock_proto = {
        .func           = bpf_sk_storage_get,
        .gpl_only       = false,
        .ret_type       = RET_PTR_TO_MAP_VALUE_OR_NULL,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_PTR_TO_CTX, /* context is 'struct sock' */
        .arg3_type      = ARG_PTR_TO_MAP_VALUE_OR_NULL,
        .arg4_type      = ARG_ANYTHING,
};

const struct bpf_func_proto bpf_sk_storage_delete_proto = {
        .func           = bpf_sk_storage_delete,
        .gpl_only       = false,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
};

static bool bpf_sk_storage_tracing_allowed(const struct bpf_prog *prog)
{
        const struct btf *btf_vmlinux;
        const struct btf_type *t;
        const char *tname;
        u32 btf_id;

        if (prog->aux->dst_prog)
                return false;

        /* Ensure the tracing program is not tracing
         * any bpf_sk_storage*() function and also
         * use the bpf_sk_storage_(get|delete) helper.
         */
        switch (prog->expected_attach_type) {
        case BPF_TRACE_ITER:
        case BPF_TRACE_RAW_TP:
                /* bpf_sk_storage has no trace point */
                return true;
        case BPF_TRACE_FENTRY:
        case BPF_TRACE_FEXIT:
                btf_vmlinux = bpf_get_btf_vmlinux();
                btf_id = prog->aux->attach_btf_id;
                t = btf_type_by_id(btf_vmlinux, btf_id);
                tname = btf_name_by_offset(btf_vmlinux, t->name_off);
                return !!strncmp(tname, "bpf_sk_storage",
                                 strlen("bpf_sk_storage"));
        default:
                return false;
        }

        return false;
}

BPF_CALL_4(bpf_sk_storage_get_tracing, struct bpf_map *, map, struct sock *, sk,
           void *, value, u64, flags)
{
        if (in_irq() || in_nmi())
                return (unsigned long)NULL;

        return (unsigned long)____bpf_sk_storage_get(map, sk, value, flags);
}

BPF_CALL_2(bpf_sk_storage_delete_tracing, struct bpf_map *, map,
           struct sock *, sk)
{
        if (in_irq() || in_nmi())
                return -EPERM;

        return ____bpf_sk_storage_delete(map, sk);
}

const struct bpf_func_proto bpf_sk_storage_get_tracing_proto = {
        .func           = bpf_sk_storage_get_tracing,
        .gpl_only       = false,
        .ret_type       = RET_PTR_TO_MAP_VALUE_OR_NULL,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_PTR_TO_BTF_ID,
        .arg2_btf_id    = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
        .arg3_type      = ARG_PTR_TO_MAP_VALUE_OR_NULL,
        .arg4_type      = ARG_ANYTHING,
        .allowed        = bpf_sk_storage_tracing_allowed,
};

const struct bpf_func_proto bpf_sk_storage_delete_tracing_proto = {
        .func           = bpf_sk_storage_delete_tracing,
        .gpl_only       = false,
        .ret_type       = RET_INTEGER,
        .arg1_type      = ARG_CONST_MAP_PTR,
        .arg2_type      = ARG_PTR_TO_BTF_ID,
        .arg2_btf_id    = &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
        .allowed        = bpf_sk_storage_tracing_allowed,
};

struct bpf_sk_storage_diag {
        u32 nr_maps;
        struct bpf_map *maps[];
};

/* The reply will be like:
 * INET_DIAG_BPF_SK_STORAGES (nla_nest)
 *      SK_DIAG_BPF_STORAGE (nla_nest)
 *              SK_DIAG_BPF_STORAGE_MAP_ID (nla_put_u32)
 *              SK_DIAG_BPF_STORAGE_MAP_VALUE (nla_reserve_64bit)
 *      SK_DIAG_BPF_STORAGE (nla_nest)
 *              SK_DIAG_BPF_STORAGE_MAP_ID (nla_put_u32)
 *              SK_DIAG_BPF_STORAGE_MAP_VALUE (nla_reserve_64bit)
 *      ....
 */
static int nla_value_size(u32 value_size)
{
        /* SK_DIAG_BPF_STORAGE (nla_nest)
         *      SK_DIAG_BPF_STORAGE_MAP_ID (nla_put_u32)
         *      SK_DIAG_BPF_STORAGE_MAP_VALUE (nla_reserve_64bit)
         */
        return nla_total_size(0) + nla_total_size(sizeof(u32)) +
                nla_total_size_64bit(value_size);
}

void bpf_sk_storage_diag_free(struct bpf_sk_storage_diag *diag)
{
        u32 i;

        if (!diag)
                return;

        for (i = 0; i < diag->nr_maps; i++)
                bpf_map_put(diag->maps[i]);

        kfree(diag);
}
EXPORT_SYMBOL_GPL(bpf_sk_storage_diag_free);

static bool diag_check_dup(const struct bpf_sk_storage_diag *diag,
                           const struct bpf_map *map)
{
        u32 i;

        for (i = 0; i < diag->nr_maps; i++) {
                if (diag->maps[i] == map)
                        return true;
        }

        return false;
}

struct bpf_sk_storage_diag *
bpf_sk_storage_diag_alloc(const struct nlattr *nla_stgs)
{
        struct bpf_sk_storage_diag *diag;
        struct nlattr *nla;
        u32 nr_maps = 0;
        int rem, err;

        /* bpf_local_storage_map is currently limited to CAP_SYS_ADMIN as
         * the map_alloc_check() side also does.
         */
        if (!bpf_capable())
                return ERR_PTR(-EPERM);

        nla_for_each_nested(nla, nla_stgs, rem) {
                if (nla_type(nla) == SK_DIAG_BPF_STORAGE_REQ_MAP_FD)
                        nr_maps++;
        }

        diag = kzalloc(sizeof(*diag) + sizeof(diag->maps[0]) * nr_maps,
                       GFP_KERNEL);
        if (!diag)
                return ERR_PTR(-ENOMEM);

        nla_for_each_nested(nla, nla_stgs, rem) {
                struct bpf_map *map;
                int map_fd;

                if (nla_type(nla) != SK_DIAG_BPF_STORAGE_REQ_MAP_FD)
                        continue;

                map_fd = nla_get_u32(nla);
                map = bpf_map_get(map_fd);
                if (IS_ERR(map)) {
                        err = PTR_ERR(map);
                        goto err_free;
                }
                if (map->map_type != BPF_MAP_TYPE_SK_STORAGE) {
                        bpf_map_put(map);
                        err = -EINVAL;
                        goto err_free;
                }
                if (diag_check_dup(diag, map)) {
                        bpf_map_put(map);
                        err = -EEXIST;
                        goto err_free;
                }
                diag->maps[diag->nr_maps++] = map;
        }

        return diag;

err_free:
        bpf_sk_storage_diag_free(diag);
        return ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(bpf_sk_storage_diag_alloc);

static int diag_get(struct bpf_local_storage_data *sdata, struct sk_buff *skb)
{
        struct nlattr *nla_stg, *nla_value;
        struct bpf_local_storage_map *smap;

        /* It cannot exceed max nlattr's payload */
        BUILD_BUG_ON(U16_MAX - NLA_HDRLEN < BPF_LOCAL_STORAGE_MAX_VALUE_SIZE);

        nla_stg = nla_nest_start(skb, SK_DIAG_BPF_STORAGE);
        if (!nla_stg)
                return -EMSGSIZE;

        smap = rcu_dereference(sdata->smap);
        if (nla_put_u32(skb, SK_DIAG_BPF_STORAGE_MAP_ID, smap->map.id))
                goto errout;

        nla_value = nla_reserve_64bit(skb, SK_DIAG_BPF_STORAGE_MAP_VALUE,
                                      smap->map.value_size,
                                      SK_DIAG_BPF_STORAGE_PAD);
        if (!nla_value)
                goto errout;

        if (map_value_has_spin_lock(&smap->map))
                copy_map_value_locked(&smap->map, nla_data(nla_value),
                                      sdata->data, true);
        else
                copy_map_value(&smap->map, nla_data(nla_value), sdata->data);

        nla_nest_end(skb, nla_stg);
        return 0;

errout:
        nla_nest_cancel(skb, nla_stg);
        return -EMSGSIZE;
}

static int bpf_sk_storage_diag_put_all(struct sock *sk, struct sk_buff *skb,
                                       int stg_array_type,
                                       unsigned int *res_diag_size)
{
        /* stg_array_type (e.g. INET_DIAG_BPF_SK_STORAGES) */
        unsigned int diag_size = nla_total_size(0);
        struct bpf_local_storage *sk_storage;
        struct bpf_local_storage_elem *selem;
        struct bpf_local_storage_map *smap;
        struct nlattr *nla_stgs;
        unsigned int saved_len;
        int err = 0;

        rcu_read_lock();

        sk_storage = rcu_dereference(sk->sk_bpf_storage);
        if (!sk_storage || hlist_empty(&sk_storage->list)) {
                rcu_read_unlock();
                return 0;
        }

        nla_stgs = nla_nest_start(skb, stg_array_type);
        if (!nla_stgs)
                /* Continue to learn diag_size */
                err = -EMSGSIZE;

        saved_len = skb->len;
        hlist_for_each_entry_rcu(selem, &sk_storage->list, snode) {
                smap = rcu_dereference(SDATA(selem)->smap);
                diag_size += nla_value_size(smap->map.value_size);

                if (nla_stgs && diag_get(SDATA(selem), skb))
                        /* Continue to learn diag_size */
                        err = -EMSGSIZE;
        }

        rcu_read_unlock();

        if (nla_stgs) {
                if (saved_len == skb->len)
                        nla_nest_cancel(skb, nla_stgs);
                else
                        nla_nest_end(skb, nla_stgs);
        }

        if (diag_size == nla_total_size(0)) {
                *res_diag_size = 0;
                return 0;
        }

        *res_diag_size = diag_size;
        return err;
}

int bpf_sk_storage_diag_put(struct bpf_sk_storage_diag *diag,
                            struct sock *sk, struct sk_buff *skb,
                            int stg_array_type,
                            unsigned int *res_diag_size)
{
        /* stg_array_type (e.g. INET_DIAG_BPF_SK_STORAGES) */
        unsigned int diag_size = nla_total_size(0);
        struct bpf_local_storage *sk_storage;
        struct bpf_local_storage_data *sdata;
        struct nlattr *nla_stgs;
        unsigned int saved_len;
        int err = 0;
        u32 i;

        *res_diag_size = 0;

        /* No map has been specified.  Dump all. */
        if (!diag->nr_maps)
                return bpf_sk_storage_diag_put_all(sk, skb, stg_array_type,
                                                   res_diag_size);

        rcu_read_lock();
        sk_storage = rcu_dereference(sk->sk_bpf_storage);
        if (!sk_storage || hlist_empty(&sk_storage->list)) {
                rcu_read_unlock();
                return 0;
        }

        nla_stgs = nla_nest_start(skb, stg_array_type);
        if (!nla_stgs)
                /* Continue to learn diag_size */
                err = -EMSGSIZE;

        saved_len = skb->len;
        for (i = 0; i < diag->nr_maps; i++) {
                sdata = bpf_local_storage_lookup(sk_storage,
                                (struct bpf_local_storage_map *)diag->maps[i],
                                false);

                if (!sdata)
                        continue;

                diag_size += nla_value_size(diag->maps[i]->value_size);

                if (nla_stgs && diag_get(sdata, skb))
                        /* Continue to learn diag_size */
                        err = -EMSGSIZE;
        }
        rcu_read_unlock();

        if (nla_stgs) {
                if (saved_len == skb->len)
                        nla_nest_cancel(skb, nla_stgs);
                else
                        nla_nest_end(skb, nla_stgs);
        }

        if (diag_size == nla_total_size(0)) {
                *res_diag_size = 0;
                return 0;
        }

        *res_diag_size = diag_size;
        return err;
}
EXPORT_SYMBOL_GPL(bpf_sk_storage_diag_put);

struct bpf_iter_seq_sk_storage_map_info {
        struct bpf_map *map;
        unsigned int bucket_id;
        unsigned skip_elems;
};

static struct bpf_local_storage_elem *
bpf_sk_storage_map_seq_find_next(struct bpf_iter_seq_sk_storage_map_info *info,
                                 struct bpf_local_storage_elem *prev_selem)
        __acquires(RCU) __releases(RCU)
{
        struct bpf_local_storage *sk_storage;
        struct bpf_local_storage_elem *selem;
        u32 skip_elems = info->skip_elems;
        struct bpf_local_storage_map *smap;
        u32 bucket_id = info->bucket_id;
        u32 i, count, n_buckets;
        struct bpf_local_storage_map_bucket *b;

        smap = (struct bpf_local_storage_map *)info->map;
        n_buckets = 1U << smap->bucket_log;
        if (bucket_id >= n_buckets)
                return NULL;

        /* try to find next selem in the same bucket */
        selem = prev_selem;
        count = 0;
        while (selem) {
                selem = hlist_entry_safe(rcu_dereference(hlist_next_rcu(&selem->map_node)),
                                         struct bpf_local_storage_elem, map_node);
                if (!selem) {
                        /* not found, unlock and go to the next bucket */
                        b = &smap->buckets[bucket_id++];
                        rcu_read_unlock();
                        skip_elems = 0;
                        break;
                }
                sk_storage = rcu_dereference(selem->local_storage);
                if (sk_storage) {
                        info->skip_elems = skip_elems + count;
                        return selem;
                }
                count++;
        }

        for (i = bucket_id; i < (1U << smap->bucket_log); i++) {
                b = &smap->buckets[i];
                rcu_read_lock();
                count = 0;
                hlist_for_each_entry_rcu(selem, &b->list, map_node) {
                        sk_storage = rcu_dereference(selem->local_storage);
                        if (sk_storage && count >= skip_elems) {
                                info->bucket_id = i;
                                info->skip_elems = count;
                                return selem;
                        }
                        count++;
                }
                rcu_read_unlock();
                skip_elems = 0;
        }

        info->bucket_id = i;
        info->skip_elems = 0;
        return NULL;
}

static void *bpf_sk_storage_map_seq_start(struct seq_file *seq, loff_t *pos)
{
        struct bpf_local_storage_elem *selem;

        selem = bpf_sk_storage_map_seq_find_next(seq->private, NULL);
        if (!selem)
                return NULL;

        if (*pos == 0)
                ++*pos;
        return selem;
}

static void *bpf_sk_storage_map_seq_next(struct seq_file *seq, void *v,
                                         loff_t *pos)
{
        struct bpf_iter_seq_sk_storage_map_info *info = seq->private;

        ++*pos;
        ++info->skip_elems;
        return bpf_sk_storage_map_seq_find_next(seq->private, v);
}

struct bpf_iter__bpf_sk_storage_map {
        __bpf_md_ptr(struct bpf_iter_meta *, meta);
        __bpf_md_ptr(struct bpf_map *, map);
        __bpf_md_ptr(struct sock *, sk);
        __bpf_md_ptr(void *, value);
};

DEFINE_BPF_ITER_FUNC(bpf_sk_storage_map, struct bpf_iter_meta *meta,
                     struct bpf_map *map, struct sock *sk,
                     void *value)

static int __bpf_sk_storage_map_seq_show(struct seq_file *seq,
                                         struct bpf_local_storage_elem *selem)
{
        struct bpf_iter_seq_sk_storage_map_info *info = seq->private;
        struct bpf_iter__bpf_sk_storage_map ctx = {};
        struct bpf_local_storage *sk_storage;
        struct bpf_iter_meta meta;
        struct bpf_prog *prog;
        int ret = 0;

        meta.seq = seq;
        prog = bpf_iter_get_info(&meta, selem == NULL);
        if (prog) {
                ctx.meta = &meta;
                ctx.map = info->map;
                if (selem) {
                        sk_storage = rcu_dereference(selem->local_storage);
                        ctx.sk = sk_storage->owner;
                        ctx.value = SDATA(selem)->data;
                }
                ret = bpf_iter_run_prog(prog, &ctx);
        }

        return ret;
}

static int bpf_sk_storage_map_seq_show(struct seq_file *seq, void *v)
{
        return __bpf_sk_storage_map_seq_show(seq, v);
}

static void bpf_sk_storage_map_seq_stop(struct seq_file *seq, void *v)
        __releases(RCU)
{
        if (!v)
                (void)__bpf_sk_storage_map_seq_show(seq, v);
        else
                rcu_read_unlock();
}

static int bpf_iter_init_sk_storage_map(void *priv_data,
                                        struct bpf_iter_aux_info *aux)
{
        struct bpf_iter_seq_sk_storage_map_info *seq_info = priv_data;

        seq_info->map = aux->map;
        return 0;
}

static int bpf_iter_attach_map(struct bpf_prog *prog,
                               union bpf_iter_link_info *linfo,
                               struct bpf_iter_aux_info *aux)
{
        struct bpf_map *map;
        int err = -EINVAL;

        if (!linfo->map.map_fd)
                return -EBADF;

        map = bpf_map_get_with_uref(linfo->map.map_fd);
        if (IS_ERR(map))
                return PTR_ERR(map);

        if (map->map_type != BPF_MAP_TYPE_SK_STORAGE)
                goto put_map;

        if (prog->aux->max_rdonly_access > map->value_size) {
                err = -EACCES;
                goto put_map;
        }

        aux->map = map;
        return 0;

put_map:
        bpf_map_put_with_uref(map);
        return err;
}

static void bpf_iter_detach_map(struct bpf_iter_aux_info *aux)
{
        bpf_map_put_with_uref(aux->map);
}

static const struct seq_operations bpf_sk_storage_map_seq_ops = {
        .start  = bpf_sk_storage_map_seq_start,
        .next   = bpf_sk_storage_map_seq_next,
        .stop   = bpf_sk_storage_map_seq_stop,
        .show   = bpf_sk_storage_map_seq_show,
};

static const struct bpf_iter_seq_info iter_seq_info = {
        .seq_ops                = &bpf_sk_storage_map_seq_ops,
        .init_seq_private       = bpf_iter_init_sk_storage_map,
        .fini_seq_private       = NULL,
        .seq_priv_size          = sizeof(struct bpf_iter_seq_sk_storage_map_info),
};

static struct bpf_iter_reg bpf_sk_storage_map_reg_info = {
        .target                 = "bpf_sk_storage_map",
        .attach_target          = bpf_iter_attach_map,
        .detach_target          = bpf_iter_detach_map,
        .show_fdinfo            = bpf_iter_map_show_fdinfo,
        .fill_link_info         = bpf_iter_map_fill_link_info,
        .ctx_arg_info_size      = 2,
        .ctx_arg_info           = {
                { offsetof(struct bpf_iter__bpf_sk_storage_map, sk),
                  PTR_TO_BTF_ID_OR_NULL },
                { offsetof(struct bpf_iter__bpf_sk_storage_map, value),
                  PTR_TO_RDWR_BUF_OR_NULL },
        },
        .seq_info               = &iter_seq_info,
};

static int __init bpf_sk_storage_map_iter_init(void)
{
        bpf_sk_storage_map_reg_info.ctx_arg_info[0].btf_id =
                btf_sock_ids[BTF_SOCK_TYPE_SOCK];
        return bpf_iter_reg_target(&bpf_sk_storage_map_reg_info);
}
late_initcall(bpf_sk_storage_map_iter_init);