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=-9.8 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 B5FC9C3F68F for ; Mon, 16 Dec 2019 21:52:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B50D21739 for ; Mon, 16 Dec 2019 21:52:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="dnrh2CdQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727627AbfLPVwA (ORCPT ); Mon, 16 Dec 2019 16:52:00 -0500 Received: from linux.microsoft.com ([13.77.154.182]:56548 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726275AbfLPVwA (ORCPT ); Mon, 16 Dec 2019 16:52:00 -0500 Received: from [10.137.112.111] (unknown [131.107.147.111]) by linux.microsoft.com (Postfix) with ESMTPSA id 4EFDF2010C1C; Mon, 16 Dec 2019 13:51:59 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 4EFDF2010C1C DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1576533119; bh=WpWDij33SIAh2NLdE1iFnpr1lDw8hAjerLphRfg5j8s=; h=Subject:From:To:Cc:References:Date:In-Reply-To:From; b=dnrh2CdQywSAEHIqti0vrXPOoP3XlYxGnnGbWkyPpM9d0QAvMeq2S3WKqub453VZP 8hIdX9/Z0zHrKzzq8/iOCPYkjqtyMrYuSUbKTD7SI5Fz9aplaoRsHd27OeLNnBW6yS m85vQVBIZ+N2K59leOloIYfclg98fkN9tTLAu1v0= Subject: Re: [PATCH v4 2/2] IMA: Call workqueue functions to measure queued keys From: Lakshmi Ramasubramanian 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> Message-ID: Date: Mon, 16 Dec 2019 13:52:26 -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: <35a6c241-9a46-2657-51d1-0c04d32a9fae@linux.microsoft.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/16/2019 1:37 PM, Lakshmi Ramasubramanian wrote: > > On 12/16/2019 1:17 PM, James Bottomley wrote: >> On Mon, 2019-12-16 at 11:20 -0800, Lakshmi Ramasubramanian wrote: >>>    => If the flag is false, mutex is taken and the flag is checked >>> again. If the flag changed from false to true between the above two >>> tests, that means another thread had raced to call >>> ima_process_queued_keys() and has  processed the queued keys. So >>> again, no further action is required. >> >> This is the problem: in the race case you may still be adding keys to >> the queue after the other thread has processed it. Those keys won't get >> processed because the flag is now false in the post check so the >> current thread won't process them either. >> >> James >> Please keep in mind that ima_queue_key() returns a boolean indicating whether or not the key was queued. This flag is set inside the lock - please see the code snippet from ima_queue_key() below: + mutex_lock(&ima_keys_mutex); + if (!ima_process_keys) { + list_add_tail(&entry->list, &ima_keys); + queued = true; + } + mutex_unlock(&ima_keys_mutex); If ima_process_keys had changed from false to true, ima_queue_key() will not queue the key and return false to ima_post_key_create_or_update(). Code snippet in ima_post_key_create_or_update(): + if (!ima_process_keys) + queued = ima_queue_key(keyring, payload, payload_len); + + if (queued) + return; If the "queued" is false, ima_post_key_create_or_update() will process the key immediately. -lakshmi