netdev - Re: [PATCH v2]IP: Send an ICMP "Fragment Reassembly Timeout" message when enabling connection track

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Date:	Fri, 22 Jan 2010 12:48:20 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Shan Wei <shanwei@...fujitsu.com>
CC:	David Miller <davem@...emloft.net>, kuznet@....inr.ac.ru,
	pekkas@...core.fi, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	eric.dumazet@...il.com, david@...e-labs.org, jorge@...2.net,
	opurdila@...acom.com,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH v2]IP: Send  an ICMP "Fragment Reassembly Timeout" message
 when enabling connection track

Shan Wei wrote:
> [PATCH v2]IP: Send an ICMP "Fragment Reassembly Timeout" message when enabling connection track
> 
> No matter whether connection track is enabled, an end host should send 
> an ICMPv4 "Fragment Reassembly Timeout" message when defrag timeout. 
> The reasons are following two points:  
> 
> 1. RFC 792 says:
>    >>>> >> > >   If a host reassembling a fragmented datagram cannot complete the
>    >>>> >> > >   reassembly due to missing fragments within its time limit it
>    >>>> >> > >   discards the datagram, and it may send a time exceeded message.
>    >>>> >> > > 
>    >>>> >> > >   If fragment zero is not available then no time exceeded need be
>    >>>> >> > >   sent at all.
>    >>>> >> > > 
>    >>>> >> > > Read more: http://www.faqs.org/rfcs/rfc792.html#ixzz0aOXRD7Wp
> 
> 2. Patrick McHardy also agrees with this opinion.   :-)   
>    About the discussion of this opinion, refer to http://patchwork.ozlabs.org/patch/41649
> 
> The patch fixed the problem like this:
> When enabling connection track, fragments are received at PRE_ROUTING HOOK.
> If they are failed to reassemble, ip_expire() will be called. 
> Before sending an ICMP "Fragment Reassembly Timeout" message, 
> the patch searches router table to get the destination entry only for host type.
> 
> The patch has been tested on both host type and route type.

Looks good to me. Would you mind adding a similar change to IPv6
(net/ipv6/netfilter/nf_conntrack_reasm.c)?

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