Re: Linux messages full of `random: get_random_u32 called from`

From: Sultan Alsawaf
Date: Sun Apr 29 2018 - 18:26:44 EST

On Sun, Apr 29, 2018 at 06:05:19PM -0400, Theodore Y. Ts'o wrote:
> It's more accurate to say that using /dev/urandom is no worse than
> before (from a few years ago). There are, alas, plenty of
> distributions and user space application programmers that basically
> got lazy using /dev/urandom, and assumed that there would be plenty of
> entropy during early system startup.
> When they switched over the getrandom(2), the most egregious examples
> of this caused pain (and they got fixed), but due to a bug in
> drivers/char/random.c, if getrandom(2) was called after the entropy
> pool was "half initialized", it would not block, but proceed.
> Is that exploitable? Well, Jann and I didn't find an _obvious_ way to
> exploit the short coming, which is this wasn't treated like an
> emergency situation ala the embarassing situation we had five years
> ago[1].
> [1]
> However, it was enough to make us be uncomfortable, which is why I
> pushed the changes that I did. At least on the devices we had at
> hand, using the distributions that we typically use, the impact seemed
> minimal. Unfortuantely, there is no way to know for sure without
> rolling out change and seeing who screams. In the ideal world,
> software would not require cryptographic randomness immediately after
> boot, before the user logs in. And ***really***, as in [1], softwaret
> should not be generating long-term public keys that are essential to
> the security of the box a few seconds immediately after the device is
> first unboxed and plugged in.i
> What would be useful is if people gave reports that listed exactly
> what laptop and distributions they are using. Just "a high spec x86
> laptop" isn't terribly useful, because *my* brand-new Dell XPS 13
> running Debian testing is working just fine. The year, model, make,
> and CPU type plus what distribution (and distro version number) you
> are running is useful, so I can assess how wide spread the unhappiness
> is going to be, and what mitigation steps make sense.
> What mitigations steps can be taken?
> If you believe in security-through-complexity (the cache architecture
> of x86 is *sooooo* complicated no one can understand it, so
> Jitterentropy / Haveged *must* be secure), or security-through-secrecy
> (the cache architecture of x86 is only avilable to internal architects
> inside Intel, so Jitterentropy / Haveged *must* be secure, never mind
> that the Intel CPU architects who were asked about it were "nervous"),
> then wiring up CONFIG_JITTERENTROPY or using haveged might be one
> approach.
> If you believe that Intel hasn't backdoored RDRAND, then installing
> rng-tools and running rngd with --enable-drng will enable RDRAND.
> That seems to be popular with various defense contractors, perhaps on
> the assumption that if it _was_ backdoored (no one knows for sure), it
> was probably with the connivance or request of the US government, who
> doesn't need to worry about spying on itself.
> Or you can use some kind of open hardware design RNG, such as
> ChoasKey[2] from Altus Metrum. But that requires using specially
> ordered hardware plugged into a USB slot, and it's probably not a mass
> solution.
> [2]
> Personally, I prefer fixing the software to simply not require
> cryptographic grade entropy before the user has logged in. Because
> it's better than the alternatives.
> - Ted

The attached patch fixes my crng init woes. With it, crng init completes 0.86
seconds into boot, but I can't help but feel like a solution this obvious would
just expose my Richard Stallman photo collection to prying eyes at the NSA.

Thoughts on the patch?