// SPDX-License-Identifier: GPL-2.0-only
/*
 * Pluggable TCP upper layer protocol support.
 *
 * Copyright (c) 2016-2017, Mellanox Technologies. All rights reserved.
 * Copyright (c) 2016-2017, Dave Watson <davejwatson@fb.com>. All rights reserved.
 *
 */

#include <linux/module.h>
#include <linux/mm.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/gfp.h>
#include <net/tcp.h>

static DEFINE_SPINLOCK(tcp_ulp_list_lock);
static LIST_HEAD(tcp_ulp_list);

/* Simple linear search, don't expect many entries! */
static struct tcp_ulp_ops *tcp_ulp_find(const char *name)
{
        struct tcp_ulp_ops *e;

        list_for_each_entry_rcu(e, &tcp_ulp_list, list,
                                lockdep_is_held(&tcp_ulp_list_lock)) {
                if (strcmp(e->name, name) == 0)
                        return e;
        }

        return NULL;
}

static const struct tcp_ulp_ops *__tcp_ulp_find_autoload(const char *name)
{
        const struct tcp_ulp_ops *ulp = NULL;

        rcu_read_lock();
        ulp = tcp_ulp_find(name);

#ifdef CONFIG_MODULES
        if (!ulp && capable(CAP_NET_ADMIN)) {
                rcu_read_unlock();
                request_module("tcp-ulp-%s", name);
                rcu_read_lock();
                ulp = tcp_ulp_find(name);
        }
#endif
        if (!ulp || !try_module_get(ulp->owner))
                ulp = NULL;

        rcu_read_unlock();
        return ulp;
}

/* Attach new upper layer protocol to the list
 * of available protocols.
 */
int tcp_register_ulp(struct tcp_ulp_ops *ulp)
{
        int ret = 0;

        spin_lock(&tcp_ulp_list_lock);
        if (tcp_ulp_find(ulp->name))
                ret = -EEXIST;
        else
                list_add_tail_rcu(&ulp->list, &tcp_ulp_list);
        spin_unlock(&tcp_ulp_list_lock);

        return ret;
}
EXPORT_SYMBOL_GPL(tcp_register_ulp);

void tcp_unregister_ulp(struct tcp_ulp_ops *ulp)
{
        spin_lock(&tcp_ulp_list_lock);
        list_del_rcu(&ulp->list);
        spin_unlock(&tcp_ulp_list_lock);

        synchronize_rcu();
}
EXPORT_SYMBOL_GPL(tcp_unregister_ulp);

/* Build string with list of available upper layer protocl values */
void tcp_get_available_ulp(char *buf, size_t maxlen)
{
        struct tcp_ulp_ops *ulp_ops;
        size_t offs = 0;

        *buf = '\0';
        rcu_read_lock();
        list_for_each_entry_rcu(ulp_ops, &tcp_ulp_list, list) {
                offs += snprintf(buf + offs, maxlen - offs,
                                 "%s%s",
                                 offs == 0 ? "" : " ", ulp_ops->name);

                if (WARN_ON_ONCE(offs >= maxlen))
                        break;
        }
        rcu_read_unlock();
}

void tcp_update_ulp(struct sock *sk, struct proto *proto,
                    void (*write_space)(struct sock *sk))
{
        struct inet_connection_sock *icsk = inet_csk(sk);

        if (icsk->icsk_ulp_ops->update)
                icsk->icsk_ulp_ops->update(sk, proto, write_space);
}

void tcp_cleanup_ulp(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);

        /* No sock_owned_by_me() check here as at the time the
         * stack calls this function, the socket is dead and
         * about to be destroyed.
         */
        if (!icsk->icsk_ulp_ops)
                return;

        if (icsk->icsk_ulp_ops->release)
                icsk->icsk_ulp_ops->release(sk);
        module_put(icsk->icsk_ulp_ops->owner);

        icsk->icsk_ulp_ops = NULL;
}

static int __tcp_set_ulp(struct sock *sk, const struct tcp_ulp_ops *ulp_ops)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        int err;

        err = -EEXIST;
        if (icsk->icsk_ulp_ops)
                goto out_err;

        if (sk->sk_socket)
                clear_bit(SOCK_SUPPORT_ZC, &sk->sk_socket->flags);

        err = -ENOTCONN;
        if (!ulp_ops->clone && sk->sk_state == TCP_LISTEN)
                goto out_err;

        err = ulp_ops->init(sk);
        if (err)
                goto out_err;

        icsk->icsk_ulp_ops = ulp_ops;
        return 0;
out_err:
        module_put(ulp_ops->owner);
        return err;
}

int tcp_set_ulp(struct sock *sk, const char *name)
{
        const struct tcp_ulp_ops *ulp_ops;

        sock_owned_by_me(sk);

        ulp_ops = __tcp_ulp_find_autoload(name);
        if (!ulp_ops)
                return -ENOENT;

        return __tcp_set_ulp(sk, ulp_ops);
}