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TOMOYO Linux Cross Reference
Linux/net/ipv4/tcp_fastopen.c

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  1 #include <linux/crypto.h>
  2 #include <linux/err.h>
  3 #include <linux/init.h>
  4 #include <linux/kernel.h>
  5 #include <linux/list.h>
  6 #include <linux/tcp.h>
  7 #include <linux/rcupdate.h>
  8 #include <linux/rculist.h>
  9 #include <net/inetpeer.h>
 10 #include <net/tcp.h>
 11 
 12 int sysctl_tcp_fastopen __read_mostly = TFO_CLIENT_ENABLE;
 13 
 14 struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
 15 
 16 static DEFINE_SPINLOCK(tcp_fastopen_ctx_lock);
 17 
 18 void tcp_fastopen_init_key_once(bool publish)
 19 {
 20         static u8 key[TCP_FASTOPEN_KEY_LENGTH];
 21 
 22         /* tcp_fastopen_reset_cipher publishes the new context
 23          * atomically, so we allow this race happening here.
 24          *
 25          * All call sites of tcp_fastopen_cookie_gen also check
 26          * for a valid cookie, so this is an acceptable risk.
 27          */
 28         if (net_get_random_once(key, sizeof(key)) && publish)
 29                 tcp_fastopen_reset_cipher(key, sizeof(key));
 30 }
 31 
 32 static void tcp_fastopen_ctx_free(struct rcu_head *head)
 33 {
 34         struct tcp_fastopen_context *ctx =
 35             container_of(head, struct tcp_fastopen_context, rcu);
 36         crypto_free_cipher(ctx->tfm);
 37         kfree(ctx);
 38 }
 39 
 40 int tcp_fastopen_reset_cipher(void *key, unsigned int len)
 41 {
 42         int err;
 43         struct tcp_fastopen_context *ctx, *octx;
 44 
 45         ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 46         if (!ctx)
 47                 return -ENOMEM;
 48         ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
 49 
 50         if (IS_ERR(ctx->tfm)) {
 51                 err = PTR_ERR(ctx->tfm);
 52 error:          kfree(ctx);
 53                 pr_err("TCP: TFO aes cipher alloc error: %d\n", err);
 54                 return err;
 55         }
 56         err = crypto_cipher_setkey(ctx->tfm, key, len);
 57         if (err) {
 58                 pr_err("TCP: TFO cipher key error: %d\n", err);
 59                 crypto_free_cipher(ctx->tfm);
 60                 goto error;
 61         }
 62         memcpy(ctx->key, key, len);
 63 
 64         spin_lock(&tcp_fastopen_ctx_lock);
 65 
 66         octx = rcu_dereference_protected(tcp_fastopen_ctx,
 67                                 lockdep_is_held(&tcp_fastopen_ctx_lock));
 68         rcu_assign_pointer(tcp_fastopen_ctx, ctx);
 69         spin_unlock(&tcp_fastopen_ctx_lock);
 70 
 71         if (octx)
 72                 call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
 73         return err;
 74 }
 75 
 76 static bool __tcp_fastopen_cookie_gen(const void *path,
 77                                       struct tcp_fastopen_cookie *foc)
 78 {
 79         struct tcp_fastopen_context *ctx;
 80         bool ok = false;
 81 
 82         rcu_read_lock();
 83         ctx = rcu_dereference(tcp_fastopen_ctx);
 84         if (ctx) {
 85                 crypto_cipher_encrypt_one(ctx->tfm, foc->val, path);
 86                 foc->len = TCP_FASTOPEN_COOKIE_SIZE;
 87                 ok = true;
 88         }
 89         rcu_read_unlock();
 90         return ok;
 91 }
 92 
 93 /* Generate the fastopen cookie by doing aes128 encryption on both
 94  * the source and destination addresses. Pad 0s for IPv4 or IPv4-mapped-IPv6
 95  * addresses. For the longer IPv6 addresses use CBC-MAC.
 96  *
 97  * XXX (TFO) - refactor when TCP_FASTOPEN_COOKIE_SIZE != AES_BLOCK_SIZE.
 98  */
 99 static bool tcp_fastopen_cookie_gen(struct request_sock *req,
100                                     struct sk_buff *syn,
101                                     struct tcp_fastopen_cookie *foc)
102 {
103         if (req->rsk_ops->family == AF_INET) {
104                 const struct iphdr *iph = ip_hdr(syn);
105 
106                 __be32 path[4] = { iph->saddr, iph->daddr, 0, 0 };
107                 return __tcp_fastopen_cookie_gen(path, foc);
108         }
109 
110 #if IS_ENABLED(CONFIG_IPV6)
111         if (req->rsk_ops->family == AF_INET6) {
112                 const struct ipv6hdr *ip6h = ipv6_hdr(syn);
113                 struct tcp_fastopen_cookie tmp;
114 
115                 if (__tcp_fastopen_cookie_gen(&ip6h->saddr, &tmp)) {
116                         struct in6_addr *buf = (struct in6_addr *) tmp.val;
117                         int i;
118 
119                         for (i = 0; i < 4; i++)
120                                 buf->s6_addr32[i] ^= ip6h->daddr.s6_addr32[i];
121                         return __tcp_fastopen_cookie_gen(buf, foc);
122                 }
123         }
124 #endif
125         return false;
126 }
127 
128 
129 /* If an incoming SYN or SYNACK frame contains a payload and/or FIN,
130  * queue this additional data / FIN.
131  */
132 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
133 {
134         struct tcp_sock *tp = tcp_sk(sk);
135 
136         if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
137                 return;
138 
139         skb = skb_clone(skb, GFP_ATOMIC);
140         if (!skb)
141                 return;
142 
143         skb_dst_drop(skb);
144         /* segs_in has been initialized to 1 in tcp_create_openreq_child().
145          * Hence, reset segs_in to 0 before calling tcp_segs_in()
146          * to avoid double counting.  Also, tcp_segs_in() expects
147          * skb->len to include the tcp_hdrlen.  Hence, it should
148          * be called before __skb_pull().
149          */
150         tp->segs_in = 0;
151         tcp_segs_in(tp, skb);
152         __skb_pull(skb, tcp_hdrlen(skb));
153         skb_set_owner_r(skb, sk);
154 
155         TCP_SKB_CB(skb)->seq++;
156         TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
157 
158         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
159         __skb_queue_tail(&sk->sk_receive_queue, skb);
160         tp->syn_data_acked = 1;
161 
162         /* u64_stats_update_begin(&tp->syncp) not needed here,
163          * as we certainly are not changing upper 32bit value (0)
164          */
165         tp->bytes_received = skb->len;
166 
167         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
168                 tcp_fin(sk);
169 }
170 
171 static struct sock *tcp_fastopen_create_child(struct sock *sk,
172                                               struct sk_buff *skb,
173                                               struct dst_entry *dst,
174                                               struct request_sock *req)
175 {
176         struct tcp_sock *tp;
177         struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
178         struct sock *child;
179         bool own_req;
180 
181         req->num_retrans = 0;
182         req->num_timeout = 0;
183         req->sk = NULL;
184 
185         child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
186                                                          NULL, &own_req);
187         if (!child)
188                 return NULL;
189 
190         spin_lock(&queue->fastopenq.lock);
191         queue->fastopenq.qlen++;
192         spin_unlock(&queue->fastopenq.lock);
193 
194         /* Initialize the child socket. Have to fix some values to take
195          * into account the child is a Fast Open socket and is created
196          * only out of the bits carried in the SYN packet.
197          */
198         tp = tcp_sk(child);
199 
200         tp->fastopen_rsk = req;
201         tcp_rsk(req)->tfo_listener = true;
202 
203         /* RFC1323: The window in SYN & SYN/ACK segments is never
204          * scaled. So correct it appropriately.
205          */
206         tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
207 
208         /* Activate the retrans timer so that SYNACK can be retransmitted.
209          * The request socket is not added to the ehash
210          * because it's been added to the accept queue directly.
211          */
212         inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
213                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
214 
215         atomic_set(&req->rsk_refcnt, 2);
216 
217         /* Now finish processing the fastopen child socket. */
218         inet_csk(child)->icsk_af_ops->rebuild_header(child);
219         tcp_init_congestion_control(child);
220         tcp_mtup_init(child);
221         tcp_init_metrics(child);
222         tcp_init_buffer_space(child);
223 
224         tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
225 
226         tcp_fastopen_add_skb(child, skb);
227 
228         tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
229         /* tcp_conn_request() is sending the SYNACK,
230          * and queues the child into listener accept queue.
231          */
232         return child;
233 }
234 
235 static bool tcp_fastopen_queue_check(struct sock *sk)
236 {
237         struct fastopen_queue *fastopenq;
238 
239         /* Make sure the listener has enabled fastopen, and we don't
240          * exceed the max # of pending TFO requests allowed before trying
241          * to validating the cookie in order to avoid burning CPU cycles
242          * unnecessarily.
243          *
244          * XXX (TFO) - The implication of checking the max_qlen before
245          * processing a cookie request is that clients can't differentiate
246          * between qlen overflow causing Fast Open to be disabled
247          * temporarily vs a server not supporting Fast Open at all.
248          */
249         fastopenq = &inet_csk(sk)->icsk_accept_queue.fastopenq;
250         if (fastopenq->max_qlen == 0)
251                 return false;
252 
253         if (fastopenq->qlen >= fastopenq->max_qlen) {
254                 struct request_sock *req1;
255                 spin_lock(&fastopenq->lock);
256                 req1 = fastopenq->rskq_rst_head;
257                 if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
258                         spin_unlock(&fastopenq->lock);
259                         NET_INC_STATS_BH(sock_net(sk),
260                                          LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
261                         return false;
262                 }
263                 fastopenq->rskq_rst_head = req1->dl_next;
264                 fastopenq->qlen--;
265                 spin_unlock(&fastopenq->lock);
266                 reqsk_put(req1);
267         }
268         return true;
269 }
270 
271 /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
272  * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
273  * cookie request (foc->len == 0).
274  */
275 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
276                               struct request_sock *req,
277                               struct tcp_fastopen_cookie *foc,
278                               struct dst_entry *dst)
279 {
280         struct tcp_fastopen_cookie valid_foc = { .len = -1 };
281         bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
282         struct sock *child;
283 
284         if (foc->len == 0) /* Client requests a cookie */
285                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
286 
287         if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
288               (syn_data || foc->len >= 0) &&
289               tcp_fastopen_queue_check(sk))) {
290                 foc->len = -1;
291                 return NULL;
292         }
293 
294         if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
295                 goto fastopen;
296 
297         if (foc->len >= 0 &&  /* Client presents or requests a cookie */
298             tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&
299             foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
300             foc->len == valid_foc.len &&
301             !memcmp(foc->val, valid_foc.val, foc->len)) {
302                 /* Cookie is valid. Create a (full) child socket to accept
303                  * the data in SYN before returning a SYN-ACK to ack the
304                  * data. If we fail to create the socket, fall back and
305                  * ack the ISN only but includes the same cookie.
306                  *
307                  * Note: Data-less SYN with valid cookie is allowed to send
308                  * data in SYN_RECV state.
309                  */
310 fastopen:
311                 child = tcp_fastopen_create_child(sk, skb, dst, req);
312                 if (child) {
313                         foc->len = -1;
314                         NET_INC_STATS_BH(sock_net(sk),
315                                          LINUX_MIB_TCPFASTOPENPASSIVE);
316                         return child;
317                 }
318                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
319         } else if (foc->len > 0) /* Client presents an invalid cookie */
320                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
321 
322         valid_foc.exp = foc->exp;
323         *foc = valid_foc;
324         return NULL;
325 }
326 

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