Re: [PATCH net-next v6 00/23] WireGuard: Secure Network Tunnel

Ard Biesheuvel
2018-09-28T07:52:09Z

On 28 September 2018 at 07:46, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> Hi Eric,
>
> On Fri, Sep 28, 2018 at 6:55 AM Eric Biggers <ebiggers@kernel.org> wrote:
>> And you still haven't answered my question about adding a new algorithm that is
>> useful to have in both APIs. You're proposing that in most cases the crypto API
>> part will need to go through Herbert while the implementation will need to go
>> through you/Greg, right? Or will you/Greg be taking both? Or will Herbert take
>> both?
>
> If an implementation enters Zinc, it will go through my tree. If it
> enters the crypto API, it will go through Herbert's tree. If there
> wind up being messy tree dependency and merge timing issues, I can
> work this out in the usual way with Herbert. I'll be sure to discuss
> these edge cases with him when we discuss. I think there's a way to
> handle that with minimum friction.
>

I would also strongly prefer that all crypto work is taken through
Herbert's tree, so we have a coherent view of it before it goes
upstream.

>> A documentation file for Zinc is a good idea. Some of the information in your
>> commit messages should be moved there too.
>
> Will do.
>
>> I'm not trying to "politicize" this, but rather determine your criteria for
>> including algorithms in Zinc, which you haven't made clear. Since for the
>> second time you've avoided answering my question about whether you'd allow the
>> SM4 cipher in Zinc, and you designed WireGuard to be "cryptographically
>> opinionated", and you were one of the loudest voices calling for the Speck
>> cipher to be removed, and your justification for Zinc complains about cipher
>> modes from "90s cryptographers", I think it's reasonable for people to wonder
>> whether as the Zinc (i.e. Linux crypto library) maintainer you will restrict the
>> inclusion of crypto algorithms to the ones you prefer, rather than the ones that
>> users need. Note that the kernel is used by people all over the world and needs
>> to support various standards, protocols, and APIs that use different crypto
>> algorithms, not always the ones we'd like; and different users have different
>> preferences. People need to know whether the Linux kernel's crypto library will
>> meet (or be allowed to meet) their crypto needs.
>
> WireGuard is indeed quite opinionated in its primitive choices, but I
> don't think it'd be wise to apply the same design to Zinc. There are
> APIs where the goal is to have a limited set of high-level functions,
> and have those implemented in only a preferred set of primitives. NaCl
> is a good example of this -- functions like "crypto_secretbox" that
> are actually xsalsapoly under the hood. Zinc doesn't intend to become
> an API like those, but rather to provide the actual primitives for use
> cases where that specific primitive is used. Sometimes the kernel is
> in the business of being able to pick its own crypto -- random.c, tcp
> sequence numbers, big_key.c, etc -- but most of the time the kernel is
> in the business of implementing other people's crypto, for specific
> devices/protocols/diskformats. And for those use cases we need not
> some high-level API like NaCl, but rather direct access to the
> primitives that are required to implement those drivers. WireGuard is
> one such example, but so would be Bluetooth, CIFS/SMB, WiFi, and so
> on. We're in the business of writing drivers, after all. So, no, I
> don't think I'd knock down the addition of a primitive because of a
> simple preference for a different primitive, if it was clearly the
> case that the driver requiring it really benefited from having
> accessible via the plain Zinc function calls. Sorry if I hadn't made
> this clear earlier -- I thought Ard had asked more or less the same
> thing about DES and I answered accordingly, but maybe that wasn't made
> clear enough there.
>
>> > For example, check out the avx blocks function. The radix conversion
>> > happens in a few different places throughout. The reason we need it
>> > separately here is because, unlike userspace, it's possible the kernel
>> > code will transition from 2^26 back to 2^64 as a result of the FPU
>> > context changing.
>>
>> IOW, you had to rewrite the x86 assembly algorithm in C and make it use a
>> different Poly1305 context format. That's a major change, where bugs can be
>> introduced -- and at least one was introduced, in fact. I'd appreciate it if
>> you were more accurate in describing your modifications and the potential risks
>> involved.
>
> A different Poly1305 context format? Not at all - it's using the exact
> same context struct as the assembly. And it's making the same
> conversion that the assembly is. There's not something "different"
> happening; that's the whole point.
>
> Also, this is not some process of frightfully transcribing assembly to
> C and hoping it all works out. This is a careful process of reasoning
> about the limbs, proving that the carries are correct, and that the
> arithmetic done in C actually corresponds to what we want. And then
> finally we check that what we've implemented is indeed the same as
> what the assembly implemented. Finally, as I mentioned, hopefully Andy
> will be folding this back into his implementations sometime soon
> anyway.
>
>> > That's a good idea. I can include some discussion about this as well in
>> > the commit message that introduces the glue code, too, I guess? I've
>> > been hesitant to fill these commit messages up even more, given there
>> > are already so many walls of text and whatnot, but if you think that'd
>> > be useful, I'll do that for v7, and also add comments.
>>
>> Please prefer to put information in the code or documentation rather than in
>> commit messages, when appropriate.
>
> Okay, no problem.
>
>> > This is complete and utter garbage, and I find its insinuations insulting
>> > and ridiculous. There is absolutely no lack of honesty and no double
>> > standard being applied whatsoever. Your attempt to cast doubt about the
>> > quality of standards applied and the integrity of the process is wholly
>> > inappropriate. When I tell you that high standards were applied and that
>> > due-diligence was done in developing a particular patch, I mean what I
>> > say.
>>
>> I
>> disagree that my concerns are "complete and utter garbage". And I think that
>> the fact that you prefer to respond by attacking me, rather than committing to
>> be more accurate in your claims and to treat all contributions fairly, is
>> problematic.
>
> I believe you have the sequence of events wrong. I've stated and made
> that there isn't a double standard, that the standards intend to be
> evenly rigorous, and I solicited your feedback on how I could best
> communicate changes in pre-merged patch series; I did the things
> you've said one should do. But your rhetoric then moved to questioning
> my integrity, and I believe that was uncalled for, inappropriate, and
> not a useful contribution to this mostly productive discussion --
> hence garbage. In other words, I provided an acceptable defense, not
> an attack. But can we move past all this schoolyard nonsense? Cut the
> rhetoric, please; it's really quite overwhelming.
>
>> It's great that you found and fixed this
>> bug on your own, and of course that raises my level of confidence in your work.
>
> Good.
>
>> Still, the v6 patchset still includes your claim that "All implementations have
>> been extensively tested and fuzzed"; so that claim was objectively wrong.
>
> I don't think that claim is wrong. The fuzzing and testing that's been
> done has been extensive, and the fuzzing and testing that continues to
> occur is extensive. As mentioned, the bug was fixed pretty much right
> after git-send-email. If you'd like I can try to space out the patch
> submissions by a little bit longer -- that would probably have various
> benefits -- but given that the netdev code is yet to receive a
> thorough review, I think we've got a bit of time before this is
> merged. The faster-paced patch cycles might inadvertently introduce
> things that get fixed immediately after sending then, unfortunately,
> but I don't think this will be the case with the final series that's
> merged. Though I'm incorporating tons and tons of feedback right now,
> I do look forward to the structure of the series settling down a
> little bit and the pace of suggestions decreasing, so that I can focus
> on auditing and verifying again. But given the dynamism and
> interesting insights of the reviews so far, I think the fast pace has
> actually been useful for elucidating the various expectations and
> suggestions of reviewers. It's most certainly improved this patchset
> in terrific ways.
>
>> Well, it doesn't help that you yourself claim that Zinc stands for
>> "Zx2c4's INsane Cryptolib"...
>
> This expansion of the acronym was intended as a totally ridiculous
> joke. I guess it wasn't received well. I'll remove it from the next
> series. Sorry.
>

As I understood from someone who was at your Kernel Recipes talk, you
mentioned that it actually stands for 'zinc is not crypto/' (note the
slash)

That is needlessly divisive and condescending, so if you want to move
past the rhetoric and the schoolyard nonsense, perhaps you can find a
better name for it? Or just put your stuff into crypto/base/,
crypto/core/ or something like that.