From patchwork Wed Feb 9 01:19:19 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Jason A. Donenfeld" X-Patchwork-Id: 541228 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 F340EC433F5 for ; Wed, 9 Feb 2022 02:40:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233050AbiBICka (ORCPT ); Tue, 8 Feb 2022 21:40:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52532 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242735AbiBIBUR (ORCPT ); Tue, 8 Feb 2022 20:20:17 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 91C79C061576; Tue, 8 Feb 2022 17:20:17 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 144E0617E7; Wed, 9 Feb 2022 01:20:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02137C004E1; Wed, 9 Feb 2022 01:20:15 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="f3g58zfE" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1644369615; 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=Epo8j6f82VaiElGEK+cLsKCLLv1wK/ngSXClGzK93nI=; b=f3g58zfEZIQTrFf4x5mRH7JVgKrccFTPWeYFBA2Oo8yebDy+QRlHo3Z3cFQ4scSdGamyhL wHR6p5y9eYFELn9MDC7NHtM8SePk1HrqavpcAZ/ZCNbNJIAKzYDZ6o9zYBU2d5WGyQzNKG wsqMinQevWdxzvwP0PoKuvhVg6baThk= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id a4f5ce73 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Wed, 9 Feb 2022 01:20:14 +0000 (UTC) From: "Jason A. Donenfeld" To: linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Cc: tytso@mit.edu, linux@dominikbrodowski.net, ebiggers@kernel.org, "Jason A. Donenfeld" Subject: [PATCH v2 9/9] random: remove outdated INT_MAX >> 6 check in urandom_read() Date: Wed, 9 Feb 2022 02:19:19 +0100 Message-Id: <20220209011919.493762-10-Jason@zx2c4.com> In-Reply-To: <20220209011919.493762-1-Jason@zx2c4.com> References: <20220209011919.493762-1-Jason@zx2c4.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org In 79a8468747c5 ("random: check for increase of entropy_count because of signed conversion"), a number of checks were added around what values were passed to account(), because account() was doing fancy fixed point fractional arithmetic, and a user had some ability to pass large values directly into it. One of things in that commit was limiting those values to INT_MAX >> 6. However, for several years now, urandom reads no longer touch entropy accounting, and so this check serves no purpose. The current flow is: urandom_read_nowarn()-->get_random_bytes_user()-->chacha20_block() We arrive at urandom_read_nowarn() in the first place either via ordinary fops, which limits reads to MAX_RW_COUNT, or via getrandom() which limits reads to INT_MAX. Cc: Theodore Ts'o Cc: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 1 - 1 file changed, 1 deletion(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index f7f9cbfe13f7..e09874c511d0 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1305,7 +1305,6 @@ static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, { int ret; - nbytes = min_t(size_t, nbytes, INT_MAX >> 6); ret = get_random_bytes_user(buf, nbytes); trace_urandom_read(8 * nbytes, 0, input_pool.entropy_count); return ret;