netdev - Re: [PATCH/RFC] netfilter: nf_conntrack

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Date:	Sun, 14 Nov 2010 20:57:44 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Kevin Cernekee <cernekee@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	netfilter-devel@...r.kernel.org, netfilter@...r.kernel.org,
	coreteam@...filter.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH/RFC] netfilter: nf_conntrack_sip: Handle quirky Cisco
 phones

Le dimanche 14 novembre 2010 à 10:33 -0800, Kevin Cernekee a écrit :
> On Sun, Nov 14, 2010 at 12:59 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > I would like to get an exact SIP exchange to make sure their is not
> > another way to handle this without adding a "Cisco" string somewhere...
> >
> > Please provide a pcap or tcpdump -A
> 
> Existing nf_nat_sip: phone sends unauthenticated REGISTER requests
> over and over again, because it is not seeing the replies sent back to
> port 50070:
> 
> 10:05:53.496479 IP 192.168.2.28.50070 > 67.215.241.250.5060: SIP, length: 723
> E`...[..@.......C...........REGISTER sip:losangeles.voip.ms SIP/2.0
> Via: SIP/2.0/
> 

Hmm, partial tcpdump... you should use" tcpdump -s 1000 -A" 

We miss the

Via: SIP/2.0/UDP 192.168.2.28:5060;branch=xxxxxxxx


Maybe a fix would be to use this "5060" port, instead of hardcoding it
like you did ?


> 
> Patched nf_nat_sip: router sends the replies back to port 5060, so the
> phone is now able to register itself and make calls:
> 
> 10:09:46.221631 IP 192.168.2.28.50618 > 67.215.241.250.5060: SIP, length: 723
> E`...G..@.......C...........REGISTER sip:losangeles.voip.ms SIP/2.0
> Via: SIP/2.0/
> 
> 10:09:46.253052 IP 67.215.241.250.5060 > 192.168.2.28.5060: SIP, length: 491
> E....+..4..$C...............SIP/2.0 100 Trying
> Via: SIP/2.0/UDP 192.168.2.28:5060
> 
> 10:09:46.253472 IP 67.215.241.250.5060 > 192.168.2.28.5060: SIP, length: 550
> E..B.,..4...C...............SIP/2.0 401 Unauthorized
> Via: SIP/2.0/UDP 192.168.2.2
> 
> 10:09:46.261602 IP 192.168.2.28.50618 > 67.215.241.250.5060: SIP, length: 900
> E`...H..@.......C...........REGISTER sip:losangeles.voip.ms SIP/2.0
> Via: SIP/2.0/
> 
> 10:09:46.290211 IP 67.215.241.250.5060 > 192.168.2.28.5060: SIP, length: 491
> E....-..4.."C...............SIP/2.0 100 Trying
> Via: SIP/2.0/UDP 192.168.2.28:5060
> 
> 10:09:46.295041 IP 67.215.241.250.5060 > 192.168.2.28.5060: SIP, length: 579
> E.._....4...C............K..SIP/2.0 200 OK
> Via: SIP/2.0/UDP 192.168.2.28:5060;bra
> 
> 
> BTW, I thought of two possible issues with the original patch:
> 
> 1) Might need to call skb_make_writable() prior to modifying the
> packet.  Presumably the second invocation inside
> nf_nat_mangle_udp_packet() will have no effect.
> 
> (Is there a cleaner way to mangle just the port number?  Most of the
> utility functions only help with modifying the data area.)
> 
> 2) I should probably be checking to make sure request == 0 before
> mangling the packet.  The current behavior is harmless if the SIP
> proxy is on port 5060, but that might not always be the case.
> 
> I can roll these, along with any other suggestions, into v2.


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