net/mptcp/syncookies.c

   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;
  30         u8 valid;
  31 };
  32
  33 #define COOKIE_JOIN_SLOTS       1024
  34
  35 static struct join_entry join_entries[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;
  36 static spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp;
  37
  38 static u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net)
  39 {
  40         static u32 mptcp_join_hash_secret __read_mostly;
  41         struct tcphdr *th = tcp_hdr(skb);
  42         u32 seq, i;
  43
  44         net_get_random_once(&mptcp_join_hash_secret,
  45                             sizeof(mptcp_join_hash_secret));
  46
  47         if (th->syn)
  48                 seq = TCP_SKB_CB(skb)->seq;
  49         else
  50                 seq = TCP_SKB_CB(skb)->seq - 1;
  51
  52         i = jhash_3words(seq, net_hash_mix(net),
  53                          (__force __u32)th->source << 16 | (__force __u32)th->dest,
  54                          mptcp_join_hash_secret);
  55
  56         return i % ARRAY_SIZE(join_entries);
  57 }
  58
  59 static void mptcp_join_store_state(struct join_entry *entry,
  60                                    const struct mptcp_subflow_request_sock *subflow_req)
  61 {
  62         entry->token = subflow_req->token;
  63         entry->remote_nonce = subflow_req->remote_nonce;
  64         entry->local_nonce = subflow_req->local_nonce;
  65         entry->backup = subflow_req->backup;
  66         entry->join_id = subflow_req->remote_id;
  67         entry->local_id = subflow_req->local_id;
  68         entry->valid = 1;
  69 }
  70
  71 void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,
  72                                        struct sk_buff *skb)
  73 {
  74         struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
  75         u32 i = mptcp_join_entry_hash(skb, net);
  76
  77         /* No use in waiting if other cpu is already using this slot --
  78          * would overwrite the data that got stored.
  79          */
  80         spin_lock_bh(&join_entry_locks[i]);
  81         mptcp_join_store_state(&join_entries[i], subflow_req);
  82         spin_unlock_bh(&join_entry_locks[i]);
  83 }
  84
  85 /* Called for a cookie-ack with MP_JOIN option present.
  86  * Look up the saved state based on skb hash & check token matches msk
  87  * in same netns.
  88  *
  89  * Caller will check msk can still accept another subflow.  The hmac
  90  * present in the cookie ACK mptcp option space will be checked later.
  91  */
  92 bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,
  93                                         struct sk_buff *skb)
  94 {
  95         struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
  96         u32 i = mptcp_join_entry_hash(skb, net);
  97         struct mptcp_sock *msk;
  98         struct join_entry *e;
  99
 100         e = &join_entries[i];
 101
 102         spin_lock_bh(&join_entry_locks[i]);
 103
 104         if (e->valid == 0) {
 105                 spin_unlock_bh(&join_entry_locks[i]);
 106                 return false;
 107         }
 108
 109         e->valid = 0;
 110
 111         msk = mptcp_token_get_sock(net, e->token);
 112         if (!msk) {
 113                 spin_unlock_bh(&join_entry_locks[i]);
 114                 return false;
 115         }
 116
 117         subflow_req->remote_nonce = e->remote_nonce;
 118         subflow_req->local_nonce = e->local_nonce;
 119         subflow_req->backup = e->backup;
 120         subflow_req->remote_id = e->join_id;
 121         subflow_req->token = e->token;
 122         subflow_req->msk = msk;
 123         spin_unlock_bh(&join_entry_locks[i]);
 124         return true;
 125 }
 126
 127 void __init mptcp_join_cookie_init(void)
 128 {
 129         int i;
 130
 131         for (i = 0; i < COOKIE_JOIN_SLOTS; i++)
 132                 spin_lock_init(&join_entry_locks[i]);
 133 }