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=-12.2 required=3.0 tests=BAYES_00, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 21D9AC433EF for ; Wed, 22 Sep 2021 02:06:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EC0E260F43 for ; Wed, 22 Sep 2021 02:06:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229658AbhIVCIK (ORCPT ); Tue, 21 Sep 2021 22:08:10 -0400 Received: from n169-112.mail.139.com ([120.232.169.112]:4684 "EHLO n169-112.mail.139.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229589AbhIVCIJ (ORCPT ); Tue, 21 Sep 2021 22:08:09 -0400 X-Greylist: delayed 576 seconds by postgrey-1.27 at vger.kernel.org; Tue, 21 Sep 2021 22:08:08 EDT X-RM-TagInfo: emlType=0 X-RM-SPAM: X-RM-SPAM-FLAG: 00000000 Received: from [192.168.255.10] (unknown[113.108.77.67]) by rmsmtp-lg-appmail-25-12028 (RichMail) with SMTP id 2efc614a8d6bb63-64fb6; Wed, 22 Sep 2021 09:56:59 +0800 (CST) X-RM-TRANSID: 2efc614a8d6bb63-64fb6 Message-ID: <3633c6e5-028c-fc77-3b8e-da9903f97ac5@139.com> Date: Wed, 22 Sep 2021 09:56:59 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.1.1 Subject: Re: [PATCH] ovl: fix null pointer when filesystem doesn't support direct IO To: Huang Jianan , linux-unionfs@vger.kernel.org, miklos@szeredi.hu, linux-erofs@lists.ozlabs.org, xiang@kernel.org, chao@kernel.org Cc: guoweichao@oppo.com, yh@oppo.com, zhangshiming@oppo.com, guanyuwei@oppo.com, jnhuang95@gmail.com, linux-kernel@vger.kernel.org References: <20210918121346.12084-1-huangjianan@oppo.com> From: Chengguang Xu In-Reply-To: <20210918121346.12084-1-huangjianan@oppo.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org 在 2021/9/18 20:13, Huang Jianan 写道: > From: Huang Jianan > > At present, overlayfs provides overlayfs inode to users. Overlayfs > inode provides ovl_aops with noop_direct_IO to avoid open failure > with O_DIRECT. But some compressed filesystems, such as erofs and > squashfs, don't support direct_IO. > > Users who use f_mapping->a_ops->direct_IO to check O_DIRECT support, > will read file through this way. This will cause overlayfs to access > a non-existent direct_IO function and cause panic due to null pointer: > > Kernel panic - not syncing: CFI failure (target: 0x0) > CPU: 6 PID: 247 Comm: loop0 > Call Trace: > panic+0x188/0x45c > __cfi_slowpath+0x0/0x254 > __cfi_slowpath+0x200/0x254 > generic_file_read_iter+0x14c/0x150 > vfs_iocb_iter_read+0xac/0x164 > ovl_read_iter+0x13c/0x2fc > lo_rw_aio+0x2bc/0x458 > loop_queue_work+0x4a4/0xbc0 > kthread_worker_fn+0xf8/0x1d0 > loop_kthread_worker_fn+0x24/0x38 > kthread+0x29c/0x310 > ret_from_fork+0x10/0x30 > > The filesystem may only support direct_IO for some file types. For > example, erofs supports direct_IO for uncompressed files. So fall > back to buffered io only when the file doesn't support direct_IO to > fix this problem. IMO, return error to user seems better option than fall back to buffered io directly. Thanks, Chengguang > > Fixes: 5b910bd615ba ("ovl: fix GPF in swapfile_activate of file from overlayfs over xfs") > Signed-off-by: Huang Jianan > --- > fs/overlayfs/file.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c > index d081faa55e83..998c60770b81 100644 > --- a/fs/overlayfs/file.c > +++ b/fs/overlayfs/file.c > @@ -296,6 +296,10 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter) > if (ret) > return ret; > > + if ((iocb->ki_flags & IOCB_DIRECT) && (!real.file->f_mapping->a_ops || > + !real.file->f_mapping->a_ops->direct_IO)) > + iocb->ki_flags &= ~IOCB_DIRECT; > + > old_cred = ovl_override_creds(file_inode(file)->i_sb); > if (is_sync_kiocb(iocb)) { > ret = vfs_iter_read(real.file, iter, &iocb->ki_pos,