1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/skbuff.h> 3 4 #include "protocol.h" 5 6 /* Syncookies do not work for JOIN requests. 7 * 8 * Unlike MP_CAPABLE, where the ACK cookie contains the needed MPTCP 9 * options to reconstruct the initial syn state, MP_JOIN does not contain 10 * the token to obtain the mptcp socket nor the server-generated nonce 11 * that was used in the cookie SYN/ACK response. 12 * 13 * Keep a small best effort state table to store the syn/synack data, 14 * indexed by skb hash. 15 * 16 * A MP_JOIN SYN packet handled by syn cookies is only stored if the 32bit 17 * token matches a known mptcp connection that can still accept more subflows. 18 * 19 * There is no timeout handling -- state is only re-constructed 20 * when the TCP ACK passed the cookie validation check. 21 */ 22 23 struct join_entry { 24 u32 token; 25 u32 remote_nonce; 26 u32 local_nonce; 27 u8 join_id; 28 u8 local_id; 29 u8 backup:1, 30 request_bkup:1; 31 u8 valid; 32 }; 33 34 #define COOKIE_JOIN_SLOTS 1024 35 36 static struct join_entry join_entries[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp; 37 static spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp; 38 39 static u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net) 40 { 41 static u32 mptcp_join_hash_secret __read_mostly; 42 struct tcphdr *th = tcp_hdr(skb); 43 u32 seq, i; 44 45 net_get_random_once(&mptcp_join_hash_secret, 46 sizeof(mptcp_join_hash_secret)); 47 48 if (th->syn) 49 seq = TCP_SKB_CB(skb)->seq; 50 else 51 seq = TCP_SKB_CB(skb)->seq - 1; 52 53 i = jhash_3words(seq, net_hash_mix(net), 54 (__force __u32)th->source << 16 | (__force __u32)th->dest, 55 mptcp_join_hash_secret); 56 57 return i % ARRAY_SIZE(join_entries); 58 } 59 60 static void mptcp_join_store_state(struct join_entry *entry, 61 const struct mptcp_subflow_request_sock *subflow_req) 62 { 63 entry->token = subflow_req->token; 64 entry->remote_nonce = subflow_req->remote_nonce; 65 entry->local_nonce = subflow_req->local_nonce; 66 entry->backup = subflow_req->backup; 67 entry->request_bkup = subflow_req->request_bkup; 68 entry->join_id = subflow_req->remote_id; 69 entry->local_id = subflow_req->local_id; 70 entry->valid = 1; 71 } 72 73 void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req, 74 struct sk_buff *skb) 75 { 76 struct net *net = read_pnet(&subflow_req->sk.req.ireq_net); 77 u32 i = mptcp_join_entry_hash(skb, net); 78 79 /* No use in waiting if other cpu is already using this slot -- 80 * would overwrite the data that got stored. 81 */ 82 spin_lock_bh(&join_entry_locks[i]); 83 mptcp_join_store_state(&join_entries[i], subflow_req); 84 spin_unlock_bh(&join_entry_locks[i]); 85 } 86 87 /* Called for a cookie-ack with MP_JOIN option present. 88 * Look up the saved state based on skb hash & check token matches msk 89 * in same netns. 90 * 91 * Caller will check msk can still accept another subflow. The hmac 92 * present in the cookie ACK mptcp option space will be checked later. 93 */ 94 bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req, 95 struct sk_buff *skb) 96 { 97 struct net *net = read_pnet(&subflow_req->sk.req.ireq_net); 98 u32 i = mptcp_join_entry_hash(skb, net); 99 struct mptcp_sock *msk; 100 struct join_entry *e; 101 102 e = &join_entries[i]; 103 104 spin_lock_bh(&join_entry_locks[i]); 105 106 if (e->valid == 0) { 107 spin_unlock_bh(&join_entry_locks[i]); 108 return false; 109 } 110 111 e->valid = 0; 112 113 msk = mptcp_token_get_sock(net, e->token); 114 if (!msk) { 115 spin_unlock_bh(&join_entry_locks[i]); 116 return false; 117 } 118 119 subflow_req->remote_nonce = e->remote_nonce; 120 subflow_req->local_nonce = e->local_nonce; 121 subflow_req->backup = e->backup; 122 subflow_req->request_bkup = e->request_bkup; 123 subflow_req->remote_id = e->join_id; 124 subflow_req->local_id = e->local_id; 125 subflow_req->token = e->token; 126 subflow_req->msk = msk; 127 spin_unlock_bh(&join_entry_locks[i]); 128 return true; 129 } 130 131 void __init mptcp_join_cookie_init(void) 132 { 133 int i; 134 135 for (i = 0; i < COOKIE_JOIN_SLOTS; i++) 136 spin_lock_init(&join_entry_locks[i]); 137 } 138