Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161156AbaDJTOe (ORCPT ); Thu, 10 Apr 2014 15:14:34 -0400 Received: from mail-pa0-f43.google.com ([209.85.220.43]:60936 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161035AbaDJTOc (ORCPT ); Thu, 10 Apr 2014 15:14:32 -0400 Message-ID: <5346ED93.9040500@amacapital.net> Date: Thu, 10 Apr 2014 12:14:27 -0700 From: Andy Lutomirski User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: tytso@mit.edu, David Herrmann , linux-kernel , Hugh Dickins , Alexander Viro , Karol Lewandowski , Kay Sievers , Daniel Mack , Lennart Poettering , John Stultz , Greg Kroah-Hartman , Tejun Heo , Johannes Weiner , "dri-devel@lists.freedesktop.org" , linux-fsdevel , linux-mm , Andrew Morton , Linus Torvalds , Ryan Lortie , "Michael Kerrisk (man-pages)" Subject: Re: [PATCH 0/6] File Sealing & memfd_create() References: <1395256011-2423-1-git-send-email-dh.herrmann@gmail.com> <20140320153250.GC20618@thunk.org> <20140320163806.GA10440@thunk.org> In-Reply-To: <20140320163806.GA10440@thunk.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/20/2014 09:38 AM, tytso@mit.edu wrote: > On Thu, Mar 20, 2014 at 04:48:30PM +0100, David Herrmann wrote: >> On Thu, Mar 20, 2014 at 4:32 PM, wrote: >>> Why not make sealing an attribute of the "struct file", and enforce it >>> at the VFS layer? That way all file system objects would have access >>> to sealing interface, and for memfd_shmem, you can't get another >>> struct file pointing at the object, the security properties would be >>> identical. >> >> Sealing as introduced here is an inode-attribute, not "struct file". >> This is intentional. For instance, a gfx-client can get a read-only FD >> via /proc/self/fd/ and pass it to the compositor so it can never >> overwrite the contents (unless the compositor has write-access to the >> inode itself, in which case it can just re-open it read-write). > > Hmm, good point. I had forgotten about the /proc/self/fd hole. > Hmm... what if we have a SEAL_PROC which forces the permissions of > /proc/self/fd to be 000? This is the second time in a week that someone has asked for a way to have a struct file (or struct inode or whatever) that can't be reopened through /proc/pid/fd. This should be quite easy to implement as a separate feature. Actually, that feature would solve a major pet peeve of mine, I think: I want something like memfd that allows me to keep the thing read-write but that whomever I pass the fd to can't change. With this feature, I could do: fd_rw = memfd_create (or O_TMPFILE or whatever) fd_ro = open(/proc/self/fd/fd_ro, O_RDONLY); fcntl(fd_ro, F_RESTRICT, F_RESTRICT_REOPEN); send fd_ro via SCM_RIGHTS. To really make this work well, I also want to SEAL_SHRINK the inode so that the receiver can verify that I'm not going to truncate the file out from under it. Bingo, fast and secure one-way IPC. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/