linux-kernel - Re: get_random_bytes returns bad randomness before seeding is complete

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Date:   Fri, 2 Jun 2017 18:48:25 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Stephan Mueller <smueller@...onox.de>,
        "Theodore Ts'o" <tytso@....edu>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: get_random_bytes returns bad randomness before seeding is complete

Further investigations: if the whack-a-mole approach is desirable,
perhaps many of those get_random_bytes calls should be converted to
get_blocking_random_bytes. In that case, this commit, which removed
this helpful API, should be reverted:

commit c2719503f5e1e6213d716bb078bdad01e28ebcbf
Author: Herbert Xu <herbert@...dor.apana.org.au>
Date:   Tue Jun 9 18:19:42 2015 +0800

   random: Remove kernel blocking API

   This patch removes the kernel blocking API as it has been completely
   replaced by the callback API.

   Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index a1576ed1d88e..d0da5d852d41 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1265,18 +1265,6 @@ void get_random_bytes(void *buf, int nbytes)
EXPORT_SYMBOL(get_random_bytes);

/*
- * Equivalent function to get_random_bytes with the difference that this
- * function blocks the request until the nonblocking_pool is initialized.
- */
-void get_blocking_random_bytes(void *buf, int nbytes)
-{
-       if (unlikely(nonblocking_pool.initialized == 0))
-               wait_event(urandom_init_wait, nonblocking_pool.initialized);
-       extract_entropy(&nonblocking_pool, buf, nbytes, 0, 0);
-}
-EXPORT_SYMBOL(get_blocking_random_bytes);
-
-/*