[PATCH] nf_conntrack_sip: check for trailing spaces

[PATCH] nf_conntrack_sip: check for trailing spaces

[Ulrich Weber]

on SIP requests, so a fragmented TCP SIP packet starting with
 INVITE,NOTIFY,OPTIONS,REFER,REGISTER,UPDATE,SUBSCRIBE
 Content-Length: 0

will not bet interpreted as an INVITE request.

Confirm with RFC 3261
 Request-Line   =  Method SP Request-URI SP SIP-Version CRLF

Signed-off-by: Ulrich Weber <ulrich.weber@riverbed.com>
---
 net/netfilter/nf_conntrack_sip.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index 7700556..e37f8da 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -1436,9 +1436,11 @@ static int process_sip_request(struct sk_buff *skb, unsigned int protoff,
 		handler = &sip_handlers[i];
 		if (handler->request == NULL)
 			continue;
-		if (*datalen < handler->len ||
+		if (*datalen < handler->len + 1 ||
 		    strncasecmp(*dptr, handler->method, handler->len))
 			continue;
+		if ((*dptr)[handler->len] != ' ')
+			continue;
 
 		if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CSEQ,
 				      &matchoff, &matchlen) <= 0) {
-- 
2.7.4

Re: [PATCH] nf_conntrack_sip: check for trailing spaces

[Pablo Neira Ayuso]

Hi Ulrich,

Cc'ing Marco Angaroni.

On Wed, Oct 19, 2016 at 10:24:02AM +0200, Ulrich Weber wrote:
> on SIP requests, so a fragmented TCP SIP packet starting with
>  INVITE,NOTIFY,OPTIONS,REFER,REGISTER,UPDATE,SUBSCRIBE
>  Content-Length: 0
> 
> will not bet interpreted as an INVITE request.
> 
> Confirm with RFC 3261
>  Request-Line   =  Method SP Request-URI SP SIP-Version CRLF

Marco has missed your email, so I'm copying and pasting what he told
me wrt. to your patch:

My understanding is that Ulrich is referring to something like an
"Allow" header of a SIP message where the header name is part of a TCP
segment and the header value is part of the following TCP segment:

Allow: INVITE,ACK,CANCEL,OPTIONS,BYE

So I think the fix (check for a space after the method name) is
correct.
However maybe the check could be made more robust, because if you have
the fragmented "Allow" header containing the method names with a space
before comma (it's permitted by SIP grammar) like you see below, you
would again think that it's the first line of the SIP message:

Allow: INVITE , ACK , CANCEL , OPTIONS , BYE

Maybe it's worth checking two bytes after method name; the first byte
must be a space and the second must a alphanumeric character: the URI
following the method name has to start with "sip:" or "sips:" or some
other scheme, which starts for sure with an ALPHA character.

Request-Line   =  Method SP Request-URI SP SIP-Version CRLF
Request-URI    =  SIP-URI / SIPS-URI / absoluteURI
absoluteURI = scheme ":" ( hier-part / opaque-part )
scheme         =  ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )

Re: [PATCH] nf_conntrack_sip: check for trailing spaces

[Ulrich Weber]

Hi Pablo,

good point, will send a new version!

Thanks
 Ulrich

On 20.10.2016 20:17, Pablo Neira Ayuso wrote:
> Hi Ulrich,
> 
> Cc'ing Marco Angaroni.
> 
> On Wed, Oct 19, 2016 at 10:24:02AM +0200, Ulrich Weber wrote:
>> on SIP requests, so a fragmented TCP SIP packet starting with
>>  INVITE,NOTIFY,OPTIONS,REFER,REGISTER,UPDATE,SUBSCRIBE
>>  Content-Length: 0
>>
>> will not bet interpreted as an INVITE request.
>>
>> Confirm with RFC 3261
>>  Request-Line   =  Method SP Request-URI SP SIP-Version CRLF
> 
> Marco has missed your email, so I'm copying and pasting what he told
> me wrt. to your patch:
> 
> My understanding is that Ulrich is referring to something like an
> "Allow" header of a SIP message where the header name is part of a TCP
> segment and the header value is part of the following TCP segment:
> 
> Allow: INVITE,ACK,CANCEL,OPTIONS,BYE
> 
> So I think the fix (check for a space after the method name) is
> correct.
> However maybe the check could be made more robust, because if you have
> the fragmented "Allow" header containing the method names with a space
> before comma (it's permitted by SIP grammar) like you see below, you
> would again think that it's the first line of the SIP message:
> 
> Allow: INVITE , ACK , CANCEL , OPTIONS , BYE
> 
> Maybe it's worth checking two bytes after method name; the first byte
> must be a space and the second must a alphanumeric character: the URI
> following the method name has to start with "sip:" or "sips:" or some
> other scheme, which starts for sure with an ALPHA character.
> 
> Request-Line   =  Method SP Request-URI SP SIP-Version CRLF
> Request-URI    =  SIP-URI / SIPS-URI / absoluteURI
> absoluteURI = scheme ":" ( hier-part / opaque-part )
> scheme         =  ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
> --
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