net/ipv4/tcp_fastopen.c

   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;
 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         u32 end_seq;
 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         if (!child)
 145                 return false;
 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
 165         /* Activate the retrans timer so that SYNACK can be retransmitted.
 166          * The request socket is not added to the SYN table of the parent
 167          * because it's been added to the accept queue directly.
 168          */
 169         inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
 170                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 171
 172         atomic_set(&req->rsk_refcnt, 1);
 173         /* Add the child socket directly into the accept queue */
 174         inet_csk_reqsk_queue_add(sk, req, child);
 175
 176         /* Now finish processing the fastopen child socket. */
 177         inet_csk(child)->icsk_af_ops->rebuild_header(child);
 178         tcp_init_congestion_control(child);
 179         tcp_mtup_init(child);
 180         tcp_init_metrics(child);
 181         tcp_init_buffer_space(child);
 182
 183         /* Queue the data carried in the SYN packet. We need to first
 184          * bump skb's refcnt because the caller will attempt to free it.
 185          * Note that IPv6 might also have used skb_get() trick
 186          * in tcp_v6_conn_request() to keep this SYN around (treq->pktopts)
 187          * So we need to eventually get a clone of the packet,
 188          * before inserting it in sk_receive_queue.
 189          *
 190          * XXX (TFO) - we honor a zero-payload TFO request for now,
 191          * (any reason not to?) but no need to queue the skb since
 192          * there is no data. How about SYN+FIN?
 193          */
 194         end_seq = TCP_SKB_CB(skb)->end_seq;
 195         if (end_seq != TCP_SKB_CB(skb)->seq + 1) {
 196                 struct sk_buff *skb2;
 197
 198                 if (unlikely(skb_shared(skb)))
 199                         skb2 = skb_clone(skb, GFP_ATOMIC);
 200                 else
 201                         skb2 = skb_get(skb);
 202
 203                 if (likely(skb2)) {
 204                         skb_dst_drop(skb2);
 205                         __skb_pull(skb2, tcp_hdrlen(skb));
 206                         skb_set_owner_r(skb2, child);
 207                         __skb_queue_tail(&child->sk_receive_queue, skb2);
 208                         tp->syn_data_acked = 1;
 209
 210                         /* u64_stats_update_begin(&tp->syncp) not needed here,
 211                          * as we certainly are not changing upper 32bit value (0)
 212                          */
 213                         tp->bytes_received = end_seq - TCP_SKB_CB(skb)->seq - 1;
 214                 } else {
 215                         end_seq = TCP_SKB_CB(skb)->seq + 1;
 216                 }
 217         }
 218         tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = end_seq;
 219         sk->sk_data_ready(sk);
 220         bh_unlock_sock(child);
 221         sock_put(child);
 222         WARN_ON(!req->sk);
 223         return true;
 224 }
 225
 226 static bool tcp_fastopen_queue_check(struct sock *sk)
 227 {
 228         struct fastopen_queue *fastopenq;
 229
 230         /* Make sure the listener has enabled fastopen, and we don't
 231          * exceed the max # of pending TFO requests allowed before trying
 232          * to validating the cookie in order to avoid burning CPU cycles
 233          * unnecessarily.
 234          *
 235          * XXX (TFO) - The implication of checking the max_qlen before
 236          * processing a cookie request is that clients can't differentiate
 237          * between qlen overflow causing Fast Open to be disabled
 238          * temporarily vs a server not supporting Fast Open at all.
 239          */
 240         fastopenq = inet_csk(sk)->icsk_accept_queue.fastopenq;
 241         if (!fastopenq || fastopenq->max_qlen == 0)
 242                 return false;
 243
 244         if (fastopenq->qlen >= fastopenq->max_qlen) {
 245                 struct request_sock *req1;
 246                 spin_lock(&fastopenq->lock);
 247                 req1 = fastopenq->rskq_rst_head;
 248                 if (!req1 || time_after(req1->rsk_timer.expires, jiffies)) {
 249                         spin_unlock(&fastopenq->lock);
 250                         NET_INC_STATS_BH(sock_net(sk),
 251                                          LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);
 252                         return false;
 253                 }
 254                 fastopenq->rskq_rst_head = req1->dl_next;
 255                 fastopenq->qlen--;
 256                 spin_unlock(&fastopenq->lock);
 257                 reqsk_put(req1);
 258         }
 259         return true;
 260 }
 261
 262 /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
 263  * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
 264  * cookie request (foc->len == 0).
 265  */
 266 bool tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
 267                       struct request_sock *req,
 268                       struct tcp_fastopen_cookie *foc,
 269                       struct dst_entry *dst)
 270 {
 271         struct tcp_fastopen_cookie valid_foc = { .len = -1 };
 272         bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
 273
 274         if (foc->len == 0) /* Client requests a cookie */
 275                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENCOOKIEREQD);
 276
 277         if (!((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) &&
 278               (syn_data || foc->len >= 0) &&
 279               tcp_fastopen_queue_check(sk))) {
 280                 foc->len = -1;
 281                 return false;
 282         }
 283
 284         if (syn_data && (sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
 285                 goto fastopen;
 286
 287         if (foc->len >= 0 &&  /* Client presents or requests a cookie */
 288             tcp_fastopen_cookie_gen(req, skb, &valid_foc) &&
 289             foc->len == TCP_FASTOPEN_COOKIE_SIZE &&
 290             foc->len == valid_foc.len &&
 291             !memcmp(foc->val, valid_foc.val, foc->len)) {
 292                 /* Cookie is valid. Create a (full) child socket to accept
 293                  * the data in SYN before returning a SYN-ACK to ack the
 294                  * data. If we fail to create the socket, fall back and
 295                  * ack the ISN only but includes the same cookie.
 296                  *
 297                  * Note: Data-less SYN with valid cookie is allowed to send
 298                  * data in SYN_RECV state.
 299                  */
 300 fastopen:
 301                 if (tcp_fastopen_create_child(sk, skb, dst, req)) {
 302                         foc->len = -1;
 303                         NET_INC_STATS_BH(sock_net(sk),
 304                                          LINUX_MIB_TCPFASTOPENPASSIVE);
 305                         return true;
 306                 }
 307                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
 308         } else if (foc->len > 0) /* Client presents an invalid cookie */
 309                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVEFAIL);
 310
 311         valid_foc.exp = foc->exp;
 312         *foc = valid_foc;
 313         return false;
 314 }
 315 EXPORT_SYMBOL(tcp_try_fastopen);