On Wed, Jan 11, 2017 at 1:09 AM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> >> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
