Patch "tcp: properly scale window in tcp_v[46]_reqsk_send_ack()" has been added to the 4.7-stable tree

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

tcp: properly scale window in tcp_v[46]_reqsk_send_ack()

to the 4.7-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-properly-scale-window-in-tcp_v_reqsk_send_ack.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Mon, 22 Aug 2016 11:31:10 -0700
Subject: tcp: properly scale window in tcp_v[46]_reqsk_send_ack()

From: Eric Dumazet <[email protected]>

[ Upstream commit 20a2b49fc538540819a0c552877086548cff8d8d ]

When sending an ack in SYN_RECV state, we must scale the offered window if wscale option was negotiated and accepted.

Tested:
Following packetdrill test demonstrates the issue :

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

// Establish a connection.
+0 < S 0:0(0) win 20000 <mss 1000,sackOK,wscale 7, nop, TS val 100 ecr 0> +0 > S. 0:0(0) ack 1 win 28960 <mss 1460,sackOK, TS val 100 ecr 100, nop, wscale 7>

+0 < . 1:11(10) ack 1 win 156 <nop,nop,TS val 99 ecr 100> // check that window is properly scaled !
+0 > . 1:1(0) ack 1 win 226 <nop,nop,TS val 200 ecr 100>

---
 net/ipv4/tcp_ipv4.c |    8 +++++++-
 net/ipv6/tcp_ipv6.c |    8 +++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

@@ -814,8 +814,14 @@ static void tcp_v4_reqsk_send_ack(const
 	u32 seq = (sk->sk_state == TCP_LISTEN) ? tcp_rsk(req)->snt_isn + 1 :
 					     tcp_sk(sk)->snd_nxt;
 
+	/* RFC 7323 2.3
+	 * The window field (SEG.WND) of every outgoing segment, with the
+	 * exception of <SYN> segments, MUST be right-shifted by
+	 * Rcv.Wind.Shift bits:
+	 */
 	tcp_v4_send_ack(sock_net(sk), skb, seq,
-			tcp_rsk(req)->rcv_nxt, req->rsk_rcv_wnd,
+			tcp_rsk(req)->rcv_nxt,
+			req->rsk_rcv_wnd >> inet_rsk(req)->rcv_wscale,
 			tcp_time_stamp,
 			req->ts_recent,
 			0,

@@ -937,9 +937,15 @@ static void tcp_v6_reqsk_send_ack(const
 	/* sk->sk_state == TCP_LISTEN -> for regular TCP_SYN_RECV
 	 * sk->sk_state == TCP_SYN_RECV -> for Fast Open.
 	 */
+	/* RFC 7323 2.3
+	 * The window field (SEG.WND) of every outgoing segment, with the
+	 * exception of <SYN> segments, MUST be right-shifted by
+	 * Rcv.Wind.Shift bits:
+	 */
 	tcp_v6_send_ack(sk, skb, (sk->sk_state == TCP_LISTEN) ?
 			tcp_rsk(req)->snt_isn + 1 : tcp_sk(sk)->snd_nxt,
-			tcp_rsk(req)->rcv_nxt, req->rsk_rcv_wnd,
+			tcp_rsk(req)->rcv_nxt,
+			req->rsk_rcv_wnd >> inet_rsk(req)->rcv_wscale,
 			tcp_time_stamp, req->ts_recent, sk->sk_bound_dev_if,
 			tcp_v6_md5_do_lookup(sk, &ipv6_hdr(skb)->daddr),
 			0, 0);

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/bonding-fix-bonding-crash.patch queue-4.7/tcp-properly-scale-window-in-tcp_v_reqsk_send_ack.patch queue-4.7/tcp-fastopen-avoid-negative-sk_forward_alloc.patch queue-4.7/udp-fix-poll-issue-with-zero-sized-packets.patch queue-4.7/tcp-fix-use-after-free-in-tcp_xmit_retransmit_queue.patch queue-4.7/tun-fix-transmit-timestamp-support.patch