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=1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,FSL_HELO_FAKE,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 CAB4CC433FF for ; Mon, 29 Jul 2019 20:46:48 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9BEC3206A2 for ; Mon, 29 Jul 2019 20:46:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="fr3N2nf2"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="K79oGysD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9BEC3206A2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ov0K9B1vyTE63hIHSt8yH+XlDqUCg178ILp95foZq1I=; b=fr3N2nf2EYdTbK LVddPxiS3LfXNPsj+DNyGu2CNYs3yHiqpnlRZNRkwI/56WHUDc6rqvDORZbAx/wikwA9rbLdZRIwI O5jwDXbGREnFlfxTivbpmAeynA2+uHPB/TZ1Vsko5pO6o2Mv3idVOzNzIf9NPtrcCJznLYUrMJbVg VjbroxdIMHUkRo6JxUM2lZyl+bL9wD+OBXbMIrq1qToE1d+aCKxTgUc2tWcONdeCRXM4or2OxMPp/ q6pan+Ap2JdxtijB1S8OVSGptt4czxIdePYOqy3SLpbpi1z5uH7hcBJf5GOM7VB1AcnAp3TopZxCA 13kuRhjqkHmirxvfVdqw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hsCXR-0003jQ-Af; Mon, 29 Jul 2019 20:46:33 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hsCXO-0003iu-SI for linux-mtd@lists.infradead.org; Mon, 29 Jul 2019 20:46:32 +0000 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" 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-Disposition: inline In-Reply-To: <20190728211730.GK6088@mit.edu> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190729_134630_945977_E45DF729 X-CRM114-Status: GOOD ( 21.02 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Satya Tangirala , linux-api@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, keyrings@vger.kernel.org, linux-mtd@lists.infradead.org, linux-crypto@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Paul Crowley Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.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 ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/