netdev - Re: [PATCH net-next] tcp: Enable TFO without a cookie on a per-socket basis

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Date:   Tue, 17 Oct 2017 10:26:58 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Christoph Paasch <cpaasch@...le.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] tcp: Enable TFO without a cookie on a per-socket basis

On Mon, Oct 16, 2017 at 11:37 PM, Christoph Paasch <cpaasch@...le.com> wrote:
> We already allow to enable TFO without a cookie by using the
> fastopen-sysctl and setting it to TFO_SERVER_COOKIE_NOT_REQD (0x200).
> This is safe to do in certain environments where we know that there
> isn't a malicous host (aka., data-centers).
>
> A server however might be talking to both sides (public Internet and
> data-center). So, this server would want to enable cookie-less TFO for
> the connections that go to the data-center while enforcing cookies for
> the traffic from the Internet.
>
> This patch exposes a socket-option to enable this (protected by
> CAP_NET_ADMIN).
>
> Signed-off-by: Christoph Paasch <cpaasch@...le.com>
> ---
>  include/linux/tcp.h      |  1 +
>  include/uapi/linux/tcp.h |  1 +
>  net/ipv4/tcp.c           | 14 ++++++++++++++
>  net/ipv4/tcp_fastopen.c  |  6 ++++--
>  4 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index 1d2c44e09e31..cda5d4dc8d70 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -228,6 +228,7 @@ struct tcp_sock {
>                 syn_fastopen_ch:1, /* Active TFO re-enabling probe */
>                 syn_data_acked:1,/* data in SYN is acked by SYN-ACK */
>                 save_syn:1,     /* Save headers of SYN packet */
> +               no_tfo_cookie:1, /* Allow send/recv SYN+data without a cookie */
can we rename to fastopen_no_cookie and move one line above so TFO
stuff is together with similar naming.

>                 is_cwnd_limited:1;/* forward progress limited by snd_cwnd? */
>         u32     tlp_high_seq;   /* snd_nxt at the time of TLP retransmit. */
>
> diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> index 15c25eccab2b..d44f4bef056c 100644
> --- a/include/uapi/linux/tcp.h
> +++ b/include/uapi/linux/tcp.h
> @@ -119,6 +119,7 @@ enum {
>  #define TCP_FASTOPEN_CONNECT   30      /* Attempt FastOpen with connect */
>  #define TCP_ULP                        31      /* Attach a ULP to a TCP connection */
>  #define TCP_MD5SIG_EXT         32      /* TCP MD5 Signature with extensions */
> +#define TCP_NO_TFO_COOKIE      33      /* Enable TFO without a TFO cookie */
>
>  struct tcp_repair_opt {
>         __u32   opt_code;
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 3b34850d361f..88c90be12d9f 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2821,6 +2821,16 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
>                         err = -EOPNOTSUPP;
>                 }
>                 break;
> +       case TCP_NO_TFO_COOKIE:
rename to TCP_FASTOPEN_NO_COOKIE for better consistency on TFO
options? I am also cooking a TCP_FASTOPEN_KEY option patch to allow
listener to update the key.

> +               if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
> +                       err = -EPERM;
> +               else if (val > 1 || val < 0)
> +                       err = -EINVAL;
> +               else if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
> +                       err = -EINVAL;
> +               else
> +                       tp->no_tfo_cookie = 1;
> +               break;
>         case TCP_TIMESTAMP:
>                 if (!tp->repair)
>                         err = -EPERM;
> @@ -3219,6 +3229,10 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
>                 val = tp->fastopen_connect;
>                 break;
>
> +       case TCP_NO_TFO_COOKIE:
> +               val = tp->no_tfo_cookie;
> +               break;
> +
>         case TCP_TIMESTAMP:
>                 val = tcp_time_stamp_raw() + tp->tsoffset;
>                 break;
> diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> index 7ee4aadcdd71..c1b00b666b43 100644
> --- a/net/ipv4/tcp_fastopen.c
> +++ b/net/ipv4/tcp_fastopen.c
> @@ -309,7 +309,8 @@ struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
>                 return NULL;
>         }
>
> -       if (syn_data && (tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD))
> +       if (syn_data && ((tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD) ||
> +                        tcp_sk(sk)->no_tfo_cookie))
>                 goto fastopen;
>
>         if (foc->len >= 0 &&  /* Client presents or requests a cookie */
> @@ -363,7 +364,8 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
>                 return false;
>         }
>
> -       if (sock_net(sk)->ipv4.sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE) {
> +       if ((sock_net(sk)->ipv4.sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE) ||
> +           tcp_sk(sk)->no_tfo_cookie) {
>                 cookie->len = -1;
>                 return true;
>         }
> --
> 2.14.1
>