[PATCH 4.2.y-ckt 87/98] tcp: fix tcpi_segs_in after connection establishment

Kamal Mostafa
2016-03-15T23:33:41Z

From: Eric Dumazet <edumazet@google.com>

commit a9d99ce28ed359d68cf6f3c1a69038aefedf6d6a upstream.

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: Kamal Mostafa <kamal@canonical.com>
---
net/ipv4/tcp_minisocks.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 4bc00cb..0e974b0 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -451,7 +451,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,

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;
@@ -813,6 +813,7 @@ int tcp_child_process(struct sock *parent, struct sock *child,
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, tcp_hdr(skb),
skb->len);
--
2.7.0