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/* SPDX-License-Identifier: GPL-2.0-or-later */
* NET Generic infrastructure for Network protocols.
* Definitions for request_sock
* Authors: Arnaldo Carvalho de Melo <>
* From code originally in include/net/tcp.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>
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;
int (*rtx_syn_ack)(const struct sock *sk,
struct request_sock *req);
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);
void (*destructor)(struct request_sock *req);
void (*syn_ack_timeout)(const struct request_sock *req);
int inet_rtx_syn_ack(const struct sock *parent, struct request_sock *req);
/* 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 cookie_ts:1; /* syncookie: encode tcpopts in timestamp */
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;
u32 *saved_syn;
u32 secid;
u32 peer_secid;
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;
static inline struct request_sock *
reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener,
bool attach_listener)
struct request_sock *req;
req = kmem_cache_alloc(ops->slab, GFP_ATOMIC | __GFP_NOWARN);
if (!req)
return NULL;
req->rsk_listener = NULL;
if (attach_listener) {
if (unlikely(!refcount_inc_not_zero(&sk_listener->sk_refcnt))) {
kmem_cache_free(ops->slab, req);
return NULL;
req->rsk_listener = sk_listener;
req->rsk_ops = ops;
req_to_sk(req)->sk_prot = sk_listener->sk_prot;
req->saved_syn = NULL;
req->num_timeout = 0;
req->num_retrans = 0;
req->sk = NULL;
refcount_set(&req->rsk_refcnt, 0);
return req;
static inline void __reqsk_free(struct request_sock *req)
if (req->rsk_listener)
kmem_cache_free(req->rsk_ops->slab, req);
static inline void reqsk_free(struct request_sock *req)
WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
static inline void reqsk_put(struct request_sock *req)
if (refcount_dec_and_test(&req->rsk_refcnt))
* 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;
u32 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_queue_alloc(struct request_sock_queue *queue);
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;
req = queue->rskq_accept_head;
if (req) {
WRITE_ONCE(queue->rskq_accept_head, req->dl_next);
if (queue->rskq_accept_head == NULL)
queue->rskq_accept_tail = NULL;
return req;
static inline void reqsk_queue_removed(struct request_sock_queue *queue,
const struct request_sock *req)
if (req->num_timeout == 0)
static inline void reqsk_queue_added(struct request_sock_queue *queue)
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);
#endif /* _REQUEST_SOCK_H */