From: Andy Lutomirski <luto@amacapital.net>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andy Lutomirski <luto@kernel.org>,
Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Eric Dumazet <edumazet@google.com>,
Eric Biggers <ebiggers3@gmail.com>,
Tom Herbert <tom@herbertland.com>,
"David S. Miller" <davem@davemloft.net>,
Alexei Starovoitov <ast@kernel.org>
Subject: Re: [PATCH v2 7/8] net: Rename TCA*BPF_DIGEST to ..._SHA256
Date: Wed, 11 Jan 2017 10:19:49 -0800 [thread overview]
Message-ID: <CALCETrVhuszdsfayLrBBkSzJ+A3m+hJjdZQWDj9FOg+2UB_ZBw@mail.gmail.com> (raw)
In-Reply-To: <5875F65A.4010904@iogearbox.net>
On Wed, Jan 11, 2017 at 1:09 AM, Daniel Borkmann <daniel@iogearbox.net> wrote:
> Hi Andy,
>
> On 01/11/2017 04:11 AM, Andy Lutomirski wrote:
>>
>> On Tue, Jan 10, 2017 at 4:50 PM, Daniel Borkmann <daniel@iogearbox.net>
>> wrote:
>>>
>>> On 01/11/2017 12:24 AM, Andy Lutomirski wrote:
>>>>
>>>>
>>>> This makes it easier to add another digest algorithm down the road if
>>>> needed. It also serves to force any programs that might have been
>>>> written against a kernel that had the old field name to notice the
>>>> change and make any necessary changes.
>>>>
>>>> This shouldn't violate any stable API policies, as no released kernel
>>>> has ever had TCA*BPF_DIGEST.
>>>
>>>
>>> Imho, this and patch 6/8 is not really needed. Should there ever
>>> another digest alg be used (doubt it), then you'd need a new nl
>>> attribute and fdinfo line anyway to keep existing stuff intact.
>>> Nobody made the claim that you can just change this underneath
>>> and not respecting abi for existing applications when I read from
>>> above that such apps now will get "forced" to notice a change.
>>
>>
>> Fair enough. I was more concerned about prerelease iproute2 versions,
>> but maybe that's a nonissue. I'll drop these two patches.
>
>
> Ok. Sleeping over this a bit, how about a general rename into
> "prog_tag" for fdinfo and TCA_BPF_TAG resp. TCA_ACT_BPF_TAG for
> the netlink attributes, fwiw, it might reduce any assumptions on
> this being made? If this would be preferable, I could cook that
> patch against -net for renaming it?
That would be fine with me.
I think there are two reasonable approaches to computing the actual tag.
1. Use a standard, modern cryptographic hash. SHA-256, SHA-512,
Blake2b, whatever. SHA-1 is a bad choice in part because it's partly
broken and in part because the implementation in lib/ is a real mess
to use (as you noticed while writing the code).
2. Use whatever algorithm you like but make the tag so short that it's
obviously not collision-free. 48 or 64 bits is probably reasonable.
The intermediate versions are just asking for trouble. Alexei wants
to make the tag shorter, but I admit I still don't understand why he
prefers that over using a better crypto hash and letting user code
truncate the tag if it wants.
next prev parent reply other threads:[~2017-01-11 18:19 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-10 23:24 [PATCH v2 0/8] Switch BPF's digest to SHA256 Andy Lutomirski
2017-01-10 23:24 ` [PATCH v2 1/8] crypto/sha256: Factor out the parts of base API that don't use shash_desc Andy Lutomirski
2017-01-10 23:24 ` [PATCH v2 2/8] crypto/sha256: Export a sha256_{init,update,final}_direct() API Andy Lutomirski
2017-01-10 23:24 ` [PATCH v2 3/8] crypto/sha256: Build the SHA256 core separately from the crypto module Andy Lutomirski
2017-01-10 23:24 ` [PATCH v2 4/8] bpf: Use SHA256 instead of SHA1 for bpf digests Andy Lutomirski
2017-01-10 23:24 ` [PATCH v2 5/8] bpf: Avoid copying the entire BPF program when hashing it Andy Lutomirski
2017-01-10 23:24 ` [PATCH v2 6/8] bpf: Rename fdinfo's prog_digest to prog_sha256 Andy Lutomirski
2017-01-10 23:24 ` [PATCH v2 7/8] net: Rename TCA*BPF_DIGEST to ..._SHA256 Andy Lutomirski
2017-01-11 0:50 ` Daniel Borkmann
2017-01-11 3:11 ` Andy Lutomirski
2017-01-11 9:09 ` Daniel Borkmann
2017-01-11 18:19 ` Andy Lutomirski [this message]
2017-01-13 23:08 ` Daniel Borkmann
2017-01-10 23:24 ` [PATCH v2 8/8] crypto/testmgr: Allocate only the required output size for hash tests Andy Lutomirski
2017-01-11 15:13 ` David Laight
2017-01-11 18:10 ` Andy Lutomirski
2017-01-12 7:47 ` Herbert Xu
2017-01-12 7:52 ` Andy Lutomirski
2017-01-12 16:44 ` Herbert Xu
2017-01-11 1:09 ` [PATCH v2 0/8] Switch BPF's digest to SHA256 Alexei Starovoitov
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