tcp: RFC2988bis + taking RTT sample from 3WHS for the passive open side

This patch lowers the default initRTO from 3secs to 1sec per
RFC2988bis. It falls back to 3secs if the SYN or SYN-ACK packet
has been retransmitted, AND the TCP timestamp option is not on.

It also adds support to take RTT sample during 3WHS on the passive
open side, just like its active open counterpart, and uses it, if
valid, to seed the initRTO for the data transmission phase.

The patch also resets ssthresh to its initial default at the
beginning of the data transmission phase, and reduces cwnd to 1 if
there has been MORE THAN ONE retransmission during 3WHS per RFC5681.

Signed-off-by: H.K. Jerry Chu <hkchu@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 6 insertions, 0 deletions

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 8b9644a8b697..89d5bf806222 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -223,6 +223,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
         ireq->wscale_ok         = tcp_opt.wscale_ok;
         ireq->tstamp_ok         = tcp_opt.saw_tstamp;
         req->ts_recent          = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
+        treq->snt_synack        = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
         treq->rcv_isn = ntohl(th->seq) - 1;
         treq->snt_isn = cookie;
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index d1fd28711ba5..a1ef61a889c3 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1341,6 +1341,7 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
         }
 have_isn:
         tcp_rsk(req)->snt_isn = isn;
+        tcp_rsk(req)->snt_synack = tcp_time_stamp;
 
         security_inet_conn_request(sk, skb, req);
 
@@ -1509,6 +1510,10 @@ static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
         tcp_sync_mss(newsk, dst_mtu(dst));
         newtp->advmss = dst_metric_advmss(dst);
         tcp_initialize_rcv_mss(newsk);
+        if (tcp_rsk(req)->snt_synack)
+                tcp_valid_rtt_meas(newsk,
+                    tcp_time_stamp - tcp_rsk(req)->snt_synack);
+        newtp->total_retrans = req->retrans;
 
         newinet->inet_daddr = newinet->inet_saddr = LOOPBACK4_IPV6;
         newinet->inet_rcv_saddr = LOOPBACK4_IPV6;