Patch "tcp: initialize max window for a new fastopen socket" has been added to the 4.9-stable tree

Patch "tcp: initialize max window for a new fastopen socket" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    tcp: initialize max window for a new fastopen socket

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-initialize-max-window-for-a-new-fastopen-socket.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Feb  1 08:50:24 CET 2017
From: Alexey Kodanev <alexey.kodanev@oracle.com>
Date: Thu, 19 Jan 2017 16:36:39 +0300
Subject: tcp: initialize max window for a new fastopen socket

From: Alexey Kodanev <alexey.kodanev@oracle.com>


[ Upstream commit 0dbd7ff3ac5017a46033a9d0a87a8267d69119d9 ]

Found that if we run LTP netstress test with large MSS (65K),
the first attempt from server to send data comparable to this
MSS on fastopen connection will be delayed by the probe timer.

Here is an example:

     < S  seq 0:0 win 43690 options [mss 65495 wscale 7 tfo cookie] length 32
     > S. seq 0:0 ack 1 win 43690 options [mss 65495 wscale 7] length 0
     < .  ack 1 win 342 length 0

Inside tcp_sendmsg(), tcp_send_mss() returns max MSS in 'mss_now',
as well as in 'size_goal'. This results the segment not queued for
transmition until all the data copied from user buffer. Then, inside
__tcp_push_pending_frames(), it breaks on send window test and
continues with the check probe timer.

Fragmentation occurs in tcp_write_wakeup()...

+0.2 > P. seq 1:43777 ack 1 win 342 length 43776
     < .  ack 43777, win 1365 length 0
     > P. seq 43777:65001 ack 1 win 342 options [...] length 21224
     ...

This also contradicts with the fact that we should bound to the half
of the window if it is large.

Fix this flaw by correctly initializing max_window. Before that, it
could have large values that affect further calculations of 'size_goal'.

Fixes: 168a8f58059a ("tcp: TCP Fast Open Server - main code path")
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_fastopen.c |    1 +
 1 file changed, 1 insertion(+)

--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -205,6 +205,7 @@ static struct sock *tcp_fastopen_create_
 	 * scaled. So correct it appropriately.
 	 */
 	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
+	tp->max_window = tp->snd_wnd;
 
 	/* Activate the retrans timer so that SYNACK can be retransmitted.
 	 * The request socket is not added to the ehash


Patches currently in stable-queue which might be from alexey.kodanev@oracle.com are

queue-4.9/tcp-initialize-max-window-for-a-new-fastopen-socket.patch