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 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 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 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 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 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 */ 100 static 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 = 4; 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 } 128 129 static 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 } 208 EXPORT_SYMBOL(tcp_fastopen_create_child); 209 210 static 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 */ 250 bool 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 */ 280 fastopen: 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 } 295 EXPORT_SYMBOL(tcp_try_fastopen); 296