From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:58782 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725905AbfFTVxn (ORCPT ); Thu, 20 Jun 2019 17:53:43 -0400 Date: Thu, 20 Jun 2019 17:52:12 -0400 From: "Theodore Ts'o" Subject: Re: [PATCH 1/6] mm/fs: don't allow writes to immutable files Message-ID: <20190620215212.GG4650@mit.edu> References: <156022836912.3227213.13598042497272336695.stgit@magnolia> <156022837711.3227213.11787906519006016743.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <156022837711.3227213.11787906519006016743.stgit@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: matthew.garrett@nebula.com, yuchao0@huawei.com, ard.biesheuvel@linaro.org, josef@toxicpanda.com, clm@fb.com, adilger.kernel@dilger.ca, viro@zeniv.linux.org.uk, jack@suse.com, dsterba@suse.com, jaegeuk@kernel.org, jk@ozlabs.org, reiserfs-devel@vger.kernel.org, linux-efi@vger.kernel.org, devel@lists.orangefs.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-nilfs@vger.kernel.org, linux-mtd@lists.infradead.org, ocfs2-devel@oss.oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org On Mon, Jun 10, 2019 at 09:46:17PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong > > The chattr manpage has this to say about immutable files: > > "A file with the 'i' attribute cannot be modified: it cannot be deleted > or renamed, no link can be created to this file, most of the file's > metadata can not be modified, and the file can not be opened in write > mode." > > Once the flag is set, it is enforced for quite a few file operations, > such as fallocate, fpunch, fzero, rm, touch, open, etc. However, we > don't check for immutability when doing a write(), a PROT_WRITE mmap(), > a truncate(), or a write to a previously established mmap. > > If a program has an open write fd to a file that the administrator > subsequently marks immutable, the program still can change the file > contents. Weird! > > The ability to write to an immutable file does not follow the manpage > promise that immutable files cannot be modified. Worse yet it's > inconsistent with the behavior of other syscalls which don't allow > modifications of immutable files. > > Therefore, add the necessary checks to make the write, mmap, and > truncate behavior consistent with what the manpage says and consistent > with other syscalls on filesystems which support IMMUTABLE. > > Signed-off-by: Darrick J. Wong I note that this patch doesn't allow writes to swap files. So Amir's generic/554 test will still fail for those file systems that don't use copy_file_range. I'm indifferent as to whether you add a new patch, or include that change in this patch, but perhaps we should fix this while we're making changes in these code paths? - Ted