netdev - Re: [PATCH 02/14] tcp: fix mark propagation with fwmark

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Date:   Thu, 26 Jan 2017 10:02:40 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH 02/14] tcp: fix mark propagation with fwmark_reflect
 enabled

On Thu, 2017-01-26 at 17:37 +0100, Pablo Neira Ayuso wrote:
> From: Pau Espin Pedrol <pespin.shar@...il.com>
> 
> Otherwise, RST packets generated by the TCP stack for non-existing
> sockets always have mark 0.
> The mark from the original packet is assigned to the netns_ipv4/6
> socket used to send the response so that it can get copied into the
> response skb when the socket sends it.
> 
> Fixes: e110861f8609 ("net: add a sysctl to reflect the fwmark on replies")
> Cc: Lorenzo Colitti <lorenzo@...gle.com>
> Signed-off-by: Pau Espin Pedrol <pau.espin@...sares.net>
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> ---
>  net/ipv4/ip_output.c | 1 +
>  net/ipv6/tcp_ipv6.c  | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index fac275c48108..b67719f45953 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1629,6 +1629,7 @@ void ip_send_unicast_reply(struct sock *sk, struct sk_buff *skb,
>  	sk->sk_protocol = ip_hdr(skb)->protocol;
>  	sk->sk_bound_dev_if = arg->bound_dev_if;
>  	sk->sk_sndbuf = sysctl_wmem_default;
> +	sk->sk_mark = fl4.flowi4_mark;
>  	err = ip_append_data(sk, &fl4, ip_reply_glue_bits, arg->iov->iov_base,
>  			     len, 0, &ipc, &rt, MSG_DONTWAIT);
>  	if (unlikely(err)) {
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 73bc8fc68acd..2b20622a5824 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -840,6 +840,7 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
>  	dst = ip6_dst_lookup_flow(ctl_sk, &fl6, NULL);
>  	if (!IS_ERR(dst)) {
>  		skb_dst_set(buff, dst);
> +		ctl_sk->sk_mark = fl6.flowi6_mark;
>  		ip6_xmit(ctl_sk, buff, &fl6, NULL, tclass);
>  		TCP_INC_STATS(net, TCP_MIB_OUTSEGS);
>  		if (rst)


This patch is wrong.

ctl_sk is a shared socket, and tcp_v6_send_response() can be called from
many different cpus at the same time.