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 91AACC77B7C for ; Thu, 4 May 2023 12:43:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229812AbjEDMnP (ORCPT ); Thu, 4 May 2023 08:43:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229980AbjEDMnP (ORCPT ); Thu, 4 May 2023 08:43:15 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 24C416185 for ; Thu, 4 May 2023 05:43:13 -0700 (PDT) Received: from canpemm500010.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4QBtjJ465fzsR5v; Thu, 4 May 2023 20:41:24 +0800 (CST) Received: from [10.174.178.185] (10.174.178.185) by canpemm500010.china.huawei.com (7.192.105.118) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Thu, 4 May 2023 20:43:10 +0800 Subject: Re: [PATCH 5/4] xfs: fix negative array access in xfs_getbmap To: "Darrick J. Wong" , References: <168296561299.290030.5324305660599413777.stgit@frogsfrogsfrogs> <20230501212434.GM59213@frogsfrogsfrogs> CC: Dave Chinner , From: "yebin (H)" Message-ID: <6453A85E.9090302@huawei.com> Date: Thu, 4 May 2023 20:43:10 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <20230501212434.GM59213@frogsfrogsfrogs> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.185] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500010.china.huawei.com (7.192.105.118) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 2023/5/2 5:24, Darrick J. Wong wrote: > From: Darrick J. Wong > > In commit 8ee81ed581ff, Ye Bin complained about an ASSERT in the bmapx > code that trips if we encounter a delalloc extent after flushing the > pagecache to disk. The ioctl code does not hold MMAPLOCK so it's > entirely possible that a racing write page fault can create a delalloc > extent after the file has been flushed. The proposed solution was to > replace the assertion with an early return that avoids filling out the > bmap recordset with a delalloc entry if the caller didn't ask for it. > > At the time, I recall thinking that the forward logic sounded ok, but > felt hesitant because I suspected that changing this code would cause > something /else/ to burst loose due to some other subtlety. > > syzbot of course found that subtlety. If all the extent mappings found > after the flush are delalloc mappings, we'll reach the end of the data > fork without ever incrementing bmv->bmv_entries. This is new, since > before we'd have emitted the delalloc mappings even though the caller > didn't ask for them. Once we reach the end, we'll try to set > BMV_OF_LAST on the -1st entry (because bmv_entries is zero) and go > corrupt something else in memory. Yay. > > I really dislike all these stupid patches that fiddle around with debug > code and break things that otherwise worked well enough. Nobody was > complaining that calling XFS_IOC_BMAPX without BMV_IF_DELALLOC would > return BMV_OF_DELALLOC records, and now we've gone from "weird behavior > that nobody cared about" to "bad behavior that must be addressed > immediately". > > Maybe I'll just ignore anything from Huawei from now on for my own sake. I am very sorry for introducing a new issue and causing you inconvenience. The issue fixed by commit 8ee81ed581ff was triggered by doing our syzkaller testingļ¼Œand my intention is to fix the issue without any malice and offend. I fully agree with you that we should be more cautious in modifying the code that was originally working well. I will do more self code review and test before sending patches to upstream. > Reported-by: syzbot+c103d3808a0de5faaf80@syzkaller.appspotmail.com > Link: https://lore.kernel.org/linux-xfs/20230412024907.GP360889@frogsfrogsfrogs/ > Fixes: 8ee81ed581ff ("xfs: fix BUG_ON in xfs_getbmap()") > Signed-off-by: Darrick J. Wong > --- > fs/xfs/xfs_bmap_util.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c > index f032d3a4b727..fbb675563208 100644 > --- a/fs/xfs/xfs_bmap_util.c > +++ b/fs/xfs/xfs_bmap_util.c > @@ -558,7 +558,9 @@ xfs_getbmap( > if (!xfs_iext_next_extent(ifp, &icur, &got)) { > xfs_fileoff_t end = XFS_B_TO_FSB(mp, XFS_ISIZE(ip)); > > - out[bmv->bmv_entries - 1].bmv_oflags |= BMV_OF_LAST; > + if (bmv->bmv_entries > 0) > + out[bmv->bmv_entries - 1].bmv_oflags |= > + BMV_OF_LAST; > > if (whichfork != XFS_ATTR_FORK && bno < end && > !xfs_getbmap_full(bmv)) { > . >