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=-9.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 79FBCC43603 for ; Wed, 18 Dec 2019 02:44:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4F1AE218AC for ; Wed, 18 Dec 2019 02:44:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="LMCpS0kR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726587AbfLRCoG (ORCPT ); Tue, 17 Dec 2019 21:44:06 -0500 Received: from linux.microsoft.com ([13.77.154.182]:51418 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726467AbfLRCoF (ORCPT ); Tue, 17 Dec 2019 21:44:05 -0500 Received: from [10.137.112.111] (unknown [131.107.147.111]) by linux.microsoft.com (Postfix) with ESMTPSA id A3D262010BB5; Tue, 17 Dec 2019 18:44:04 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com A3D262010BB5 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1576637044; bh=lhbqkcIxtSGFiHrpURYzmG/2lyOyf1FLYAbQkLhbFoM=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=LMCpS0kRwj8p+N5zhvFRGGx/1yYQCKbwK8lQFQb55D9dE72G9lNdS/OsftJWwrlfb Do3v/0cq4iDtnX0naXP9sAL92Moq0BnzNJKM9aYEt3njkeqxqdTEFfOV2kc7FnzbMy rEMdH/5+zzH3qNSrcIvA/jYFul8XA9cbn8/eV1xs= Subject: Re: [PATCH v4 2/2] IMA: Call workqueue functions to measure queued keys To: James Bottomley , zohar@linux.ibm.com, linux-integrity@vger.kernel.org Cc: eric.snowberg@oracle.com, dhowells@redhat.com, mathew.j.martineau@linux.intel.com, matthewgarrett@google.com, sashal@kernel.org, jamorris@linux.microsoft.com, linux-kernel@vger.kernel.org, keyrings@vger.kernel.org References: <20191213171827.28657-1-nramas@linux.microsoft.com> <20191213171827.28657-3-nramas@linux.microsoft.com> <1576257955.8504.20.camel@HansenPartnership.com> <39624b97-245c-ed05-27c5-588787aacc00@linux.microsoft.com> <1576423353.3343.3.camel@HansenPartnership.com> <1568ff14-316f-f2c4-84d4-7ca4c0a1936a@linux.microsoft.com> <1576479187.3784.1.camel@HansenPartnership.com> <8844a360-6d1e-1435-db7c-fd7739487168@linux.microsoft.com> <1576531022.3365.6.camel@HansenPartnership.com> <35a6c241-9a46-2657-51d1-0c04d32a9fae@linux.microsoft.com> <152580f3-2a1f-fa33-cc25-f25747a470a5@linux.microsoft.com> <1576634499.14900.10.camel@HansenPartnership.com> From: Lakshmi Ramasubramanian Message-ID: Date: Tue, 17 Dec 2019 18:44:31 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <1576634499.14900.10.camel@HansenPartnership.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On 12/17/2019 6:01 PM, James Bottomley wrote: > > This code is confusing me: > > + /* > + * To avoid holding the mutex when processing queued keys, > + * transfer the queued keys with the mutex held to a temp list, > + * release the mutex, and then process the queued keys from > + * the temp list. > + * > + * Since ima_process_keys is set to true, any new key will be > + * processed immediately and not be queued. > + */ > + INIT_LIST_HEAD(&temp_ima_keys); > + > + mutex_lock(&ima_keys_mutex); > + > + if (!ima_process_keys) { > + ima_process_keys = true; > + > + if (!list_empty(&ima_keys)) { > + list_for_each_entry_safe(entry, tmp, &ima_keys, list) > + list_move_tail(&entry->list, &temp_ima_keys); > + process = true; > + } > + } > + > + mutex_unlock(&ima_keys_mutex); > + > > The direct implication of the comment and the lock dance with the > temporary list and the processed flag is that stuff can be added to the > ima_keys list after you drop the mutex. Your explanation in the prior > couple of emails says that nothing can be added because the > ima_process_keys flag setting prevents it. If the latter is true, you > can simply drop the lock after setting the flag and rely on ima_keys > not changing to run it through process_buffer_measurement without > needing any of the intermediate list or the processed flag. If the > latter isn't true then any key added to ima_keys after the mutex is > dropped is never processed. > > James Once the flag is set no new key will be added to ima_keys list. You are right - if the flag is set with the lock taken, then there is no need for the temp list. After dropping the lock, measurement can be done directly from ima_keys list. Thanks for reviewing the code. I'll send an update tomorrow. -lakshmi