1#include <linux/err.h>
2#include <linux/init.h>
3#include <linux/kernel.h>
4#include <linux/list.h>
5#include <linux/tcp.h>
6#include <linux/rcupdate.h>
7#include <linux/rculist.h>
8#include <net/inetpeer.h>
9#include <net/tcp.h>
10
11int sysctl_tcp_fastopen __read_mostly = TFO_CLIENT_ENABLE;
12
13struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
14
15static DEFINE_SPINLOCK(tcp_fastopen_ctx_lock);
16
17void tcp_fastopen_init_key_once(bool publish)
18{
19	static u8 key[TCP_FASTOPEN_KEY_LENGTH];
20
21	/* tcp_fastopen_reset_cipher publishes the new context
22	 * atomically, so we allow this race happening here.
23	 *
24	 * All call sites of tcp_fastopen_cookie_gen also check
25	 * for a valid cookie, so this is an acceptable risk.
26	 */
27	if (net_get_random_once(key, sizeof(key)) && publish)
28		tcp_fastopen_reset_cipher(key, sizeof(key));
29}
30
31static void tcp_fastopen_ctx_free(struct rcu_head *head)
32{
33	struct tcp_fastopen_context *ctx =
34	    container_of(head, struct tcp_fastopen_context, rcu);
35	crypto_free_cipher(ctx->tfm);
36	kfree(ctx);
37}
38
39int tcp_fastopen_reset_cipher(void *key, unsigned int len)
40{
41	int err;
42	struct tcp_fastopen_context *ctx, *octx;
43
44	ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
45	if (!ctx)
46		return -ENOMEM;
47	ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
48
49	if (IS_ERR(ctx->tfm)) {
50		err = PTR_ERR(ctx->tfm);
51error:		kfree(ctx);
52		pr_err("TCP: TFO aes cipher alloc error: %d\n", err);
53		return err;
54	}
55	err = crypto_cipher_setkey(ctx->tfm, key, len);
56	if (err) {
57		pr_err("TCP: TFO cipher key error: %d\n", err);
58		crypto_free_cipher(ctx->tfm);
59		goto error;
60	}
61	memcpy(ctx->key, key, len);
62
63	spin_lock(&tcp_fastopen_ctx_lock);
64
65	octx = rcu_dereference_protected(tcp_fastopen_ctx,
66				lockdep_is_held(&tcp_fastopen_ctx_lock));
67	rcu_assign_pointer(tcp_fastopen_ctx, ctx);
68	spin_unlock(&tcp_fastopen_ctx_lock);
69
70	if (octx)
71		call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
72	return err;
73}
74
75static bool __tcp_fastopen_cookie_gen(const void *path,
76				      struct tcp_fastopen_cookie *foc)
77{
78	struct tcp_fastopen_context *ctx;
79	bool ok = false;
80
81	tcp_fastopen_init_key_once(true);
82
83	rcu_read_lock();
84	ctx = rcu_dereference(tcp_fastopen_ctx);
85	if (ctx) {
86		crypto_cipher_encrypt_one(ctx->tfm, foc->val, path);
87		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
88		ok = true;
89	}
90	rcu_read_unlock();
91	return ok;
92}
93
94/* Generate the fastopen cookie by doing aes128 encryption on both
95 * the source and destination addresses. Pad 0s for IPv4 or IPv4-mapped-IPv6
96 * addresses. For the longer IPv6 addresses use CBC-MAC.
97 *
98 * XXX (TFO) - refactor when TCP_FASTOPEN_COOKIE_SIZE != AES_BLOCK_SIZE.
99 */
100static bool tcp_fastopen_cookie_gen(struct request_sock *req,
101				    struct sk_buff *syn,
102				    struct tcp_fastopen_cookie *foc)
103{
104	if (req->rsk_ops->family == AF_INET) {
105		const struct iphdr *iph = ip_hdr(syn);
106
107		__be32 path[4] = { iph->saddr, iph->daddr, 0, 0 };
108		return __tcp_fastopen_cookie_gen(path, foc);
109	}
110
111#if IS_ENABLED(CONFIG_IPV6)
112	if (req->rsk_ops->family == AF_INET6) {
113		const struct ipv6hdr *ip6h = ipv6_hdr(syn);
114		struct tcp_fastopen_cookie tmp;
115
116		if (__tcp_fastopen_cookie_gen(&ip6h->saddr, &tmp)) {
117			struct in6_addr *buf = (struct in6_addr *) tmp.val;
118			int i;
119
120			for (i = 0; i < 4; i++)
121				buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
122			return __tcp_fastopen_cookie_gen(buf, foc);
123		}
124	}
125#endif
126	return false;
127}
128
129static bool tcp_fastopen_create_child(struct sock *sk,
130				      struct sk_buff *skb,
131				      struct dst_entry *dst,
132				      struct request_sock *req)
133{
134	struct tcp_sock *tp;
135	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
136	struct sock *child;
137
138	req->num_retrans = 0;
139	req->num_timeout = 0;
140	req->sk = NULL;
141
142	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
143	if (child == NULL)
144		return false;
145
146	spin_lock(&queue->fastopenq->lock);
147	queue->fastopenq->qlen++;
148	spin_unlock(&queue->fastopenq->lock);
149
150	/* Initialize the child socket. Have to fix some values to take
151	 * into account the child is a Fast Open socket and is created
152	 * only out of the bits carried in the SYN packet.
153	 */
154	tp = tcp_sk(child);
155
156	tp->fastopen_rsk = req;
157	/* Do a hold on the listner sk so that if the listener is being
158	 * closed, the child that has been accepted can live on and still
159	 * access listen_lock.
160	 */
161	sock_hold(sk);
162	tcp_rsk(req)->listener = sk;
163
164	/* RFC1323: The window in SYN & SYN/ACK segments is never
165	 * scaled. So correct it appropriately.
166	 */
167	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
168
169	/* Activate the retrans timer so that SYNACK can be retransmitted.
170	 * The request socket is not added to the SYN table of the parent
171	 * because it's been added to the accept queue directly.
172	 */
173	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
174				  TCP_TIMEOUT_INIT, TCP_RTO_MAX);
175
176	/* Add the child socket directly into the accept queue */
177	inet_csk_reqsk_queue_add(sk, req, child);
178
179	/* Now finish processing the fastopen child socket. */
180	inet_csk(child)->icsk_af_ops->rebuild_header(child);
181	tcp_init_congestion_control(child);
182	tcp_mtup_init(child);
183	tcp_init_metrics(child);
184	tcp_init_buffer_space(child);
185
186	/* Queue the data carried in the SYN packet. We need to first
187	 * bump skb's refcnt because the caller will attempt to free it.
188	 *
189	 * XXX (TFO) - we honor a zero-payload TFO request for now,
190	 * (any reason not to?) but no need to queue the skb since
191	 * there is no data. How about SYN+FIN?
192	 */
193	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1) {
194		skb = skb_get(skb);
195		skb_dst_drop(skb);
196		__skb_pull(skb, tcp_hdr(skb)->doff * 4);
197		skb_set_owner_r(skb, child);
198		__skb_queue_tail(&child->sk_receive_queue, skb);
199		tp->syn_data_acked = 1;
200	}
201	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
202	sk->sk_data_ready(sk);
203	bh_unlock_sock(child);
204	sock_put(child);
205	WARN_ON(req->sk == NULL);
206	return true;
207}
208EXPORT_SYMBOL(tcp_fastopen_create_child);
209
210static bool tcp_fastopen_queue_check(struct sock *sk)
211{
212	struct fastopen_queue *fastopenq;
213
214	/* Make sure the listener has enabled fastopen, and we don't
215	 * exceed the max # of pending TFO requests allowed before trying
216	 * to validating the cookie in order to avoid burning CPU cycles
217	 * unnecessarily.
218	 *
219	 * XXX (TFO) - The implication of checking the max_qlen before
220	 * processing a cookie request is that clients can't differentiate
221	 * between qlen overflow causing Fast Open to be disabled
222	 * temporarily vs a server not supporting Fast Open at all.
223	 */
224	fastopenq = inet_csk(sk)->icsk_accept_queue.fastopenq;
225	if (fastopenq == NULL || fastopenq->max_qlen == 0)
226		return false;
227
228	if (fastopenq->qlen >= fastopenq->max_qlen) {
229		struct request_sock *req1;
230		spin_lock(&fastopenq->lock);
231		req1 = fastopenq->rskq_rst_head;
232		if ((req1 == NULL) || time_after(req1->expires, jiffies)) {
233			spin_unlock(&fastopenq->lock);
234			NET_INC_STATS_BH(sock_net(sk),
235					 LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
236			return false;
237		}
238		fastopenq->rskq_rst_head = req1->dl_next;
239		fastopenq->qlen--;
240		spin_unlock(&fastopenq->lock);
241		reqsk_free(req1);
242	}
243	return true;
244}
245
246/* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
247 * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
248 * cookie request (foc->len == 0).
249 */
250bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
251		      struct request_sock *req,
252		      struct tcp_fastopen_cookie *foc,
253		      struct dst_entry *dst)
254{
255	struct tcp_fastopen_cookie valid_foc = { .len = -1 };
256	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
257
258	if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
259	      (syn_data || foc->len >= 0) &&
260	      tcp_fastopen_queue_check(sk))) {
261		foc->len = -1;
262		return false;
263	}
264
265	if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
266		goto fastopen;
267
268	if (tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&
269	    foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
270	    foc->len == valid_foc.len &&
271	    !memcmp(foc->val, valid_foc.val, foc->len)) {
272		/* Cookie is valid. Create a (full) child socket to accept
273		 * the data in SYN before returning a SYN-ACK to ack the
274		 * data. If we fail to create the socket, fall back and
275		 * ack the ISN only but includes the same cookie.
276		 *
277		 * Note: Data-less SYN with valid cookie is allowed to send
278		 * data in SYN_RECV state.
279		 */
280fastopen:
281		if (tcp_fastopen_create_child(sk, skb, dst, req)) {
282			foc->len = -1;
283			NET_INC_STATS_BH(sock_net(sk),
284					 LINUX_MIB_TCPFASTOPENPASSIVE);
285			return true;
286		}
287	}
288
289	NET_INC_STATS_BH(sock_net(sk), foc->len ?
290			 LINUX_MIB_TCPFASTOPENPASSIVEFAIL :
291			 LINUX_MIB_TCPFASTOPENCOOKIEREQD);
292	*foc = valid_foc;
293	return false;
294}
295EXPORT_SYMBOL(tcp_try_fastopen);
296