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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 1168CC43331 for ; Mon, 11 Nov 2019 08:25:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE0802084F for ; Mon, 11 Nov 2019 08:25:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726829AbfKKIZM (ORCPT ); Mon, 11 Nov 2019 03:25:12 -0500 Received: from relay.sw.ru ([185.231.240.75]:58224 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726768AbfKKIZM (ORCPT ); Mon, 11 Nov 2019 03:25:12 -0500 Received: from [172.16.25.5] by relay.sw.ru with esmtp (Exim 4.92.3) (envelope-from ) id 1iU50L-00018h-TL; Mon, 11 Nov 2019 11:24:58 +0300 Subject: Re: [PATCH v3 1/2] kasan: detect negative size in memory operation function To: Dmitry Vyukov Cc: Walter Wu , Alexander Potapenko , Matthias Brugger , kasan-dev , Linux-MM , LKML , Linux ARM , wsd_upstream References: <20191104020519.27988-1-walter-zh.wu@mediatek.com> <34bf9c08-d2f2-a6c6-1dbe-29b1456d8284@virtuozzo.com> From: Andrey Ryabinin Message-ID: <20df03c5-e733-98b0-84e9-8d52ddce5c98@virtuozzo.com> Date: Mon, 11 Nov 2019 11:24:36 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/11/19 10:57 AM, Dmitry Vyukov wrote: > On Fri, Nov 8, 2019 at 11:32 PM Andrey Ryabinin wrote: >>> diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c >>> index 36c645939bc9..52a92c7db697 100644 >>> --- a/mm/kasan/generic_report.c >>> +++ b/mm/kasan/generic_report.c >>> @@ -107,6 +107,24 @@ static const char *get_wild_bug_type(struct kasan_access_info *info) >>> >>> const char *get_bug_type(struct kasan_access_info *info) >>> { >>> + /* >>> + * If access_size is negative numbers, then it has three reasons >>> + * to be defined as heap-out-of-bounds bug type. >>> + * 1) Casting negative numbers to size_t would indeed turn up as >>> + * a large size_t and its value will be larger than ULONG_MAX/2, >>> + * so that this can qualify as out-of-bounds. >>> + * 2) If KASAN has new bug type and user-space passes negative size, >>> + * then there are duplicate reports. So don't produce new bug type >>> + * in order to prevent duplicate reports by some systems >>> + * (e.g. syzbot) to report the same bug twice. >>> + * 3) When size is negative numbers, it may be passed from user-space. >>> + * So we always print heap-out-of-bounds in order to prevent that >>> + * kernel-space and user-space have the same bug but have duplicate >>> + * reports. >>> + */ >> >> Completely fail to understand 2) and 3). 2) talks something about *NOT* producing new bug >> type, but at the same time you code actually does that. >> 3) says something about user-space which have nothing to do with kasan. > > The idea was to use one of the existing bug titles so that syzbot does > not produce 2 versions for OOBs where size is user-controlled. We > don't know if it's overflow from heap, global or stack, but heap is > the most common bug, so saying heap overflow will reduce chances of > producing duplicates the most. > But for all of this to work we do need to use one of the existing bug titles. The "heap-out-of-bounds" is not one of the existing bug titles.