netdev - Re: [PATCH] net: gre: don't pull skb if dealing with icmp message

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Message-ID: <CALnjE+rkN5Nsoq0sOYaTH5gncPKUiK+ppBRc68ap7Vs-kYfqbw@mail.gmail.com>
Date:	Tue, 21 Jan 2014 10:27:37 -0800
From:	Pravin Shelar <pshelar@...ira.com>
To:	Duan Jiong <duanj.fnst@...fujitsu.com>
Cc:	David Miller <davem@...emloft.net>,
	Daniel Borkmann <dborkman@...hat.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: gre: don't pull skb if dealing with icmp message

On Sun, Jan 19, 2014 at 5:37 PM, Duan Jiong <duanj.fnst@...fujitsu.com> wrote:
> 于 2014年01月20日 05:08, Pravin Shelar 写道:
>> On Sun, Jan 19, 2014 at 12:35 AM, Duan Jiong <duanj.fnst@...fujitsu.com> wrote:
>>>
>>> When dealing with icmp messages, the skb->data points the
>>> ip header that triggered the sending of the icmp message.
>>>
>>> In gre_cisco_err(), the parse_gre_header() is called, and the
>>> iptunnel_pull_header() is called to pull the skb at the end of
>>> the parse_gre_header(). Unfortunately, the ipgre_err still needs
>>> the skb->data points the ip header following the icmp layer,
>>> and those ip addresses in ip header will be used to look up
>>> tunnel by ip_tunnel_lookup().
>>>
>> This looks like bug.
>> Can you use ip_hdr() rather than skb->data in ipgre_err().
>> Same is done in ipgre_rcv().
>
> That's maybe not a good idea. The ip_hdr() will the return the outmost
> ip header, but we need inner ip header following the icmp layer.
>
Why do you want to use inner ip header?
If you want to really look at original packet header, you can
calculate it from outer iph header rather than changing fast path
parse_gre_header() function.
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