netdev - Re: [PATCH net-next 3/3] net/tcp_fastopen: Remove mss check in tcp_write

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Date:   Thu, 20 Apr 2017 17:29:27 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Wei Wang <weiwan@...gle.com>
Cc:     netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 3/3] net/tcp_fastopen: Remove mss check in tcp_write_timeout()

On Thu, Apr 20, 2017 at 2:45 PM, Wei Wang <weiwan@...gle.com> wrote:
> From: Wei Wang <weiwan@...gle.com>
>
> Christoph Paasch from Apple found another firewall issue for TFO:
> After successful 3WHS using TFO, server and client starts to exchange
> data. Afterwards, a 10s idle time occurs on this connection. After that,
> firewall starts to drop every packet on this connection.
>
> The fix for this issue is to extend existing firewall blackhole detection
> logic in tcp_write_timeout() by removing the mss check.
>
> Signed-off-by: Wei Wang <weiwan@...gle.com>
Acked-by: Yuchung Cheng <ycheng@...gle.com>

> ---
>  net/ipv4/tcp_timer.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index b2ab411c6d37..14672543cf0b 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -201,11 +201,10 @@ static int tcp_write_timeout(struct sock *sk)
>                 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0, 0)) {
>                         /* Some middle-boxes may black-hole Fast Open _after_
>                          * the handshake. Therefore we conservatively disable
> -                        * Fast Open on this path on recurring timeouts with
> -                        * few or zero bytes acked after Fast Open.
> +                        * Fast Open on this path on recurring timeouts after
> +                        * successful Fast Open.
>                          */
> -                       if (tp->syn_data_acked &&
> -                           tp->bytes_acked <= tp->rx_opt.mss_clamp) {
> +                       if (tp->syn_data_acked) {
>                                 tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
>                                 if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1)
>                                         NET_INC_STATS(sock_net(sk),
> --
> 2.12.2.816.g2cccc81164-goog
>