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Date: Wed, 9 May 2018 20:32:15 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Jon Maxwell <jmaxwell37@...il.com>, davem@...emloft.net
Cc: kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
jmaxwell@...hat.com
Subject: Re: [PATCH net-next] tcp: Add mark for TIMEWAIT sockets
On 05/09/2018 07:07 PM, Jon Maxwell wrote:
> Aidan McGurn from Openwave Mobility systems reported the following bug:
>
> "Marked routing is broken on customer deployment. Its effects are large
> increase in Uplink retransmissions caused by the client never receiving
> the final ACK to their FINACK - this ACK misses the mark and routes out
> of the incorrect route."
>
> Currently marks are added to sk_buffs for replies when the "fwmark_reflect"
> sysctl is enabled. But not for TIME_WAIT sockets where the original socket had
> sk->sk_mark set via setsockopt(SO_MARK..).
>
> Fix this in IPv4/v6 by adding tw->tw_mark for TIME_WAIT sockets. Copy the the
> original sk->sk_mark in __inet_twsk_hashdance() to the new tw->tw_mark location.
> Then copy this into ctl_sk->sk_mark so that the skb gets sent with the correct
> mark. Do the same for resets. Give the "fwmark_reflect" sysctl precedence over
> sk->sk_mark so that netfilter rules are still honored.
>
> Signed-off-by: Jon Maxwell <jmaxwell37@...il.com>
> ---
> include/net/inet_timewait_sock.h | 1 +
> net/ipv4/ip_output.c | 3 ++-
> net/ipv4/tcp_ipv4.c | 18 ++++++++++++++++--
> net/ipv4/tcp_minisocks.c | 1 +
> net/ipv6/tcp_ipv6.c | 8 +++++++-
> 5 files changed, 27 insertions(+), 4 deletions(-)
>
> diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
> index c7be1ca8e562..659d8ed5a3bc 100644
> --- a/include/net/inet_timewait_sock.h
> +++ b/include/net/inet_timewait_sock.h
> @@ -62,6 +62,7 @@ struct inet_timewait_sock {
> #define tw_dr __tw_common.skc_tw_dr
>
> int tw_timeout;
> + __u32 tw_mark;
> volatile unsigned char tw_substate;
> unsigned char tw_rcv_wscale;
>
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index 95adb171f852..cca4412dc4cb 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1539,6 +1539,7 @@ void ip_send_unicast_reply(struct sock *sk, struct sk_buff *skb,
> struct sk_buff *nskb;
> int err;
> int oif;
> + __u32 mark = IP4_REPLY_MARK(net, skb->mark);
>
> if (__ip_options_echo(net, &replyopts.opt.opt, skb, sopt))
> return;
> @@ -1561,7 +1562,7 @@ void ip_send_unicast_reply(struct sock *sk, struct sk_buff *skb,
> oif = skb->skb_iif;
>
> flowi4_init_output(&fl4, oif,
> - IP4_REPLY_MARK(net, skb->mark),
> + mark ? (mark) : sk->sk_mark,
You can avoid the declaration of mark variable and simply use here :
IP4_REPLY_MARK(net, skb->mark) ?: sk->sk_mark,
> RT_TOS(arg->tos),
> RT_SCOPE_UNIVERSE, ip_hdr(skb)->protocol,
> ip_reply_arg_flowi_flags(arg),
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index f70586b50838..fbee36579c83 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -621,6 +621,7 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
> struct sock *sk1 = NULL;
> #endif
> struct net *net;
> + struct sock *ctl_sk;
>
> /* Never send a reset in response to a reset. */
> if (th->rst)
> @@ -723,11 +724,17 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
> arg.tos = ip_hdr(skb)->tos;
> arg.uid = sock_net_uid(net, sk && sk_fullsock(sk) ? sk : NULL);
> local_bh_disable();
> - ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
> + ctl_sk = *this_cpu_ptr(net->ipv4.tcp_sk);
> + if (sk && sk->sk_state == TCP_TIME_WAIT)
> + ctl_sk->sk_mark = inet_twsk(sk)->tw_mark;
> + else if (sk && sk_fullsock(sk))
> + ctl_sk->sk_mark = sk->sk_mark;
> + ip_send_unicast_reply(ctl_sk,
> skb, &TCP_SKB_CB(skb)->header.h4.opt,
> ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
> &arg, arg.iov[0].iov_len);
>
> + ctl_sk->sk_mark = 0;
> __TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
> __TCP_INC_STATS(net, TCP_MIB_OUTRSTS);
> local_bh_enable();
> @@ -759,6 +766,7 @@ static void tcp_v4_send_ack(const struct sock *sk,
> } rep;
> struct net *net = sock_net(sk);
> struct ip_reply_arg arg;
> + struct sock *ctl_sk;
>
> memset(&rep.th, 0, sizeof(struct tcphdr));
> memset(&arg, 0, sizeof(arg));
> @@ -809,11 +817,17 @@ static void tcp_v4_send_ack(const struct sock *sk,
> arg.tos = tos;
> arg.uid = sock_net_uid(net, sk_fullsock(sk) ? sk : NULL);
> local_bh_disable();
> - ip_send_unicast_reply(*this_cpu_ptr(net->ipv4.tcp_sk),
> + ctl_sk = *this_cpu_ptr(net->ipv4.tcp_sk);
> + if (sk && sk->sk_state == TCP_TIME_WAIT)
> + ctl_sk->sk_mark = inet_twsk(sk)->tw_mark;
> + else if (sk && sk_fullsock(sk))
> + ctl_sk->sk_mark = sk->sk_mark;
> + ip_send_unicast_reply(ctl_sk,
> skb, &TCP_SKB_CB(skb)->header.h4.opt,
> ip_hdr(skb)->saddr, ip_hdr(skb)->daddr,
> &arg, arg.iov[0].iov_len);
>
> + ctl_sk->sk_mark = 0;
> __TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
> local_bh_enable();
> }
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index 57b5468b5139..f867658b4b30 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -263,6 +263,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
> struct inet_sock *inet = inet_sk(sk);
>
> tw->tw_transparent = inet->transparent;
> + tw->tw_mark = sk->sk_mark;
> tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale;
> tcptw->tw_rcv_nxt = tp->rcv_nxt;
> tcptw->tw_snd_nxt = tp->snd_nxt;
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 6d664d83cd16..a6f876125091 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -803,6 +803,7 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
> unsigned int tot_len = sizeof(struct tcphdr);
> struct dst_entry *dst;
> __be32 *topt;
> + __u32 mark = IP6_REPLY_MARK(net, skb->mark);
>
> if (tsecr)
> tot_len += TCPOLEN_TSTAMP_ALIGNED;
> @@ -871,11 +872,16 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
> fl6.flowi6_oif = oif;
> }
>
> - fl6.flowi6_mark = IP6_REPLY_MARK(net, skb->mark);
> + if (sk && sk->sk_state == TCP_TIME_WAIT)
> + ctl_sk->sk_mark = inet_twsk(sk)->tw_mark;
> + else if (sk && sk_fullsock(sk))
> + ctl_sk->sk_mark = sk->sk_mark;
Unfortunately IPv6 has a single net->ipv6.tcp_sk, shared by all cpus.
So writing ctl_sk->sk_mark is racy on SMP hosts.
I would suggest using a local variable, and not touch ctl_sk->sk_mark
For consistency, you could do the same for IPv4, even if IPv4 currently uses per-cpu sockets
> + fl6.flowi6_mark = mark ? (mark) : ctl_sk->sk_mark;
> fl6.fl6_dport = t1->dest;
> fl6.fl6_sport = t1->source;
> fl6.flowi6_uid = sock_net_uid(net, sk && sk_fullsock(sk) ? sk : NULL);
> security_skb_classify_flow(skb, flowi6_to_flowi(&fl6));
> + ctl_sk->sk_mark = 0;
>
> /* Pass a socket to ip6_dst_lookup either it is for RST
> * Underlying function will use this to retrieve the network
>
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