Date: Thu, 29 Jan 2009 11:29:24 -0600 From: Peter Lei <peter.lei@ieee.org> To: =?ISO-8859-1?Q?Michael_T=FCxen?= <Michael.Tuexen@lurchi.franken.de> Cc: freebsd-net@freebsd.org, Yann WANWANSCAPPEL <yann.wanwanscappel@free.fr> Subject: Re: SCTP, possible bug in peer authentication key Message-ID: <0EEEB325-C7AF-468F-9374-EFED1BD3B3E4@ieee.org> In-Reply-To: <A36412A3-53FA-4738-A875-8DFB78C8FE58@lurchi.franken.de> References: <4980B747.7070400@free.fr> <A36412A3-53FA-4738-A875-8DFB78C8FE58@lurchi.franken.de>
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There's a corresponding change that is needed for pulling the auth info
out of the cookie for the other direction (i.e. server side =20
handling). I've
committed that into the SCTP project repo, and should also get in with
Randall's next commit.
--peter
On Jan 29, 2009, at 2:23 AM, Michael T=FCxen wrote:
> 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 =3D sizeof(*p_random) + random_len + sizeof(*chunks) + =20
>> 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 =20
>> false if
>> peer SCTP does not require any chunk to be authenticated (this =20
>> typically
>> occurs if peer does not support ASCONF).
>>
>>> =46rom 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 =20
>> 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 =20=
>> 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 !=3D NULL) {
>> .....
>> }
>>
>> I think the calculated keylen should be something like this :
>>
>> keylen =3D sizeof(*p_random) + random_len + sizeof(*hmacs) + =
hmacs_len;
>>
>> if (chunks !=3D NULL) {
>> keylen +=3D sizeof(*chunks) + num_chunks
>> }
>>
>> This problem results in authenticated packets sent from peer SCTP =20
>> to be
>> discarded.
>>
>> The problem does not occurs if peer SCTP is modified to send an empty
>> Chunk List Parameter, (eg num_chunks =3D 0 in the decoding).
>>
>> Br,
>> Yann
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> freebsd-net@freebsd.org mailing list
>> http://lists.freebsd.org/mailman/listinfo/freebsd-net
>> To unsubscribe, send any mail to "freebsd-net-=20
>> unsubscribe@freebsd.org"
>>
>
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