tcp: Add mark for TIMEWAIT sockets

This version has some suggestions by Eric Dumazet:

- Use a local variable for the mark in IPv6 instead of ctl_sk to avoid SMP
races.
- Use the more elegant "IP4_REPLY_MARK(net, skb->mark) ?: sk->sk_mark"
statement.
- Factorize code as sk_fullsock() check is not necessary.

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 TW sockets that 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 progate this 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@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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;
 

net/ipv4/ip_output.c

@@ -1561,7 +1561,7 @@ 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),
+			   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),

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 +724,16 @@ 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)
+		ctl_sk->sk_mark = (sk->sk_state == TCP_TIME_WAIT) ?
+				   inet_twsk(sk)->tw_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 +765,7 @@ 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 +816,16 @@ 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)
+		ctl_sk->sk_mark = (sk->sk_state == TCP_TIME_WAIT) ?
+				   inet_twsk(sk)->tw_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();
 }

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;

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 = 0;
 
 	if (tsecr)
 		tot_len += TCPOLEN_TSTAMP_ALIGNED;
@@ -871,7 +872,10 @@ 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)
+		mark = (sk->sk_state == TCP_TIME_WAIT) ?
+			inet_twsk(sk)->tw_mark : sk->sk_mark;
+	fl6.flowi6_mark = IP6_REPLY_MARK(net, skb->mark) ?: mark;
 	fl6.fl6_dport = t1->dest;
 	fl6.fl6_sport = t1->source;
 	fl6.flowi6_uid = sock_net_uid(net, sk && sk_fullsock(sk) ? sk : NULL);