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         u32 i = skb_get_hash(skb) ^ net_hash_mix(net);
  41
  42         return i % ARRAY_SIZE(join_entries);
  43 }
  44
  45 static void mptcp_join_store_state(struct join_entry *entry,
  46                                    const struct mptcp_subflow_request_sock *subflow_req)
  47 {
  48         entry->token = subflow_req->token;
  49         entry->remote_nonce = subflow_req->remote_nonce;
  50         entry->local_nonce = subflow_req->local_nonce;
  51         entry->backup = subflow_req->backup;
  52         entry->join_id = subflow_req->remote_id;
  53         entry->local_id = subflow_req->local_id;
  54         entry->valid = 1;
  55 }
  56
  57 void subflow_init_req_cookie_join_save(const struct mptcp_subflow_request_sock *subflow_req,
  58                                        struct sk_buff *skb)
  59 {
  60         struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
  61         u32 i = mptcp_join_entry_hash(skb, net);
  62
  63         /* No use in waiting if other cpu is already using this slot --
  64          * would overwrite the data that got stored.
  65          */
  66         spin_lock_bh(&join_entry_locks[i]);
  67         mptcp_join_store_state(&join_entries[i], subflow_req);
  68         spin_unlock_bh(&join_entry_locks[i]);
  69 }
  70
  71 /* Called for a cookie-ack with MP_JOIN option present.
  72  * Look up the saved state based on skb hash & check token matches msk
  73  * in same netns.
  74  *
  75  * Caller will check msk can still accept another subflow.  The hmac
  76  * present in the cookie ACK mptcp option space will be checked later.
  77  */
  78 bool mptcp_token_join_cookie_init_state(struct mptcp_subflow_request_sock *subflow_req,
  79                                         struct sk_buff *skb)
  80 {
  81         struct net *net = read_pnet(&subflow_req->sk.req.ireq_net);
  82         u32 i = mptcp_join_entry_hash(skb, net);
  83         struct mptcp_sock *msk;
  84         struct join_entry *e;
  85
  86         e = &join_entries[i];
  87
  88         spin_lock_bh(&join_entry_locks[i]);
  89
  90         if (e->valid == 0) {
  91                 spin_unlock_bh(&join_entry_locks[i]);
  92                 return false;
  93         }
  94
  95         e->valid = 0;
  96
  97         msk = mptcp_token_get_sock(e->token);
  98         if (!msk) {
  99                 spin_unlock_bh(&join_entry_locks[i]);
 100                 return false;
 101         }
 102
 103         /* If this fails, the token got re-used in the mean time by another
 104          * mptcp socket in a different netns, i.e. entry is outdated.
 105          */
 106         if (!net_eq(sock_net((struct sock *)msk), net))
 107                 goto err_put;
 108
 109         subflow_req->remote_nonce = e->remote_nonce;
 110         subflow_req->local_nonce = e->local_nonce;
 111         subflow_req->backup = e->backup;
 112         subflow_req->remote_id = e->join_id;
 113         subflow_req->token = e->token;
 114         subflow_req->msk = msk;
 115         spin_unlock_bh(&join_entry_locks[i]);
 116         return true;
 117
 118 err_put:
 119         spin_unlock_bh(&join_entry_locks[i]);
 120         sock_put((struct sock *)msk);
 121         return false;
 122 }
 123
 124 void __init mptcp_join_cookie_init(void)
 125 {
 126         int i;
 127
 128         for (i = 0; i < COOKIE_JOIN_SLOTS; i++)
 129                 spin_lock_init(&join_entry_locks[i]);
 130 }