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=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 A7721C56202 for ; Tue, 17 Nov 2020 13:14:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C70F2225B for ; Tue, 17 Nov 2020 13:14:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="y+30f/Yv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729975AbgKQNN4 (ORCPT ); Tue, 17 Nov 2020 08:13:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:44366 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729941AbgKQNNr (ORCPT ); Tue, 17 Nov 2020 08:13:47 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E73EA2151B; Tue, 17 Nov 2020 13:13:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605618826; bh=j+q9e5I7bDq0E+WLqGswa+faDIMGj7OmgmhmlzHZOfY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=y+30f/YvTgzpLtngmn+qr/zHYyHMWZUCHcs3hYPnQ7DBu5FslV8yRB55LWCGQD0hA DfCK5P4+SXWnIJvSe4OF+VbjcTxsxrd7v34VpN3zoUc/URpHBjCEF7G4maDrrF6Qry R8r1XPhEsAgqgfXBTE2Z5m34Wkc35PJOEOpXffKQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Brian Foster , "Darrick J. Wong" , Sasha Levin Subject: [PATCH 4.14 20/85] xfs: flush new eof page on truncate to avoid post-eof corruption Date: Tue, 17 Nov 2020 14:04:49 +0100 Message-Id: <20201117122112.026112733@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201117122111.018425544@linuxfoundation.org> References: <20201117122111.018425544@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Brian Foster [ Upstream commit 869ae85dae64b5540e4362d7fe4cd520e10ec05c ] It is possible to expose non-zeroed post-EOF data in XFS if the new EOF page is dirty, backed by an unwritten block and the truncate happens to race with writeback. iomap_truncate_page() will not zero the post-EOF portion of the page if the underlying block is unwritten. The subsequent call to truncate_setsize() will, but doesn't dirty the page. Therefore, if writeback happens to complete after iomap_truncate_page() (so it still sees the unwritten block) but before truncate_setsize(), the cached page becomes inconsistent with the on-disk block. A mapped read after the associated page is reclaimed or invalidated exposes non-zero post-EOF data. For example, consider the following sequence when run on a kernel modified to explicitly flush the new EOF page within the race window: $ xfs_io -fc "falloc 0 4k" -c fsync /mnt/file $ xfs_io -c "pwrite 0 4k" -c "truncate 1k" /mnt/file ... $ xfs_io -c "mmap 0 4k" -c "mread -v 1k 8" /mnt/file 00000400: 00 00 00 00 00 00 00 00 ........ $ umount /mnt/; mount /mnt/ $ xfs_io -c "mmap 0 4k" -c "mread -v 1k 8" /mnt/file 00000400: cd cd cd cd cd cd cd cd ........ Update xfs_setattr_size() to explicitly flush the new EOF page prior to the page truncate to ensure iomap has the latest state of the underlying block. Fixes: 68a9f5e7007c ("xfs: implement iomap based buffered write path") Signed-off-by: Brian Foster Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong Signed-off-by: Sasha Levin --- fs/xfs/xfs_iops.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c index 4e6f2c8574f7e..42c670a313518 100644 --- a/fs/xfs/xfs_iops.c +++ b/fs/xfs/xfs_iops.c @@ -879,6 +879,16 @@ xfs_setattr_size( if (newsize > oldsize) { error = xfs_zero_eof(ip, newsize, oldsize, &did_zeroing); } else { + /* + * iomap won't detect a dirty page over an unwritten block (or a + * cow block over a hole) and subsequently skips zeroing the + * newly post-EOF portion of the page. Flush the new EOF to + * convert the block before the pagecache truncate. + */ + error = filemap_write_and_wait_range(inode->i_mapping, newsize, + newsize); + if (error) + return error; error = iomap_truncate_page(inode, newsize, &did_zeroing, &xfs_iomap_ops); } -- 2.27.0