linux/net/mptcp/syncookies.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/skbuff.h>

#include "protocol.h"

/* Syncookies do not work for JOIN requests.
 *
 * Unlike MP_CAPABLE, where the ACK cookie contains the needed MPTCP
 * options to reconstruct the initial syn state, MP_JOIN does not contain
 * the token to obtain the mptcp socket nor the server-generated nonce
 * that was used in the cookie SYN/ACK response.
 *
 * Keep a small best effort state table to store the syn/synack data,
 * indexed by skb hash.
 *
 * A MP_JOIN SYN packet handled by syn cookies is only stored if the 32bit
 * token matches a known mptcp connection that can still accept more subflows.
 *
 * There is no timeout handling -- state is only re-constructed
 * when the TCP ACK passed the cookie validation check.
 */

struct join_entry { … };

#define COOKIE_JOIN_SLOTS …

static struct join_entry join_entries[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;
static spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;

static u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net)
{ … }

static void mptcp_join_store_state(struct join_entry *entry,
				   const struct mptcp_subflow_request_sock *subflow_req)
{ … }

void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,
				       struct sk_buff *skb)
{ … }

/* Called for a cookie-ack with MP_JOIN option present.
 * Look up the saved state based on skb hash & check token matches msk
 * in same netns.
 *
 * Caller will check msk can still accept another subflow.  The hmac
 * present in the cookie ACK mptcp option space will be checked later.
 */
bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,
					struct sk_buff *skb)
{ … }

void __init mptcp_join_cookie_init(void)
{ … }