1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Pluggable TCP congestion control support and newReno
4 * congestion control.
5 * Based on ideas from I/O scheduler support and Web100.
6 *
7 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
8 */
9
10#define pr_fmt(fmt) "TCP: " fmt
11
12#include <linux/module.h>
13#include <linux/mm.h>
14#include <linux/types.h>
15#include <linux/list.h>
16#include <linux/gfp.h>
17#include <linux/jhash.h>
18#include <net/tcp.h>
19#include <trace/events/tcp.h>
20
21static DEFINE_SPINLOCK(tcp_cong_list_lock);
22static LIST_HEAD(tcp_cong_list);
23
24/* Simple linear search, don't expect many entries! */
25struct tcp_congestion_ops *tcp_ca_find(const char *name)
26{
27	struct tcp_congestion_ops *e;
28
29	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
30		if (strcmp(e->name, name) == 0)
31			return e;
32	}
33
34	return NULL;
35}
36
37void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
38{
39	struct inet_connection_sock *icsk = inet_csk(sk);
40
41	trace_tcp_cong_state_set(sk, ca_state);
42
43	if (icsk->icsk_ca_ops->set_state)
44		icsk->icsk_ca_ops->set_state(sk, ca_state);
45	icsk->icsk_ca_state = ca_state;
46}
47
48/* Must be called with rcu lock held */
49static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
50						       const char *name)
51{
52	struct tcp_congestion_ops *ca = tcp_ca_find(name);
53
54#ifdef CONFIG_MODULES
55	if (!ca && capable(CAP_NET_ADMIN)) {
56		rcu_read_unlock();
57		request_module("tcp_%s", name);
58		rcu_read_lock();
59		ca = tcp_ca_find(name);
60	}
61#endif
62	return ca;
63}
64
65/* Simple linear search, not much in here. */
66struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
67{
68	struct tcp_congestion_ops *e;
69
70	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
71		if (e->key == key)
72			return e;
73	}
74
75	return NULL;
76}
77
78int tcp_validate_congestion_control(struct tcp_congestion_ops *ca)
79{
80	/* all algorithms must implement these */
81	if (!ca->ssthresh || !ca->undo_cwnd ||
82	    !(ca->cong_avoid || ca->cong_control)) {
83		pr_err("%s does not implement required ops\n", ca->name);
84		return -EINVAL;
85	}
86
87	return 0;
88}
89
90/* Attach new congestion control algorithm to the list
91 * of available options.
92 */
93int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
94{
95	int ret;
96
97	ret = tcp_validate_congestion_control(ca);
98	if (ret)
99		return ret;
100
101	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
102
103	spin_lock(&tcp_cong_list_lock);
104	if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
105		pr_notice("%s already registered or non-unique key\n",
106			  ca->name);
107		ret = -EEXIST;
108	} else {
109		list_add_tail_rcu(&ca->list, &tcp_cong_list);
110		pr_debug("%s registered\n", ca->name);
111	}
112	spin_unlock(&tcp_cong_list_lock);
113
114	return ret;
115}
116EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
117
118/*
119 * Remove congestion control algorithm, called from
120 * the module's remove function.  Module ref counts are used
121 * to ensure that this can't be done till all sockets using
122 * that method are closed.
123 */
124void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
125{
126	spin_lock(&tcp_cong_list_lock);
127	list_del_rcu(&ca->list);
128	spin_unlock(&tcp_cong_list_lock);
129
130	/* Wait for outstanding readers to complete before the
131	 * module gets removed entirely.
132	 *
133	 * A try_module_get() should fail by now as our module is
134	 * in "going" state since no refs are held anymore and
135	 * module_exit() handler being called.
136	 */
137	synchronize_rcu();
138}
139EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
140
141/* Replace a registered old ca with a new one.
142 *
143 * The new ca must have the same name as the old one, that has been
144 * registered.
145 */
146int tcp_update_congestion_control(struct tcp_congestion_ops *ca, struct tcp_congestion_ops *old_ca)
147{
148	struct tcp_congestion_ops *existing;
149	int ret = 0;
150
151	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
152
153	spin_lock(&tcp_cong_list_lock);
154	existing = tcp_ca_find_key(old_ca->key);
155	if (ca->key == TCP_CA_UNSPEC || !existing || strcmp(existing->name, ca->name)) {
156		pr_notice("%s not registered or non-unique key\n",
157			  ca->name);
158		ret = -EINVAL;
159	} else if (existing != old_ca) {
160		pr_notice("invalid old congestion control algorithm to replace\n");
161		ret = -EINVAL;
162	} else {
163		/* Add the new one before removing the old one to keep
164		 * one implementation available all the time.
165		 */
166		list_add_tail_rcu(&ca->list, &tcp_cong_list);
167		list_del_rcu(&existing->list);
168		pr_debug("%s updated\n", ca->name);
169	}
170	spin_unlock(&tcp_cong_list_lock);
171
172	/* Wait for outstanding readers to complete before the
173	 * module or struct_ops gets removed entirely.
174	 */
175	if (!ret)
176		synchronize_rcu();
177
178	return ret;
179}
180
181u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
182{
183	const struct tcp_congestion_ops *ca;
184	u32 key = TCP_CA_UNSPEC;
185
186	might_sleep();
187
188	rcu_read_lock();
189	ca = tcp_ca_find_autoload(net, name);
190	if (ca) {
191		key = ca->key;
192		*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
193	}
194	rcu_read_unlock();
195
196	return key;
197}
198
199char *tcp_ca_get_name_by_key(u32 key, char *buffer)
200{
201	const struct tcp_congestion_ops *ca;
202	char *ret = NULL;
203
204	rcu_read_lock();
205	ca = tcp_ca_find_key(key);
206	if (ca)
207		ret = strncpy(buffer, ca->name,
208			      TCP_CA_NAME_MAX);
209	rcu_read_unlock();
210
211	return ret;
212}
213
214/* Assign choice of congestion control. */
215void tcp_assign_congestion_control(struct sock *sk)
216{
217	struct net *net = sock_net(sk);
218	struct inet_connection_sock *icsk = inet_csk(sk);
219	const struct tcp_congestion_ops *ca;
220
221	rcu_read_lock();
222	ca = rcu_dereference(net->ipv4.tcp_congestion_control);
223	if (unlikely(!bpf_try_module_get(ca, ca->owner)))
224		ca = &tcp_reno;
225	icsk->icsk_ca_ops = ca;
226	rcu_read_unlock();
227
228	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
229	if (ca->flags & TCP_CONG_NEEDS_ECN)
230		INET_ECN_xmit(sk);
231	else
232		INET_ECN_dontxmit(sk);
233}
234
235void tcp_init_congestion_control(struct sock *sk)
236{
237	struct inet_connection_sock *icsk = inet_csk(sk);
238
239	tcp_sk(sk)->prior_ssthresh = 0;
240	if (icsk->icsk_ca_ops->init)
241		icsk->icsk_ca_ops->init(sk);
242	if (tcp_ca_needs_ecn(sk))
243		INET_ECN_xmit(sk);
244	else
245		INET_ECN_dontxmit(sk);
246	icsk->icsk_ca_initialized = 1;
247}
248
249static void tcp_reinit_congestion_control(struct sock *sk,
250					  const struct tcp_congestion_ops *ca)
251{
252	struct inet_connection_sock *icsk = inet_csk(sk);
253
254	tcp_cleanup_congestion_control(sk);
255	icsk->icsk_ca_ops = ca;
256	icsk->icsk_ca_setsockopt = 1;
257	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
258
259	if (ca->flags & TCP_CONG_NEEDS_ECN)
260		INET_ECN_xmit(sk);
261	else
262		INET_ECN_dontxmit(sk);
263
264	if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
265		tcp_init_congestion_control(sk);
266}
267
268/* Manage refcounts on socket close. */
269void tcp_cleanup_congestion_control(struct sock *sk)
270{
271	struct inet_connection_sock *icsk = inet_csk(sk);
272
273	if (icsk->icsk_ca_ops->release)
274		icsk->icsk_ca_ops->release(sk);
275	bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner);
276}
277
278/* Used by sysctl to change default congestion control */
279int tcp_set_default_congestion_control(struct net *net, const char *name)
280{
281	struct tcp_congestion_ops *ca;
282	const struct tcp_congestion_ops *prev;
283	int ret;
284
285	rcu_read_lock();
286	ca = tcp_ca_find_autoload(net, name);
287	if (!ca) {
288		ret = -ENOENT;
289	} else if (!bpf_try_module_get(ca, ca->owner)) {
290		ret = -EBUSY;
291	} else if (!net_eq(net, &init_net) &&
292			!(ca->flags & TCP_CONG_NON_RESTRICTED)) {
293		/* Only init netns can set default to a restricted algorithm */
294		ret = -EPERM;
295	} else {
296		prev = xchg(&net->ipv4.tcp_congestion_control, ca);
297		if (prev)
298			bpf_module_put(prev, prev->owner);
299
300		ca->flags |= TCP_CONG_NON_RESTRICTED;
301		ret = 0;
302	}
303	rcu_read_unlock();
304
305	return ret;
306}
307
308/* Set default value from kernel configuration at bootup */
309static int __init tcp_congestion_default(void)
310{
311	return tcp_set_default_congestion_control(&init_net,
312						  CONFIG_DEFAULT_TCP_CONG);
313}
314late_initcall(tcp_congestion_default);
315
316/* Build string with list of available congestion control values */
317void tcp_get_available_congestion_control(char *buf, size_t maxlen)
318{
319	struct tcp_congestion_ops *ca;
320	size_t offs = 0;
321
322	rcu_read_lock();
323	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
324		offs += snprintf(buf + offs, maxlen - offs,
325				 "%s%s",
326				 offs == 0 ? "" : " ", ca->name);
327
328		if (WARN_ON_ONCE(offs >= maxlen))
329			break;
330	}
331	rcu_read_unlock();
332}
333
334/* Get current default congestion control */
335void tcp_get_default_congestion_control(struct net *net, char *name)
336{
337	const struct tcp_congestion_ops *ca;
338
339	rcu_read_lock();
340	ca = rcu_dereference(net->ipv4.tcp_congestion_control);
341	strncpy(name, ca->name, TCP_CA_NAME_MAX);
342	rcu_read_unlock();
343}
344
345/* Built list of non-restricted congestion control values */
346void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
347{
348	struct tcp_congestion_ops *ca;
349	size_t offs = 0;
350
351	*buf = '\0';
352	rcu_read_lock();
353	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
354		if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
355			continue;
356		offs += snprintf(buf + offs, maxlen - offs,
357				 "%s%s",
358				 offs == 0 ? "" : " ", ca->name);
359
360		if (WARN_ON_ONCE(offs >= maxlen))
361			break;
362	}
363	rcu_read_unlock();
364}
365
366/* Change list of non-restricted congestion control */
367int tcp_set_allowed_congestion_control(char *val)
368{
369	struct tcp_congestion_ops *ca;
370	char *saved_clone, *clone, *name;
371	int ret = 0;
372
373	saved_clone = clone = kstrdup(val, GFP_USER);
374	if (!clone)
375		return -ENOMEM;
376
377	spin_lock(&tcp_cong_list_lock);
378	/* pass 1 check for bad entries */
379	while ((name = strsep(&clone, " ")) && *name) {
380		ca = tcp_ca_find(name);
381		if (!ca) {
382			ret = -ENOENT;
383			goto out;
384		}
385	}
386
387	/* pass 2 clear old values */
388	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
389		ca->flags &= ~TCP_CONG_NON_RESTRICTED;
390
391	/* pass 3 mark as allowed */
392	while ((name = strsep(&val, " ")) && *name) {
393		ca = tcp_ca_find(name);
394		WARN_ON(!ca);
395		if (ca)
396			ca->flags |= TCP_CONG_NON_RESTRICTED;
397	}
398out:
399	spin_unlock(&tcp_cong_list_lock);
400	kfree(saved_clone);
401
402	return ret;
403}
404
405/* Change congestion control for socket. If load is false, then it is the
406 * responsibility of the caller to call tcp_init_congestion_control or
407 * tcp_reinit_congestion_control (if the current congestion control was
408 * already initialized.
409 */
410int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
411			       bool cap_net_admin)
412{
413	struct inet_connection_sock *icsk = inet_csk(sk);
414	const struct tcp_congestion_ops *ca;
415	int err = 0;
416
417	if (icsk->icsk_ca_dst_locked)
418		return -EPERM;
419
420	rcu_read_lock();
421	if (!load)
422		ca = tcp_ca_find(name);
423	else
424		ca = tcp_ca_find_autoload(sock_net(sk), name);
425
426	/* No change asking for existing value */
427	if (ca == icsk->icsk_ca_ops) {
428		icsk->icsk_ca_setsockopt = 1;
429		goto out;
430	}
431
432	if (!ca)
433		err = -ENOENT;
434	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin))
435		err = -EPERM;
436	else if (!bpf_try_module_get(ca, ca->owner))
437		err = -EBUSY;
438	else
439		tcp_reinit_congestion_control(sk, ca);
440 out:
441	rcu_read_unlock();
442	return err;
443}
444
445/* Slow start is used when congestion window is no greater than the slow start
446 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
447 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
448 * something better;) a packet is only considered (s)acked in its entirety to
449 * defend the ACK attacks described in the RFC. Slow start processes a stretch
450 * ACK of degree N as if N acks of degree 1 are received back to back except
451 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
452 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
453 */
454__bpf_kfunc u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
455{
456	u32 cwnd = min(tcp_snd_cwnd(tp) + acked, tp->snd_ssthresh);
457
458	acked -= cwnd - tcp_snd_cwnd(tp);
459	tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp));
460
461	return acked;
462}
463EXPORT_SYMBOL_GPL(tcp_slow_start);
464
465/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
466 * for every packet that was ACKed.
467 */
468__bpf_kfunc void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
469{
470	/* If credits accumulated at a higher w, apply them gently now. */
471	if (tp->snd_cwnd_cnt >= w) {
472		tp->snd_cwnd_cnt = 0;
473		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
474	}
475
476	tp->snd_cwnd_cnt += acked;
477	if (tp->snd_cwnd_cnt >= w) {
478		u32 delta = tp->snd_cwnd_cnt / w;
479
480		tp->snd_cwnd_cnt -= delta * w;
481		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + delta);
482	}
483	tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
484}
485EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
486
487/*
488 * TCP Reno congestion control
489 * This is special case used for fallback as well.
490 */
491/* This is Jacobson's slow start and congestion avoidance.
492 * SIGCOMM '88, p. 328.
493 */
494__bpf_kfunc void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
495{
496	struct tcp_sock *tp = tcp_sk(sk);
497
498	if (!tcp_is_cwnd_limited(sk))
499		return;
500
501	/* In "safe" area, increase. */
502	if (tcp_in_slow_start(tp)) {
503		acked = tcp_slow_start(tp, acked);
504		if (!acked)
505			return;
506	}
507	/* In dangerous area, increase slowly. */
508	tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
509}
510EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
511
512/* Slow start threshold is half the congestion window (min 2) */
513__bpf_kfunc u32 tcp_reno_ssthresh(struct sock *sk)
514{
515	const struct tcp_sock *tp = tcp_sk(sk);
516
517	return max(tcp_snd_cwnd(tp) >> 1U, 2U);
518}
519EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
520
521__bpf_kfunc u32 tcp_reno_undo_cwnd(struct sock *sk)
522{
523	const struct tcp_sock *tp = tcp_sk(sk);
524
525	return max(tcp_snd_cwnd(tp), tp->prior_cwnd);
526}
527EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
528
529struct tcp_congestion_ops tcp_reno = {
530	.flags		= TCP_CONG_NON_RESTRICTED,
531	.name		= "reno",
532	.owner		= THIS_MODULE,
533	.ssthresh	= tcp_reno_ssthresh,
534	.cong_avoid	= tcp_reno_cong_avoid,
535	.undo_cwnd	= tcp_reno_undo_cwnd,
536};
537