/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * NET          Generic infrastructure for Network protocols.
 *
 *              Definitions for request_sock
 *
 * Authors:     Arnaldo Carvalho de Melo <acme@conectiva.com.br>
 *
 *              From code originally in include/net/tcp.h
 */
#ifndef _REQUEST_SOCK_H
#define _REQUEST_SOCK_H

#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/bug.h>
#include <linux/refcount.h>

#include <net/sock.h>
#include <net/rstreason.h>

struct request_sock;
struct sk_buff;
struct dst_entry;
struct proto;

struct request_sock_ops {
        int             family;
        unsigned int    obj_size;
        struct kmem_cache       *slab;
        char            *slab_name;
        void            (*send_ack)(const struct sock *sk, struct sk_buff *skb,
                                    struct request_sock *req);
        void            (*send_reset)(const struct sock *sk,
                                      struct sk_buff *skb,
                                      enum sk_rst_reason reason);
        void            (*destructor)(struct request_sock *req);
};

struct saved_syn {
        u32 mac_hdrlen;
        u32 network_hdrlen;
        u32 tcp_hdrlen;
        u8 data[];
};

/* struct request_sock - mini sock to represent a connection request
 */
struct request_sock {
        struct sock_common              __req_common;
#define rsk_refcnt                      __req_common.skc_refcnt
#define rsk_hash                        __req_common.skc_hash
#define rsk_listener                    __req_common.skc_listener
#define rsk_window_clamp                __req_common.skc_window_clamp
#define rsk_rcv_wnd                     __req_common.skc_rcv_wnd

        struct request_sock             *dl_next;
        u16                             mss;
        u8                              num_retrans; /* number of retransmits */
        u8                              syncookie:1; /* True if
                                                      * 1) tcpopts needs to be encoded in
                                                      *    TS of SYN+ACK
                                                      * 2) ACK is validated by BPF kfunc.
                                                      */
        u8                              num_timeout:7; /* number of timeouts */
        u32                             ts_recent;
        struct timer_list               rsk_timer;
        const struct request_sock_ops   *rsk_ops;
        struct sock                     *sk;
        struct saved_syn                *saved_syn;
        u32                             secid;
        u32                             peer_secid;
        u32                             timeout;
};

static inline struct request_sock *inet_reqsk(const struct sock *sk)
{
        return (struct request_sock *)sk;
}

static inline struct sock *req_to_sk(struct request_sock *req)
{
        return (struct sock *)req;
}

/**
 * skb_steal_sock - steal a socket from an sk_buff
 * @skb: sk_buff to steal the socket from
 * @refcounted: is set to true if the socket is reference-counted
 * @prefetched: is set to true if the socket was assigned from bpf
 */
static inline struct sock *skb_steal_sock(struct sk_buff *skb,
                                          bool *refcounted, bool *prefetched)
{
        struct sock *sk = skb->sk;

        if (!sk) {
                *prefetched = false;
                *refcounted = false;
                return NULL;
        }

        *prefetched = skb_sk_is_prefetched(skb);
        if (*prefetched) {
#if IS_ENABLED(CONFIG_SYN_COOKIES)
                if (sk->sk_state == TCP_NEW_SYN_RECV && inet_reqsk(sk)->syncookie) {
                        struct request_sock *req = inet_reqsk(sk);

                        *refcounted = false;
                        sk = req->rsk_listener;
                        req->rsk_listener = NULL;
                        return sk;
                }
#endif
                *refcounted = sk_is_refcounted(sk);
        } else {
                *refcounted = true;
        }

        skb->destructor = NULL;
        skb->sk = NULL;
        return sk;
}

void __reqsk_free(struct request_sock *req);

static inline void reqsk_free(struct request_sock *req)
{
        DEBUG_NET_WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
        __reqsk_free(req);
}

static inline void reqsk_put(struct request_sock *req)
{
        if (refcount_dec_and_test(&req->rsk_refcnt))
                __reqsk_free(req);
}

/*
 * For a TCP Fast Open listener -
 *      lock - protects the access to all the reqsk, which is co-owned by
 *              the listener and the child socket.
 *      qlen - pending TFO requests (still in TCP_SYN_RECV).
 *      max_qlen - max TFO reqs allowed before TFO is disabled.
 *
 *      XXX (TFO) - ideally these fields can be made as part of "listen_sock"
 *      structure above. But there is some implementation difficulty due to
 *      listen_sock being part of request_sock_queue hence will be freed when
 *      a listener is stopped. But TFO related fields may continue to be
 *      accessed even after a listener is closed, until its sk_refcnt drops
 *      to 0 implying no more outstanding TFO reqs. One solution is to keep
 *      listen_opt around until sk_refcnt drops to 0. But there is some other
 *      complexity that needs to be resolved. E.g., a listener can be disabled
 *      temporarily through shutdown()->tcp_disconnect(), and re-enabled later.
 */
struct fastopen_queue {
        struct request_sock     *rskq_rst_head; /* Keep track of past TFO */
        struct request_sock     *rskq_rst_tail; /* requests that caused RST.
                                                 * This is part of the defense
                                                 * against spoofing attack.
                                                 */
        spinlock_t      lock;
        int             qlen;           /* # of pending (TCP_SYN_RECV) reqs */
        int             max_qlen;       /* != 0 iff TFO is currently enabled */

        struct tcp_fastopen_context __rcu *ctx; /* cipher context for cookie */
};

/** struct request_sock_queue - queue of request_socks
 *
 * @rskq_accept_head - FIFO head of established children
 * @rskq_accept_tail - FIFO tail of established children
 * @rskq_defer_accept - User waits for some data after accept()
 *
 */
struct request_sock_queue {
        spinlock_t              rskq_lock;
        u8                      rskq_defer_accept;
        u8                      synflood_warned;

        atomic_t                qlen;
        atomic_t                young;

        struct request_sock     *rskq_accept_head;
        struct request_sock     *rskq_accept_tail;
        struct fastopen_queue   fastopenq;  /* Check max_qlen != 0 to determine
                                             * if TFO is enabled.
                                             */
};

void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
                           bool reset);

static inline bool reqsk_queue_empty(const struct request_sock_queue *queue)
{
        return READ_ONCE(queue->rskq_accept_head) == NULL;
}

static inline struct request_sock *reqsk_queue_remove(struct request_sock_queue *queue,
                                                      struct sock *parent)
{
        struct request_sock *req;

        spin_lock_bh(&queue->rskq_lock);
        req = queue->rskq_accept_head;
        if (req) {
                sk_acceptq_removed(parent);
                WRITE_ONCE(queue->rskq_accept_head, req->dl_next);
                if (queue->rskq_accept_head == NULL)
                        queue->rskq_accept_tail = NULL;
        }
        spin_unlock_bh(&queue->rskq_lock);
        return req;
}

static inline void reqsk_queue_removed(struct request_sock_queue *queue,
                                       const struct request_sock *req)
{
        if (req->num_timeout == 0)
                atomic_dec(&queue->young);
        atomic_dec(&queue->qlen);
}

static inline void reqsk_queue_added(struct request_sock_queue *queue)
{
        atomic_inc(&queue->young);
        atomic_inc(&queue->qlen);
}

static inline int reqsk_queue_len(const struct request_sock_queue *queue)
{
        return atomic_read(&queue->qlen);
}

static inline int reqsk_queue_len_young(const struct request_sock_queue *queue)
{
        return atomic_read(&queue->young);
}

/* RFC 7323 2.3 Using the Window Scale Option
 *  The window field (SEG.WND) of every outgoing segment, with the
 *  exception of <SYN> segments, MUST be right-shifted by
 *  Rcv.Wind.Shift bits.
 *
 * This means the SEG.WND carried in SYNACK can not exceed 65535.
 * We use this property to harden TCP stack while in NEW_SYN_RECV state.
 */
static inline u32 tcp_synack_window(const struct request_sock *req)
{
        return min(req->rsk_rcv_wnd, 65535U);
}
#endif /* _REQUEST_SOCK_H */