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

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Message-ID: <8f464cee-55e4-47c3-3666-629ed548167a@gmail.com>
Date:   Mon, 19 Jun 2023 17:59:10 +0100
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Dmitry Safonov <dima@...sta.com>, 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>,
        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

On 6/19/23 17:41, Dmitry Safonov wrote:
> On 6/19/23 17:31, Dmitry Safonov wrote:
>> 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
> 
> Oh, yeah, forgot to mention, there are another 2 tests for TCP_CLOSE
> socket (just a new one), that has both TCP-AO and TCP-MD5 keys and tries
> to call connect(). In discussion with the team, it seems really
> unexpected situation and better to force userspace to remove either AO
> or MD5 key before calling connect(). Those from the output in [1] are:
> 
>> ok 39 AO+MD5 server: client with both [TCP-MD5] and TCP-AO keys:
> connect() was prevented
>> ok 40 AO+MD5 server: client with both TCP-MD5 and [TCP-AO] keys:
> connect() was prevented

And while starring at the selftest results, I noticed in the output
sample a copy-n-paste typo for VRFs, this:
> ok 60 VRF: TCP-AO key (l3index=0) + TCP-MD5 key (no l3index)
> ok 61 VRF: TCP-MD5 key (no l3index) + TCP-AO key (l3index=0)

Should be read as
> ok 60 VRF: TCP-AO key (l3index=0) + TCP-MD5 key (l3index=N)
> ok 61 VRF: TCP-MD5 key (l3index=N) + TCP-AO key (l3index=0)

(those checks are corresponding to the table in VRF-support commit [2])


>> 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

[2]
https://lore.kernel.org/all/20230614230947.3954084-22-dima@arista.com/T/#u

Thanks,
             Dmitry