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=-5.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 60771C433FF for ; Tue, 13 Aug 2019 00:14:38 +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 2FC0020665 for ; Tue, 13 Aug 2019 00:14:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="LUGJflTO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2FC0020665 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=mit.edu 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=cb4R1KwIqUiXMwW49p1j0GXvCaYyyZQseNLvpazqda8=; b=LUGJflTOlBCsi5 6GTVf5GK0fe1uHkSVCRuH22jsUNbkgMS8baa3m3bKdWoje1y6Qs8RVrys7bt7tiFiWe0yq8wx1dO+ klDPwnVppqBVU1jzdv52+oW3zXxs2mBSSm4ZdfUVbaUwbPsV0oSVo0JALtfkxx/4m1aJKy3hrnkDA Z5MwA0wlv1UPMGKjNZkkY7kt5uDeQ7FCD+S/at9XjGx17zdpPJ15uJfNQET4Hj5HyTMW6QSSaDmWe xSW7F61FM+QCpUGL3BhMebF2bPY6XeL/BJQfPIb7dfTuNq+DcJx+BHLFuTu0gZID/7PNxFkZplOZ5 Hy5BNrsTu+9v/yGAshMw==; 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 1hxKS8-0002sF-Qv; Tue, 13 Aug 2019 00:14:16 +0000 Received: from outgoing-auth-1.mit.edu ([18.9.28.11] helo=outgoing.mit.edu) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hxKS5-0002rq-81 for linux-mtd@lists.infradead.org; Tue, 13 Aug 2019 00:14:14 +0000 Received: from callcc.thunk.org (guestnat-104-133-9-109.corp.google.com [104.133.9.109] (may be forged)) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id x7D0E7I4017125 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 12 Aug 2019 20:14:08 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id 1BBDD4218EF; Mon, 12 Aug 2019 20:14:07 -0400 (EDT) Date: Mon, 12 Aug 2019 20:14:07 -0400 From: "Theodore Y. Ts'o" To: Eric Biggers Subject: Re: [PATCH v8 14/20] fscrypt: allow unprivileged users to add/remove keys for v2 policies Message-ID: <20190813001406.GI28705@mit.edu> References: <20190805162521.90882-1-ebiggers@kernel.org> <20190805162521.90882-15-ebiggers@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190805162521.90882-15-ebiggers@kernel.org> 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-20190812_171413_456916_D3634C86 X-CRM114-Status: GOOD ( 19.28 ) 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, Jaegeuk Kim , 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 Mon, Aug 05, 2019 at 09:25:15AM -0700, Eric Biggers wrote: > From: Eric Biggers > > Allow the FS_IOC_ADD_ENCRYPTION_KEY and FS_IOC_REMOVE_ENCRYPTION_KEY > ioctls to be used by non-root users to add and remove encryption keys > from the filesystem-level crypto keyrings, subject to limitations. > > Motivation: while privileged fscrypt key management is sufficient for > some users (e.g. Android and Chromium OS, where a privileged process > manages all keys), the old API by design also allows non-root users to > set up and use encrypted directories, and we don't want to regress on > that. Especially, we don't want to force users to continue using the > old API, running into the visibility mismatch between files and keyrings > and being unable to "lock" encrypted directories. > > Intuitively, the ioctls have to be privileged since they manipulate > filesystem-level state. However, it's actually safe to make them > unprivileged if we very carefully enforce some specific limitations. > > First, each key must be identified by a cryptographic hash so that a > user can't add the wrong key for another user's files. For v2 > encryption policies, we use the key_identifier for this. v1 policies > don't have this, so managing keys for them remains privileged. > > Second, each key a user adds is charged to their quota for the keyrings > service. Thus, a user can't exhaust memory by adding a huge number of > keys. By default each non-root user is allowed up to 200 keys; this can > be changed using the existing sysctl 'kernel.keys.maxkeys'. > > Third, if multiple users add the same key, we keep track of those users > of the key (of which there remains a single copy), and won't really > remove the key, i.e. "lock" the encrypted files, until all those users > have removed it. This prevents denial of service attacks that would be > possible under simpler schemes, such allowing the first user who added a > key to remove it -- since that could be a malicious user who has > compromised the key. Of course, encryption keys should be kept secret, > but the idea is that using encryption should never be *less* secure than > not using encryption, even if your key was compromised. > > We tolerate that a user will be unable to really remove a key, i.e. > unable to "lock" their encrypted files, if another user has added the > same key. But in a sense, this is actually a good thing because it will > avoid providing a false notion of security where a key appears to have > been removed when actually it's still in memory, available to any > attacker who compromises the operating system kernel. > > Signed-off-by: Eric Biggers Looks good. I'd probably would have used either "mk_secret_sem" or "mk->mk_secret_sem" in the comments, instead of "->mk_securet_sem", but that's just a personal style preference. Since you consistently used the latter, I assume that's a deliberate choice, which is fine. Feel free to add: Reviewed-by: Theodore Ts'o ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/