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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, stable@vger.kernel.org,
        Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.4 041/137] tcp: fix tcpi_segs_in after connection establishment
Date: Mon, 18 Apr 2016 11:28:23 +0900
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4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit a9d99ce28ed359d68cf6f3c1a69038aefedf6d6a ]

If final packet (ACK) of 3WHS is lost, it appears we do not properly
account the following incoming segment into tcpi_segs_in

While we are at it, starts segs_in with one, to count the SYN packet.

We do not yet count number of SYN we received for a request sock, we
might add this someday.

packetdrill script showing proper behavior after fix :

// Tests tcpi_segs_in when 3rd packet (ACK) of 3WHS is lost
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
   +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
   +0 bind(3, ..., ...) = 0
   +0 listen(3, 1) = 0

   +0 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop>
   +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+.020 < P. 1:1001(1000) ack 1 win 32792

   +0 accept(3, ..., ...) = 4

+.000 %{ assert tcpi_segs_in == 2, 'tcpi_segs_in=%d' % tcpi_segs_in }%

Fixes: 2efd055c53c06 ("tcp: add tcpi_segs_in and tcpi_segs_out to tcp_info")
Signed-off-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_minisocks.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -458,7 +458,7 @@ struct sock *tcp_create_openreq_child(co
 
 		newtp->rcv_wup = newtp->copied_seq =
 		newtp->rcv_nxt = treq->rcv_isn + 1;
-		newtp->segs_in = 0;
+		newtp->segs_in = 1;
 
 		newtp->snd_sml = newtp->snd_una =
 		newtp->snd_nxt = newtp->snd_up = treq->snt_isn + 1;
@@ -818,6 +818,7 @@ int tcp_child_process(struct sock *paren
 	int ret = 0;
 	int state = child->sk_state;
 
+	tcp_sk(child)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
 	if (!sock_owned_by_user(child)) {
 		ret = tcp_rcv_state_process(child, skb);
 		/* Wakeup parent, send SIGIO */