1/* SPDX-License-Identifier: GPL-2.0-or-later */
2/*
3 * NET Generic infrastructure for Network protocols.
4 *
5 * Definitions for request_sock
6 *
7 * Authors: Arnaldo Carvalho de Melo <acme@conectiva.com.br>
8 *
9 * From code originally in include/net/tcp.h
10 */
11#ifndef _REQUEST_SOCK_H
12#define _REQUEST_SOCK_H
13
14#include <linux/slab.h>
15#include <linux/spinlock.h>
16#include <linux/types.h>
17#include <linux/bug.h>
18#include <linux/refcount.h>
19
20#include <net/sock.h>
21#include <net/rstreason.h>
22
23struct request_sock;
24struct sk_buff;
25struct dst_entry;
26struct proto;
27
28struct request_sock_ops {
29 int family;
30 unsigned int obj_size;
31 struct kmem_cache *slab;
32 char *slab_name;
33 void (*send_ack)(const struct sock *sk, struct sk_buff *skb,
34 struct request_sock *req);
35 void (*send_reset)(const struct sock *sk,
36 struct sk_buff *skb,
37 enum sk_rst_reason reason);
38 void (*destructor)(struct request_sock *req);
39};
40
41struct saved_syn {
42 u32 mac_hdrlen;
43 u32 network_hdrlen;
44 u32 tcp_hdrlen;
45 u8 data[];
46};
47
48/* struct request_sock - mini sock to represent a connection request
49 */
50struct request_sock {
51 struct sock_common __req_common;
52#define rsk_refcnt __req_common.skc_refcnt
53#define rsk_hash __req_common.skc_hash
54#define rsk_listener __req_common.skc_listener
55#define rsk_window_clamp __req_common.skc_window_clamp
56#define rsk_rcv_wnd __req_common.skc_rcv_wnd
57
58 struct request_sock *dl_next;
59 u16 mss;
60 u8 num_retrans; /* number of retransmits */
61 u8 syncookie:1; /* True if
62 * 1) tcpopts needs to be encoded in
63 * TS of SYN+ACK
64 * 2) ACK is validated by BPF kfunc.
65 */
66 u8 num_timeout:7; /* number of timeouts */
67 u32 ts_recent;
68 struct timer_list rsk_timer;
69 const struct request_sock_ops *rsk_ops;
70 struct sock *sk;
71 struct saved_syn *saved_syn;
72 u32 secid;
73 u32 peer_secid;
74 u32 timeout;
75};
76
77static inline struct request_sock *inet_reqsk(const struct sock *sk)
78{
79 return (struct request_sock *)sk;
80}
81
82static inline struct sock *req_to_sk(struct request_sock *req)
83{
84 return (struct sock *)req;
85}
86
87/**
88 * skb_steal_sock - steal a socket from an sk_buff
89 * @skb: sk_buff to steal the socket from
90 * @refcounted: is set to true if the socket is reference-counted
91 * @prefetched: is set to true if the socket was assigned from bpf
92 */
93static inline struct sock *skb_steal_sock(struct sk_buff *skb,
94 bool *refcounted, bool *prefetched)
95{
96 struct sock *sk = skb->sk;
97
98 if (!sk) {
99 *prefetched = false;
100 *refcounted = false;
101 return NULL;
102 }
103
104 *prefetched = skb_sk_is_prefetched(skb);
105 if (*prefetched) {
106#if IS_ENABLED(CONFIG_SYN_COOKIES)
107 if (sk->sk_state == TCP_NEW_SYN_RECV && inet_reqsk(sk)->syncookie) {
108 struct request_sock *req = inet_reqsk(sk);
109
110 *refcounted = false;
111 sk = req->rsk_listener;
112 req->rsk_listener = NULL;
113 return sk;
114 }
115#endif
116 *refcounted = sk_is_refcounted(sk);
117 } else {
118 *refcounted = true;
119 }
120
121 skb->destructor = NULL;
122 skb->sk = NULL;
123 return sk;
124}
125
126static inline void __reqsk_free(struct request_sock *req)
127{
128 req->rsk_ops->destructor(req);
129 if (req->rsk_listener)
130 sock_put(sk: req->rsk_listener);
131 kfree(objp: req->saved_syn);
132 kmem_cache_free(s: req->rsk_ops->slab, objp: req);
133}
134
135static inline void reqsk_free(struct request_sock *req)
136{
137 DEBUG_NET_WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
138 __reqsk_free(req);
139}
140
141static inline void reqsk_put(struct request_sock *req)
142{
143 if (refcount_dec_and_test(r: &req->rsk_refcnt))
144 __reqsk_free(req);
145}
146
147/*
148 * For a TCP Fast Open listener -
149 * lock - protects the access to all the reqsk, which is co-owned by
150 * the listener and the child socket.
151 * qlen - pending TFO requests (still in TCP_SYN_RECV).
152 * max_qlen - max TFO reqs allowed before TFO is disabled.
153 *
154 * XXX (TFO) - ideally these fields can be made as part of "listen_sock"
155 * structure above. But there is some implementation difficulty due to
156 * listen_sock being part of request_sock_queue hence will be freed when
157 * a listener is stopped. But TFO related fields may continue to be
158 * accessed even after a listener is closed, until its sk_refcnt drops
159 * to 0 implying no more outstanding TFO reqs. One solution is to keep
160 * listen_opt around until sk_refcnt drops to 0. But there is some other
161 * complexity that needs to be resolved. E.g., a listener can be disabled
162 * temporarily through shutdown()->tcp_disconnect(), and re-enabled later.
163 */
164struct fastopen_queue {
165 struct request_sock *rskq_rst_head; /* Keep track of past TFO */
166 struct request_sock *rskq_rst_tail; /* requests that caused RST.
167 * This is part of the defense
168 * against spoofing attack.
169 */
170 spinlock_t lock;
171 int qlen; /* # of pending (TCP_SYN_RECV) reqs */
172 int max_qlen; /* != 0 iff TFO is currently enabled */
173
174 struct tcp_fastopen_context __rcu *ctx; /* cipher context for cookie */
175};
176
177/** struct request_sock_queue - queue of request_socks
178 *
179 * @rskq_accept_head - FIFO head of established children
180 * @rskq_accept_tail - FIFO tail of established children
181 * @rskq_defer_accept - User waits for some data after accept()
182 *
183 */
184struct request_sock_queue {
185 spinlock_t rskq_lock;
186 u8 rskq_defer_accept;
187 u8 synflood_warned;
188
189 atomic_t qlen;
190 atomic_t young;
191
192 struct request_sock *rskq_accept_head;
193 struct request_sock *rskq_accept_tail;
194 struct fastopen_queue fastopenq; /* Check max_qlen != 0 to determine
195 * if TFO is enabled.
196 */
197};
198
199void reqsk_queue_alloc(struct request_sock_queue *queue);
200
201void reqsk_fastopen_remove(struct sock *sk, struct request_sock *req,
202 bool reset);
203
204static inline bool reqsk_queue_empty(const struct request_sock_queue *queue)
205{
206 return READ_ONCE(queue->rskq_accept_head) == NULL;
207}
208
209static inline struct request_sock *reqsk_queue_remove(struct request_sock_queue *queue,
210 struct sock *parent)
211{
212 struct request_sock *req;
213
214 spin_lock_bh(lock: &queue->rskq_lock);
215 req = queue->rskq_accept_head;
216 if (req) {
217 sk_acceptq_removed(sk: parent);
218 WRITE_ONCE(queue->rskq_accept_head, req->dl_next);
219 if (queue->rskq_accept_head == NULL)
220 queue->rskq_accept_tail = NULL;
221 }
222 spin_unlock_bh(lock: &queue->rskq_lock);
223 return req;
224}
225
226static inline void reqsk_queue_removed(struct request_sock_queue *queue,
227 const struct request_sock *req)
228{
229 if (req->num_timeout == 0)
230 atomic_dec(v: &queue->young);
231 atomic_dec(v: &queue->qlen);
232}
233
234static inline void reqsk_queue_added(struct request_sock_queue *queue)
235{
236 atomic_inc(v: &queue->young);
237 atomic_inc(v: &queue->qlen);
238}
239
240static inline int reqsk_queue_len(const struct request_sock_queue *queue)
241{
242 return atomic_read(v: &queue->qlen);
243}
244
245static inline int reqsk_queue_len_young(const struct request_sock_queue *queue)
246{
247 return atomic_read(v: &queue->young);
248}
249
250/* RFC 7323 2.3 Using the Window Scale Option
251 * The window field (SEG.WND) of every outgoing segment, with the
252 * exception of <SYN> segments, MUST be right-shifted by
253 * Rcv.Wind.Shift bits.
254 *
255 * This means the SEG.WND carried in SYNACK can not exceed 65535.
256 * We use this property to harden TCP stack while in NEW_SYN_RECV state.
257 */
258static inline u32 tcp_synack_window(const struct request_sock *req)
259{
260 return min(req->rsk_rcv_wnd, 65535U);
261}
262#endif /* _REQUEST_SOCK_H */
263

source code of linux/include/net/request_sock.h