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 CE034C433F5 for ; Mon, 17 Jan 2022 04:03:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236970AbiAQEDw (ORCPT ); Sun, 16 Jan 2022 23:03:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36668 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234174AbiAQEDw (ORCPT ); Sun, 16 Jan 2022 23:03:52 -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 CB62BC061574 for ; Sun, 16 Jan 2022 20:03:51 -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 2C29260C35; Mon, 17 Jan 2022 04:03:51 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6525FC36AE3; Mon, 17 Jan 2022 04:03:49 +0000 (UTC) Subject: Re: [PATCH v2 RESEND] m68k/kernel: array out of bound access in process_uboot_commandline To: Hangyu Hua , geert@linux-m68k.org Cc: schwab@linux-m68k.org, linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org References: <20220113015854.9326-1-hbh25y@gmail.com> From: Greg Ungerer Message-ID: <95d91f5f-c5e1-0750-ebb9-b6839aecdc7c@linux-m68k.org> Date: Mon, 17 Jan 2022 14:03:45 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20220113015854.9326-1-hbh25y@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-m68k@vger.kernel.org Hi Hangyu, On 13/1/22 11:58 am, Hangyu Hua wrote: > When the size of commandp >= size, array out of bound write occurs because > len == 0. > > Signed-off-by: Hangyu Hua > --- > arch/m68k/kernel/uboot.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/m68k/kernel/uboot.c b/arch/m68k/kernel/uboot.c > index 928dbd33fc4a..63eaf3c3ddcd 100644 > --- a/arch/m68k/kernel/uboot.c > +++ b/arch/m68k/kernel/uboot.c > @@ -101,5 +101,6 @@ __init void process_uboot_commandline(char *commandp, int size) > } > > parse_uboot_commandline(commandp, len); > - commandp[len - 1] = 0; > + if (len > 0) > + commandp[len - 1] = 0; > } > I am not convinced this is wrong for the reason you think it is. Looking at the code in its entirety: __init void process_uboot_commandline(char *commandp, int size) { int len, n; n = strnlen(commandp, size); commandp += n; len = size - n; if (len) { /* Add the whitespace separator */ *commandp++ = ' '; len--; } parse_uboot_commandline(commandp, len); commandp[len - 1] = 0; } "commandp" is moved based on the return of the strnlen(). So in the case of commandp actually being full of valid characters (so n == size, and thus len == 0) the commandp technically points outside of its real size at that point. But "command[[len - 1]" would actually be pointing to the last char in the original commandp array (so the original commandp[size - 1]). Well at least if you are happy with the use of negative array indexes. Clearly this could be structured better. There is no point in calling parse_uboot_commandline() if len == 0, or even if len == 1, since you cannot add anymore to the command line, it is full. Regards Greg