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
11 int sysctl_tcp_fastopen __read_mostly = TFO_CLIENT_ENABLE;
12
13 struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
14
15 static DEFINE_SPINLOCK(tcp_fastopen_ctx_lock);
16
tcp_fastopen_init_key_once(bool publish)17 void 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
tcp_fastopen_ctx_free(struct rcu_head * head)31 static 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
tcp_fastopen_reset_cipher(void * key,unsigned int len)39 int 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);
51 error: 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
__tcp_fastopen_cookie_gen(const void * path,struct tcp_fastopen_cookie * foc)75 static 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 */
tcp_fastopen_cookie_gen(struct request_sock * req,struct sk_buff * syn,struct tcp_fastopen_cookie * foc)98 static 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 = &tmp.addr;
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
tcp_fastopen_create_child(struct sock * sk,struct sk_buff * skb,struct dst_entry * dst,struct request_sock * req)127 static struct sock *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 bool own_req;
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 NULL, &own_req);
144 if (!child)
145 return NULL;
146
147 spin_lock(&queue->fastopenq.lock);
148 queue->fastopenq.qlen++;
149 spin_unlock(&queue->fastopenq.lock);
150
151 /* Initialize the child socket. Have to fix some values to take
152 * into account the child is a Fast Open socket and is created
153 * only out of the bits carried in the SYN packet.
154 */
155 tp = tcp_sk(child);
156
157 tp->fastopen_rsk = req;
158 tcp_rsk(req)->tfo_listener = true;
159
160 /* RFC1323: The window in SYN & SYN/ACK segments is never
161 * scaled. So correct it appropriately.
162 */
163 tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
164 tp->max_window = tp->snd_wnd;
165
166 /* Activate the retrans timer so that SYNACK can be retransmitted.
167 * The request socket is not added to the ehash
168 * because it's been added to the accept queue directly.
169 */
170 inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
171 TCP_TIMEOUT_INIT, TCP_RTO_MAX);
172
173 atomic_set(&req->rsk_refcnt, 2);
174
175 /* Now finish processing the fastopen child socket. */
176 inet_csk(child)->icsk_af_ops->rebuild_header(child);
177 tcp_init_congestion_control(child);
178 tcp_mtup_init(child);
179 tcp_init_metrics(child);
180 tcp_init_buffer_space(child);
181
182 /* Queue the data carried in the SYN packet.
183 * We used to play tricky games with skb_get().
184 * With lockless listener, it is a dead end.
185 * Do not think about it.
186 *
187 * XXX (TFO) - we honor a zero-payload TFO request for now,
188 * (any reason not to?) but no need to queue the skb since
189 * there is no data. How about SYN+FIN?
190 */
191 end_seq = TCP_SKB_CB(skb)->end_seq;
192 if (end_seq != TCP_SKB_CB(skb)->seq + 1) {
193 struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
194
195 if (likely(skb2)) {
196 skb_dst_drop(skb2);
197 __skb_pull(skb2, tcp_hdrlen(skb));
198 skb_set_owner_r(skb2, child);
199 __skb_queue_tail(&child->sk_receive_queue, skb2);
200 tp->syn_data_acked = 1;
201
202 /* u64_stats_update_begin(&tp->syncp) not needed here,
203 * as we certainly are not changing upper 32bit value (0)
204 */
205 tp->bytes_received = end_seq - TCP_SKB_CB(skb)->seq - 1;
206 } else {
207 end_seq = TCP_SKB_CB(skb)->seq + 1;
208 }
209 }
210 tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = end_seq;
211 /* tcp_conn_request() is sending the SYNACK,
212 * and queues the child into listener accept queue.
213 */
214 return child;
215 }
216
tcp_fastopen_queue_check(struct sock * sk)217 static bool tcp_fastopen_queue_check(struct sock *sk)
218 {
219 struct fastopen_queue *fastopenq;
220
221 /* Make sure the listener has enabled fastopen, and we don't
222 * exceed the max # of pending TFO requests allowed before trying
223 * to validating the cookie in order to avoid burning CPU cycles
224 * unnecessarily.
225 *
226 * XXX (TFO) - The implication of checking the max_qlen before
227 * processing a cookie request is that clients can't differentiate
228 * between qlen overflow causing Fast Open to be disabled
229 * temporarily vs a server not supporting Fast Open at all.
230 */
231 fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
232 if (fastopenq->max_qlen == 0)
233 return false;
234
235 if (fastopenq->qlen >= fastopenq->max_qlen) {
236 struct request_sock *req1;
237 spin_lock(&fastopenq->lock);
238 req1 = fastopenq->rskq_rst_head;
239 if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
240 spin_unlock(&fastopenq->lock);
241 NET_INC_STATS_BH(sock_net(sk),
242 LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
243 return false;
244 }
245 fastopenq->rskq_rst_head = req1->dl_next;
246 fastopenq->qlen--;
247 spin_unlock(&fastopenq->lock);
248 reqsk_put(req1);
249 }
250 return true;
251 }
252
253 /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
254 * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
255 * cookie request (foc->len == 0).
256 */
tcp_try_fastopen(struct sock * sk,struct sk_buff * skb,struct request_sock * req,struct tcp_fastopen_cookie * foc,struct dst_entry * dst)257 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
258 struct request_sock *req,
259 struct tcp_fastopen_cookie *foc,
260 struct dst_entry *dst)
261 {
262 struct tcp_fastopen_cookie valid_foc = { .len = -1 };
263 bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
264 struct sock *child;
265
266 if (foc->len == 0) /* Client requests a cookie */
267 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
268
269 if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
270 (syn_data || foc->len >= 0) &&
271 tcp_fastopen_queue_check(sk))) {
272 foc->len = -1;
273 return NULL;
274 }
275
276 if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
277 goto fastopen;
278
279 if (foc->len >= 0 && /* Client presents or requests a cookie */
280 tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&
281 foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
282 foc->len == valid_foc.len &&
283 !memcmp(foc->val, valid_foc.val, foc->len)) {
284 /* Cookie is valid. Create a (full) child socket to accept
285 * the data in SYN before returning a SYN-ACK to ack the
286 * data. If we fail to create the socket, fall back and
287 * ack the ISN only but includes the same cookie.
288 *
289 * Note: Data-less SYN with valid cookie is allowed to send
290 * data in SYN_RECV state.
291 */
292 fastopen:
293 child = tcp_fastopen_create_child(sk, skb, dst, req);
294 if (child) {
295 foc->len = -1;
296 NET_INC_STATS_BH(sock_net(sk),
297 LINUX_MIB_TCPFASTOPENPASSIVE);
298 return child;
299 }
300 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
301 } else if (foc->len > 0) /* Client presents an invalid cookie */
302 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
303
304 valid_foc.exp = foc->exp;
305 *foc = valid_foc;
306 return NULL;
307 }
308