Subject: [PATCH net-next] ipv6: add tos reflection in TCP reset and ack

From: Wei Wang <[email-masked]>
Date: Tue, 8 Sep 2020 14:29:02 -0700

Currently, ipv6 stack does not do any TOS reflection. To make the
behavior consistent with v4 stack, this commit adds TOS reflection in
tcp_v6_reqsk_send_ack() and tcp_v6_send_reset(). We clear the lower
2-bit ECN value of the received TOS in compliance with RFC 3168 6.1.5
robustness principles.

Signed-off-by: Wei Wang <[email-masked]>
Signed-off-by: Eric Dumazet <[email-masked]>
---
 net/ipv6/tcp_ipv6.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 87a633e1fbef..04efa3ee80ef 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -959,8 +959,8 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
 	dst = ip6_dst_lookup_flow(sock_net(ctl_sk), ctl_sk, &fl6, NULL);
 	if (!IS_ERR(dst)) {
 		skb_dst_set(buff, dst);
-		ip6_xmit(ctl_sk, buff, &fl6, fl6.flowi6_mark, NULL, tclass,
-			 priority);
+		ip6_xmit(ctl_sk, buff, &fl6, fl6.flowi6_mark, NULL,
+			 tclass & ~INET_ECN_MASK, priority);
 		TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
 		if (rst)
 			TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
@@ -1068,8 +1068,8 @@ static void tcp_v6_send_reset(const struct sock *sk, struct sk_buff *skb)
 			label = ip6_flowlabel(ipv6h);
 	}
 
-	tcp_v6_send_response(sk, skb, seq, ack_seq, 0, 0, 0, oif, key, 1, 0,
-			     label, priority);
+	tcp_v6_send_response(sk, skb, seq, ack_seq, 0, 0, 0, oif, key, 1,
+			     ipv6_get_dsfield(ipv6h), label, priority);
 
 #ifdef CONFIG_TCP_MD5SIG
 out:
@@ -1122,7 +1122,7 @@ static void tcp_v6_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
 			tcp_time_stamp_raw() + tcp_rsk(req)->ts_off,
 			req->ts_recent, sk->sk_bound_dev_if,
 			tcp_v6_md5_do_lookup(sk, &ipv6_hdr(skb)->saddr, l3index),
-			0, 0, sk->sk_priority);
+			ipv6_get_dsfield(ipv6_hdr(skb)), 0, sk->sk_priority);
 }

-- 
2.28.0.526.ge36021eeef-goog