// 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 <shemminger@osdl.org>
   */

  #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>
  
  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;
  }

  /* Must be called with rcu lock held */

  static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
  						       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;
  }

  /*

   * Attach new congestion control algorithm to the list

   * of available options.
   */
  int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
  {
  	int ret = 0;

  	/* 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
  ", ca->name);

  		return -EINVAL;
  	}

  	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
  ",
  			  ca->name);

  		ret = -EEXIST;
  	} else {

  		list_add_tail_rcu(&ca->list, &tcp_cong_list);

  		pr_debug("%s registered
  ", 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);

  u32 tcp_ca_get_key_by_name(struct net *net, 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(net, name);

  	if (ca) {
  		key = ca->key;
  		*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
  	}

  	rcu_read_unlock();
  
  	return key;
  }
  EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
  
  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)
  		ret = strncpy(buffer, ca->name,
  			      TCP_CA_NAME_MAX);
  	rcu_read_unlock();
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);

  /* 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(net, name);
  	if (!ca) {
  		ret = -ENOENT;

  	} else if (!bpf_try_module_get(ca, ca->owner)) {

  		ret = -EBUSY;
  	} 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);

  	strncpy(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(sock_net(sk), 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.

   */

  u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)

  {

  	u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);

  	acked -= cwnd - tp->snd_cwnd;

  	tp->snd_cwnd = 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.
   */

  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;
  		tp->snd_cwnd++;
  	}

  	tp->snd_cwnd_cnt += acked;

  	if (tp->snd_cwnd_cnt >= w) {

  		u32 delta = tp->snd_cwnd_cnt / w;
  
  		tp->snd_cwnd_cnt -= delta * w;
  		tp->snd_cwnd += delta;

  	}

  	tp->snd_cwnd = min(tp->snd_cwnd, 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.
   */

  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, tp->snd_cwnd, acked);

  }
  EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
  
  /* Slow start threshold is half the congestion window (min 2) */

  u32 tcp_reno_ssthresh(struct sock *sk)

  {

  	const struct tcp_sock *tp = tcp_sk(sk);

  	return max(tp->snd_cwnd >> 1U, 2U);
  }
  EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);

  u32 tcp_reno_undo_cwnd(struct sock *sk)
  {
  	const struct tcp_sock *tp = tcp_sk(sk);

  	return max(tp->snd_cwnd, 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,

  };