Re: [PATCH/RFC] netfilter: nf_conntrack_sip: Handle quirky Cisco phones

[Kevin Cernekee]

On Sun, Nov 14, 2010 at 12:59 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> 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`...[..@.r.....C...........REGISTER sip:losangeles.voip.ms SIP/2.0
Via: SIP/2.0/

10:05:53.587370 IP 67.215.241.250.5060 > 192.168.2.28.50070: SIP, length: 486
E.......3..fC...............SIP/2.0 100 Trying
Via: SIP/2.0/UDP 192.168.2.28:5060

10:05:53.587807 IP 67.215.241.250.5060 > 192.168.2.28.50070: SIP, length: 550
E..B....3..%C...............SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 192.168.2.2

10:05:57.496541 IP 192.168.2.28.50070 > 67.215.241.250.5060: SIP, length: 723
E`...\..@.r.....C...........REGISTER sip:losangeles.voip.ms SIP/2.0
Via: SIP/2.0/

10:05:57.526716 IP 67.215.241.250.5060 > 192.168.2.28.50070: SIP, length: 486
E.......3..dC...............SIP/2.0 100 Trying
Via: SIP/2.0/UDP 192.168.2.28:5060

10:05:57.527162 IP 67.215.241.250.5060 > 192.168.2.28.50070: SIP, length: 550
E..B....3..#C...............SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 192.168.2.2

10:06:01.486821 IP 192.168.2.28.50070 > 67.215.241.250.5060: SIP, length: 723
E`...]..@.r.....C...........REGISTER sip:losangeles.voip.ms SIP/2.0
Via: SIP/2.0/

10:06:01.515611 IP 67.215.241.250.5060 > 192.168.2.28.50070: SIP, length: 486
E.......3..bC...............SIP/2.0 100 Trying
Via: SIP/2.0/UDP 192.168.2.28:5060

10:06:01.516024 IP 67.215.241.250.5060 > 192.168.2.28.50070: SIP, length: 550
E..B....3..!C...............SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 192.168.2.2

... continues forever ...


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..@.p.....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..@.p.....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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