Re: [PATCH v3 04/13] crypto/rng: ensure that the RNG is ready before using

On Tue, Jun 06, 2017 at 05:56:20AM +0200, Jason A. Donenfeld wrote:

Hey Ted,

On Tue, Jun 6, 2017 at 5:00 AM, Theodore Ts'o [off-list ref] wrote:

quoted

Note that crypto_rng_reset() is called by big_key_init() in
security/keys/big_key.c as a late_initcall().  So if we are on a
system where the crng doesn't get initialized until during the system
boot scripts, and big_key is compiled directly into the kernel, the
boot could end up deadlocking.

There may be other instances of where crypto_rng_reset() is called by
an initcall, so big_key_init() may not be an exhaustive enumeration of
potential problems.  But this is an example of why the synchronous
API, although definitely much more convenient, can end up being a trap
for the unwary....

Thanks for pointing this out. I'll look more closely into it and see
if I can figure out a good way of approaching this.

Would it work for wait_for_random_bytes() to include a

    WARN_ON(system_state < SYSTEM_RUNNING);

to catch those kinds of cases?

    - Kevin