net-tcp: Fast Open base

This patch impelements the common code for both the client and server.

1. TCP Fast Open option processing. Since Fast Open does not have an
   option number assigned by IANA yet, it shares the experiment option
   code 254 by implementing draft-ietf-tcpm-experimental-options
   with a 16 bits magic number 0xF989. This enables global experiments
   without clashing the scarce(2) experimental options available for TCP.

   When the draft status becomes standard (maybe), the client should
   switch to the new option number assigned while the server supports
   both numbers for transistion.

2. The new sysctl tcp_fastopen

3. A place holder init function

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 4 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index fdd49f1b7a5..a06bb8959e7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3732,7 +3732,8 @@ old_ack:
  * the fast version below fails.
  */
 void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx,
-                       const u8 **hvpp, int estab)
+                       const u8 **hvpp, int estab,
+                       struct tcp_fastopen_cookie *foc)
 {
         const unsigned char *ptr;
         const struct tcphdr *th = tcp_hdr(skb);
@@ -3839,8 +3840,25 @@ void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *o
                                         break;
                                 }
                                 break;
-                        }
 
+                        case TCPOPT_EXP:
+                                /* Fast Open option shares code 254 using a
+                                 * 16 bits magic number. It's valid only in
+                                 * SYN or SYN-ACK with an even size.
+                                 */
+                                if (opsize < TCPOLEN_EXP_FASTOPEN_BASE ||
+                                    get_unaligned_be16(ptr) != TCPOPT_FASTOPEN_MAGIC ||
+                                    foc == NULL || !th->syn || (opsize & 1))
+                                        break;
+                                foc->len = opsize - TCPOLEN_EXP_FASTOPEN_BASE;
+                                if (foc->len >= TCP_FASTOPEN_COOKIE_MIN &&
+                                    foc->len <= TCP_FASTOPEN_COOKIE_MAX)
+                                        memcpy(foc->val, ptr + 2, foc->len);
+                                else if (foc->len != 0)
+                                        foc->len = -1;
+                                break;
+
+                        }
                         ptr += opsize-2;
                         length -= opsize;
                 }
@@ -3882,7 +3900,7 @@ static bool tcp_fast_parse_options(const struct sk_buff *skb,
                 if (tcp_parse_aligned_timestamp(tp, th))
                         return true;
         }
-        tcp_parse_options(skb, &tp->rx_opt, hvpp, 1);
+        tcp_parse_options(skb, &tp->rx_opt, hvpp, 1, NULL);
         return true;
 }
 
@@ -5637,7 +5655,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
         struct tcp_cookie_values *cvp = tp->cookie_values;
         int saved_clamp = tp->rx_opt.mss_clamp;
 
-        tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0);
+        tcp_parse_options(skb, &tp->rx_opt, &hash_location, 0, NULL);
 
         if (th->ack) {
                 /* rfc793: