linux-kernel - Re: [PATCH v7 04/22] net/tcp: Prevent TCP-MD5 with TCP-AO being set

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Message-ID: <1c2537d0-cf64-c010-fec6-9fa9ad758f42@arista.com>
Date:   Mon, 19 Jun 2023 17:31:00 +0100
From:   Dmitry Safonov <dima@...sta.com>
To:     David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Bob Gilligan <gilligan@...sta.com>,
        Dan Carpenter <error27@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Donald Cassidy <dcassidy@...hat.com>,
        Eric Biggers <ebiggers@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Francesco Ruggeri <fruggeri05@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Ivan Delalande <colona@...sta.com>,
        Leonard Crestez <cdleonard@...il.com>,
        Salam Noureddine <noureddine@...sta.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH v7 04/22] net/tcp: Prevent TCP-MD5 with TCP-AO being set

Hi David,

On 6/18/23 18:50, David Ahern wrote:
> On 6/14/23 4:09 PM, Dmitry Safonov wrote:
>> Be as conservative as possible: if there is TCP-MD5 key for a given peer
>> regardless of L3 interface - don't allow setting TCP-AO key for the same
>> peer. According to RFC5925, TCP-AO is supposed to replace TCP-MD5 and
>> there can't be any switch between both on any connected tuple.
>> Later it can be relaxed, if there's a use, but in the beginning restrict
>> any intersection.
>>
>> Note: it's still should be possible to set both TCP-MD5 and TCP-AO keys
>> on a listening socket for *different* peers.
> 
> Does the testsuite cover use of both MD5 and AO for a single listening
> socket with different peers and then other tests covering attempts to
> use both for a same peer?

Thanks for the question, I have written the following tests for
AO/MD5/unsigned listening socket [1]:

1. Listener with TCP-AO key, which has addr = INADDR_ANY
2. Listener with TCP-MD5 key, which has tcpm_addr = INADDR_ANY
3. Listener without any key

Then there's AO_REQUIRED thing, which BGP folks asked to introduce,
which is (7.3) from RFC5925, an option that is per-ao_info, which makes
such socket accepting only TCP-AO enabled segments.

So, 4. Listener with TCP-AO, AO_REQUIRED flag.

And then, going to non-INADDR_ANY:
5. Listener with TCP-AO and TCP-MD5 keys for different peers.

Here again, for each of AO/MD5/unsigned methods, attempt to connect:
6. outside of both key peers
7. inside correct key: i.e. TCP-MD5 client to TCP-MD5 matching key
8. to a wrong key: i.e. TCP-AO client to TCP-MD5 matching key

And another type of checks are the ones expecting *setsockopt()* to fail:
9. Adding TCP-AO key that matches the same peer as TCP-MD5 key
10. The reverse situation
11. Adding TCP-MD5 key to AO_REQUIRED socket
12. Setting AO_REQUIRED on a socket with TCP-MD5 key
13. Adding TCP-AO key on already established connection without any key

And then another bunch of tests that check TCP-AO/TCP-MD5/unsigned
interaction in non/default VRFs.
I think the output of selftest [1] is more-or-less self-descriptive,
correct me if I could improve that.

[1]
https://github.com/0x7f454c46/linux/commit/d7b321f2b5a481e5ff0e80e2e0b3503b1ddb9817

Thanks,
            Dmitry