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 <herbert@xxxxxxxxxxxxxxxxxxx> > Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> > --- > 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
