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>

1 files changed, 17 insertions, 3 deletions

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 21075ce19cb6..e0a4b56644aa 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/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;
         }