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Subject[PATCH 4.2 23/61] tcp: disable Fast Open on timeouts after handshake
Date
4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yuchung Cheng <ycheng@google.com>

[ Upstream commit 0e45f4da5981895e885dd72fe912a3f8e32bae73 ]

Some middle-boxes black-hole the data after the Fast Open handshake
(https://www.ietf.org/proceedings/94/slides/slides-94-tcpm-13.pdf).
The exact reason is unknown. The work-around is to disable Fast Open
temporarily after multiple recurring timeouts with few or no data
delivered in the established state.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/tcp_timer.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -176,6 +176,18 @@ static int tcp_write_timeout(struct sock
syn_set = true;
} else {
if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
+ /* Some middle-boxes may black-hole Fast Open _after_
+ * the handshake. Therefore we conservatively disable
+ * Fast Open on this path on recurring timeouts with
+ * few or zero bytes acked after Fast Open.
+ */
+ if (tp->syn_data_acked &&
+ tp->bytes_acked <= tp->rx_opt.mss_clamp) {
+ tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
+ if (icsk->icsk_retransmits == sysctl_tcp_retries1)
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPFASTOPENACTIVEFAIL);
+ }
/* Black hole detection */
tcp_mtu_probing(icsk, sk);




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