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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 D1CB6C433DF for ; Tue, 28 Jul 2020 21:50:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A838B2075D for ; Tue, 28 Jul 2020 21:50:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595973044; bh=CMGacDVfTN94BI5w3YcmjNfFox9Yr7ccfGOB0osi8HA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=PjHtsHpCZtbdn08pmqWjb9AzlV7S+jhsdlDlawoX+fsLowCAF4WV4WCgvKgSJoyfj eQVEqi+iEKAJ/F+Rs3oTAEudnZRvNvWWlWEM+XD8l0f7IS9N7v30Gv2s8NgKgkLBzb DxwYFgTz6cA5gUAz6VA32HTDS181mxwFQOkMOwIs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729476AbgG1Vuo (ORCPT ); Tue, 28 Jul 2020 17:50:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:59390 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728149AbgG1Vuo (ORCPT ); Tue, 28 Jul 2020 17:50:44 -0400 Received: from gmail.com (unknown [104.132.1.76]) (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 90B1F2070A; Tue, 28 Jul 2020 21:50:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595973043; bh=CMGacDVfTN94BI5w3YcmjNfFox9Yr7ccfGOB0osi8HA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TF27vO0vUnRyvzaVF2d1RKzKyj5K+a7CKnkLShPaAUfVdKqUPTLoQVe43ypffe+ix Z9/VC9KciOR5TDGgWp6o35wQt1vueBvy+totihjiP8TbxHXPOkzOoTrdjUxUrCBT62 IMuIyAUjPjSe2iBHeebnRuZzCT4zdQMC/oS9ud7s= Date: Tue, 28 Jul 2020 14:50:41 -0700 From: Eric Biggers To: Deven Bowers Cc: agk@redhat.com, axboe@kernel.dk, snitzer@redhat.com, jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com, viro@zeniv.linux.org.uk, paul@paul-moore.com, eparis@redhat.com, jannh@google.com, dm-devel@redhat.com, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-audit@redhat.com, tyhicks@linux.microsoft.com, linux-kernel@vger.kernel.org, corbet@lwn.net, sashal@kernel.org, jaskarankhurana@linux.microsoft.com, mdsakib@microsoft.com, nramas@linux.microsoft.com, pasha.tatashin@soleen.com Subject: Re: [RFC PATCH v5 06/11] dm-verity: move signature check after tree validation Message-ID: <20200728215041.GF4053562@gmail.com> References: <20200728213614.586312-1-deven.desai@linux.microsoft.com> <20200728213614.586312-7-deven.desai@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200728213614.586312-7-deven.desai@linux.microsoft.com> Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Tue, Jul 28, 2020 at 02:36:06PM -0700, Deven Bowers wrote: > The CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG introduced by Jaskaran was > intended to be used to allow an LSM to enforce verifications for all > dm-verity volumes. > > However, with it's current implementation, this signature verification > occurs after the merkel-tree is validated, as a result the signature can > pass initial verification by passing a matching root-hash and signature. > This results in an unreadable block_device, but that has passed signature > validation (and subsequently, would be marked as verified). > > This change moves the signature verification to after the merkel-tree has > finished validation. > > Signed-off-by: Deven Bowers > --- > drivers/md/dm-verity-target.c | 44 ++++------ > drivers/md/dm-verity-verify-sig.c | 140 ++++++++++++++++++++++-------- > drivers/md/dm-verity-verify-sig.h | 24 +++-- > drivers/md/dm-verity.h | 2 +- > 4 files changed, 134 insertions(+), 76 deletions(-) > > diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c > index eec9f252e935..fabc173aa7b3 100644 > --- a/drivers/md/dm-verity-target.c > +++ b/drivers/md/dm-verity-target.c > @@ -471,9 +471,9 @@ static int verity_verify_io(struct dm_verity_io *io) > struct bvec_iter start; > unsigned b; > struct crypto_wait wait; > + int r; > > for (b = 0; b < io->n_blocks; b++) { > - int r; > sector_t cur_block = io->block + b; > struct ahash_request *req = verity_io_hash_req(v, io); > > @@ -530,6 +530,16 @@ static int verity_verify_io(struct dm_verity_io *io) > return -EIO; > } > > + /* > + * At this point, the merkel tree has finished validating. > + * if signature was specified, validate the signature here. > + */ > + r = verity_verify_root_hash(v); > + if (r < 0) { > + DMERR_LIMIT("signature mismatch"); > + return r; > + } > + > return 0; > } This doesn't make any sense. This just moves the signature verification to some random I/O. The whole point of dm-verity is that data is verified on demand. You can't know whether any particular data or hash block is consistent with the root hash or not until it is read and verified. When the first I/O completes it might have just checked one block of a billion. Not to mention that you didn't consider locking at all. - Eric