[PATCH next] tcp: fastopen: fix rcv_wup initialization for TFO server on SYN/data

[PATCH next] tcp: fastopen: fix rcv_wup initialization for TFO server on SYN/data

[Neal Cardwell]

Yuchung noticed that on the first TFO server data packet sent after
the (TFO) handshake, the server echoed the TCP timestamp value in the
SYN/data instead of the timestamp value in the final ACK of the
handshake. This problem did not happen on regular opens.

The tcp_replace_ts_recent() logic that decides whether to remember an
incoming TS value needs tp->rcv_wup to hold the latest receive
sequence number that we have ACKed (latest tp->rcv_nxt we have
ACKed). This commit fixes this issue by ensuring that a TFO server
properly updates tp->rcv_wup to match tp->rcv_nxt at the time it sends
a SYN/ACK for the SYN/data.

Reported-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Fixes: 168a8f58059a ("tcp: TCP Fast Open Server - main code path")
---
 net/ipv4/tcp_fastopen.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 54d9f9b..62a5751 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -226,6 +226,7 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
 	tcp_fastopen_add_skb(child, skb);
 
 	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
+	tp->rcv_wup = tp->rcv_nxt;
 	/* tcp_conn_request() is sending the SYNACK,
 	 * and queues the child into listener accept queue.
 	 */
-- 
2.8.0.rc3.226.g39d4020

Re: [PATCH next] tcp: fastopen: fix rcv_wup initialization for TFO server on SYN/data

[Neal Cardwell]

Sorry, there's a typo in the subject line: that should be "net" rather
than "next" (I'm proposing "net" since it's a bug fix).

Looks like "git am" strips this mistake, but I'm happy to resubmit if it helps.

thanks,
neal

Re: [PATCH next] tcp: fastopen: fix rcv_wup initialization for TFO server on SYN/data

[David Miller]

From: Neal Cardwell <ncardwell@google.com>
Date: Tue, 30 Aug 2016 11:55:23 -0400

> Yuchung noticed that on the first TFO server data packet sent after
> the (TFO) handshake, the server echoed the TCP timestamp value in the
> SYN/data instead of the timestamp value in the final ACK of the
> handshake. This problem did not happen on regular opens.
> 
> The tcp_replace_ts_recent() logic that decides whether to remember an
> incoming TS value needs tp->rcv_wup to hold the latest receive
> sequence number that we have ACKed (latest tp->rcv_nxt we have
> ACKed). This commit fixes this issue by ensuring that a TFO server
> properly updates tp->rcv_wup to match tp->rcv_nxt at the time it sends
> a SYN/ACK for the SYN/data.
> 
> Reported-by: Yuchung Cheng <ycheng@google.com>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
> Fixes: 168a8f58059a ("tcp: TCP Fast Open Server - main code path")

Applied to 'net', thanks.