Re: SIP messages with no/invalid CSeq are dropped by nf_ct_sip, 400 Bad Request is expected instead

[Christophe Leroy <christophe.leroy@c-s.fr>]

Le 24/09/2015 13:19, Patrick McHardy a écrit :
> On 24.09, Christophe Leroy wrote:
>> I have an issue with the SIP conntrack:
>>
>> In commit 30f33e6dee [NETFILTER]: nf_conntrack_sip: support method specific
>> request/response handling
>> Modified by b20ab9cc63 netfilter: nf_ct_helper: better logging for dropped
>> packets
>>
>> SIP requests with no CSeq header are dropped by kernel before reaching the
>> user app.
>>
>> According to RFC4475 "Session Initiation Protocol (SIP) Torture Test
>> Messages", requests with invalid CSeq should be responded with 400 Bad
>> Request, and that's what my app does, but it can only do it if it receives
>> the request.
> I don't see anything about missing CSeq-headers in that RFC, could you point
> me to the correct chapter?
>
RFC4475 gives no exemple explicitly about missing CSeq-headers, but it 
has some exemples for bad CSeq-headers in §3.1.2.4, §3.1.2.17 and §3.3.8 
where it expects 400 Bad request response.

In addition, §3.3.1 "Missing Required Header Fields" shows that 400 Bad 
Request is also expected in the case of missing Call-ID, From, or To 
mandatory headers. Taking into account RFC3261 §8.1.1, CSeq is also a 
mandatory header in the same way as Call-ID, From, or To, so the same 
answer should be expected.

RFC3261 §21.4.1 shows that 400 Bad request is to be used for missing 
headers.

Christophe