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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 C569BC3F68F for ; Thu, 23 Jan 2020 02:25:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A6F7924673 for ; Thu, 23 Jan 2020 02:25:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726227AbgAWCZC (ORCPT ); Wed, 22 Jan 2020 21:25:02 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:47698 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725933AbgAWCZB (ORCPT ); Wed, 22 Jan 2020 21:25:01 -0500 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 35ADC651C4DD263FBCD7; Thu, 23 Jan 2020 10:24:58 +0800 (CST) Received: from [127.0.0.1] (10.133.219.224) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.439.0; Thu, 23 Jan 2020 10:24:55 +0800 Subject: Re: [PATCH] jffs2: Fix integer underflow in jffs2_rtime_compress To: Richard Weinberger CC: , , , References: <20181215162350.12489-1-richard@nod.at> <2142335.HPRDAJu19m@blindfold> From: Hou Tao Message-ID: Date: Thu, 23 Jan 2020 10:24:55 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <2142335.HPRDAJu19m@blindfold> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.133.219.224] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Richard, On 2018/12/20 18:45, Richard Weinberger wrote: > Am Donnerstag, 20. Dezember 2018, 11:43:08 CET schrieb Hou Tao: >> >> On 2018/12/16 0:23, Richard Weinberger wrote: >>> The rtime compressor assumes that at least two bytes are >>> compressed. >>> If we try to compress just one byte, the loop condition will >>> wrap around and an out-of-bounds write happens. >>> >>> Cc: >>> Signed-off-by: Richard Weinberger >>> --- >>> fs/jffs2/compr_rtime.c | 3 +++ >>> 1 file changed, 3 insertions(+) >>> It seems that it doesn't incur any harm because the minimal allocated >> size will be 8-bytes and jffs2_rtime_compress() will write 2-bytes into >> the allocated buffer. > > Are you sure about that? I saw odd kernel behavior and KASAN complained too. > Sorry for the later reply. Yes. KASAN complains but it doesn't incur any harm because the minimal allocated size returned by kmalloc() will be 8-bytes. But we better fix it, because it's bad to depend on the implementation of kmalloc(). It seems that mtd-utils has already fixed it years ago. Maybe we can use it directly ? And your fix also looks good to me, so Reviewed-by: Hou Tao commit e8457f16306ad6e2c8708275bf42b5dfff40fffd Author: Enrico Scholz Date: Thu Jun 24 15:02:40 2010 +0200 mkfs.jffs2: fix integer underflow in jffs2_rtime_compress() When '*dstlen' is 0 or 1, comparison will return wrong result. Reported by valgrind as ==5919== Invalid write of size 1 ==5919== at 0x40564E: jffs2_rtime_compress (compr_rtime.c:51) ==5919== by 0x40676B: jffs2_compress (compr.c:246) ==5919== by 0x403EE4: recursive_populate_directory (mkfs.jffs2.c:884) ==5919== Address 0x4e1bdb1 is 0 bytes after a block of size 1 alloc'd ==5919== at 0x4A0515D: malloc (vg_replace_malloc.c:195) ==5919== by 0x40671C: jffs2_compress (compr.c:229) ==5919== by 0x403EE4: recursive_populate_directory (mkfs.jffs2.c:884) Signed-off-by: Enrico Scholz Signed-off-by: Artem Bityutskiy diff --git a/compr_rtime.c b/compr_rtime.c index 131536c..5613963 100644 --- a/compr_rtime.c +++ b/compr_rtime.c @@ -32,7 +32,7 @@ static int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out memset(positions,0,sizeof(positions)); - while (pos < (*sourcelen) && outpos <= (*dstlen)-2) { + while (pos < (*sourcelen) && outpos+2 <= (*dstlen)) { int backpos, runlen=0; unsigned char value; > Thanks, > //richard > > > > . >