net/mptcp/token.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /* Multipath TCP token management
  * Copyright (c) 2017 - 2019, Intel Corporation.
  *
  * Note: This code is based on mptcp_ctrl.c from multipath-tcp.org,
  *       authored by:
  *
  *       Sébastien Barré <sebastien.barre@uclouvain.be>
  *       Christoph Paasch <christoph.paasch@uclouvain.be>
  *       Jaakko Korkeaniemi <jaakko.korkeaniemi@aalto.fi>
  *       Gregory Detal <gregory.detal@uclouvain.be>
  *       Fabien Duchêne <fabien.duchene@uclouvain.be>
  *       Andreas Seelinger <Andreas.Seelinger@rwth-aachen.de>
  *       Lavkesh Lahngir <lavkesh51@gmail.com>
  *       Andreas Ripke <ripke@neclab.eu>
  *       Vlad Dogaru <vlad.dogaru@intel.com>
  *       Octavian Purdila <octavian.purdila@intel.com>
  *       John Ronan <jronan@tssg.org>
  *       Catalin Nicutar <catalin.nicutar@gmail.com>
  *       Brandon Heller <brandonh@stanford.edu>
  */

 #define pr_fmt(fmt) "MPTCP: " fmt

 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/memblock.h>
 #include <linux/ip.h>
 #include <linux/tcp.h>
 #include <net/sock.h>
 #include <net/inet_common.h>
 #include <net/protocol.h>
 #include <net/mptcp.h>
 #include "protocol.h"

 #define TOKEN_MAX_RETRIES	4
 #define TOKEN_MAX_CHAIN_LEN	4

 struct token_bucket {
 	spinlock_t		lock;
 	int			chain_len;
 	struct hlist_nulls_head	req_chain;
 	struct hlist_nulls_head	msk_chain;
 };

 static struct token_bucket *token_hash __read_mostly;
 static unsigned int token_mask __read_mostly;

 static struct token_bucket *token_bucket(u32 token)
 {
 	return &token_hash[token & token_mask];
 }

 /* called with bucket lock held */
 static struct mptcp_subflow_request_sock *
 __token_lookup_req(struct token_bucket *t, u32 token)
 {
 	struct mptcp_subflow_request_sock *req;
 	struct hlist_nulls_node *pos;

 	hlist_nulls_for_each_entry_rcu(req, pos, &t->req_chain, token_node)
 		if (req->token == token)
 			return req;
 	return NULL;
 }

 /* called with bucket lock held */
 static struct mptcp_sock *
 __token_lookup_msk(struct token_bucket *t, u32 token)
 {
 	struct hlist_nulls_node *pos;
 	struct sock *sk;

 	sk_nulls_for_each_rcu(sk, pos, &t->msk_chain)
 		if (mptcp_sk(sk)->token == token)
 			return mptcp_sk(sk);
 	return NULL;
 }

 static bool __token_bucket_busy(struct token_bucket *t, u32 token)
 {
 	return !token || t->chain_len >= TOKEN_MAX_CHAIN_LEN ||
 	       __token_lookup_req(t, token) || __token_lookup_msk(t, token);
 }

 static void mptcp_crypto_key_gen_sha(u64 *key, u32 *token, u64 *idsn)
 {
 	/* we might consider a faster version that computes the key as a
 	 * hash of some information available in the MPTCP socket. Use
 	 * random data at the moment, as it's probably the safest option
 	 * in case multiple sockets are opened in different namespaces at
 	 * the same time.
 	 */
 	get_random_bytes(key, sizeof(u64));
 	mptcp_crypto_key_sha(*key, token, idsn);
 }

 /**
  * mptcp_token_new_request - create new key/idsn/token for subflow_request
  * @req: the request socket
  *
  * This function is called when a new mptcp connection is coming in.
  *
  * It creates a unique token to identify the new mptcp connection,
  * a secret local key and the initial data sequence number (idsn).
  *
  * Returns 0 on success.
  */
 int mptcp_token_new_request(struct request_sock *req)
 {
 	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
 	struct token_bucket *bucket;
 	u32 token;

 	mptcp_crypto_key_sha(subflow_req->local_key,
 			     &subflow_req->token,
 			     &subflow_req->idsn);
 	pr_debug("req=%p local_key=%llu, token=%u, idsn=%llu\n",
 		 req, subflow_req->local_key, subflow_req->token,
 		 subflow_req->idsn);

 	token = subflow_req->token;
 	bucket = token_bucket(token);
 	spin_lock_bh(&bucket->lock);
 	if (__token_bucket_busy(bucket, token)) {
 		spin_unlock_bh(&bucket->lock);
 		return -EBUSY;
 	}

 	hlist_nulls_add_head_rcu(&subflow_req->token_node, &bucket->req_chain);
 	bucket->chain_len++;
 	spin_unlock_bh(&bucket->lock);
 	return 0;
 }

 /**
  * mptcp_token_new_connect - create new key/idsn/token for subflow
  * @sk: the socket that will initiate a connection
  *
  * This function is called when a new outgoing mptcp connection is
  * initiated.
  *
  * It creates a unique token to identify the new mptcp connection,
  * a secret local key and the initial data sequence number (idsn).
  *
  * On success, the mptcp connection can be found again using
  * the computed token at a later time, this is needed to process
  * join requests.
  *
  * returns 0 on success.
  */
 int mptcp_token_new_connect(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 	int retries = TOKEN_MAX_RETRIES;
 	struct token_bucket *bucket;

 again:
 	mptcp_crypto_key_gen_sha(&subflow->local_key, &subflow->token,
 				 &subflow->idsn);

 	bucket = token_bucket(subflow->token);
 	spin_lock_bh(&bucket->lock);
 	if (__token_bucket_busy(bucket, subflow->token)) {
 		spin_unlock_bh(&bucket->lock);
 		if (!--retries)
 			return -EBUSY;
 		goto again;
 	}

 	pr_debug("ssk=%p, local_key=%llu, token=%u, idsn=%llu\n",
 		 sk, subflow->local_key, subflow->token, subflow->idsn);

 	WRITE_ONCE(msk->token, subflow->token);
 	__sk_nulls_add_node_rcu((struct sock *)msk, &bucket->msk_chain);
 	bucket->chain_len++;
 	spin_unlock_bh(&bucket->lock);
 	return 0;
 }

 /**
  * mptcp_token_accept - replace a req sk with full sock in token hash
  * @req: the request socket to be removed
  * @msk: the just cloned socket linked to the new connection
  *
  * Called when a SYN packet creates a new logical connection, i.e.
  * is not a join request.
  */
 void mptcp_token_accept(struct mptcp_subflow_request_sock *req,
 			struct mptcp_sock *msk)
 {
 	struct mptcp_subflow_request_sock *pos;
 	struct token_bucket *bucket;

 	bucket = token_bucket(req->token);
 	spin_lock_bh(&bucket->lock);

 	/* pedantic lookup check for the moved token */
 	pos = __token_lookup_req(bucket, req->token);
 	if (!WARN_ON_ONCE(pos != req))
 		hlist_nulls_del_init_rcu(&req->token_node);
 	__sk_nulls_add_node_rcu((struct sock *)msk, &bucket->msk_chain);
 	spin_unlock_bh(&bucket->lock);
 }

 bool mptcp_token_exists(u32 token)
 {
 	struct hlist_nulls_node *pos;
 	struct token_bucket *bucket;
 	struct mptcp_sock *msk;
 	struct sock *sk;

 	rcu_read_lock();
 	bucket = token_bucket(token);

 again:
 	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
 		msk = mptcp_sk(sk);
 		if (READ_ONCE(msk->token) == token)
 			goto found;
 	}
 	if (get_nulls_value(pos) != (token & token_mask))
 		goto again;

 	rcu_read_unlock();
 	return false;
 found:
 	rcu_read_unlock();
 	return true;
 }

 /**
  * mptcp_token_get_sock - retrieve mptcp connection sock using its token
  * @net: restrict to this namespace
  * @token: token of the mptcp connection to retrieve
  *
  * This function returns the mptcp connection structure with the given token.
  * A reference count on the mptcp socket returned is taken.
  *
  * returns NULL if no connection with the given token value exists.
  */
 struct mptcp_sock *mptcp_token_get_sock(struct net *net, u32 token)
 {
 	struct hlist_nulls_node *pos;
 	struct token_bucket *bucket;
 	struct mptcp_sock *msk;
 	struct sock *sk;

 	rcu_read_lock();
 	bucket = token_bucket(token);

 again:
 	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
 		msk = mptcp_sk(sk);
 		if (READ_ONCE(msk->token) != token ||
 		    !net_eq(sock_net(sk), net))
 			continue;

 		if (!refcount_inc_not_zero(&sk->sk_refcnt))
 			goto not_found;

 		if (READ_ONCE(msk->token) != token ||
 		    !net_eq(sock_net(sk), net)) {
 			sock_put(sk);
 			goto again;
 		}
 		goto found;
 	}
 	if (get_nulls_value(pos) != (token & token_mask))
 		goto again;

 not_found:
 	msk = NULL;

 found:
 	rcu_read_unlock();
 	return msk;
 }
 EXPORT_SYMBOL_GPL(mptcp_token_get_sock);

 /**
  * mptcp_token_iter_next - iterate over the token container from given pos
  * @net: namespace to be iterated
  * @s_slot: start slot number
  * @s_num: start number inside the given lock
  *
  * This function returns the first mptcp connection structure found inside the
  * token container starting from the specified position, or NULL.
  *
  * On successful iteration, the iterator is move to the next position and the
  * the acquires a reference to the returned socket.
  */
 struct mptcp_sock *mptcp_token_iter_next(const struct net *net, long *s_slot,
 					 long *s_num)
 {
 	struct mptcp_sock *ret = NULL;
 	struct hlist_nulls_node *pos;
 	int slot, num = 0;

 	for (slot = *s_slot; slot <= token_mask; *s_num = 0, slot++) {
 		struct token_bucket *bucket = &token_hash[slot];
 		struct sock *sk;

 		num = 0;

 		if (hlist_nulls_empty(&bucket->msk_chain))
 			continue;

 		rcu_read_lock();
 		sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
 			++num;
 			if (!net_eq(sock_net(sk), net))
 				continue;

 			if (num <= *s_num)
 				continue;

 			if (!refcount_inc_not_zero(&sk->sk_refcnt))
 				continue;

 			if (!net_eq(sock_net(sk), net)) {
 				sock_put(sk);
 				continue;
 			}

 			ret = mptcp_sk(sk);
 			rcu_read_unlock();
 			goto out;
 		}
 		rcu_read_unlock();
 	}

 out:
 	*s_slot = slot;
 	*s_num = num;
 	return ret;
 }
 EXPORT_SYMBOL_GPL(mptcp_token_iter_next);

 /**
  * mptcp_token_destroy_request - remove mptcp connection/token
  * @req: mptcp request socket dropping the token
  *
  * Remove the token associated to @req.
  */
 void mptcp_token_destroy_request(struct request_sock *req)
 {
 	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
 	struct mptcp_subflow_request_sock *pos;
 	struct token_bucket *bucket;

 	if (hlist_nulls_unhashed(&subflow_req->token_node))
 		return;

 	bucket = token_bucket(subflow_req->token);
 	spin_lock_bh(&bucket->lock);
 	pos = __token_lookup_req(bucket, subflow_req->token);
 	if (!WARN_ON_ONCE(pos != subflow_req)) {
 		hlist_nulls_del_init_rcu(&pos->token_node);
 		bucket->chain_len--;
 	}
 	spin_unlock_bh(&bucket->lock);
 }

 /**
  * mptcp_token_destroy - remove mptcp connection/token
  * @msk: mptcp connection dropping the token
  *
  * Remove the token associated to @msk
  */
 void mptcp_token_destroy(struct mptcp_sock *msk)
 {
 	struct token_bucket *bucket;
 	struct mptcp_sock *pos;

 	if (sk_unhashed((struct sock *)msk))
 		return;

 	bucket = token_bucket(msk->token);
 	spin_lock_bh(&bucket->lock);
 	pos = __token_lookup_msk(bucket, msk->token);
 	if (!WARN_ON_ONCE(pos != msk)) {
 		__sk_nulls_del_node_init_rcu((struct sock *)pos);
 		bucket->chain_len--;
 	}
 	spin_unlock_bh(&bucket->lock);
 }

 void __init mptcp_token_init(void)
 {
 	int i;

 	token_hash = alloc_large_system_hash("MPTCP token",
 					     sizeof(struct token_bucket),
 					     0,
 					     20,/* one slot per 1MB of memory */
 					     HASH_ZERO,
 					     NULL,
 					     &token_mask,
 					     0,
 					     64 * 1024);
 	for (i = 0; i < token_mask + 1; ++i) {
 		INIT_HLIST_NULLS_HEAD(&token_hash[i].req_chain, i);
 		INIT_HLIST_NULLS_HEAD(&token_hash[i].msk_chain, i);
 		spin_lock_init(&token_hash[i].lock);
 	}
 }

 #if IS_MODULE(CONFIG_MPTCP_KUNIT_TESTS)
 EXPORT_SYMBOL_GPL(mptcp_token_new_request);
 EXPORT_SYMBOL_GPL(mptcp_token_new_connect);
 EXPORT_SYMBOL_GPL(mptcp_token_accept);
 EXPORT_SYMBOL_GPL(mptcp_token_destroy_request);
 EXPORT_SYMBOL_GPL(mptcp_token_destroy);
 #endif
	// SPDX-License-Identifier: GPL-2.0
	/* Multipath TCP token management
	* Copyright (c) 2017 - 2019, Intel Corporation.
	*
	* Note: This code is based on mptcp_ctrl.c from multipath-tcp.org,
	* authored by:
	*
	* Sébastien Barré <sebastien.barre@uclouvain.be>
	* Christoph Paasch <christoph.paasch@uclouvain.be>
	* Jaakko Korkeaniemi <jaakko.korkeaniemi@aalto.fi>
	* Gregory Detal <gregory.detal@uclouvain.be>
	* Fabien Duchêne <fabien.duchene@uclouvain.be>
	* Andreas Seelinger <Andreas.Seelinger@rwth-aachen.de>
	* Lavkesh Lahngir <lavkesh51@gmail.com>
	* Andreas Ripke <ripke@neclab.eu>
	* Vlad Dogaru <vlad.dogaru@intel.com>
	* Octavian Purdila <octavian.purdila@intel.com>
	* John Ronan <jronan@tssg.org>
	* Catalin Nicutar <catalin.nicutar@gmail.com>
	* Brandon Heller <brandonh@stanford.edu>
	*/

	#define pr_fmt(fmt) "MPTCP: " fmt

	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/memblock.h>
	#include <linux/ip.h>
	#include <linux/tcp.h>
	#include <net/sock.h>
	#include <net/inet_common.h>
	#include <net/protocol.h>
	#include <net/mptcp.h>
	#include "protocol.h"

	#define TOKEN_MAX_RETRIES 4
	#define TOKEN_MAX_CHAIN_LEN 4

	struct token_bucket {
	spinlock_t lock;
	int chain_len;
	struct hlist_nulls_head req_chain;
	struct hlist_nulls_head msk_chain;
	};

	static struct token_bucket *token_hash __read_mostly;
	static unsigned int token_mask __read_mostly;

	static struct token_bucket *token_bucket(u32 token)
	{
	return &token_hash[token & token_mask];
	}

	/* called with bucket lock held */
	static struct mptcp_subflow_request_sock *
	__token_lookup_req(struct token_bucket *t, u32 token)
	{
	struct mptcp_subflow_request_sock *req;
	struct hlist_nulls_node *pos;

	hlist_nulls_for_each_entry_rcu(req, pos, &t->req_chain, token_node)
	if (req->token == token)
	return req;
	return NULL;
	}

	/* called with bucket lock held */
	static struct mptcp_sock *
	__token_lookup_msk(struct token_bucket *t, u32 token)
	{
	struct hlist_nulls_node *pos;
	struct sock *sk;

	sk_nulls_for_each_rcu(sk, pos, &t->msk_chain)
	if (mptcp_sk(sk)->token == token)
	return mptcp_sk(sk);
	return NULL;
	}

	static bool __token_bucket_busy(struct token_bucket *t, u32 token)
	{
	return !token \|\| t->chain_len >= TOKEN_MAX_CHAIN_LEN \|\|
	__token_lookup_req(t, token) \|\| __token_lookup_msk(t, token);
	}

	static void mptcp_crypto_key_gen_sha(u64 key, u32 token, u64 *idsn)
	{
	/* we might consider a faster version that computes the key as a
	* hash of some information available in the MPTCP socket. Use
	* random data at the moment, as it's probably the safest option
	* in case multiple sockets are opened in different namespaces at
	* the same time.
	*/
	get_random_bytes(key, sizeof(u64));
	mptcp_crypto_key_sha(*key, token, idsn);
	}

	/**
	* mptcp_token_new_request - create new key/idsn/token for subflow_request
	* @req: the request socket
	*
	* This function is called when a new mptcp connection is coming in.
	*
	* It creates a unique token to identify the new mptcp connection,
	* a secret local key and the initial data sequence number (idsn).
	*
	* Returns 0 on success.
	*/
	int mptcp_token_new_request(struct request_sock *req)
	{
	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
	struct token_bucket *bucket;
	u32 token;

	mptcp_crypto_key_sha(subflow_req->local_key,
	&subflow_req->token,
	&subflow_req->idsn);
	pr_debug("req=%p local_key=%llu, token=%u, idsn=%llu\n",
	req, subflow_req->local_key, subflow_req->token,
	subflow_req->idsn);

	token = subflow_req->token;
	bucket = token_bucket(token);
	spin_lock_bh(&bucket->lock);
	if (__token_bucket_busy(bucket, token)) {
	spin_unlock_bh(&bucket->lock);
	return -EBUSY;
	}

	hlist_nulls_add_head_rcu(&subflow_req->token_node, &bucket->req_chain);
	bucket->chain_len++;
	spin_unlock_bh(&bucket->lock);
	return 0;
	}

	/**
	* mptcp_token_new_connect - create new key/idsn/token for subflow
	* @sk: the socket that will initiate a connection
	*
	* This function is called when a new outgoing mptcp connection is
	* initiated.
	*
	* It creates a unique token to identify the new mptcp connection,
	* a secret local key and the initial data sequence number (idsn).
	*
	* On success, the mptcp connection can be found again using
	* the computed token at a later time, this is needed to process
	* join requests.
	*
	* returns 0 on success.
	*/
	int mptcp_token_new_connect(struct sock *sk)
	{
	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
	int retries = TOKEN_MAX_RETRIES;
	struct token_bucket *bucket;

	again:
	mptcp_crypto_key_gen_sha(&subflow->local_key, &subflow->token,
	&subflow->idsn);

	bucket = token_bucket(subflow->token);
	spin_lock_bh(&bucket->lock);
	if (__token_bucket_busy(bucket, subflow->token)) {
	spin_unlock_bh(&bucket->lock);
	if (!--retries)
	return -EBUSY;
	goto again;
	}

	pr_debug("ssk=%p, local_key=%llu, token=%u, idsn=%llu\n",
	sk, subflow->local_key, subflow->token, subflow->idsn);

	WRITE_ONCE(msk->token, subflow->token);
	__sk_nulls_add_node_rcu((struct sock *)msk, &bucket->msk_chain);
	bucket->chain_len++;
	spin_unlock_bh(&bucket->lock);
	return 0;
	}

	/**
	* mptcp_token_accept - replace a req sk with full sock in token hash
	* @req: the request socket to be removed
	* @msk: the just cloned socket linked to the new connection
	*
	* Called when a SYN packet creates a new logical connection, i.e.
	* is not a join request.
	*/
	void mptcp_token_accept(struct mptcp_subflow_request_sock *req,
	struct mptcp_sock *msk)
	{
	struct mptcp_subflow_request_sock *pos;
	struct token_bucket *bucket;

	bucket = token_bucket(req->token);
	spin_lock_bh(&bucket->lock);

	/* pedantic lookup check for the moved token */
	pos = __token_lookup_req(bucket, req->token);
	if (!WARN_ON_ONCE(pos != req))
	hlist_nulls_del_init_rcu(&req->token_node);
	__sk_nulls_add_node_rcu((struct sock *)msk, &bucket->msk_chain);
	spin_unlock_bh(&bucket->lock);
	}

	bool mptcp_token_exists(u32 token)
	{
	struct hlist_nulls_node *pos;
	struct token_bucket *bucket;
	struct mptcp_sock *msk;
	struct sock *sk;

	rcu_read_lock();
	bucket = token_bucket(token);

	again:
	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
	msk = mptcp_sk(sk);
	if (READ_ONCE(msk->token) == token)
	goto found;
	}
	if (get_nulls_value(pos) != (token & token_mask))
	goto again;

	rcu_read_unlock();
	return false;
	found:
	rcu_read_unlock();
	return true;
	}

	/**
	* mptcp_token_get_sock - retrieve mptcp connection sock using its token
	* @net: restrict to this namespace
	* @token: token of the mptcp connection to retrieve
	*
	* This function returns the mptcp connection structure with the given token.
	* A reference count on the mptcp socket returned is taken.
	*
	* returns NULL if no connection with the given token value exists.
	*/
	struct mptcp_sock mptcp_token_get_sock(struct net net, u32 token)
	{
	struct hlist_nulls_node *pos;
	struct token_bucket *bucket;
	struct mptcp_sock *msk;
	struct sock *sk;

	rcu_read_lock();
	bucket = token_bucket(token);

	again:
	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
	msk = mptcp_sk(sk);
	if (READ_ONCE(msk->token) != token \|\|
	!net_eq(sock_net(sk), net))
	continue;

	if (!refcount_inc_not_zero(&sk->sk_refcnt))
	goto not_found;

	if (READ_ONCE(msk->token) != token \|\|
	!net_eq(sock_net(sk), net)) {
	sock_put(sk);
	goto again;
	}
	goto found;
	}
	if (get_nulls_value(pos) != (token & token_mask))
	goto again;

	not_found:
	msk = NULL;

	found:
	rcu_read_unlock();
	return msk;
	}
	EXPORT_SYMBOL_GPL(mptcp_token_get_sock);

	/**
	* mptcp_token_iter_next - iterate over the token container from given pos
	* @net: namespace to be iterated
	* @s_slot: start slot number
	* @s_num: start number inside the given lock
	*
	* This function returns the first mptcp connection structure found inside the
	* token container starting from the specified position, or NULL.
	*
	* On successful iteration, the iterator is move to the next position and the
	* the acquires a reference to the returned socket.
	*/
	struct mptcp_sock mptcp_token_iter_next(const struct net net, long *s_slot,
	long *s_num)
	{
	struct mptcp_sock *ret = NULL;
	struct hlist_nulls_node *pos;
	int slot, num = 0;

	for (slot = s_slot; slot <= token_mask; s_num = 0, slot++) {
	struct token_bucket *bucket = &token_hash[slot];
	struct sock *sk;

	num = 0;

	if (hlist_nulls_empty(&bucket->msk_chain))
	continue;

	rcu_read_lock();
	sk_nulls_for_each_rcu(sk, pos, &bucket->msk_chain) {
	++num;
	if (!net_eq(sock_net(sk), net))
	continue;

	if (num <= *s_num)
	continue;

	if (!refcount_inc_not_zero(&sk->sk_refcnt))
	continue;

	if (!net_eq(sock_net(sk), net)) {
	sock_put(sk);
	continue;
	}

	ret = mptcp_sk(sk);
	rcu_read_unlock();
	goto out;
	}
	rcu_read_unlock();
	}

	out:
	*s_slot = slot;
	*s_num = num;
	return ret;
	}
	EXPORT_SYMBOL_GPL(mptcp_token_iter_next);

	/**
	* mptcp_token_destroy_request - remove mptcp connection/token
	* @req: mptcp request socket dropping the token
	*
	* Remove the token associated to @req.
	*/
	void mptcp_token_destroy_request(struct request_sock *req)
	{
	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
	struct mptcp_subflow_request_sock *pos;
	struct token_bucket *bucket;

	if (hlist_nulls_unhashed(&subflow_req->token_node))
	return;

	bucket = token_bucket(subflow_req->token);
	spin_lock_bh(&bucket->lock);
	pos = __token_lookup_req(bucket, subflow_req->token);
	if (!WARN_ON_ONCE(pos != subflow_req)) {
	hlist_nulls_del_init_rcu(&pos->token_node);
	bucket->chain_len--;
	}
	spin_unlock_bh(&bucket->lock);
	}

	/**
	* mptcp_token_destroy - remove mptcp connection/token
	* @msk: mptcp connection dropping the token
	*
	* Remove the token associated to @msk
	*/
	void mptcp_token_destroy(struct mptcp_sock *msk)
	{
	struct token_bucket *bucket;
	struct mptcp_sock *pos;

	if (sk_unhashed((struct sock *)msk))
	return;

	bucket = token_bucket(msk->token);
	spin_lock_bh(&bucket->lock);
	pos = __token_lookup_msk(bucket, msk->token);
	if (!WARN_ON_ONCE(pos != msk)) {
	__sk_nulls_del_node_init_rcu((struct sock *)pos);
	bucket->chain_len--;
	}
	spin_unlock_bh(&bucket->lock);
	}

	void __init mptcp_token_init(void)
	{
	int i;

	token_hash = alloc_large_system_hash("MPTCP token",
	sizeof(struct token_bucket),
	0,
	20,/* one slot per 1MB of memory */
	HASH_ZERO,
	NULL,
	&token_mask,
	0,
	64 * 1024);
	for (i = 0; i < token_mask + 1; ++i) {
	INIT_HLIST_NULLS_HEAD(&token_hash[i].req_chain, i);
	INIT_HLIST_NULLS_HEAD(&token_hash[i].msk_chain, i);
	spin_lock_init(&token_hash[i].lock);
	}
	}

	#if IS_MODULE(CONFIG_MPTCP_KUNIT_TESTS)
	EXPORT_SYMBOL_GPL(mptcp_token_new_request);
	EXPORT_SYMBOL_GPL(mptcp_token_new_connect);
	EXPORT_SYMBOL_GPL(mptcp_token_accept);
	EXPORT_SYMBOL_GPL(mptcp_token_destroy_request);
	EXPORT_SYMBOL_GPL(mptcp_token_destroy);
	#endif