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

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Date:   Mon, 16 Oct 2017 23:37:14 -0700
From:   Christoph Paasch <cpaasch@...le.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: [PATCH net-next] tcp: Enable TFO without a cookie on a per-socket basis

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 */
 		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:
+		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