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Message-ID: <CAHmME9omJTaP1C=yUh3913Cv1gF1pBtpy9cmEMyJG4yw_dnZWQ@mail.gmail.com>
Date: Fri, 2 Jun 2017 17:53:39 +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
Subject: Re: get_random_bytes returns bad randomness before seeding is complete
(Meanwhile...)
In my own code, I'm currently playing with a workaround that looks like this:
--- a/src/main.c
+++ b/src/main.c
+#include <linux/completion.h>
+#include <linux/random.h>
+struct rng_initializer {
+ struct completion done;
+ struct random_ready_callback cb;
+};
+static void rng_initialized_callback(struct random_ready_callback *cb)
+{
+ complete(&container_of(cb, struct rng_initializer, cb)->done);
+}
+
static int __init mod_init(void)
{
int ret;
+ struct rng_initializer rng = {
+ .done = COMPLETION_INITIALIZER(rng.done),
+ .cb = { .owner = THIS_MODULE, .func = rng_initialized_callback }
+ };
+
+ ret = add_random_ready_callback(&rng.cb);
+ if (!ret)
+ wait_for_completion(&rng.done);
+ else if (ret != -EALREADY)
+ return ret;
do_things_with_get_random_bytes_maybe();
Depending on the situation, however, I could imagine that
wait_for_completion never returning, if its blocking activity that
contributes to the seed actually being available, if this is called
from a compiled-in module, so I find this a bit sub-optimal...
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