Am Freitag, 17. Juni 2016, 15:56:13 schrieb David Jaša: Hi David, > Hi Stephan, > > thank you for your thorough reply, > > On St, 2016-06-15 at 18:58 +0200, Stephan Mueller wrote: > > Am Mittwoch, 15. Juni 2016, 18:17:43 schrieb David Jaša: > > > > Hi David, > > > > > Hello Stephan, > > > > > > Did you consider blocking urandom output or returning error until > > > initialized? Given the speed of initialization you report, it shouldn't > > > break any userspace apps while making sure that nobody uses predictable > > > pseudoranom numbers. > > > > My LRNG will definitely touch the beginning of the initramfs booting until > > it is fully seeded. As these days the initramfs is driven by systemd > > which always pulls from /dev/urandom, we cannot block as this would block > > systemd. In Ted's last patch, he mentioned that he tried to make > > /dev/urandom block which caused user space pain. > > I was thinking along the lines that "almost every important package > supports FreeBSD as well where they have to handle the condition so > option to switch to Rather Break Than Generate Weak Keys would be nice" > - but I didn't expect that systemd could be a roadblock here. :-/ > > I was also thinking of little devices where OpenWRT or proprietary > Linux-based systems run that ended up with predictable keys way too > ofter (or as in OpenWRT's case, with cumbersome tutorials how to > generate keys elsewhere). I have some ideas on how to handle that issue -- let me run some tests and I will report back. > > > But if you use the getrandom system call, it works like /dev/urandom but > > blocks until the DRBG behind /dev/urandom is fully initialized. > > > > > I was considering asking for patch (or even trying to write it myself) > > > to make current urandom block/fail when not initialized but that would > > > surely have to be off by default over "never break userspace" rule (even > > > if it means way too easy security problem with both random and urandom). > > > Properties of your urandom implementation makes this point moot and it > > > could make the random/urandom wars over. > > > > That patch unfortunately will not work. But if you are interested in that > > blocking /dev/urandom behavior for your application, use getrandom. > > I'm QA with a touch of sysadmin so the numbers of apps to fix is large > and I don't have neither control over the projects nor abilities to > patch them all myself. :) Sure, I can understand that :-) > > > > Best Regards, > > > > > > David Jaša > > > > Ciao > > Stephan > > BTW when looking at an old BSI's issue with Linux urandom that Jarod > Wilson tried to solve with this series: > https://www.spinics.net/lists/linux-crypto/msg06113.html > I was thinking: > 1) wouldn't it help for large urandom consumers if kernel created a DRBG > instance for each of them? It would likely enhance performance and solve > BSI's concern of predicting what numbers could other urandom consumers > obtain at cost of memory footprint That issue is partly solved with my patch set: I have one DRBG per NUMA node where all DRBG instances are equally treated. Surely that patch could be expanded on a per-CPU instance. But let us try to use the per-NUMA implementation and see whether that helps. Besides, the legacy /dev/urandom delivers about 12 MB/s on my system whereas the DRBG delivers more than 800MB/s. So, we have quite some performance improvement. Note, Ted's patch has a similar implementation. > and then, after reading paper associated with this series: > 2) did you evaluate use of intermediate DRBG fed by primary generator to > instantiate per-node DRBG's? It would allow initialization of all > secondary DRBGs right after primary generator initialization. That is exactly what I do. > > Cheers, > > David Ciao Stephan -- 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
