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	rcu_read_lock();
82	ctx = rcu_dereference(tcp_fastopen_ctx);
83	if (ctx) {
84		crypto_cipher_encrypt_one(ctx->tfm, foc->val, path);
85		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
86		ok = true;
87	}
88	rcu_read_unlock();
89	return ok;
90}
91
92/* Generate the fastopen cookie by doing aes128 encryption on both
93 * the source and destination addresses. Pad 0s for IPv4 or IPv4-mapped-IPv6
94 * addresses. For the longer IPv6 addresses use CBC-MAC.
95 *
96 * XXX (TFO) - refactor when TCP_FASTOPEN_COOKIE_SIZE != AES_BLOCK_SIZE.
97 */
98static bool tcp_fastopen_cookie_gen(struct request_sock *req,
99				    struct sk_buff *syn,
100				    struct tcp_fastopen_cookie *foc)
101{
102	if (req->rsk_ops->family == AF_INET) {
103		const struct iphdr *iph = ip_hdr(syn);
104
105		__be32 path[4] = { iph->saddr, iph->daddr, 0, 0 };
106		return __tcp_fastopen_cookie_gen(path, foc);
107	}
108
109#if IS_ENABLED(CONFIG_IPV6)
110	if (req->rsk_ops->family == AF_INET6) {
111		const struct ipv6hdr *ip6h = ipv6_hdr(syn);
112		struct tcp_fastopen_cookie tmp;
113
114		if (__tcp_fastopen_cookie_gen(&ip6h->saddr, &tmp)) {
115			struct in6_addr *buf = (struct in6_addr *) tmp.val;
116			int i;
117
118			for (i = 0; i < 4; i++)
119				buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
120			return __tcp_fastopen_cookie_gen(buf, foc);
121		}
122	}
123#endif
124	return false;
125}
126
127static bool tcp_fastopen_create_child(struct sock *sk,
128				      struct sk_buff *skb,
129				      struct dst_entry *dst,
130				      struct request_sock *req)
131{
132	struct tcp_sock *tp;
133	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
134	struct sock *child;
135	u32 end_seq;
136
137	req->num_retrans = 0;
138	req->num_timeout = 0;
139	req->sk = NULL;
140
141	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
142	if (!child)
143		return false;
144
145	spin_lock(&queue->fastopenq->lock);
146	queue->fastopenq->qlen++;
147	spin_unlock(&queue->fastopenq->lock);
148
149	/* Initialize the child socket. Have to fix some values to take
150	 * into account the child is a Fast Open socket and is created
151	 * only out of the bits carried in the SYN packet.
152	 */
153	tp = tcp_sk(child);
154
155	tp->fastopen_rsk = req;
156	tcp_rsk(req)->tfo_listener = true;
157
158	/* RFC1323: The window in SYN & SYN/ACK segments is never
159	 * scaled. So correct it appropriately.
160	 */
161	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
162
163	/* Activate the retrans timer so that SYNACK can be retransmitted.
164	 * The request socket is not added to the SYN table of the parent
165	 * because it's been added to the accept queue directly.
166	 */
167	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
168				  TCP_TIMEOUT_INIT, TCP_RTO_MAX);
169
170	atomic_set(&req->rsk_refcnt, 1);
171	/* Add the child socket directly into the accept queue */
172	inet_csk_reqsk_queue_add(sk, req, child);
173
174	/* Now finish processing the fastopen child socket. */
175	inet_csk(child)->icsk_af_ops->rebuild_header(child);
176	tcp_init_congestion_control(child);
177	tcp_mtup_init(child);
178	tcp_init_metrics(child);
179	tcp_init_buffer_space(child);
180
181	/* Queue the data carried in the SYN packet. We need to first
182	 * bump skb's refcnt because the caller will attempt to free it.
183	 * Note that IPv6 might also have used skb_get() trick
184	 * in tcp_v6_conn_request() to keep this SYN around (treq->pktopts)
185	 * So we need to eventually get a clone of the packet,
186	 * before inserting it in sk_receive_queue.
187	 *
188	 * XXX (TFO) - we honor a zero-payload TFO request for now,
189	 * (any reason not to?) but no need to queue the skb since
190	 * there is no data. How about SYN+FIN?
191	 */
192	end_seq = TCP_SKB_CB(skb)->end_seq;
193	if (end_seq != TCP_SKB_CB(skb)->seq + 1) {
194		struct sk_buff *skb2;
195
196		if (unlikely(skb_shared(skb)))
197			skb2 = skb_clone(skb, GFP_ATOMIC);
198		else
199			skb2 = skb_get(skb);
200
201		if (likely(skb2)) {
202			skb_dst_drop(skb2);
203			__skb_pull(skb2, tcp_hdrlen(skb));
204			skb_set_owner_r(skb2, child);
205			__skb_queue_tail(&child->sk_receive_queue, skb2);
206			tp->syn_data_acked = 1;
207
208			/* u64_stats_update_begin(&tp->syncp) not needed here,
209			 * as we certainly are not changing upper 32bit value (0)
210			 */
211			tp->bytes_received = end_seq - TCP_SKB_CB(skb)->seq - 1;
212		} else {
213			end_seq = TCP_SKB_CB(skb)->seq + 1;
214		}
215	}
216	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = end_seq;
217	sk->sk_data_ready(sk);
218	bh_unlock_sock(child);
219	sock_put(child);
220	WARN_ON(!req->sk);
221	return true;
222}
223
224static bool tcp_fastopen_queue_check(struct sock *sk)
225{
226	struct fastopen_queue *fastopenq;
227
228	/* Make sure the listener has enabled fastopen, and we don't
229	 * exceed the max # of pending TFO requests allowed before trying
230	 * to validating the cookie in order to avoid burning CPU cycles
231	 * unnecessarily.
232	 *
233	 * XXX (TFO) - The implication of checking the max_qlen before
234	 * processing a cookie request is that clients can't differentiate
235	 * between qlen overflow causing Fast Open to be disabled
236	 * temporarily vs a server not supporting Fast Open at all.
237	 */
238	fastopenq = inet_csk(sk)->icsk_accept_queue.fastopenq;
239	if (!fastopenq || fastopenq->max_qlen == 0)
240		return false;
241
242	if (fastopenq->qlen >= fastopenq->max_qlen) {
243		struct request_sock *req1;
244		spin_lock(&fastopenq->lock);
245		req1 = fastopenq->rskq_rst_head;
246		if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
247			spin_unlock(&fastopenq->lock);
248			NET_INC_STATS_BH(sock_net(sk),
249					 LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
250			return false;
251		}
252		fastopenq->rskq_rst_head = req1->dl_next;
253		fastopenq->qlen--;
254		spin_unlock(&fastopenq->lock);
255		reqsk_put(req1);
256	}
257	return true;
258}
259
260/* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
261 * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
262 * cookie request (foc->len == 0).
263 */
264bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
265		      struct request_sock *req,
266		      struct tcp_fastopen_cookie *foc,
267		      struct dst_entry *dst)
268{
269	struct tcp_fastopen_cookie valid_foc = { .len = -1 };
270	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
271
272	if (foc->len == 0) /* Client requests a cookie */
273		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
274
275	if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
276	      (syn_data || foc->len >= 0) &&
277	      tcp_fastopen_queue_check(sk))) {
278		foc->len = -1;
279		return false;
280	}
281
282	if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
283		goto fastopen;
284
285	if (foc->len >= 0 &&  /* Client presents or requests a cookie */
286	    tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&
287	    foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
288	    foc->len == valid_foc.len &&
289	    !memcmp(foc->val, valid_foc.val, foc->len)) {
290		/* Cookie is valid. Create a (full) child socket to accept
291		 * the data in SYN before returning a SYN-ACK to ack the
292		 * data. If we fail to create the socket, fall back and
293		 * ack the ISN only but includes the same cookie.
294		 *
295		 * Note: Data-less SYN with valid cookie is allowed to send
296		 * data in SYN_RECV state.
297		 */
298fastopen:
299		if (tcp_fastopen_create_child(sk, skb, dst, req)) {
300			foc->len = -1;
301			NET_INC_STATS_BH(sock_net(sk),
302					 LINUX_MIB_TCPFASTOPENPASSIVE);
303			return true;
304		}
305		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
306	} else if (foc->len > 0) /* Client presents an invalid cookie */
307		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
308
309	valid_foc.exp = foc->exp;
310	*foc = valid_foc;
311	return false;
312}
313EXPORT_SYMBOL(tcp_try_fastopen);
314