TCPCT part 1d: define TCP cookie option, extend existing struct's

Data structures are carefully composed to require minimal additions.
For example, the struct tcp_options_received cookie_plus variable fits
between existing 16-bit and 8-bit variables, requiring no additional
space (taking alignment into consideration).  There are no additions to
tcp_request_sock, and only 1 pointer in tcp_sock.

This is a significantly revised implementation of an earlier (year-old)
patch that no longer applies cleanly, with permission of the original
author (Adam Langley):

    http://thread.gmane.org/gmane.linux.network/102586

The principle difference is using a TCP option to carry the cookie nonce,
instead of a user configured offset in the data.  This is more flexible and
less subject to user configuration error.  Such a cookie option has been
suggested for many years, and is also useful without SYN data, allowing
several related concepts to use the same extension option.

    "Re: SYN floods (was: does history repeat itself?)", September 9, 1996.
    http://www.merit.net/mail.archives/nanog/1996-09/msg00235.html

    "Re: what a new TCP header might look like", May 12, 1998.
    ftp://ftp.isi.edu/end2end/end2end-interest-1998.mail

These functions will also be used in subsequent patches that implement
additional features.

Requires:
   TCPCT part 1a: add request_values parameter for sending SYNACK
   TCPCT part 1b: generate Responder Cookie secret
   TCPCT part 1c: sysctl_tcp_cookie_size, socket option TCP_COOKIE_TRANSACTIONS

Signed-off-by: William.Allen.Simpson@gmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 38 insertions, 8 deletions

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index d3f6bbfc76f0..96852af43ca7 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -383,14 +383,43 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                 const struct inet_request_sock *ireq = inet_rsk(req);
                 struct tcp_request_sock *treq = tcp_rsk(req);
                 struct inet_connection_sock *newicsk = inet_csk(newsk);
-                struct tcp_sock *newtp;
+                struct tcp_sock *newtp = tcp_sk(newsk);
+                struct tcp_sock *oldtp = tcp_sk(sk);
+                struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
+
+                /* TCP Cookie Transactions require space for the cookie pair,
+                 * as it differs for each connection.  There is no need to
+                 * copy any s_data_payload stored at the original socket.
+                 * Failure will prevent resuming the connection.
+                 *
+                 * Presumed copied, in order of appearance:
+                 *      cookie_in_always, cookie_out_never
+                 */
+                if (oldcvp != NULL) {
+                        struct tcp_cookie_values *newcvp =
+                                kzalloc(sizeof(*newtp->cookie_values),
+                                        GFP_ATOMIC);
+
+                        if (newcvp != NULL) {
+                                kref_init(&newcvp->kref);
+                                newcvp->cookie_desired =
+                                                oldcvp->cookie_desired;
+                                newtp->cookie_values = newcvp;
+                        } else {
+                                /* Not Yet Implemented */
+                                newtp->cookie_values = NULL;
+                        }
+                }
 
                 /* Now setup tcp_sock */
-                newtp = tcp_sk(newsk);
                 newtp->pred_flags = 0;
-                newtp->rcv_wup = newtp->copied_seq = newtp->rcv_nxt = treq->rcv_isn + 1;
-                newtp->snd_sml = newtp->snd_una = newtp->snd_nxt = treq->snt_isn + 1;
-                newtp->snd_up = treq->snt_isn + 1;
+
+                newtp->rcv_wup = newtp->copied_seq =
+                newtp->rcv_nxt = treq->rcv_isn + 1;
+
+                newtp->snd_sml = newtp->snd_una =
+                newtp->snd_nxt = newtp->snd_up =
+                        treq->snt_isn + 1 + tcp_s_data_size(oldtp);
 
                 tcp_prequeue_init(newtp);
 
@@ -423,8 +452,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                 tcp_set_ca_state(newsk, TCP_CA_Open);
                 tcp_init_xmit_timers(newsk);
                 skb_queue_head_init(&newtp->out_of_order_queue);
-                newtp->write_seq = treq->snt_isn + 1;
-                newtp->pushed_seq = newtp->write_seq;
+                newtp->write_seq = newtp->pushed_seq =
+                        treq->snt_isn + 1 + tcp_s_data_size(oldtp);
 
                 newtp->rx_opt.saw_tstamp = 0;
 
@@ -590,7 +619,8 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
          * Invalid ACK: reset will be sent by listening socket
          */
         if ((flg & TCP_FLAG_ACK) &&
-            (TCP_SKB_CB(skb)->ack_seq != tcp_rsk(req)->snt_isn + 1))
+            (TCP_SKB_CB(skb)->ack_seq !=
+             tcp_rsk(req)->snt_isn + 1 + tcp_s_data_size(tcp_sk(sk))))
                 return sk;
 
         /* Also, it would be not so bad idea to check rcv_tsecr, which