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=0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,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 14B98C76186 for ; Mon, 29 Jul 2019 20:46:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D7E762070B for ; Mon, 29 Jul 2019 20:46:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564433192; bh=DNMh2YRc0dQISTUq/gkVxZiJ3MfUwE+LBvvMLd0sx0w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=joIicFjuBOkAhOWCDuV6vqnB09B/flnDgzyFOVFBKWl31fzTjK04g4pxCRVJhUKeZ 4pGSS3FJqWfh1ZogawkF8KLgRi9XzMmhwSMWVboAoGopQgiokedW1ap3ExX/SYQViU wDvv10s2TL/nYsxLshYVUJzmucFpAwRsWbWFqydw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729471AbfG2Uqb (ORCPT ); Mon, 29 Jul 2019 16:46:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:48640 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729079AbfG2Uqb (ORCPT ); Mon, 29 Jul 2019 16:46:31 -0400 Received: from gmail.com (unknown [104.132.1.77]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2D6B0206A2; Mon, 29 Jul 2019 20:46:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564433190; bh=DNMh2YRc0dQISTUq/gkVxZiJ3MfUwE+LBvvMLd0sx0w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=K79oGysDbp1R9KcVqj1mKpfGB23D0dx9KzJwL1URFJI/8PotFaTXB1QXv/9jPmJ5e cd4dzd2ixOf8QsiHSDEd5r1iJBny2qYoC0vd1z0wpsTIbfCpr52p94FTMkHI78oJ2t NisulN2mchZN4cYXAX27Nu925MXHkVW50WusaYRo= Date: Mon, 29 Jul 2019 13:46:28 -0700 From: Eric Biggers To: "Theodore Y. Ts'o" Cc: linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, linux-api@vger.kernel.org, linux-crypto@vger.kernel.org, keyrings@vger.kernel.org, Paul Crowley , Satya Tangirala Subject: Re: [PATCH v7 10/16] fscrypt: v2 encryption policy support Message-ID: <20190729204627.GH169027@gmail.com> Mail-Followup-To: "Theodore Y. Ts'o" , linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, linux-api@vger.kernel.org, linux-crypto@vger.kernel.org, keyrings@vger.kernel.org, Paul Crowley , Satya Tangirala References: <20190726224141.14044-1-ebiggers@kernel.org> <20190726224141.14044-11-ebiggers@kernel.org> <20190728211730.GK6088@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190728211730.GK6088@mit.edu> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On Sun, Jul 28, 2019 at 05:17:30PM -0400, Theodore Y. Ts'o wrote: > On Fri, Jul 26, 2019 at 03:41:35PM -0700, Eric Biggers wrote: > > @@ -319,6 +329,31 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg) > > if (!capable(CAP_SYS_ADMIN)) > > goto out_wipe_secret; > > > > + if (arg.key_spec.type != FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) { > > This should be "== FSCRYPT_KEY_SPEC_TYPE_INDENTIFIER" instead. That's > because you use the identifier part of the union: > > > + /* Calculate the key identifier and return it to userspace. */ > > + err = fscrypt_hkdf_expand(&secret.hkdf, > > + HKDF_CONTEXT_KEY_IDENTIFIER, > > + NULL, 0, arg.key_spec.u.identifier, > > If we ever add a new key specifier type, and alternative in the union, > this is going to come back to bite us. Well, I did it this way because the next patch changes the code to: if (arg.key_spec.type == FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR) { ... } else { ... } We already validated that it's either TYPE_DESCRIPTOR or TYPE_IDENTIFIER. But I guess to be more clear I'll just make it handle the default case again. switch (arg.key_spec.type) { case FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR: ... break; case FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER: ... break; default: err = -EINVAL; break; } > > > + if (policy->version == FSCRYPT_POLICY_V1) { > > + /* > > + * The original encryption policy version provided no way of > > + * verifying that the correct master key was supplied, which was > > + * insecure in scenarios where multiple users have access to the > > + * same encrypted files (even just read-only access). > > Which scenario do you have in mind? With read-only access, Alice can > fetch the encryption policy for a directory, and introduce a key with > the same descriptor, but the "wrong" key, but that's only going to > affect Alice's use of the key. It won't affect what key is used by > Bob, since Alice doesn't have write access to Bob's keyrings. > > If what you mean is the risk when there is a single global > filesystem-specific keyring, where Alice could introduce a "wrong" key > identified with a specific descriptor, then sure, Alice could trick > Bob into encrypting his data with the wrong key (one known to Alice). > But we don't allow keys usable by V1 policies to be used in the > filesystem-specific keyring, do we? > The scenario is that Alice lists the directory with the wrong key, then Bob lists the directory too and gets the wrong filenames. This happens because the inode, fscrypt_info, dentry cache, page cache, etc. are the same for everyone. Bob's key is never looked up because the inode already has a key cached. This also applies to regular files and symlinks. - Eric