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authorWei Wang <weiwan@google.com>2017-04-20 14:45:46 -0700
committerDavid S. Miller <davem@davemloft.net>2017-04-24 14:27:17 -0400
commitcf1ef3f0719b4dcb74810ed507e2a2540f9811b4 (patch)
tree1b070be7a31eb3557e7f0701a6aca667b1eb13dd /include/net
parentMerge tag 'mlx5-updates-2017-04-22' of git://git.kernel.org/pub/scm/linux/kernel/git/saeed/linux (diff)
downloadlinux-dev-cf1ef3f0719b4dcb74810ed507e2a2540f9811b4.tar.xz
linux-dev-cf1ef3f0719b4dcb74810ed507e2a2540f9811b4.zip
net/tcp_fastopen: Disable active side TFO in certain scenarios
Middlebox firewall issues can potentially cause server's data being blackholed after a successful 3WHS using TFO. Following are the related reports from Apple: https://www.nanog.org/sites/default/files/Paasch_Network_Support.pdf Slide 31 identifies an issue where the client ACK to the server's data sent during a TFO'd handshake is dropped. C ---> syn-data ---> S C <--- syn/ack ----- S C (accept & write) C <---- data ------- S C ----- ACK -> X S [retry and timeout] https://www.ietf.org/proceedings/94/slides/slides-94-tcpm-13.pdf Slide 5 shows a similar situation that the server's data gets dropped after 3WHS. C ---- syn-data ---> S C <--- syn/ack ----- S C ---- ack --------> S S (accept & write) C? X <- data ------ S [retry and timeout] This is the worst failure b/c the client can not detect such behavior to mitigate the situation (such as disabling TFO). Failing to proceed, the application (e.g., SSL library) may simply timeout and retry with TFO again, and the process repeats indefinitely. The proposed solution is to disable active TFO globally under the following circumstances: 1. client side TFO socket detects out of order FIN 2. client side TFO socket receives out of order RST We disable active side TFO globally for 1hr at first. Then if it happens again, we disable it for 2h, then 4h, 8h, ... And we reset the timeout to 1hr if a client side TFO sockets not opened on loopback has successfully received data segs from server. And we examine this condition during close(). The rational behind it is that when such firewall issue happens, application running on the client should eventually close the socket as it is not able to get the data it is expecting. Or application running on the server should close the socket as it is not able to receive any response from client. In both cases, out of order FIN or RST will get received on the client given that the firewall will not block them as no data are in those frames. And we want to disable active TFO globally as it helps if the middle box is very close to the client and most of the connections are likely to fail. Also, add a debug sysctl: tcp_fastopen_blackhole_detect_timeout_sec: the initial timeout to use when firewall blackhole issue happens. This can be set and read. When setting it to 0, it means to disable the active disable logic. Signed-off-by: Wei Wang <weiwan@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net')
-rw-r--r--include/net/tcp.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index cc6ae0a95201..c1abc2abbdcb 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1506,6 +1506,12 @@ struct tcp_fastopen_context {
struct rcu_head rcu;
};
+extern unsigned int sysctl_tcp_fastopen_blackhole_timeout;
+void tcp_fastopen_active_disable(void);
+bool tcp_fastopen_active_should_disable(struct sock *sk);
+void tcp_fastopen_active_disable_ofo_check(struct sock *sk);
+void tcp_fastopen_active_timeout_reset(void);
+
/* Latencies incurred by various limits for a sender. They are
* chronograph-like stats that are mutually exclusive.
*/