From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753729AbbAYM3E (ORCPT ); Sun, 25 Jan 2015 07:29:04 -0500 Received: from a.ns.miles-group.at ([95.130.255.143]:65275 "EHLO radon.swed.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753516AbbAYM3B (ORCPT ); Sun, 25 Jan 2015 07:29:01 -0500 Message-ID: <54C4E181.4080004@nod.at> Date: Sun, 25 Jan 2015 13:28:49 +0100 From: Richard Weinberger User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Alexander Holler CC: =?UTF-8?B?UMOhZHJhaWcgQnJhZHk=?= , LKML , linux-kbuild , Michal Marek , David Howells , Linus Torvalds Subject: Re: [PATCH v2] modsign: use shred to overwrite the private key before deleting it References: <54C2F4F8.20809@draigBrady.com> <1422096327-4483-1-git-send-email-holler@ahsoftware.de> <54C383E0.9060408@ahsoftware.de> <54C38B6D.1060806@ahsoftware.de> <54C3901D.8040406@ahsoftware.de> <54C45153.2050703@draigBrady.com> <54C4583A.5040505@ahsoftware.de> <54C4C65A.2020403@ahsoftware.de> <54C4CC05.9090602@ahsoftware.de> <54C4D6BA.4080308@ahsoftware.de> <54C4E080.4020507@ahsoftware.de> In-Reply-To: <54C4E080.4020507@ahsoftware.de> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 25.01.2015 um 13:24 schrieb Alexander Holler: > Am 25.01.2015 um 13:08 schrieb Richard Weinberger: >> On Sun, Jan 25, 2015 at 12:42 PM, Alexander Holler wrote: >>> Now, after I ended up into flaming a lot (sorry again, but this topic made >>> me angry for so long and I had to spent too much time to get rid of unwanted >>> content and answering other peoples question in regard to that topic), I >>> should offer something more useful. >>> >>> So I've written down in some short words, how I think it could be done: >>> >>> First offer a syscall named sunlink() (or whatever name) which fails if it >>> can't overwrite or securely trim the contents of a file before deleting it. >>> >>> That could be done like this: >>> >>> (1) If it's a SSD or MMC without offering "Secure Trim" fail. >>> (2) If it's a plain FLASH or conventional harddisk where writing a block >>> means that block will be overwritten or if it's a SSD or MMC with "Secure >>> Trim) go on with >>> (3) Identify the blocks which contain the file contents (should be doable by >>> using the same mechanisms used to read and write a file) >>> (4) Mark the file as deleted >>> (5) Overwrite or securely trim blocks which can be deleted completely >>> (6) Build new blocks for blocks which can only partly deleted because they >>> contain information still used by the FS or other files >>> (7) Instruct the FS to us the new blocks instead of the old ones >>> (8) Overwrite or securely trim the old blocks which previously contained >>> partly information of other stuff. >>> >>> Afterwards use that new syscall in shred. >>> >>> Of course, this is just a totally simplified instruction in regard to how >>> complicated filesystems have become, but I think there isn't any black magic >>> involved in offering the user a simple way to really delete files. >> >> Or add support for the "s" chattr to major filesystems. >> > And change the manpage for the 's' attribute to change the "overwriting with zero" with some other wording. > > But thanks for the hint. I wasn't aware of that bit (maybe because it's still useless on most filesystems). > > But the above silly instruction might still help in implementing support for the 's' attribute. > > Also I wonder what happens if you delete a file with such an attribute on e.g. an SSD. I assume the user just gets a false positive that the file is deleted, which isn't much > different to what nowadays happens and doesn't therefor really help. The implementation will be challenging. Especially for modern filesytems like btrfs or f2fs which are copy-on-write based. Thanks, //richard