// 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_ids.h>
#include <linux/bpf_local_storage.h>
#include <net/sock.h>
#include <uapi/linux/sock_diag.h>
#include <uapi/linux/btf.h>

#define BPF_LOCAL_STORAGE_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_CLONE)

static struct bpf_local_storage_map_bucket *
select_bucket(struct bpf_local_storage_map *smap,
              struct bpf_local_storage_elem *selem)
{
        return &smap->buckets[hash_ptr(selem, smap->bucket_log)];
}

static int mem_charge(struct bpf_local_storage_map *smap, void *owner, u32 size)
{
        struct bpf_map *map = &smap->map;

        if (!map->ops->map_local_storage_charge)
                return 0;

        return map->ops->map_local_storage_charge(smap, owner, size);
}

static void mem_uncharge(struct bpf_local_storage_map *smap, void *owner,
                         u32 size)
{
        struct bpf_map *map = &smap->map;

        if (map->ops->map_local_storage_uncharge)
                map->ops->map_local_storage_uncharge(smap, owner, size);
}

static struct bpf_local_storage __rcu **
owner_storage(struct bpf_local_storage_map *smap, void *owner)
{
        struct bpf_map *map = &smap->map;

        return map->ops->map_owner_storage_ptr(owner);
}

static bool selem_linked_to_storage(const struct bpf_local_storage_elem *selem)
{
        return !hlist_unhashed(&selem->snode);
}

static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
{
        return !hlist_unhashed(&selem->map_node);
}

struct bpf_local_storage_elem *
bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
                void *value, bool charge_mem)
{
        struct bpf_local_storage_elem *selem;

        if (charge_mem && mem_charge(smap, owner, smap->elem_size))
                return NULL;

        selem = bpf_map_kzalloc(&smap->map, smap->elem_size,
                                GFP_ATOMIC | __GFP_NOWARN);
        if (selem) {
                if (value)
                        memcpy(SDATA(selem)->data, value, smap->map.value_size);
                return selem;
        }

        if (charge_mem)
                mem_uncharge(smap, owner, smap->elem_size);

        return NULL;
}

/* local_storage->lock must be held and selem->local_storage == local_storage.
 * The caller must ensure selem->smap is still valid to be
 * dereferenced for its smap->elem_size and smap->cache_idx.
 */
bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
                                     struct bpf_local_storage_elem *selem,
                                     bool uncharge_mem)
{
        struct bpf_local_storage_map *smap;
        bool free_local_storage;
        void *owner;

        smap = rcu_dereference(SDATA(selem)->smap);
        owner = local_storage->owner;

        /* All uncharging on the owner must be done first.
         * The owner may be freed once the last selem is unlinked
         * from local_storage.
         */
        if (uncharge_mem)
                mem_uncharge(smap, owner, smap->elem_size);

        free_local_storage = hlist_is_singular_node(&selem->snode,
                                                    &local_storage->list);
        if (free_local_storage) {
                mem_uncharge(smap, owner, sizeof(struct bpf_local_storage));
                local_storage->owner = NULL;

                /* After this RCU_INIT, owner may be freed and cannot be used */
                RCU_INIT_POINTER(*owner_storage(smap, owner), NULL);

                /* local_storage is not freed now.  local_storage->lock is
                 * still held and raw_spin_unlock_bh(&local_storage->lock)
                 * will be done by the caller.
                 *
                 * Although the unlock will be done under
                 * rcu_read_lock(),  it is more intutivie to
                 * read if kfree_rcu(local_storage, rcu) is done
                 * after the raw_spin_unlock_bh(&local_storage->lock).
                 *
                 * Hence, a "bool free_local_storage" is returned
                 * to the caller which then calls the kfree_rcu()
                 * after unlock.
                 */
        }
        hlist_del_init_rcu(&selem->snode);
        if (rcu_access_pointer(local_storage->cache[smap->cache_idx]) ==
            SDATA(selem))
                RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);

        kfree_rcu(selem, rcu);

        return free_local_storage;
}

static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
{
        struct bpf_local_storage *local_storage;
        bool free_local_storage = false;

        if (unlikely(!selem_linked_to_storage(selem)))
                /* selem has already been unlinked from sk */
                return;

        local_storage = rcu_dereference(selem->local_storage);
        raw_spin_lock_bh(&local_storage->lock);
        if (likely(selem_linked_to_storage(selem)))
                free_local_storage = bpf_selem_unlink_storage_nolock(
                        local_storage, selem, true);
        raw_spin_unlock_bh(&local_storage->lock);

        if (free_local_storage)
                kfree_rcu(local_storage, rcu);
}

void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
                                   struct bpf_local_storage_elem *selem)
{
        RCU_INIT_POINTER(selem->local_storage, local_storage);
        hlist_add_head_rcu(&selem->snode, &local_storage->list);
}

void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
{
        struct bpf_local_storage_map *smap;
        struct bpf_local_storage_map_bucket *b;

        if (unlikely(!selem_linked_to_map(selem)))
                /* selem has already be unlinked from smap */
                return;

        smap = rcu_dereference(SDATA(selem)->smap);
        b = select_bucket(smap, selem);
        raw_spin_lock_bh(&b->lock);
        if (likely(selem_linked_to_map(selem)))
                hlist_del_init_rcu(&selem->map_node);
        raw_spin_unlock_bh(&b->lock);
}

void bpf_selem_link_map(struct bpf_local_storage_map *smap,
                        struct bpf_local_storage_elem *selem)
{
        struct bpf_local_storage_map_bucket *b = select_bucket(smap, selem);

        raw_spin_lock_bh(&b->lock);
        RCU_INIT_POINTER(SDATA(selem)->smap, smap);
        hlist_add_head_rcu(&selem->map_node, &b->list);
        raw_spin_unlock_bh(&b->lock);
}

void bpf_selem_unlink(struct bpf_local_storage_elem *selem)
{
        /* Always unlink from map before unlinking from local_storage
         * because selem will be freed after successfully unlinked from
         * the local_storage.
         */
        bpf_selem_unlink_map(selem);
        __bpf_selem_unlink_storage(selem);
}

struct bpf_local_storage_data *
bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
                         struct bpf_local_storage_map *smap,
                         bool cacheit_lockit)
{
        struct bpf_local_storage_data *sdata;
        struct bpf_local_storage_elem *selem;

        /* Fast path (cache hit) */
        sdata = rcu_dereference(local_storage->cache[smap->cache_idx]);
        if (sdata && rcu_access_pointer(sdata->smap) == smap)
                return sdata;

        /* Slow path (cache miss) */
        hlist_for_each_entry_rcu(selem, &local_storage->list, snode)
                if (rcu_access_pointer(SDATA(selem)->smap) == smap)
                        break;

        if (!selem)
                return NULL;

        sdata = SDATA(selem);
        if (cacheit_lockit) {
                /* spinlock is needed to avoid racing with the
                 * parallel delete.  Otherwise, publishing an already
                 * deleted sdata to the cache will become a use-after-free
                 * problem in the next bpf_local_storage_lookup().
                 */
                raw_spin_lock_bh(&local_storage->lock);
                if (selem_linked_to_storage(selem))
                        rcu_assign_pointer(local_storage->cache[smap->cache_idx],
                                           sdata);
                raw_spin_unlock_bh(&local_storage->lock);
        }

        return sdata;
}

static int check_flags(const struct bpf_local_storage_data *old_sdata,
                       u64 map_flags)
{
        if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
                /* elem already exists */
                return -EEXIST;

        if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
                /* elem doesn't exist, cannot update it */
                return -ENOENT;

        return 0;
}

int bpf_local_storage_alloc(void *owner,
                            struct bpf_local_storage_map *smap,
                            struct bpf_local_storage_elem *first_selem)
{
        struct bpf_local_storage *prev_storage, *storage;
        struct bpf_local_storage **owner_storage_ptr;
        int err;

        err = mem_charge(smap, owner, sizeof(*storage));
        if (err)
                return err;

        storage = bpf_map_kzalloc(&smap->map, sizeof(*storage),
                                  GFP_ATOMIC | __GFP_NOWARN);
        if (!storage) {
                err = -ENOMEM;
                goto uncharge;
        }

        INIT_HLIST_HEAD(&storage->list);
        raw_spin_lock_init(&storage->lock);
        storage->owner = owner;

        bpf_selem_link_storage_nolock(storage, first_selem);
        bpf_selem_link_map(smap, first_selem);

        owner_storage_ptr =
                (struct bpf_local_storage **)owner_storage(smap, owner);
        /* Publish storage to the owner.
         * Instead of using any lock of the kernel object (i.e. owner),
         * cmpxchg will work with any kernel object regardless what
         * the running context is, bh, irq...etc.
         *
         * From now on, the owner->storage pointer (e.g. sk->sk_bpf_storage)
         * is protected by the storage->lock.  Hence, when freeing
         * the owner->storage, the storage->lock must be held before
         * setting owner->storage ptr to NULL.
         */
        prev_storage = cmpxchg(owner_storage_ptr, NULL, storage);
        if (unlikely(prev_storage)) {
                bpf_selem_unlink_map(first_selem);
                err = -EAGAIN;
                goto uncharge;

                /* Note that even first_selem was linked to smap's
                 * bucket->list, first_selem can be freed immediately
                 * (instead of kfree_rcu) because
                 * bpf_local_storage_map_free() does a
                 * synchronize_rcu() before walking the bucket->list.
                 * Hence, no one is accessing selem from the
                 * bucket->list under rcu_read_lock().
                 */
        }

        return 0;

uncharge:
        kfree(storage);
        mem_uncharge(smap, owner, sizeof(*storage));
        return err;
}

/* sk cannot be going away because it is linking new elem
 * to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
 * Otherwise, it will become a leak (and other memory issues
 * during map destruction).
 */
struct bpf_local_storage_data *
bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
                         void *value, u64 map_flags)
{
        struct bpf_local_storage_data *old_sdata = NULL;
        struct bpf_local_storage_elem *selem;
        struct bpf_local_storage *local_storage;
        int err;

        /* BPF_EXIST and BPF_NOEXIST cannot be both set */
        if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
            /* BPF_F_LOCK can only be used in a value with spin_lock */
            unlikely((map_flags & BPF_F_LOCK) &&
                     !map_value_has_spin_lock(&smap->map)))
                return ERR_PTR(-EINVAL);

        local_storage = rcu_dereference(*owner_storage(smap, owner));
        if (!local_storage || hlist_empty(&local_storage->list)) {
                /* Very first elem for the owner */
                err = check_flags(NULL, map_flags);
                if (err)
                        return ERR_PTR(err);

                selem = bpf_selem_alloc(smap, owner, value, true);
                if (!selem)
                        return ERR_PTR(-ENOMEM);

                err = bpf_local_storage_alloc(owner, smap, selem);
                if (err) {
                        kfree(selem);
                        mem_uncharge(smap, owner, smap->elem_size);
                        return ERR_PTR(err);
                }

                return SDATA(selem);
        }

        if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
                /* Hoping to find an old_sdata to do inline update
                 * such that it can avoid taking the local_storage->lock
                 * and changing the lists.
                 */
                old_sdata =
                        bpf_local_storage_lookup(local_storage, smap, false);
                err = check_flags(old_sdata, map_flags);
                if (err)
                        return ERR_PTR(err);
                if (old_sdata && selem_linked_to_storage(SELEM(old_sdata))) {
                        copy_map_value_locked(&smap->map, old_sdata->data,
                                              value, false);
                        return old_sdata;
                }
        }

        raw_spin_lock_bh(&local_storage->lock);

        /* Recheck local_storage->list under local_storage->lock */
        if (unlikely(hlist_empty(&local_storage->list))) {
                /* A parallel del is happening and local_storage is going
                 * away.  It has just been checked before, so very
                 * unlikely.  Return instead of retry to keep things
                 * simple.
                 */
                err = -EAGAIN;
                goto unlock_err;
        }

        old_sdata = bpf_local_storage_lookup(local_storage, smap, false);
        err = check_flags(old_sdata, map_flags);
        if (err)
                goto unlock_err;

        if (old_sdata && (map_flags & BPF_F_LOCK)) {
                copy_map_value_locked(&smap->map, old_sdata->data, value,
                                      false);
                selem = SELEM(old_sdata);
                goto unlock;
        }

        /* local_storage->lock is held.  Hence, we are sure
         * we can unlink and uncharge the old_sdata successfully
         * later.  Hence, instead of charging the new selem now
         * and then uncharge the old selem later (which may cause
         * a potential but unnecessary charge failure),  avoid taking
         * a charge at all here (the "!old_sdata" check) and the
         * old_sdata will not be uncharged later during
         * bpf_selem_unlink_storage_nolock().
         */
        selem = bpf_selem_alloc(smap, owner, value, !old_sdata);
        if (!selem) {
                err = -ENOMEM;
                goto unlock_err;
        }

        /* First, link the new selem to the map */
        bpf_selem_link_map(smap, selem);

        /* Second, link (and publish) the new selem to local_storage */
        bpf_selem_link_storage_nolock(local_storage, selem);

        /* Third, remove old selem, SELEM(old_sdata) */
        if (old_sdata) {
                bpf_selem_unlink_map(SELEM(old_sdata));
                bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
                                                false);
        }

unlock:
        raw_spin_unlock_bh(&local_storage->lock);
        return SDATA(selem);

unlock_err:
        raw_spin_unlock_bh(&local_storage->lock);
        return ERR_PTR(err);
}

u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
{
        u64 min_usage = U64_MAX;
        u16 i, res = 0;

        spin_lock(&cache->idx_lock);

        for (i = 0; i < BPF_LOCAL_STORAGE_CACHE_SIZE; i++) {
                if (cache->idx_usage_counts[i] < min_usage) {
                        min_usage = cache->idx_usage_counts[i];
                        res = i;

                        /* Found a free cache_idx */
                        if (!min_usage)
                                break;
                }
        }
        cache->idx_usage_counts[res]++;

        spin_unlock(&cache->idx_lock);

        return res;
}

void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
                                      u16 idx)
{
        spin_lock(&cache->idx_lock);
        cache->idx_usage_counts[idx]--;
        spin_unlock(&cache->idx_lock);
}

void bpf_local_storage_map_free(struct bpf_local_storage_map *smap)
{
        struct bpf_local_storage_elem *selem;
        struct bpf_local_storage_map_bucket *b;
        unsigned int i;

        /* Note that this map might be concurrently cloned from
         * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
         * RCU read section to finish before proceeding. New RCU
         * read sections should be prevented via bpf_map_inc_not_zero.
         */
        synchronize_rcu();

        /* bpf prog and the userspace can no longer access this map
         * now.  No new selem (of this map) can be added
         * to the owner->storage or to the map bucket's list.
         *
         * The elem of this map can be cleaned up here
         * or when the storage is freed e.g.
         * by bpf_sk_storage_free() during __sk_destruct().
         */
        for (i = 0; i < (1U << smap->bucket_log); i++) {
                b = &smap->buckets[i];

                rcu_read_lock();
                /* No one is adding to b->list now */
                while ((selem = hlist_entry_safe(
                                rcu_dereference_raw(hlist_first_rcu(&b->list)),
                                struct bpf_local_storage_elem, map_node))) {
                        bpf_selem_unlink(selem);
                        cond_resched_rcu();
                }
                rcu_read_unlock();
        }

        /* While freeing the storage we may still need to access the map.
         *
         * e.g. when bpf_sk_storage_free() has unlinked selem from the map
         * which then made the above while((selem = ...)) loop
         * exit immediately.
         *
         * However, while freeing the storage one still needs to access the
         * smap->elem_size to do the uncharging in
         * bpf_selem_unlink_storage_nolock().
         *
         * Hence, wait another rcu grace period for the storage to be freed.
         */
        synchronize_rcu();

        kvfree(smap->buckets);
        kfree(smap);
}

int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
{
        if (attr->map_flags & ~BPF_LOCAL_STORAGE_CREATE_FLAG_MASK ||
            !(attr->map_flags & BPF_F_NO_PREALLOC) ||
            attr->max_entries ||
            attr->key_size != sizeof(int) || !attr->value_size ||
            /* Enforce BTF for userspace sk dumping */
            !attr->btf_key_type_id || !attr->btf_value_type_id)
                return -EINVAL;

        if (!bpf_capable())
                return -EPERM;

        if (attr->value_size > BPF_LOCAL_STORAGE_MAX_VALUE_SIZE)
                return -E2BIG;

        return 0;
}

struct bpf_local_storage_map *bpf_local_storage_map_alloc(union bpf_attr *attr)
{
        struct bpf_local_storage_map *smap;
        unsigned int i;
        u32 nbuckets;

        smap = kzalloc(sizeof(*smap), GFP_USER | __GFP_NOWARN | __GFP_ACCOUNT);
        if (!smap)
                return ERR_PTR(-ENOMEM);
        bpf_map_init_from_attr(&smap->map, attr);

        nbuckets = roundup_pow_of_two(num_possible_cpus());
        /* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
        nbuckets = max_t(u32, 2, nbuckets);
        smap->bucket_log = ilog2(nbuckets);

        smap->buckets = kvcalloc(sizeof(*smap->buckets), nbuckets,
                                 GFP_USER | __GFP_NOWARN | __GFP_ACCOUNT);
        if (!smap->buckets) {
                kfree(smap);
                return ERR_PTR(-ENOMEM);
        }

        for (i = 0; i < nbuckets; i++) {
                INIT_HLIST_HEAD(&smap->buckets[i].list);
                raw_spin_lock_init(&smap->buckets[i].lock);
        }

        smap->elem_size =
                sizeof(struct bpf_local_storage_elem) + attr->value_size;

        return smap;
}

int bpf_local_storage_map_check_btf(const struct bpf_map *map,
                                    const struct btf *btf,
                                    const struct btf_type *key_type,
                                    const struct btf_type *value_type)
{
        u32 int_data;

        if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
                return -EINVAL;

        int_data = *(u32 *)(key_type + 1);
        if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
                return -EINVAL;

        return 0;
}