From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A21C0156C2 for ; Thu, 9 May 2024 17:07:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715274442; cv=none; b=TYUmbUwi+gZvo25/TkZCr6RWyyKySAWtvTrNsJCn5wgIpPzgP5xMLw1WR8bP2a3Zl0HF0a4JVPB28F3WTa3zyMTeoHh/UvPU6C1DVcAuqcktSiV8tGGZlYWeKV0uo+3hqBxLQbziN/vpG28U1xLfNP/EjA1TTIYx7UBtQIWx16o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715274442; c=relaxed/simple; bh=JTqRwvs7ATnblMDzbI8kYx5IrTBxMWNprcLAXd5ODXg=; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References: MIME-Version:Content-Type; b=pZrXb7GkbblKb6VNWvtflnrB31xyjC7Vw2uK8ohGtQO030PUnVHic1X9tY5qY/ZsetzFz3GKayDF95l3TlTDur3eijq3Jit8i1X3nEZdaBw5ZXNRMAzyu9FJhd9xto2GNnny0+rUlvORBY00aemg8pLpw3FNIW093uGYQJ+OoeE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=GvpKdYu1; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="GvpKdYu1" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1715274439; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1Ca9Pf11lzbP4jlatyhKofM52bEPeu8vNmdS1FsH4a8=; b=GvpKdYu10fnHDW/pAoyK20EECRTJN/Yec8Sow2na6ca6Jc0DaUwN+Rqcd9dAwzM34sF2Nr pb9GzTIbh/vMFHEhBxGN4T6FJVQ28pnUuYGyYScmpFQG3HifUkBUXmOstiOWHkHpwdtvSD ymBkaQTaKH7QV3JuzvR3zdMZNMbVkP8= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-182-Y19FXQdzO2eI8S9NubSUHw-1; Thu, 09 May 2024 13:07:16 -0400 X-MC-Unique: Y19FXQdzO2eI8S9NubSUHw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 71A903802292; Thu, 9 May 2024 17:07:14 +0000 (UTC) Received: from file1-rdu.file-001.prod.rdu2.dc.redhat.com (unknown [10.11.5.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CB1CB1169588; Thu, 9 May 2024 17:07:13 +0000 (UTC) Received: by file1-rdu.file-001.prod.rdu2.dc.redhat.com (Postfix, from userid 12668) id A5F3A30C1B8F; Thu, 9 May 2024 17:07:13 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by file1-rdu.file-001.prod.rdu2.dc.redhat.com (Postfix) with ESMTP id 9F5133E683; Thu, 9 May 2024 19:07:13 +0200 (CEST) Date: Thu, 9 May 2024 19:07:13 +0200 (CEST) From: Mikulas Patocka To: Fan Wu cc: corbet@lwn.net, zohar@linux.ibm.com, jmorris@namei.org, serge@hallyn.com, tytso@mit.edu, ebiggers@kernel.org, axboe@kernel.dk, agk@redhat.com, snitzer@kernel.org, eparis@redhat.com, paul@paul-moore.com, linux-doc@vger.kernel.org, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, fsverity@lists.linux.dev, linux-block@vger.kernel.org, dm-devel@lists.linux.dev, audit@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v18 12/21] dm: add finalize hook to target_type In-Reply-To: <212b02a8-f5f0-4433-a726-1639dda61790@linux.microsoft.com> Message-ID: References: <1714775551-22384-1-git-send-email-wufan@linux.microsoft.com> <1714775551-22384-13-git-send-email-wufan@linux.microsoft.com> <212b02a8-f5f0-4433-a726-1639dda61790@linux.microsoft.com> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 On Wed, 8 May 2024, Fan Wu wrote: > > > On 5/8/2024 10:17 AM, Mikulas Patocka wrote: > > > > > > On Fri, 3 May 2024, Fan Wu wrote: > > > >> This patch adds a target finalize hook. > >> > >> The hook is triggered just before activating an inactive table of a > >> mapped device. If it returns an error the __bind get cancelled. > >> > >> The dm-verity target will use this hook to attach the dm-verity's > >> roothash metadata to the block_device struct of the mapped device. > >> > >> Signed-off-by: Fan Wu > > > > Hi > > > > Why not use the preresume callback? > > > > Is there some reason why do we need a new callback instead of using the > > existing one? > > > > Mikulas > Thanks for the suggestion. > > Mike suggested the new finalize() callback. I think the reason for not using > the preresume() callback is that there are multiple points that can fail > before activating an inactive table of a mapped device which can potentially > lead to inconsistent state. > > In our specific case, we are trying to associate dm-verity's roothash metadata > with the block_device struct of the mapped device inside the callback. > > If we use the preresume() callback for the work and an error occurs between > the callback and the table activation, this leave the block_device struct in > an inconsistent state. The preresume callback is the final GO/NO-GO decision point. If all the targets return zero in their preresume callback, then there's no turning back and the table will be activated. > This is because now the block device contains the roothash metadata of it's > inactive table due to the preresume() callback, but the activation failed so > the mapped device is still using the old table. > > The new finalize() callback guarantees that the callback happens just before > the table activation, thus avoiding the inconsistency. In your patch, it doesn't guarantee that. do_resume calls dm_swap_table, dm_swap_table calls __bind, __bind calls ti->type->finalize. Then we go back to do_resume and call dm_resume which calls __dm_resume which calls dm_table_resume_targets which calls the preresume callback on all the targets. If some of them fails, it returns a failure (despite the fact that ti->type->finalize succeeded), if all of them succeed, it calls the resume callback on all of them. So, it seems that the preresume callback provides the guarantee that you looking for. > -Fan Mikulas