T.38 FAX support via nf_nat_sip,nf_conntrack_sip

T.38 FAX support via nf_nat_sip,nf_conntrack_sip

[Florian Fuessl]

Hi,

T.38 FAX support via nf_nat_sip,nf_conntraack_sip does currently not seem to
work, because the REINVITE for the codec change is not handled correctly at
the moment (Figure: Fax Pass-Through and Call Flow diagram i.e. at
http://docwiki.cisco.com/wiki/Cisco_IOS_Voice_Troubleshooting_and_Monitoring
_--_Fax_Call_Flow )

Do you have an idea how to patch this problem?

-Florian

RE: T.38 FAX support via nf_nat_sip,nf_conntrack_sip

[Florian Fuessl]

I've an update regarding this issue:

According to my packet dumps the nf_conntrack_sip.c function:

static int process_sdp(struct sk_buff *skb,
                       const char **dptr, unsigned int *datalen,
                       unsigned int cseq)
{
[...]
        /* Update session connection and owner addresses */
        nf_nat_sdp_session = rcu_dereference(nf_nat_sdp_session_hook);
        if (nf_nat_sdp_session && ct->status & IPS_NAT_MASK)
                ret = nf_nat_sdp_session(skb, dptr, sdpoff, datalen,
&rtp_addr);

        if (ret == NF_ACCEPT && i > 0)
                help->help.ct_sip_info.invite_cseq = cseq;

        return ret;
}

... seems to rewrite the SIP/SDP (IN IP4) owner address and connection
address with garbage IP data on REINVITE packets sourcing from NAT outbound
to NAT inbound.

For example:
REINVITE packet sourcing from NAT outbound with connection information:
SIP Call IN IP4 212.77.188.67
... will be rewritten by the garbage IP address:
SIP Call IN IP4 128.41.188.128

Should this information not only be rewritten for packets sourcing from NAT
inbound to NAT outbound? 
What information does nf_nat_sip,nf_conntrack_sip read in order to determine
the garbage IP? Is this maybe a security (buffer) problem, too?

Sorry I'm no coder, so any help is very welcome :)

-Florian

> -----Original Message-----
> From: netfilter-devel-owner@vger.kernel.org [mailto:netfilter-devel-
> owner@vger.kernel.org] On Behalf Of Florian Fuessl
> Sent: Monday, September 28, 2009 7:10 PM
> To: netfilter-devel@vger.kernel.org
> Subject: T.38 FAX support via nf_nat_sip,nf_conntrack_sip
> 
> Hi,
> 
> T.38 FAX support via nf_nat_sip,nf_conntraack_sip does currently not
> seem to
> work, because the REINVITE for the codec change is not handled
> correctly at
> the moment (Figure: Fax Pass-Through and Call Flow diagram i.e. at
> http://docwiki.cisco.com/wiki/Cisco_IOS_Voice_Troubleshooting_and_Monit
> oring
> _--_Fax_Call_Flow )
> 
> Do you have an idea how to patch this problem?
> 
> -Florian
> 
> --
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