From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9EE9BC433F5 for ; Sat, 12 Feb 2022 12:23:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234784AbiBLMXg (ORCPT ); Sat, 12 Feb 2022 07:23:36 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:41146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229506AbiBLMXe (ORCPT ); Sat, 12 Feb 2022 07:23:34 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5387A24BE5 for ; Sat, 12 Feb 2022 04:23:31 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id F010BB80691 for ; Sat, 12 Feb 2022 12:23:29 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F84FC340E7; Sat, 12 Feb 2022 12:23:28 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="ODF4alSn" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1644668607; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LWzS0mxyHFBKh8dXUL5dPMBahNNosCP3EmVR3IgONbg=; b=ODF4alSnFZv0Vo4Y4ftU0BsLfvKnCmUXAh/Npp+RBclNrjOVgiFcdmKEdF5xfO/oLXF0Or zagaFN0cmyyCYV9qKnCgY/c8xV4lrB1UILRDAXHQ7lyqe6CySrY5dllGfTt7aYBri7YqyC 9xeZDxs0PXmCtuZQK1JjN61X5GFNyiw= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 5cdef4b8 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Sat, 12 Feb 2022 12:23:27 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-kernel@vger.kernel.org, linux@dominikbrodowski.net Cc: "Jason A. Donenfeld" , Theodore Ts'o Subject: [PATCH v2 01/10] random: introduce drain_entropy() helper to declutter crng_reseed() Date: Sat, 12 Feb 2022 13:23:09 +0100 Message-Id: <20220212122318.623435-2-Jason@zx2c4.com> In-Reply-To: <20220212122318.623435-1-Jason@zx2c4.com> References: <20220212122318.623435-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In preparation for separating responsibilities, break out the entropy count management part of crng_reseed() into its own function. No functional changes. Cc: Theodore Ts'o Cc: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 35 +++++++++++++++++++++++------------ 1 file changed, 23 insertions(+), 12 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 44a20a1a1b3a..436b146b33be 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -260,6 +260,7 @@ static struct { }; static void extract_entropy(void *buf, size_t nbytes); +static bool drain_entropy(void *buf, size_t nbytes); static void crng_reseed(void); @@ -453,22 +454,13 @@ static void crng_slow_load(const void *cp, size_t len) static void crng_reseed(void) { unsigned long flags; - int entropy_count; unsigned long next_gen; u8 key[CHACHA_KEY_SIZE]; bool finalize_init = false; - /* First we make sure we have POOL_MIN_BITS of entropy in the pool, - * and then we drain all of it. Only then can we extract a new key. - */ - do { - entropy_count = READ_ONCE(input_pool.entropy_count); - if (entropy_count < POOL_MIN_BITS) - return; - } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); - extract_entropy(key, sizeof(key)); - wake_up_interruptible(&random_write_wait); - kill_fasync(&fasync, SIGIO, POLL_OUT); + /* Only reseed if we can, to prevent brute forcing a small amount of new bits. */ + if (!drain_entropy(key, sizeof(key))) + return; /* We copy the new key into the base_crng, overwriting the old one, * and update the generation counter. We avoid hitting ULONG_MAX, @@ -893,6 +885,25 @@ static void extract_entropy(void *buf, size_t nbytes) memzero_explicit(&block, sizeof(block)); } +/* + * First we make sure we have POOL_MIN_BITS of entropy in the pool, + * and then we drain all of it. Only then can we extract a new key + * with extract_entropy(). + */ +static bool drain_entropy(void *buf, size_t nbytes) +{ + unsigned int entropy_count; + do { + entropy_count = READ_ONCE(input_pool.entropy_count); + if (entropy_count < POOL_MIN_BITS) + return false; + } while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count); + extract_entropy(buf, nbytes); + wake_up_interruptible(&random_write_wait); + kill_fasync(&fasync, SIGIO, POLL_OUT); + return true; +} + #define warn_unseeded_randomness(previous) \ _warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous)) -- 2.35.0