net/ipv4/tcp_fastopen.c

   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 }