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 B4882C4167B for ; Fri, 27 May 2022 11:56:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352792AbiE0Lzk (ORCPT ); Fri, 27 May 2022 07:55:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40104 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352793AbiE0Luw (ORCPT ); Fri, 27 May 2022 07:50:52 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A5501269B6; Fri, 27 May 2022 04:45:22 -0700 (PDT) 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 sin.source.kernel.org (Postfix) with ESMTPS id D2C1ACE1164; Fri, 27 May 2022 11:45:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E65B5C385A9; Fri, 27 May 2022 11:45:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1653651919; bh=s6T+HuT78bAP0HH1vMwcpZGWnTvNxrhKCd8tLlgc4lE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kskKI+FT047460vEP/Q6bHt/q1i89kVyK+EsQnyo2MsMYD3f06qDcGydsO/GXBK4f Uj2Mc24qQb+BJOMdon6FsFGYSyGl3oggLisB6CoC+EwbAS01vlZBGWA1qTjF2T9ir7 cZD3ETAGDqMHlv2STKBujq5E/M3gclZIJrRrB26A= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dominik Brodowski , "Jason A. Donenfeld" Subject: [PATCH 5.17 093/111] random: avoid initializing twice in credit race Date: Fri, 27 May 2022 10:50:05 +0200 Message-Id: <20220527084832.577576318@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220527084819.133490171@linuxfoundation.org> References: <20220527084819.133490171@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Jason A. Donenfeld" commit fed7ef061686cc813b1f3d8d0edc6c35b4d3537b upstream. Since all changes of crng_init now go through credit_init_bits(), we can fix a long standing race in which two concurrent callers of credit_init_bits() have the new bit count >= some threshold, but are doing so with crng_init as a lower threshold, checked outside of a lock, resulting in crng_reseed() or similar being called twice. In order to fix this, we can use the original cmpxchg value of the bit count, and only change crng_init when the bit count transitions from below a threshold to meeting the threshold. Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -821,7 +821,7 @@ static void extract_entropy(void *buf, s static void credit_init_bits(size_t nbits) { - unsigned int init_bits, orig, add; + unsigned int new, orig, add; unsigned long flags; if (crng_ready() || !nbits) @@ -831,12 +831,12 @@ static void credit_init_bits(size_t nbit do { orig = READ_ONCE(input_pool.init_bits); - init_bits = min_t(unsigned int, POOL_BITS, orig + add); - } while (cmpxchg(&input_pool.init_bits, orig, init_bits) != orig); + new = min_t(unsigned int, POOL_BITS, orig + add); + } while (cmpxchg(&input_pool.init_bits, orig, new) != orig); - if (!crng_ready() && init_bits >= POOL_READY_BITS) + if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) crng_reseed(); - else if (unlikely(crng_init == CRNG_EMPTY && init_bits >= POOL_EARLY_BITS)) { + else if (orig < POOL_EARLY_BITS && new >= POOL_EARLY_BITS) { spin_lock_irqsave(&base_crng.lock, flags); if (crng_init == CRNG_EMPTY) { extract_entropy(base_crng.key, sizeof(base_crng.key));