Date: Fri, 23 Dec 2016 08:42:28 -0800 From: Andy Lutomirski <luto@...capital.net> To: Daniel Borkmann <daniel@...earbox.net> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>, Alexei Starovoitov <alexei.starovoitov@...il.com>, "Jason A. Donenfeld" <Jason@...c4.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "Theodore Ts'o" <tytso@....edu>, Netdev <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, David Laight <David.Laight@...lab.com>, Eric Dumazet <edumazet@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Eric Biggers <ebiggers3@...il.com>, Tom Herbert <tom@...bertland.com>, Andi Kleen <ak@...ux.intel.com>, "David S. Miller" <davem@...emloft.net>, Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com> Subject: Re: BPF hash algo (Re: Re: [PATCH v7 3/6] random: use SipHash in place of MD5) On Fri, Dec 23, 2016 at 8:23 AM, Andy Lutomirski <luto@...capital.net> wrote: > On Fri, Dec 23, 2016 at 3:59 AM, Daniel Borkmann <daniel@...earbox.net> wrote: >> On 12/23/2016 11:59 AM, Hannes Frederic Sowa wrote: >>> >>> On Fri, 2016-12-23 at 11:04 +0100, Daniel Borkmann wrote: >>>> >>>> On 12/22/2016 05:59 PM, Hannes Frederic Sowa wrote: >>>>> >>>>> On Thu, 2016-12-22 at 08:07 -0800, Andy Lutomirski wrote: >> >> [...] >> >>>>> The hashing is not a proper sha1 neither, unfortunately. I think that >>>>> is why it will have a custom implementation in iproute2? >>>> >>>> >>>> Still trying to catch up on this admittedly bit confusing thread. I >>>> did run automated tests over couple of days comparing the data I got >>>> from fdinfo with the one from af_alg and found no mismatch on the test >>>> cases varying from min to max possible program sizes. In the process >>>> of testing, as you might have seen on netdev, I found couple of other >>>> bugs in bpf code along the way and fixed them up as well. So my question, >>>> do you or Andy or anyone participating in claiming this have any >>>> concrete data or test cases that suggests something different? If yes, >>>> I'm very curious to hear about it and willing fix it up, of course. >>>> When I'm back from pto I'll prep and cook up my test suite to be >>>> included into the selftests/bpf/, should have done this initially, >>>> sorry about that. I'll also post something to expose the alg, that >>>> sounds fine to me. >>> >>> >>> Looking into your code closer, I noticed that you indeed seem to do the >>> finalization of sha-1 by hand by aligning and padding the buffer >>> accordingly and also patching in the necessary payload length. >>> >>> Apologies for my side for claiming that this is not correct sha1 >>> output, I was only looking at sha_transform and its implementation and >>> couldn't see the padding and finalization round with embedding the data >>> length in there and hadn't thought of it being done manually. >>> >>> Anyway, is it difficult to get the sha finalization into some common >>> code library? It is not very bpf specific and crypto code reviewers >>> won't find it there at all. >> >> >> Yes, sure, I'll rework it that way (early next year when I'm back if >> that's fine with you). > > Can we make it SHA-256 before 4.10 comes out, though? This really > looks like it will be used in situations where collisions matter and > it will be exposed to malicious programs, and SHA-1 should not be used > for new designs for this purpose because it simply isn't long enough. > > Also, a SHA-1 digest isn't a pile of u32s, so u32 digest[...] is very > misleading. That should be u8 or, at the very least, __be32. > > I realize that there isn't a sha-256 implementation in lib, but would > it really be so bad to make the bpf digest only work (for now) when > crypto is enabled? I would *love* to see the crypto core learn how to > export simple primitives for direct use without needing the whole > crypto core, and this doesn't seem particularly hard to do, but I > don't think that's 4.10 material. I'm going to try to send out RFC patches for all of this today or tomorrow. It doesn't look bad at all. --Andy
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