// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2018 Facebook
 */
#include <linux/bpf.h>
#include <linux/err.h>
#include <linux/sock_diag.h>
#include <net/sock_reuseport.h>

struct reuseport_array {
        struct bpf_map map;
        struct sock __rcu *ptrs[];
};

static struct reuseport_array *reuseport_array(struct bpf_map *map)
{
        return (struct reuseport_array *)map;
}

/* The caller must hold the reuseport_lock */
void bpf_sk_reuseport_detach(struct sock *sk)
{
        struct sock __rcu **socks;

        write_lock_bh(&sk->sk_callback_lock);
        socks = sk->sk_user_data;
        if (socks) {
                WRITE_ONCE(sk->sk_user_data, NULL);
                /*
                 * Do not move this NULL assignment outside of
                 * sk->sk_callback_lock because there is
                 * a race with reuseport_array_free()
                 * which does not hold the reuseport_lock.
                 */
                RCU_INIT_POINTER(*socks, NULL);
        }
        write_unlock_bh(&sk->sk_callback_lock);
}

static int reuseport_array_alloc_check(union bpf_attr *attr)
{
        if (attr->value_size != sizeof(u32) &&
            attr->value_size != sizeof(u64))
                return -EINVAL;

        return array_map_alloc_check(attr);
}

static void *reuseport_array_lookup_elem(struct bpf_map *map, void *key)
{
        struct reuseport_array *array = reuseport_array(map);
        u32 index = *(u32 *)key;

        if (unlikely(index >= array->map.max_entries))
                return NULL;

        return rcu_dereference(array->ptrs[index]);
}

/* Called from syscall only */
static int reuseport_array_delete_elem(struct bpf_map *map, void *key)
{
        struct reuseport_array *array = reuseport_array(map);
        u32 index = *(u32 *)key;
        struct sock *sk;
        int err;

        if (index >= map->max_entries)
                return -E2BIG;

        if (!rcu_access_pointer(array->ptrs[index]))
                return -ENOENT;

        spin_lock_bh(&reuseport_lock);

        sk = rcu_dereference_protected(array->ptrs[index],
                                       lockdep_is_held(&reuseport_lock));
        if (sk) {
                write_lock_bh(&sk->sk_callback_lock);
                WRITE_ONCE(sk->sk_user_data, NULL);
                RCU_INIT_POINTER(array->ptrs[index], NULL);
                write_unlock_bh(&sk->sk_callback_lock);
                err = 0;
        } else {
                err = -ENOENT;
        }

        spin_unlock_bh(&reuseport_lock);

        return err;
}

static void reuseport_array_free(struct bpf_map *map)
{
        struct reuseport_array *array = reuseport_array(map);
        struct sock *sk;
        u32 i;

        synchronize_rcu();

        /*
         * ops->map_*_elem() will not be able to access this
         * array now. Hence, this function only races with
         * bpf_sk_reuseport_detach() which was triggerred by
         * close() or disconnect().
         *
         * This function and bpf_sk_reuseport_detach() are
         * both removing sk from "array".  Who removes it
         * first does not matter.
         *
         * The only concern here is bpf_sk_reuseport_detach()
         * may access "array" which is being freed here.
         * bpf_sk_reuseport_detach() access this "array"
         * through sk->sk_user_data _and_ with sk->sk_callback_lock
         * held which is enough because this "array" is not freed
         * until all sk->sk_user_data has stopped referencing this "array".
         *
         * Hence, due to the above, taking "reuseport_lock" is not
         * needed here.
         */

        /*
         * Since reuseport_lock is not taken, sk is accessed under
         * rcu_read_lock()
         */
        rcu_read_lock();
        for (i = 0; i < map->max_entries; i++) {
                sk = rcu_dereference(array->ptrs[i]);
                if (sk) {
                        write_lock_bh(&sk->sk_callback_lock);
                        /*
                         * No need for WRITE_ONCE(). At this point,
                         * no one is reading it without taking the
                         * sk->sk_callback_lock.
                         */
                        sk->sk_user_data = NULL;
                        write_unlock_bh(&sk->sk_callback_lock);
                        RCU_INIT_POINTER(array->ptrs[i], NULL);
                }
        }
        rcu_read_unlock();

        /*
         * Once reaching here, all sk->sk_user_data is not
         * referenceing this "array".  "array" can be freed now.
         */
        bpf_map_area_free(array);
}

static struct bpf_map *reuseport_array_alloc(union bpf_attr *attr)
{
        int err, numa_node = bpf_map_attr_numa_node(attr);
        struct reuseport_array *array;
        u64 cost, array_size;

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

        array_size = sizeof(*array);
        array_size += (u64)attr->max_entries * sizeof(struct sock *);

        /* make sure there is no u32 overflow later in round_up() */
        cost = array_size;
        if (cost >= U32_MAX - PAGE_SIZE)
                return ERR_PTR(-ENOMEM);
        cost = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

        err = bpf_map_precharge_memlock(cost);
        if (err)
                return ERR_PTR(err);

        /* allocate all map elements and zero-initialize them */
        array = bpf_map_area_alloc(array_size, numa_node);
        if (!array)
                return ERR_PTR(-ENOMEM);

        /* copy mandatory map attributes */
        bpf_map_init_from_attr(&array->map, attr);
        array->map.pages = cost;

        return &array->map;
}

int bpf_fd_reuseport_array_lookup_elem(struct bpf_map *map, void *key,
                                       void *value)
{
        struct sock *sk;
        int err;

        if (map->value_size != sizeof(u64))
                return -ENOSPC;

        rcu_read_lock();
        sk = reuseport_array_lookup_elem(map, key);
        if (sk) {
                *(u64 *)value = sock_gen_cookie(sk);
                err = 0;
        } else {
                err = -ENOENT;
        }
        rcu_read_unlock();

        return err;
}

static int
reuseport_array_update_check(const struct reuseport_array *array,
                             const struct sock *nsk,
                             const struct sock *osk,
                             const struct sock_reuseport *nsk_reuse,
                             u32 map_flags)
{
        if (osk && map_flags == BPF_NOEXIST)
                return -EEXIST;

        if (!osk && map_flags == BPF_EXIST)
                return -ENOENT;

        if (nsk->sk_protocol != IPPROTO_UDP && nsk->sk_protocol != IPPROTO_TCP)
                return -ENOTSUPP;

        if (nsk->sk_family != AF_INET && nsk->sk_family != AF_INET6)
                return -ENOTSUPP;

        if (nsk->sk_type != SOCK_STREAM && nsk->sk_type != SOCK_DGRAM)
                return -ENOTSUPP;

        /*
         * sk must be hashed (i.e. listening in the TCP case or binded
         * in the UDP case) and
         * it must also be a SO_REUSEPORT sk (i.e. reuse cannot be NULL).
         *
         * Also, sk will be used in bpf helper that is protected by
         * rcu_read_lock().
         */
        if (!sock_flag(nsk, SOCK_RCU_FREE) || !sk_hashed(nsk) || !nsk_reuse)
                return -EINVAL;

        /* READ_ONCE because the sk->sk_callback_lock may not be held here */
        if (READ_ONCE(nsk->sk_user_data))
                return -EBUSY;

        return 0;
}

/*
 * Called from syscall only.
 * The "nsk" in the fd refcnt.
 * The "osk" and "reuse" are protected by reuseport_lock.
 */
int bpf_fd_reuseport_array_update_elem(struct bpf_map *map, void *key,
                                       void *value, u64 map_flags)
{
        struct reuseport_array *array = reuseport_array(map);
        struct sock *free_osk = NULL, *osk, *nsk;
        struct sock_reuseport *reuse;
        u32 index = *(u32 *)key;
        struct socket *socket;
        int err, fd;

        if (map_flags > BPF_EXIST)
                return -EINVAL;

        if (index >= map->max_entries)
                return -E2BIG;

        if (map->value_size == sizeof(u64)) {
                u64 fd64 = *(u64 *)value;

                if (fd64 > S32_MAX)
                        return -EINVAL;
                fd = fd64;
        } else {
                fd = *(int *)value;
        }

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

        nsk = socket->sk;
        if (!nsk) {
                err = -EINVAL;
                goto put_file;
        }

        /* Quick checks before taking reuseport_lock */
        err = reuseport_array_update_check(array, nsk,
                                           rcu_access_pointer(array->ptrs[index]),
                                           rcu_access_pointer(nsk->sk_reuseport_cb),
                                           map_flags);
        if (err)
                goto put_file;

        spin_lock_bh(&reuseport_lock);
        /*
         * Some of the checks only need reuseport_lock
         * but it is done under sk_callback_lock also
         * for simplicity reason.
         */
        write_lock_bh(&nsk->sk_callback_lock);

        osk = rcu_dereference_protected(array->ptrs[index],
                                        lockdep_is_held(&reuseport_lock));
        reuse = rcu_dereference_protected(nsk->sk_reuseport_cb,
                                          lockdep_is_held(&reuseport_lock));
        err = reuseport_array_update_check(array, nsk, osk, reuse, map_flags);
        if (err)
                goto put_file_unlock;

        /* Ensure reuse->reuseport_id is set */
        err = reuseport_get_id(reuse);
        if (err < 0)
                goto put_file_unlock;

        WRITE_ONCE(nsk->sk_user_data, &array->ptrs[index]);
        rcu_assign_pointer(array->ptrs[index], nsk);
        free_osk = osk;
        err = 0;

put_file_unlock:
        write_unlock_bh(&nsk->sk_callback_lock);

        if (free_osk) {
                write_lock_bh(&free_osk->sk_callback_lock);
                WRITE_ONCE(free_osk->sk_user_data, NULL);
                write_unlock_bh(&free_osk->sk_callback_lock);
        }

        spin_unlock_bh(&reuseport_lock);
put_file:
        fput(socket->file);
        return err;
}

/* Called from syscall */
static int reuseport_array_get_next_key(struct bpf_map *map, void *key,
                                        void *next_key)
{
        struct reuseport_array *array = reuseport_array(map);
        u32 index = key ? *(u32 *)key : U32_MAX;
        u32 *next = (u32 *)next_key;

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

        if (index == array->map.max_entries - 1)
                return -ENOENT;

        *next = index + 1;
        return 0;
}

const struct bpf_map_ops reuseport_array_ops = {
        .map_alloc_check = reuseport_array_alloc_check,
        .map_alloc = reuseport_array_alloc,
        .map_free = reuseport_array_free,
        .map_lookup_elem = reuseport_array_lookup_elem,
        .map_get_next_key = reuseport_array_get_next_key,
        .map_delete_elem = reuseport_array_delete_elem,
};