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 }
134
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