Messages in this thread | | | Date | Thu, 13 Dec 2018 22:58:21 -0500 | From | "Theodore Y. Ts'o" <> | Subject | Re: [PATCH v2] Allow hwrng to initialize crng. |
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On Thu, Dec 13, 2018 at 10:48:07AM +0100, Ard Biesheuvel wrote: > > @@ -64,13 +65,19 @@ static size_t rng_buffer_size(void) > > static void add_early_randomness(struct hwrng *rng) > > { > > int bytes_read; > > - size_t size = min_t(size_t, 16, rng_buffer_size()); > > + /* Read enough to initialize crng. */ > > + size_t size = min_t(size_t, > > + 2*CHACHA20_KEY_SIZE, > > This should be as symbolic constant that retains its meaning even if > we move away from ChaCha20 or modify the current implementation
Also, rng_buffer_size() could be less than 2*hCHACHA20_KEY_SIZE, at which point your goal wouldn't be realized. What I'd recommend is to keep the line:
size_t size = min_t(size_t, 16, rng_buffer_size());
But to loop until rng_is_initialized() returns true or bytes_read is 0. If you want to be paranoid, you could also break out of the loop it isn't initialized after, say, 8 times through the loop.
Cheers,
- Ted
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