On Mon, Dec 26, 2016 at 5:36 PM, Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > On Sat, Dec 24, 2016 at 08:59:53PM +0100, Daniel Borkmann wrote: >> On 12/24/2016 03:22 AM, Andy Lutomirski wrote: >> >BPF digests are intended to be used to avoid reloading programs that >> >are already loaded. For use cases (CRIU?) where untrusted programs >> >are involved, intentional hash collisions could cause the wrong BPF >> >program to execute. Additionally, if BPF digests are ever used >> >in-kernel to skip verification, a hash collision could give privilege >> >escalation directly. >> >> Just for the record, digests will never ever be used to skip the >> verification step, so I don't know why this idea even comes up >> here (?) or is part of the changelog? As this will never be done >> anyway, rather drop that part so we can avoid confusion on this? > > +1 to what Daniel said above. > > For the others let me explain what this patch set is actually > trying to accomplish. The patch: a) cleans up the code and b) uses a cryptographic hash that is actually believed to satisfy the definition of a cryptographic hash. There's no excuse for not doing b. > and I have an obvious NACK for bpf related patches 3,4,5,6. Did you *read* the ones that were pure cleanups? > > sha1 is 20 bytes which is already a bit long to print and copy paste by humans. > whereas 4 byte jhash is a bit too short, since collisions are not that rare > and may lead to incorrect assumptions from the users that develop the programs. > I would prefer something in 6-10 byte range that prevents collisions most of > the time and short to print as hex, but I don't know of anything like this > in the existing kernel and inventing bpf specific hash is not great. > Another requirement for debugging (and prog_digest) that user space > should be able to produce the same hash without asking kernel, so > sha1 fits that as well, since it's well known and easy to put into library. Then truncate them in user space. -- 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
