Date: Fri, 30 Jan 2009 09:41:50 +0100 From: =?ISO-8859-1?Q?Michael_T=FCxen?= <Michael.Tuexen@lurchi.franken.de> To: "Muggeridge, Matt" <Matt.Muggeridge@hp.com> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, Yann WANWANSCAPPEL <yann.wanwanscappel@free.fr> Subject: Re: SCTP, possible bug in peer authentication key Message-ID: <0D5E2F07-ABE5-46D8-8060-570E4B2AFD71@lurchi.franken.de> In-Reply-To: <DAE8EEF9700DC84CB97414D6CF6FCA713E79BEC1EF@GVW1160EXB.americas.hpqcorp.net> References: <4980B747.7070400@free.fr> <A36412A3-53FA-4738-A875-8DFB78C8FE58@lurchi.franken.de> <DAE8EEF9700DC84CB97414D6CF6FCA713E79BEC1EF@GVW1160EXB.americas.hpqcorp.net>
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Hi Matt,
Peter Lei (who wrote the AUTH code) already fixed that in Randalls CVS
server.
So it will show up when Randall syncs the repositories next time.
Thank you for pointing that out. I missed that...
Best regards
Michael
On Jan 30, 2009, at 2:37 AM, Muggeridge, Matt wrote:
>> I think I found a bug in the SCTP authentication code, in
>> sctp_load_addresses_from_init() in sctp_pcb.c
>
> I noticed the same calculation appears in
> sctp_auth.c:sctp_auth_get_cookie_params(). Does this fix also need
> to be applied there?
>
> Cheers,
> Matt.
>
> -----Original Message-----
> From: Michael Tüxen [mailto:Michael.Tuexen@lurchi.franken.de]
> Sent: Thursday, 29 January 2009 6:23 PM
> To: Yann WANWANSCAPPEL
> Cc: freebsd-net@freebsd.org
> Subject: Re: SCTP, possible bug in peer authentication key
>
> Hi Yann,
>
> very good catch! You are right.
>
> I have committed your patch to Randalls repository, so it will show
> up in the FreeBSD sources soon (next time he syncs them)...
>
> Best regards
> Michael
>
> On Jan 28, 2009, at 8:51 PM, Yann WANWANSCAPPEL wrote:
>
>> Hi all,
>>
>> I think I found a bug in the SCTP authentication code, in
>> sctp_load_addresses_from_init() in sctp_pcb.c
>>
>> keylen = sizeof(*p_random) + random_len + sizeof(*chunks) +
>> num_chunks
>> +
>> sizeof(*hmacs) + hmacs_len;
>>
>> The keylen calculation assumes the Chunk List Parameter (CHUNKS)
>> vl-param was present in the received INIT packet, which can be false
>> if peer SCTP does not require any chunk to be authenticated (this
>> typically occurs if peer does not support ASCONF).
>>
>>> From RFC 4895, 6.1
>>
>> * An SCTP endpoint has a list of chunks it only accepts if they are
>> * received in an authenticated way. This list is included in the
>> INIT
>> * and INIT-ACK, and MAY be omitted if it is empty. Since this list
>> * does not change during the lifetime of the SCTP endpoint there is
>> no
>> * problem in case of INIT collision.
>>
>> This case is properly handled later in the build of the key
>>
>> /* append in the AUTH chunks */
>> if (chunks != NULL) {
>> .....
>> }
>>
>> I think the calculated keylen should be something like this :
>>
>> keylen = sizeof(*p_random) + random_len + sizeof(*hmacs) + hmacs_len;
>>
>> if (chunks != NULL) {
>> keylen += sizeof(*chunks) + num_chunks }
>>
>> This problem results in authenticated packets sent from peer SCTP to
>> be discarded.
>>
>> The problem does not occurs if peer SCTP is modified to send an empty
>> Chunk List Parameter, (eg num_chunks = 0 in the decoding).
>>
>> Br,
>> Yann
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>>
>
>
>
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