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 27149C433EF for ; Fri, 27 May 2022 09:04:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350352AbiE0JE3 (ORCPT ); Fri, 27 May 2022 05:04:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350461AbiE0I77 (ORCPT ); Fri, 27 May 2022 04:59:59 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E04795D5C0; Fri, 27 May 2022 01:55:57 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 6CC4361CB7; Fri, 27 May 2022 08:55:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 47306C385B8; Fri, 27 May 2022 08:55:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1653641756; bh=Ve6NfPpdS1r05uyDwxztOFOgYNEeL5kzJRoMP9JvtMs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZY4FmL6y8TdecJTQaoJNhliuhozPzUuSd40UHPGC28C4TsmiizEgo11eqf7ax32j+ eVbASixqPL/JkzOB0FM+2zO01u+a8MckK2qpqMAe9CrBX+aO+8UIBXGeeTDaMSdvQq b/rNhxOlG5SdrKzhawc8ywIgbmu3Yyylv/7TVc1w= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Theodore Tso , Dominik Brodowski , Jann Horn , Eric Biggers , "Jason A. Donenfeld" Subject: [PATCH 5.17 020/111] random: remove outdated INT_MAX >> 6 check in urandom_read() Date: Fri, 27 May 2022 10:48:52 +0200 Message-Id: <20220527084822.188475049@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 434537ae54ad37e93555de21b6ac8133d6d773a9 upstream. 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. The first >> 3 was for bytes to bits, and the next >> 3 was for bits to 1/8 fractional bits. 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() Of course, we don't want that size_t to be truncated when adding it into the ssize_t. But 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 Reviewed-by: Dominik Brodowski Reviewed-by: Jann Horn Reviewed-by: Eric Biggers Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1286,9 +1286,8 @@ void rand_initialize_disk(struct gendisk static ssize_t urandom_read_nowarn(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { - int ret; + ssize_t ret; - nbytes = min_t(size_t, nbytes, INT_MAX >> 6); ret = get_random_bytes_user(buf, nbytes); trace_urandom_read(nbytes, input_pool.entropy_count); return ret;