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 32B97C433EF for ; Fri, 13 May 2022 10:24:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1379485AbiEMKYI (ORCPT ); Fri, 13 May 2022 06:24:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55066 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1379422AbiEMKXi (ORCPT ); Fri, 13 May 2022 06:23:38 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6E99D178560 for ; Fri, 13 May 2022 03:23:19 -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 ams.source.kernel.org (Postfix) with ESMTPS id 2D61AB82D74 for ; Fri, 13 May 2022 10:23:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E211C34100; Fri, 13 May 2022 10:23:16 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="p0hyA9bC" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1652437394; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8oam4uQpj40FXUylUvCQDj4pkGlt2TutOpdMK9XnVVA=; b=p0hyA9bCLfWirBqsLr28cFLNt3fvOgsRbfypam++KexYG4fYHBEQXjs4DgkYpD99uIgxLB A/7U+xhG6rJIo3gSiJrFkEs0Eo7ZkM37oJyvmva5U5696Mixq9D104yuY1Xfov3+I84mVZ 5ym9BWS+x7TtUwImc3qt+GcgfNQ91kQ= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 4506914a (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Fri, 13 May 2022 10:23:14 +0000 (UTC) Date: Fri, 13 May 2022 12:23:13 +0200 From: "Jason A. Donenfeld" To: Dominik Brodowski Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] random: avoid init'ing twice in credit race Message-ID: References: <20220509121409.529788-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dominik, On Fri, May 13, 2022 at 08:23:40AM +0200, Dominik Brodowski wrote: > Am Mon, May 09, 2022 at 02:14:08PM +0200 schrieb Jason A. Donenfeld: > > 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. > > Sidenote: crng_reseed() did manage quite fine if called twice in short > order. With regards to crng_finialize, it did, but not with regards to prematurely emptying patches and all that. IOW, buggy but not that bad. > > > 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. > > > > Cc: Dominik Brodowski > > Signed-off-by: Jason A. Donenfeld > > Reviewed-by: Dominik Brodowski > > Thanks, > Dominik Jason