netdev - Re: [PATCH v2] ip6tnl: do route updating for redirect in ip6_tnl

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Date:	Fri, 20 Sep 2013 18:43:08 +0800
From:	Duan Jiong <duanj.fnst@...fujitsu.com>
To:	David Miller <davem@...emloft.net>
CC:	djduanjiong@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2] ip6tnl: do route updating for redirect in ip6_tnl_err()

于 2013年09月20日 02:02, David Miller 写道:
> From: Duan Jiong <djduanjiong@...il.com>
> Date: Tue, 17 Sep 2013 20:27:57 -0700
> 
>> After the ip6_tnl_err() is called, the rel_msg is assigned to
>> 0, and the ip4ip6_err() will return directly, the instruction
>> below will not be executed.
>>
>> In rfc2473, we can know that the tunnel ICMP redirect message
>> should not be reported to the source of the original packet,
>> so we can handle it in ip6_tnl_err().
>>
>> Signed-off-by: Duan Jiong <duanj.fnst@...fujitsu.com>
> 
> I do not think this change is correct.
> 
>> @@ -576,9 +579,6 @@ ip4ip6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
>>  		rel_type = ICMP_DEST_UNREACH;
>>  		rel_code = ICMP_FRAG_NEEDED;
>>  		break;
>> -	case NDISC_REDIRECT:
>> -		rel_type = ICMP_REDIRECT;
>> -		rel_code = ICMP_REDIR_HOST;
>>  	default:
>>  		return 0;
>>  	}
> 
> The bug is a missing "break;" statement for this case, and:

You can read the ip6_tnl_err(). when the message is NDISC_REDIRECT, the
rel_msg is assigned to 0, then 

 561         if (rel_msg == 0)
 562                 return 0;

the function ip4ip6_err() return directly. so even though you add "break;"
statement for this case, the redirect message will not be handled.

> 
>> @@ -637,8 +637,6 @@ ip4ip6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
>>  
>>  		skb_dst(skb2)->ops->update_pmtu(skb_dst(skb2), NULL, skb2, rel_info);
>>  	}
>> -	if (rel_type == ICMP_REDIRECT)
>> -		skb_dst(skb2)->ops->redirect(skb_dst(skb2), NULL, skb2);
>>  
> 
> We absolutely must run the ipv4 dst_ops redirect handler here so you must
> keep this code around as well.
> 

Because the Redirect Message is sent to tunnel entry-point, so the target address in
Redirect ICMPv6 Message is an ipv6 address, then we could not run the ipv4 dst_ops 
redirect handler here.

Thanks,
  Duan

> The only change you need to make is to add the missing break;
> statement to ip4ip6_err() and then also add appropriate NDISC_REDIRECT
> handling to ip6ip6_err().


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