// SPDX-License-Identifier: GPL-2.0-only
/*
* Pluggable TCP congestion control support and newReno
* congestion control.
* Based on ideas from I/O scheduler support and Web100.
*
* Copyright (C) 2005 Stephen Hemminger <[email protected]>
*/
#define pr_fmt(fmt) "TCP: " fmt
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/gfp.h>
#include <linux/jhash.h>
#include <net/tcp.h>
#include <trace/events/tcp.h>
static DEFINE_SPINLOCK(tcp_cong_list_lock);
static LIST_HEAD(tcp_cong_list);
/* Simple linear search, don't expect many entries! */
struct tcp_congestion_ops *tcp_ca_find(const char *name)
{
struct tcp_congestion_ops *e;
list_for_each_entry_rcu(e, &tcp_cong_list, list) {
if (strcmp(e->name, name) == 0)
return e;
}
return NULL;
}
void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
{
struct inet_connection_sock *icsk = inet_csk(sk);
trace_tcp_cong_state_set(sk, ca_state);
if (icsk->icsk_ca_ops->set_state)
icsk->icsk_ca_ops->set_state(sk, ca_state);
icsk->icsk_ca_state = ca_state;
}
/* Must be called with rcu lock held */
static struct tcp_congestion_ops *tcp_ca_find_autoload(const char *name)
{
struct tcp_congestion_ops *ca = tcp_ca_find(name);
#ifdef CONFIG_MODULES
if (!ca && capable(CAP_NET_ADMIN)) {
rcu_read_unlock();
request_module("tcp_%s", name);
rcu_read_lock();
ca = tcp_ca_find(name);
}
#endif
return ca;
}
/* Simple linear search, not much in here. */
struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
{
struct tcp_congestion_ops *e;
list_for_each_entry_rcu(e, &tcp_cong_list, list) {
if (e->key == key)
return e;
}
return NULL;
}
int tcp_validate_congestion_control(struct tcp_congestion_ops *ca)
{
/* all algorithms must implement these */
if (!ca->ssthresh || !ca->undo_cwnd ||
!(ca->cong_avoid || ca->cong_control)) {
pr_err("%s does not implement required ops\n", ca->name);
return -EINVAL;
}
return 0;
}
/* Attach new congestion control algorithm to the list
* of available options.
*/
int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
{
int ret;
ret = tcp_validate_congestion_control(ca);
if (ret)
return ret;
ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
spin_lock(&tcp_cong_list_lock);
if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
pr_notice("%s already registered or non-unique key\n",
ca->name);
ret = -EEXIST;
} else {
list_add_tail_rcu(&ca->list, &tcp_cong_list);
pr_debug("%s registered\n", ca->name);
}
spin_unlock(&tcp_cong_list_lock);
return ret;
}
EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
/*
* Remove congestion control algorithm, called from
* the module's remove function. Module ref counts are used
* to ensure that this can't be done till all sockets using
* that method are closed.
*/
void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
{
spin_lock(&tcp_cong_list_lock);
list_del_rcu(&ca->list);
spin_unlock(&tcp_cong_list_lock);
/* Wait for outstanding readers to complete before the
* module gets removed entirely.
*
* A try_module_get() should fail by now as our module is
* in "going" state since no refs are held anymore and
* module_exit() handler being called.
*/
synchronize_rcu();
}
EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
/* Replace a registered old ca with a new one.
*
* The new ca must have the same name as the old one, that has been
* registered.
*/
int tcp_update_congestion_control(struct tcp_congestion_ops *ca, struct tcp_congestion_ops *old_ca)
{
struct tcp_congestion_ops *existing;
int ret = 0;
ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
spin_lock(&tcp_cong_list_lock);
existing = tcp_ca_find_key(old_ca->key);
if (ca->key == TCP_CA_UNSPEC || !existing || strcmp(existing->name, ca->name)) {
pr_notice("%s not registered or non-unique key\n",
ca->name);
ret = -EINVAL;
} else if (existing != old_ca) {
pr_notice("invalid old congestion control algorithm to replace\n");
ret = -EINVAL;
} else {
/* Add the new one before removing the old one to keep
* one implementation available all the time.
*/
list_add_tail_rcu(&ca->list, &tcp_cong_list);
list_del_rcu(&existing->list);
pr_debug("%s updated\n", ca->name);
}
spin_unlock(&tcp_cong_list_lock);
/* Wait for outstanding readers to complete before the
* module or struct_ops gets removed entirely.
*/
if (!ret)
synchronize_rcu();
return ret;
}
u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
{
const struct tcp_congestion_ops *ca;
u32 key = TCP_CA_UNSPEC;
might_sleep();
rcu_read_lock();
ca = tcp_ca_find_autoload(name);
if (ca) {
key = ca->key;
*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
}
rcu_read_unlock();
return key;
}
char *tcp_ca_get_name_by_key(u32 key, char *buffer)
{
const struct tcp_congestion_ops *ca;
char *ret = NULL;
rcu_read_lock();
ca = tcp_ca_find_key(key);
if (ca) {
strscpy(buffer, ca->name, TCP_CA_NAME_MAX);
ret = buffer;
}
rcu_read_unlock();
return ret;
}
/* Assign choice of congestion control. */
void tcp_assign_congestion_control(struct sock *sk)
{
struct net *net = sock_net(sk);
struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_congestion_ops *ca;
rcu_read_lock();
ca = rcu_dereference(net->ipv4.tcp_congestion_control);
if (unlikely(!bpf_try_module_get(ca, ca->owner)))
ca = &tcp_reno;
icsk->icsk_ca_ops = ca;
rcu_read_unlock();
memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
if (ca->flags & TCP_CONG_NEEDS_ECN)
INET_ECN_xmit(sk);
else
INET_ECN_dontxmit(sk);
}
void tcp_init_congestion_control(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
tcp_sk(sk)->prior_ssthresh = 0;
if (icsk->icsk_ca_ops->init)
icsk->icsk_ca_ops->init(sk);
if (tcp_ca_needs_ecn(sk))
INET_ECN_xmit(sk);
else
INET_ECN_dontxmit(sk);
icsk->icsk_ca_initialized = 1;
}
static void tcp_reinit_congestion_control(struct sock *sk,
const struct tcp_congestion_ops *ca)
{
struct inet_connection_sock *icsk = inet_csk(sk);
tcp_cleanup_congestion_control(sk);
icsk->icsk_ca_ops = ca;
icsk->icsk_ca_setsockopt = 1;
memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
if (ca->flags & TCP_CONG_NEEDS_ECN)
INET_ECN_xmit(sk);
else
INET_ECN_dontxmit(sk);
if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
tcp_init_congestion_control(sk);
}
/* Manage refcounts on socket close. */
void tcp_cleanup_congestion_control(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
if (icsk->icsk_ca_ops->release)
icsk->icsk_ca_ops->release(sk);
bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner);
}
/* Used by sysctl to change default congestion control */
int tcp_set_default_congestion_control(struct net *net, const char *name)
{
struct tcp_congestion_ops *ca;
const struct tcp_congestion_ops *prev;
int ret;
rcu_read_lock();
ca = tcp_ca_find_autoload(name);
if (!ca) {
ret = -ENOENT;
} else if (!bpf_try_module_get(ca, ca->owner)) {
ret = -EBUSY;
} else if (!net_eq(net, &init_net) &&
!(ca->flags & TCP_CONG_NON_RESTRICTED)) {
/* Only init netns can set default to a restricted algorithm */
ret = -EPERM;
} else {
prev = xchg(&net->ipv4.tcp_congestion_control, ca);
if (prev)
bpf_module_put(prev, prev->owner);
ca->flags |= TCP_CONG_NON_RESTRICTED;
ret = 0;
}
rcu_read_unlock();
return ret;
}
/* Set default value from kernel configuration at bootup */
static int __init tcp_congestion_default(void)
{
return tcp_set_default_congestion_control(&init_net,
CONFIG_DEFAULT_TCP_CONG);
}
late_initcall(tcp_congestion_default);
/* Build string with list of available congestion control values */
void tcp_get_available_congestion_control(char *buf, size_t maxlen)
{
struct tcp_congestion_ops *ca;
size_t offs = 0;
rcu_read_lock();
list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
offs += snprintf(buf + offs, maxlen - offs,
"%s%s",
offs == 0 ? "" : " ", ca->name);
if (WARN_ON_ONCE(offs >= maxlen))
break;
}
rcu_read_unlock();
}
/* Get current default congestion control */
void tcp_get_default_congestion_control(struct net *net, char *name)
{
const struct tcp_congestion_ops *ca;
rcu_read_lock();
ca = rcu_dereference(net->ipv4.tcp_congestion_control);
strscpy(name, ca->name, TCP_CA_NAME_MAX);
rcu_read_unlock();
}
/* Built list of non-restricted congestion control values */
void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
{
struct tcp_congestion_ops *ca;
size_t offs = 0;
*buf = '\0';
rcu_read_lock();
list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
continue;
offs += snprintf(buf + offs, maxlen - offs,
"%s%s",
offs == 0 ? "" : " ", ca->name);
if (WARN_ON_ONCE(offs >= maxlen))
break;
}
rcu_read_unlock();
}
/* Change list of non-restricted congestion control */
int tcp_set_allowed_congestion_control(char *val)
{
struct tcp_congestion_ops *ca;
char *saved_clone, *clone, *name;
int ret = 0;
saved_clone = clone = kstrdup(val, GFP_USER);
if (!clone)
return -ENOMEM;
spin_lock(&tcp_cong_list_lock);
/* pass 1 check for bad entries */
while ((name = strsep(&clone, " ")) && *name) {
ca = tcp_ca_find(name);
if (!ca) {
ret = -ENOENT;
goto out;
}
}
/* pass 2 clear old values */
list_for_each_entry_rcu(ca, &tcp_cong_list, list)
ca->flags &= ~TCP_CONG_NON_RESTRICTED;
/* pass 3 mark as allowed */
while ((name = strsep(&val, " ")) && *name) {
ca = tcp_ca_find(name);
WARN_ON(!ca);
if (ca)
ca->flags |= TCP_CONG_NON_RESTRICTED;
}
out:
spin_unlock(&tcp_cong_list_lock);
kfree(saved_clone);
return ret;
}
/* Change congestion control for socket. If load is false, then it is the
* responsibility of the caller to call tcp_init_congestion_control or
* tcp_reinit_congestion_control (if the current congestion control was
* already initialized.
*/
int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
bool cap_net_admin)
{
struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_congestion_ops *ca;
int err = 0;
if (icsk->icsk_ca_dst_locked)
return -EPERM;
rcu_read_lock();
if (!load)
ca = tcp_ca_find(name);
else
ca = tcp_ca_find_autoload(name);
/* No change asking for existing value */
if (ca == icsk->icsk_ca_ops) {
icsk->icsk_ca_setsockopt = 1;
goto out;
}
if (!ca)
err = -ENOENT;
else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin))
err = -EPERM;
else if (!bpf_try_module_get(ca, ca->owner))
err = -EBUSY;
else
tcp_reinit_congestion_control(sk, ca);
out:
rcu_read_unlock();
return err;
}
/* Slow start is used when congestion window is no greater than the slow start
* threshold. We base on RFC2581 and also handle stretch ACKs properly.
* We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
* something better;) a packet is only considered (s)acked in its entirety to
* defend the ACK attacks described in the RFC. Slow start processes a stretch
* ACK of degree N as if N acks of degree 1 are received back to back except
* ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
* returns the leftover acks to adjust cwnd in congestion avoidance mode.
*/
__bpf_kfunc u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
{
u32 cwnd = min(tcp_snd_cwnd(tp) + acked, tp->snd_ssthresh);
acked -= cwnd - tcp_snd_cwnd(tp);
tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp));
return acked;
}
EXPORT_SYMBOL_GPL(tcp_slow_start);
/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
* for every packet that was ACKed.
*/
__bpf_kfunc void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
{
/* If credits accumulated at a higher w, apply them gently now. */
if (tp->snd_cwnd_cnt >= w) {
tp->snd_cwnd_cnt = 0;
tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
}
tp->snd_cwnd_cnt += acked;
if (tp->snd_cwnd_cnt >= w) {
u32 delta = tp->snd_cwnd_cnt / w;
tp->snd_cwnd_cnt -= delta * w;
tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + delta);
}
tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
}
EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
/*
* TCP Reno congestion control
* This is special case used for fallback as well.
*/
/* This is Jacobson's slow start and congestion avoidance.
* SIGCOMM '88, p. 328.
*/
__bpf_kfunc void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
struct tcp_sock *tp = tcp_sk(sk);
if (!tcp_is_cwnd_limited(sk))
return;
/* In "safe" area, increase. */
if (tcp_in_slow_start(tp)) {
acked = tcp_slow_start(tp, acked);
if (!acked)
return;
}
/* In dangerous area, increase slowly. */
tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
}
EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
/* Slow start threshold is half the congestion window (min 2) */
__bpf_kfunc u32 tcp_reno_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
return max(tcp_snd_cwnd(tp) >> 1U, 2U);
}
EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
__bpf_kfunc u32 tcp_reno_undo_cwnd(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
return max(tcp_snd_cwnd(tp), tp->prior_cwnd);
}
EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
struct tcp_congestion_ops tcp_reno = {
.flags = TCP_CONG_NON_RESTRICTED,
.name = "reno",
.owner = THIS_MODULE,
.ssthresh = tcp_reno_ssthresh,
.cong_avoid = tcp_reno_cong_avoid,
.undo_cwnd = tcp_reno_undo_cwnd,
};
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