Re: [PATCH v2 7/8] net: Rename TCA*BPF_DIGEST to ..._SHA256

On 01/11/2017 07:19 PM, Andy Lutomirski wrote:

On Wed, Jan 11, 2017 at 1:09 AM, Daniel Borkmann [off-list ref] wrote:

[...]

quoted

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.

Yeah agree, I've just sent a patch to rework this a bit and it got
also reasonably small for net. Cleanups, if needed, can be done in
net-next once that's pulled into it.

Thanks,
Daniel