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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT 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 A69B8C28CC6 for ; Wed, 5 Jun 2019 09:27:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B91920684 for ; Wed, 5 Jun 2019 09:27:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726921AbfFEJ1a (ORCPT ); Wed, 5 Jun 2019 05:27:30 -0400 Received: from mx2.suse.de ([195.135.220.15]:33230 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726862AbfFEJ1a (ORCPT ); Wed, 5 Jun 2019 05:27:30 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 19441AEA3; Wed, 5 Jun 2019 09:27:29 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 556701E3C2F; Wed, 5 Jun 2019 11:27:28 +0200 (CEST) Date: Wed, 5 Jun 2019 11:27:28 +0200 From: Jan Kara To: Dave Chinner Cc: Jan Kara , linux-ext4@vger.kernel.org, Ted Tso , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Amir Goldstein , stable@vger.kernel.org Subject: Re: [PATCH 2/2] ext4: Fix stale data exposure when read races with hole punch Message-ID: <20190605092728.GB7433@quack2.suse.cz> References: <20190603132155.20600-1-jack@suse.cz> <20190603132155.20600-3-jack@suse.cz> <20190605012551.GJ16786@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190605012551.GJ16786@dread.disaster.area> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed 05-06-19 11:25:51, Dave Chinner wrote: > On Mon, Jun 03, 2019 at 03:21:55PM +0200, Jan Kara wrote: > > Hole puching currently evicts pages from page cache and then goes on to > > remove blocks from the inode. This happens under both i_mmap_sem and > > i_rwsem held exclusively which provides appropriate serialization with > > racing page faults. However there is currently nothing that prevents > > ordinary read(2) from racing with the hole punch and instantiating page > > cache page after hole punching has evicted page cache but before it has > > removed blocks from the inode. This page cache page will be mapping soon > > to be freed block and that can lead to returning stale data to userspace > > or even filesystem corruption. > > > > Fix the problem by protecting reads as well as readahead requests with > > i_mmap_sem. > > > > CC: stable@vger.kernel.org > > Reported-by: Amir Goldstein > > Signed-off-by: Jan Kara > > --- > > fs/ext4/file.c | 35 +++++++++++++++++++++++++++++++---- > > 1 file changed, 31 insertions(+), 4 deletions(-) > > > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > > index 2c5baa5e8291..a21fa9f8fb5d 100644 > > --- a/fs/ext4/file.c > > +++ b/fs/ext4/file.c > > @@ -34,6 +34,17 @@ > > #include "xattr.h" > > #include "acl.h" > > > > +static ssize_t ext4_file_buffered_read(struct kiocb *iocb, struct iov_iter *to) > > +{ > > + ssize_t ret; > > + struct inode *inode = file_inode(iocb->ki_filp); > > + > > + down_read(&EXT4_I(inode)->i_mmap_sem); > > + ret = generic_file_read_iter(iocb, to); > > + up_read(&EXT4_I(inode)->i_mmap_sem); > > + return ret; > > Isn't i_mmap_sem taken in the page fault path? What makes it safe > to take here both outside and inside the mmap_sem at the same time? > I mean, the whole reason for i_mmap_sem existing is that the inode > i_rwsem can't be taken both outside and inside the i_mmap_sem at the > same time, so what makes the i_mmap_sem different? Drat, you're right that read path may take page fault which will cause lock inversion with mmap_sem. Just my xfstests run apparently didn't trigger this as I didn't get any lockdep splat. Thanks for catching this! Honza -- Jan Kara SUSE Labs, CR