netdev - Re: [RFC 1/3] tcp: randomize tcp timestamp offsets for each connection

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Date:   Thu, 25 Aug 2016 14:06:54 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     netdev@...r.kernel.org
Subject: Re: [RFC 1/3] tcp: randomize tcp timestamp offsets for each
 connection

On Thu, 2016-08-25 at 22:31 +0200, Florian Westphal wrote:
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Thu, 2016-08-18 at 14:48 +0200, Florian Westphal wrote:
> > It seems tcp_v4_reqsk_send_ack() and tcp_v6_reqsk_send_ack() were not
> > taken into account.
> > 
> > See commit 20a2b49fc5385 changelog
> > packetdrill test showing the possible issue if the TS sent on an ACK in
> > SYN_RECV state is wrong.
> 
> Thanks a lot Eric, I'll fix this.

I would try :

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 47683c798f57..c2bf284239f6 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -826,7 +826,7 @@ static void tcp_v4_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
 
        tcp_v4_send_ack(sock_net(sk), skb, seq,
                        tcp_rsk(req)->rcv_nxt, req->rsk_rcv_wnd,
-                       tcp_time_stamp,
+                       tcp_time_stamp + tcp_rsk(req)->ts_off,
                        req->ts_recent,
                        0,
                        tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->daddr,
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index ce029c090f94..6411aa378b1b 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -955,7 +955,8 @@ static void tcp_v6_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
        tcp_v6_send_ack(sk, skb, (sk->sk_state == TCP_LISTEN) ?
                        tcp_rsk(req)->snt_isn + 1 : tcp_sk(sk)->snd_nxt,
                        tcp_rsk(req)->rcv_nxt, req->rsk_rcv_wnd,
-                       tcp_time_stamp, req->ts_recent, sk->sk_bound_dev_if,
+                       tcp_time_stamp + tcp_rsk(req)->ts_off,
+                       req->ts_recent, sk->sk_bound_dev_if,
                        tcp_v6_md5_do_lookup(sk, &ipv6_hdr(skb)->daddr),
                        0, 0);
 }