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=-7.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 BF166C43216 for ; Tue, 17 Aug 2021 14:13:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAA8660FD8 for ; Tue, 17 Aug 2021 14:13:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231172AbhHQONz (ORCPT ); Tue, 17 Aug 2021 10:13:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240098AbhHQONy (ORCPT ); Tue, 17 Aug 2021 10:13:54 -0400 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 543D2C06179A for ; Tue, 17 Aug 2021 07:13:21 -0700 (PDT) Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=[IPv6:::1]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1mFzq7-0005xZ-ST; Tue, 17 Aug 2021 16:13:15 +0200 Subject: Re: [PATCH v2] fscrypt: support trusted keys To: Mimi Zohar , Eric Biggers , Jarkko Sakkinen Cc: "Theodore Y. Ts'o" , Jaegeuk Kim , kernel@pengutronix.de, James Morris , "Serge E. Hallyn" , James Bottomley , Sumit Garg , David Howells , linux-fscrypt@vger.kernel.org, linux-crypto@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, keyrings@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210806150928.27857-1-a.fatoum@pengutronix.de> <20210809094408.4iqwsx77u64usfx6@kernel.org> <20210810180636.vqwaeftv7alsodgn@kernel.org> <20210810212140.sdq5dq2wy5uaj7h7@kernel.org> <20210811001743.ofzkwdwa6rcjsf4d@kernel.org> <0e69a0aa394dd20347b06ae4e700aa17d52583ef.camel@linux.ibm.com> <285cb263d9c1c16f3918c98dd36074ef16568e6d.camel@linux.ibm.com> From: Ahmad Fatoum Message-ID: Date: Tue, 17 Aug 2021 16:13:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <285cb263d9c1c16f3918c98dd36074ef16568e6d.camel@linux.ibm.com> Content-Type: text/plain; charset=iso-8859-15 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: a.fatoum@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-crypto@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On 17.08.21 15:55, Mimi Zohar wrote: > On Tue, 2021-08-17 at 15:04 +0200, Ahmad Fatoum wrote: >> Hi, >> >> On 12.08.21 02:54, Mimi Zohar wrote: >>> On Wed, 2021-08-11 at 10:16 -0700, Eric Biggers wrote: >>> >>>> Neither of you actually answered my question, which is whether the support for >>>> trusted keys in dm-crypt is a mistake. I think you're saying that it is? That >>>> would imply that fscrypt shouldn't support trusted keys, but rather encrypted >>>> keys -- which conflicts with Ahmad's patch which is adding support for trusted >>>> keys. Note that your reasoning for this is not documented at all in the >>>> trusted-encrypted keys documentation; it needs to be (email threads don't really >>>> matter), otherwise how would anyone know when/how to use this feature? >>> >>> True, but all of the trusted-encrypted key examples in the >>> documentation are "encrypted" type keys, encrypted/decrypted based on a >>> "trusted" type key. There are no examples of using the "trusted" key >>> type directly. Before claiming that adding "trusted" key support in >>> dm-crypt was a mistake, we should ask Ahmad why he felt dm-crypt needed >>> to directly support "trusted" type keys. >> >> I wanted to persist the dm-crypt key as a sealed blob. With encrypted keys, >> I would have to persist and unseal two blobs (load trusted key blob, load >> encrypted key blob rooted to trusted key) with no extra benefit. >> >> I thus added direct support for trusted keys. Jarkko even commented on the >> thread, but didn't voice objection to the approach (or agreement for that >> matter), so I assumed the approach is fine. >> >> I can see the utility of using a single trusted key for TPMs, but for CAAM, >> I see none and having an encrypted key for every trusted key just makes >> it more cumbersome. >> >> In v1 here, I added encrypted key support as well, but dropped it for v2, >> because I am not in a position to justify its use. Now that you and Eric >> discussed it, should I send v3 with support for both encrypted and trusted >> keys like with dm-crypt or how should we proceed? > > With some applications, the indirection is important. It allows the > "encrypted" key type to be updated/re-encypted based on a new "trusted" > key, without affecting the on disk encrypted key usage. Those applications were already able to use the encrypted key support in dm-crypt. For those where re-encryption/PCR-sealing isn't required, direct trusted key support offers a simpler way to integrate. > As much as I expected, directly using "trusted" keys is a result of the > new trusted key sources. More users = more use cases. You make it sound like a negative thing. > I have no opinion as to whether this is/isn't a valid usecase. So you'd be fine with merging trusted key support as is and leave encrypted key support to someone who has a valid use case and wants to argue in its favor? Cheers, Ahmad > > thanks, > > Mimi > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |