From patchwork Fri Feb 25 21:23:11 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Theodore Ts'o X-Patchwork-Id: 12760959 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 C1C1CC4332F for ; Fri, 25 Feb 2022 21:23:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238440AbiBYVYF (ORCPT ); Fri, 25 Feb 2022 16:24:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238419AbiBYVYE (ORCPT ); Fri, 25 Feb 2022 16:24:04 -0500 Received: from outgoing.mit.edu (outgoing-auth-1.mit.edu [18.9.28.11]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C25FA182D8E; Fri, 25 Feb 2022 13:23:30 -0800 (PST) Received: from cwcc.thunk.org (pool-108-7-220-252.bstnma.fios.verizon.net [108.7.220.252]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 21PLNBLr009217 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 25 Feb 2022 16:23:12 -0500 Received: by cwcc.thunk.org (Postfix, from userid 15806) id 8674315C0038; Fri, 25 Feb 2022 16:23:11 -0500 (EST) Date: Fri, 25 Feb 2022 16:23:11 -0500 From: "Theodore Ts'o" To: Eric Biggers Cc: Lee Jones , linux-ext4@vger.kernel.org, Christoph Hellwig , Dave Chinner , Goldwyn Rodrigues , "Darrick J . Wong" , Bob Peterson , Damien Le Moal , Andreas Gruenbacher , Ritesh Harjani , Greg Kroah-Hartman , Johannes Thumshirn , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, cluster-devel@redhat.com, linux-kernel@vger.kernel.org Subject: [PATCH -v3] ext4: don't BUG if kernel subsystems dirty pages without asking ext4 first Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org [un]pin_user_pages_remote is dirtying pages without properly warning the file system in advance. This was noted by Jan Kara in 2018[1] and more recently has resulted in bug reports by Syzbot in various Android kernels[2]. This is technically a bug in mm/gup.c, but arguably ext4 is fragile in that a buggy kernel subsystem which dirty pages without properly notifying the file system causes ext4 to BUG, while other file systems are not (although user data likely will be lost). I suspect in real life it is rare that people are using RDMA into file-backed memory, which is why no one has complained to ext4 developers except fuzzing programs. So instead of crashing with a BUG, issue a warning (since there may be potential data loss) and just mark the page as clean to avoid unprivileged denial of service attacks until the problem can be properly fixed. More discussion and background can be found in the thread starting at [2]. [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz [2] https://lore.kernel.org/r/Yg0m6IjcNmfaSokM@google.com Reported-by: syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com Reported-by: Lee Jones Signed-off-by: Theodore Ts'o Reported-by: syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com Reported-by: Lee Jones Signed-off-by: Theodore Ts'o Reviewed-by: Christoph Hellwig Reported-by: syzbot+d59332e2db681cf18f0318a06e994ebbb529a8db@syzkaller.appspotmail.com Reported-by: Lee Jones Signed-off-by: Theodore Ts'o --- fs/ext4/inode.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 01c9e4f743ba..008fe8750109 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -1993,6 +1993,15 @@ static int ext4_writepage(struct page *page, else len = PAGE_SIZE; + /* Should never happen but for bugs in other kernel subsystems */ + if (!page_has_buffers(page)) { + ext4_warning_inode(inode, + "page %lu does not have buffers attached", page->index); + ClearPageDirty(page); + unlock_page(page); + return 0; + } + page_bufs = page_buffers(page); /* * We cannot do block allocation or other extent handling in this @@ -2588,12 +2597,28 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd) (mpd->wbc->sync_mode == WB_SYNC_NONE)) || unlikely(page->mapping != mapping)) { unlock_page(page); - continue; + goto out; } wait_on_page_writeback(page); BUG_ON(PageWriteback(page)); + /* + * Should never happen but for buggy code in + * other subsystems that call + * set_page_dirty() without properly warning + * the file system first. See [1] for more + * information. + * + * [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz + */ + if (!page_has_buffers(page)) { + ext4_warning_inode(mpd->inode, "page %lu does not have buffers attached", page->index); + ClearPageDirty(page); + unlock_page(page); + continue; + } + if (mpd->map.m_len == 0) mpd->first_page = page->index; mpd->next_page = page->index + 1;