From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:49573 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730055AbfFJBni (ORCPT ); Sun, 9 Jun 2019 21:43:38 -0400 Date: Sun, 9 Jun 2019 21:43:29 -0400 From: "Theodore Ts'o" Subject: Re: [PATCH 1/8] mm/fs: don't allow writes to immutable files Message-ID: <20190610014329.GA3266@mit.edu> References: <155552786671.20411.6442426840435740050.stgit@magnolia> <155552787330.20411.11893581890744963309.stgit@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <155552787330.20411.11893581890744963309.stgit@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-mm@kvack.org On Wed, Apr 17, 2019 at 12:04:33PM -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 Thanks, looks good. I'm going to take this patch through the ext4 tree since it doesn't have any dependencies on the rest of the patch series. - Ted