From 861602b57730a5c6d3e0b1e4ca7133ca9a8b8538 Mon Sep 17 00:00:00 2001 From: Alexander Duyck Date: Thu, 19 Nov 2020 13:23:51 -0800 Subject: [PATCH] tcp: Allow full IP tos/IPv6 tclass to be reflected in L3 header An issue was recently found where DCTCP SYN/ACK packets did not have the ECT bit set in the L3 header. A bit of code review found that the recent change referenced below had gone though and added a mask that prevented the ECN bits from being populated in the L3 header. This patch addresses that by rolling back the mask so that it is only applied to the flags coming from the incoming TCP request instead of applying it to the socket tos/tclass field. Doing this the ECT bits were restored in the SYN/ACK packets in my testing. One thing that is not addressed by this patch set is the fact that tcp_reflect_tos appears to be incompatible with ECN based congestion avoidance algorithms. At a minimum the feature should likely be documented which it currently isn't. Fixes: ac8f1710c12b ("tcp: reflect tos value received in SYN to the socket") Signed-off-by: Alexander Duyck Acked-by: Wei Wang Signed-off-by: Jakub Kicinski --- net/ipv4/tcp_ipv4.c | 5 +++-- net/ipv6/tcp_ipv6.c | 6 +++--- 2 files changed, 6 insertions(+), 5 deletions(-) diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 7352c097ae48..25d35a56ceba 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -981,7 +981,8 @@ static int tcp_v4_send_synack(const struct sock *sk, struct dst_entry *dst, skb = tcp_make_synack(sk, dst, req, foc, synack_type, syn_skb); tos = sock_net(sk)->ipv4.sysctl_tcp_reflect_tos ? - tcp_rsk(req)->syn_tos : inet_sk(sk)->tos; + tcp_rsk(req)->syn_tos & ~INET_ECN_MASK : + inet_sk(sk)->tos; if (skb) { __tcp_v4_send_check(skb, ireq->ir_loc_addr, ireq->ir_rmt_addr); @@ -990,7 +991,7 @@ static int tcp_v4_send_synack(const struct sock *sk, struct dst_entry *dst, err = ip_build_and_send_pkt(skb, sk, ireq->ir_loc_addr, ireq->ir_rmt_addr, rcu_dereference(ireq->ireq_opt), - tos & ~INET_ECN_MASK); + tos); rcu_read_unlock(); err = net_xmit_eval(err); } diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 8db59f4e5f13..3d49e8d0afee 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -530,12 +530,12 @@ static int tcp_v6_send_synack(const struct sock *sk, struct dst_entry *dst, rcu_read_lock(); opt = ireq->ipv6_opt; tclass = sock_net(sk)->ipv4.sysctl_tcp_reflect_tos ? - tcp_rsk(req)->syn_tos : np->tclass; + tcp_rsk(req)->syn_tos & ~INET_ECN_MASK : + np->tclass; if (!opt) opt = rcu_dereference(np->opt); err = ip6_xmit(sk, skb, fl6, sk->sk_mark, opt, - tclass & ~INET_ECN_MASK, - sk->sk_priority); + tclass, sk->sk_priority); rcu_read_unlock(); err = net_xmit_eval(err); }