On Tue, Jun 06, 2017 at 02:50:59AM +0200, Jason A. Donenfeld wrote:
> Otherwise, we might be seeding the RNG using bad randomness, which is
> dangerous.
>
> Cc: Herbert Xu <herb...@gondor.apana.org.au>
> Signed-off-by: Jason A. Donenfeld <ja...@zx2c4.com>
> ---
> crypto/rng.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/crypto/rng.c b/crypto/rng.c
> index f46dac5288b9..e042437e64b4 100644
> --- a/crypto/rng.c
> +++ b/crypto/rng.c
> @@ -48,12 +48,14 @@ int crypto_rng_reset(struct crypto_rng *tfm, const u8
> *seed, unsigned int slen)
> if (!buf)
> return -ENOMEM;
>
> - get_random_bytes(buf, slen);
> + err = get_random_bytes_wait(buf, slen);
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....
- Ted
