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