netdev - RE: [PATCH] tcp: RST: binding oif to iif for tcp v4

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Date:	Fri, 3 Feb 2012 16:56:53 -0500
From:	Shawn Lu <shawn.lu@...csson.com>
To:	Ben Greear <greearb@...delatech.com>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xiaoclu@...il.com" <xiaoclu@...il.com>
Subject: RE: [PATCH] tcp: RST: binding oif to iif for tcp v4

I have the same issue when using  SO_BINDTODEVICE to bind to specifc interface,  RST is getting lost in ip_route_output_key.  

-----Original Message-----
From: Ben Greear [mailto:greearb@...delatech.com] 
Sent: Friday, February 03, 2012 1:40 PM
To: Eric Dumazet
Cc: Shawn Lu; davem@...emloft.net; netdev@...r.kernel.org; xiaoclu@...il.com
Subject: Re: [PATCH] tcp: RST: binding oif to iif for tcp v4

On 02/03/2012 01:31 PM, Eric Dumazet wrote:
> Le vendredi 03 février 2012 à 12:16 -0800, Shawn Lu a écrit :
>> Binding RST packet outgoing interface to incomming interface for tcp 
>> v4. This has few benefits:
>> 1. tcp_v6_send_reset already did that.
>
> I dont think so. ipv6 makes no special provision for RST.
>
>> 2. This helps tcp connect with SO_BINDTODEVICE set. When connection 
>> is lost, we still able to sending out RST using same interface.
>
> I dont understand this.

I have been using a similar patch for years now.  When using routing rules that depend on binding to an interface, the RST isn't always bound properly without this fix.

My code looks like this:

@@ -650,6 +650,7 @@ static void tcp_v4_send_reset(struct sock *sk, struct sk_buff *skb)
  				      arg.iov[0].iov_len, IPPROTO_TCP, 0);
  	arg.csumoffset = offsetof(struct tcphdr, check) / 2;
  	arg.flags = (sk && inet_sk(sk)->transparent) ? IP_REPLY_ARG_NOSRCCHECK : 0;
+	arg.bound_dev_if = skb_rtable(skb)->rt_iif;

  	net = dev_net(skb_dst(skb)->dev);
  	ip_send_reply(net->ipv4.tcp_sock, skb, ip_hdr(skb)->saddr,


It was originally written by Patrick McHardy, but I've hacked it a bit over the years to keep it compiling.  It seems to work fine.

Thanks,
Ben


--
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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