tcp: RFC7413 option support for Fast Open client
Fast Open has been using an experimental option with a magic number
(RFC6994). This patch makes the client by default use the RFC7413
option (34) to get and send Fast Open cookies. This patch makes
the client solicit cookies from a given server first with the
RFC7413 option. If that fails to elicit a cookie, then it tries
the RFC6994 experimental option. If that also fails, it uses the
RFC7413 option on all subsequent connect attempts. If the server
returns a Fast Open cookie then the client caches the form of the
option that successfully elicited a cookie, and uses that form on
later connects when it presents that cookie.
The idea is to gradually obsolete the use of experimental options as
the servers and clients upgrade, while keeping the interoperability
meanwhile.
Signed-off-by: Daniel Lee <Longinus00@gmail.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 78ecc4a..a51d63a 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -28,7 +28,8 @@
struct tcp_fastopen_metrics {
u16 mss;
- u16 syn_loss:10; /* Recurring Fast Open SYN losses */
+ u16 syn_loss:10, /* Recurring Fast Open SYN losses */
+ try_exp:2; /* Request w/ exp. option (once) */
unsigned long last_syn_loss; /* Last Fast Open SYN loss */
struct tcp_fastopen_cookie cookie;
};
@@ -131,6 +132,8 @@
if (fastopen_clear) {
tm->tcpm_fastopen.mss = 0;
tm->tcpm_fastopen.syn_loss = 0;
+ tm->tcpm_fastopen.try_exp = 0;
+ tm->tcpm_fastopen.cookie.exp = false;
tm->tcpm_fastopen.cookie.len = 0;
}
}
@@ -713,6 +716,8 @@
if (tfom->mss)
*mss = tfom->mss;
*cookie = tfom->cookie;
+ if (cookie->len <= 0 && tfom->try_exp == 1)
+ cookie->exp = true;
*syn_loss = tfom->syn_loss;
*last_syn_loss = *syn_loss ? tfom->last_syn_loss : 0;
} while (read_seqretry(&fastopen_seqlock, seq));
@@ -721,7 +726,8 @@
}
void tcp_fastopen_cache_set(struct sock *sk, u16 mss,
- struct tcp_fastopen_cookie *cookie, bool syn_lost)
+ struct tcp_fastopen_cookie *cookie, bool syn_lost,
+ u16 try_exp)
{
struct dst_entry *dst = __sk_dst_get(sk);
struct tcp_metrics_block *tm;
@@ -738,6 +744,9 @@
tfom->mss = mss;
if (cookie && cookie->len > 0)
tfom->cookie = *cookie;
+ else if (try_exp > tfom->try_exp &&
+ tfom->cookie.len <= 0 && !tfom->cookie.exp)
+ tfom->try_exp = try_exp;
if (syn_lost) {
++tfom->syn_loss;
tfom->last_syn_loss = jiffies;