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 static struct sock *tcp_fastopen_create_child(struct sock *sk, 129 struct sk_buff *skb, 130 struct dst_entry *dst, 131 struct request_sock *req) 132 { 133 struct tcp_sock *tp; 134 struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue; 135 struct sock *child; 136 u32 end_seq; 137 bool own_req; 138 139 req->num_retrans = 0; 140 req->num_timeout = 0; 141 req->sk = NULL; 142 143 child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, 144 NULL, &own_req); 145 if (!child) 146 return NULL; 147 148 spin_lock(&queue->fastopenq.lock); 149 queue->fastopenq.qlen++; 150 spin_unlock(&queue->fastopenq.lock); 151 152 /* Initialize the child socket. Have to fix some values to take 153 * into account the child is a Fast Open socket and is created 154 * only out of the bits carried in the SYN packet. 155 */ 156 tp = tcp_sk(child); 157 158 tp->fastopen_rsk = req; 159 tcp_rsk(req)->tfo_listener = true; 160 161 /* RFC1323: The window in SYN & SYN/ACK segments is never 162 * scaled. So correct it appropriately. 163 */ 164 tp->snd_wnd = ntohs(tcp_hdr(skb)->window); 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 } 216 217 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 */ 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