tcp: Configure TFO without cookie per socket and/or per route

We already allow to enable TFO without a cookie by using the
fastopen-sysctl and setting it to TFO_SERVER_COOKIE_NOT_REQD (or
TFO_CLIENT_NO_COOKIE).
This is safe to do in certain environments where we know that there
isn't a malicous host (aka., data-centers) or when the
application-protocol already provides an authentication mechanism in the
first flight of data.

A server however might be providing multiple services or talking to both
sides (public Internet and data-center). So, this server would want to
enable cookie-less TFO for certain services and/or for connections that
go to the data-center.

This patch exposes a socket-option and a per-route attribute to enable such
fine-grained configurations.

Signed-off-by: Christoph Paasch <cpaasch@apple.com>
Reviewed-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/tcp.h

@@ -215,7 +215,8 @@ struct tcp_sock {
 	u8	chrono_type:2,	/* current chronograph type */
 		rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
 		fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */
-		unused:4;
+		fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */
+		unused:3;
 	u8	nonagle     : 4,/* Disable Nagle algorithm?             */
 		thin_lto    : 1,/* Use linear timeouts for thin streams */
 		unused1	    : 1,

include/net/tcp.h

@@ -1567,7 +1567,8 @@ int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
 void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb);
 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
 			      struct request_sock *req,
-			      struct tcp_fastopen_cookie *foc);
+			      struct tcp_fastopen_cookie *foc,
+			      const struct dst_entry *dst);
 void tcp_fastopen_init_key_once(struct net *net);
 bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
 			     struct tcp_fastopen_cookie *cookie);

include/uapi/linux/rtnetlink.h

@@ -430,6 +430,8 @@ enum {
 #define RTAX_QUICKACK RTAX_QUICKACK
 	RTAX_CC_ALGO,
 #define RTAX_CC_ALGO RTAX_CC_ALGO
+	RTAX_FASTOPEN_NO_COOKIE,
+#define RTAX_FASTOPEN_NO_COOKIE RTAX_FASTOPEN_NO_COOKIE
 	__RTAX_MAX
 };
 

include/uapi/linux/tcp.h

@@ -120,6 +120,7 @@ enum {
 #define TCP_ULP			31	/* Attach a ULP to a TCP connection */
 #define TCP_MD5SIG_EXT		32	/* TCP MD5 Signature with extensions */
 #define TCP_FASTOPEN_KEY	33	/* Set the key for Fast Open (cookie) */
+#define TCP_FASTOPEN_NO_COOKIE	34	/* Enable TFO without a TFO cookie */
 
 struct tcp_repair_opt {
 	__u32	opt_code;

net/ipv4/tcp.c

@@ -2836,6 +2836,14 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 			err = -EOPNOTSUPP;
 		}
 		break;
+	case TCP_FASTOPEN_NO_COOKIE:
+		if (val > 1 || val < 0)
+			err = -EINVAL;
+		else if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
+			err = -EINVAL;
+		else
+			tp->fastopen_no_cookie = val;
+		break;
 	case TCP_TIMESTAMP:
 		if (!tp->repair)
 			err = -EPERM;
@@ -3256,6 +3264,10 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 		val = tp->fastopen_connect;
 		break;
 
+	case TCP_FASTOPEN_NO_COOKIE:
+		val = tp->fastopen_no_cookie;
+		break;
+
 	case TCP_TIMESTAMP:
 		val = tcp_time_stamp_raw() + tp->tsoffset;
 		break;

net/ipv4/tcp_fastopen.c

@@ -310,13 +310,23 @@ static bool tcp_fastopen_queue_check(struct sock *sk)
 	return true;
 }
 
+static bool tcp_fastopen_no_cookie(const struct sock *sk,
+				   const struct dst_entry *dst,
+				   int flag)
+{
+	return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
+	       tcp_sk(sk)->fastopen_no_cookie ||
+	       (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
+}
+
 /* Returns true if we should perform Fast Open on the SYN. The cookie (foc)
  * may be updated and return the client in the SYN-ACK later. E.g., Fast Open
  * cookie request (foc->len == 0).
  */
 struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
 			      struct request_sock *req,
-			      struct tcp_fastopen_cookie *foc)
+			      struct tcp_fastopen_cookie *foc,
+			      const struct dst_entry *dst)
 {
 	bool syn_data = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
 	int tcp_fastopen = sock_net(sk)->ipv4.sysctl_tcp_fastopen;
@@ -333,7 +343,8 @@ 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_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
 		goto fastopen;
 
 	if (foc->len >= 0 &&  /* Client presents or requests a cookie */
@@ -370,6 +381,7 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
 			       struct tcp_fastopen_cookie *cookie)
 {
 	unsigned long last_syn_loss = 0;
+	const struct dst_entry *dst;
 	int syn_loss = 0;
 
 	tcp_fastopen_cache_get(sk, mss, cookie, &syn_loss, &last_syn_loss);
@@ -387,7 +399,9 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
 		return false;
 	}
 
-	if (sock_net(sk)->ipv4.sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE) {
+	dst = __sk_dst_get(sk);
+
+	if (tcp_fastopen_no_cookie(sk, dst, TFO_CLIENT_NO_COOKIE)) {
 		cookie->len = -1;
 		return true;
 	}

net/ipv4/tcp_input.c

@@ -6332,7 +6332,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	tcp_openreq_init_rwin(req, sk, dst);
 	if (!want_cookie) {
 		tcp_reqsk_record_syn(sk, req, skb);
-		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc);
+		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
 	}
 	if (fastopen_sk) {
 		af_ops->send_synack(fastopen_sk, dst, &fl, req,