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=-15.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 21F21C43214 for ; Fri, 27 Aug 2021 06:42:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0293D60FC4 for ; Fri, 27 Aug 2021 06:42:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242469AbhH0GnI (ORCPT ); Fri, 27 Aug 2021 02:43:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54576 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230522AbhH0GnG (ORCPT ); Fri, 27 Aug 2021 02:43:06 -0400 Received: from ha0.nfschina.com (unknown [IPv6:2400:dd01:100f:2:d63d:7eff:fe08:eb3f]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 047E3C061757; Thu, 26 Aug 2021 23:42:16 -0700 (PDT) Received: from localhost (unknown [127.0.0.1]) by ha0.nfschina.com (Postfix) with ESMTP id EC8AAAE0DCB; Fri, 27 Aug 2021 14:41:18 +0800 (CST) X-Virus-Scanned: amavisd-new at test.com Received: from ha0.nfschina.com ([127.0.0.1]) by localhost (ha0.nfschina.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id bonB99NEQbAx; Fri, 27 Aug 2021 14:40:58 +0800 (CST) Received: from [172.30.18.174] (unknown [180.167.10.98]) (Authenticated sender: liqiong@nfschina.com) by ha0.nfschina.com (Postfix) with ESMTPA id CFABBAE0DB0; Fri, 27 Aug 2021 14:40:57 +0800 (CST) Subject: Re: [PATCH] ima: fix deadlock within RCU list of ima_rules To: THOBY Simon , Mimi Zohar Cc: "dmitry.kasatkin@gmail.com" , "jmorris@namei.org" , "serge@hallyn.com" , "linux-integrity@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20210819101529.28001-1-liqiong@nfschina.com> <20210824085747.23604-1-liqiong@nfschina.com> <3ba4da9d-fa7b-c486-0c48-67cee4d5de6d@nfschina.com> <2c4f61ff68544b2627fc4a38ad1e4109184ec68a.camel@linux.ibm.com> <5a032a1b-f763-a0e4-8ea2-803872bd7174@nfschina.com> <1e464ae0-28e1-6511-ab89-52b5cd1a0841@nfschina.com> <3ef6906b-ccf1-0ab8-180b-b71568e22443@viveris.fr> From: liqiong Message-ID: Date: Fri, 27 Aug 2021 14:41:52 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <3ef6906b-ccf1-0ab8-180b-b71568e22443@viveris.fr> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Simon, Thanks for you help, i may got it, here is the new commit message: The current IMA ruleset is identified by the variable "ima_rules" that default to "&ima_default_rules". When loading a custom policy for the first time, the variable is updated to "&ima_policy_rules" instead. That update isn't RCU-safe, and deadlocks are possible. Because some functions like ima_match_policy() may loop indefinitely over traversing the "ima_default_rules" as list_for_each_entry_rcu(). When iterating over the default ruleset back to head, value of "&entry->list" is "&ima_default_rules", and "ima_rules" may have been updated to "&ima_policy_rules", the loop condition (&entry->list != ima_rules) stay alway true, traversing doesn't terminate, cause soft lockup and RCU stalls. Introduce a temporary value for "ima_rules" when iterating over the ruleset to avoid the deadlocks. Signed-off-by: liqiong --- security/integrity/ima/ima_policy.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index fd5d46e511f1..e92b197bfd3c 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c Thanks liqiong 在 2021年08月26日 17:01, THOBY Simon 写道: > Hi liqiong, > > On 8/26/21 10:15 AM, liqiong wrote: >> Hi Simon, >> >> Thanks for your help, your advice is clear, can i just use it, >> how about this: >> >> >> The current IMA ruleset is identified by the variable "ima_rules", >> and the pointer starts pointing at the list "ima_default_rules". > After reading it again, maybe > "The current IMA ruleset is identified by the variable "ima_rules", > that defaults to "&ima_default_rules".'? > >> When loading a custom policy for the first time, the variable is >> updated to point to the list "ima_policy_rules" instead. That update >> isn't RCU-safe, and deadlocks are possible. > I think what Mimi was trying to say is that you could add the high-level > overview above, but keep the details. Sorry if I wasn't clearer in my > earlier messages. > > Consider re-adding your previous paragraph > """ > As a consequence, when traversing the ruleset, some functions like ima_match_policy() > may loop indefinitely over "ima_default_rules" as list_for_each_entry_rcu() doesn't > terminate (after the update, "ima_rules" no longer points to the list head, so the > loop condition stays always true), causing RCU stalls. > """ > (note: I tweaked it above, feel free to fix it) >> Introduce a temporary value for "ima_rules" when iterating over >> the ruleset to avoid the deadlocks. > ... while keeping this a separate paragraph. > >> >> Signed-off-by: liqiong >> --- >> security/integrity/ima/ima_policy.c | 17 ++++++++++++----- >> 1 file changed, 12 insertions(+), 5 deletions(-) >> >> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c >> index fd5d46e511f1..e92b197bfd3c 100644 >> --- a/security/integrity/ima/ima_policy.c >> +++ b/security/integrity/ima/ima_policy.c >> >> >> >> Thanks >> >> liqiong