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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35E84C433DF for ; Fri, 14 Aug 2020 02:38:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0495F20768 for ; Fri, 14 Aug 2020 02:38:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597372701; bh=5BqXQK5WCJSTx1xuZ99dJlnoRjlBLK83T9Mfanz/2hQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=RKlH+M6r7q0xspMS1IzXTmozqdScmWVihQOgxHgvbKuvHwkzLgdnTfP0zN+CNGYhR hKgdVP9MY8LoMzY3E2bPDLr1XXHT5qFznOe11mRb8t0DABfumYQ9kO0n/bNoSqrvr0 ws9Qal0/XV7RlxBUkduQLC8Ew43s7p0yr49Lwj3g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726636AbgHNCiU (ORCPT ); Thu, 13 Aug 2020 22:38:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:55358 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726568AbgHNCiT (ORCPT ); Thu, 13 Aug 2020 22:38:19 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 32A8820716; Fri, 14 Aug 2020 02:38:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597372699; bh=5BqXQK5WCJSTx1xuZ99dJlnoRjlBLK83T9Mfanz/2hQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=TVSPc72nPkfi9NAFEnGe6ZGf36NcazYo+X9OqkpOWXSiAbwKhSqqqTPXMIXSP6swh r5PCe5kIVLsCke8IIVjf7FeLWX3Me0EmW5bczF2bAiWBHICdYXxF4UNrXR4AMrNcoh TzjpQILOa1Grlwf/B5rpJqYv3UOZnd/jgE3qqYYk= Date: Thu, 13 Aug 2020 19:38:18 -0700 From: Andrew Morton To: Steven Rostedt Cc: LKML , Masami Hiramatsu Subject: Re: [PATCH] bootconfig: Fix off-by-one in xbc_node_compose_key_after() Message-Id: <20200813193818.a44ea9afc447f57d470b2def@linux-foundation.org> In-Reply-To: <20200813183050.029a6003@oasis.local.home> References: <20200813183050.029a6003@oasis.local.home> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 13 Aug 2020 18:30:50 -0400 Steven Rostedt wrote: > From: Steven Rostedt (VMware) > > While reviewing some patches for bootconfig, I noticed the following > code in xbc_node_compose_key_after(): > > ret = snprintf(buf, size, "%s%s", xbc_node_get_data(node), > depth ? "." : ""); > if (ret < 0) > return ret; > if (ret > size) { > size = 0; > } else { > size -= ret; > buf += ret; > } > > But snprintf() returns the number of bytes that would be written, not > the number of bytes that are written (ignoring the nul terminator). > This means that if the number of non null bytes written were to equal > size, then the nul byte, which snprintf() always adds, will overwrite > that last byte. > > ret = snprintf(buf, 5, "hello"); > printf("buf = '%s'\n", buf); > printf("ret = %d\n", ret); > > produces: > > buf = 'hell' > ret = 5 > > The string was truncated without ret being greater than 5. > Test (ret >= size) for overwrite. What are the end-user visible effects of the bug? IOW, why cc:stable?