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=-17.5 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 8CD8EC432BE for ; Wed, 25 Aug 2021 11:46:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6140C60ED6 for ; Wed, 25 Aug 2021 11:46:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240219AbhHYLqr (ORCPT ); Wed, 25 Aug 2021 07:46:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232199AbhHYLqq (ORCPT ); Wed, 25 Aug 2021 07:46:46 -0400 Received: from ha0.nfschina.com (unknown [IPv6:2400:dd01:100f:2:d63d:7eff:fe08:eb3f]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E505BC061757; Wed, 25 Aug 2021 04:45:58 -0700 (PDT) Received: from localhost (unknown [127.0.0.1]) by ha0.nfschina.com (Postfix) with ESMTP id 9AD0AAE0DC7; Wed, 25 Aug 2021 19:45:17 +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 bZVhb-isVgmc; Wed, 25 Aug 2021 19:44:56 +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 6768FAE0D1B; Wed, 25 Aug 2021 19:44:56 +0800 (CST) Subject: Re: [PATCH] ima: fix deadlock within RCU list of ima_rules To: Mimi Zohar Cc: THOBY Simon , "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> From: liqiong Message-ID: <5a032a1b-f763-a0e4-8ea2-803872bd7174@nfschina.com> Date: Wed, 25 Aug 2021 19:45:33 +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: 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 Mimi, This copy may be better. subject: ima: fix deadlock when iterating over the init "ima_rules" list. When traversing back to head, the init "ima_rules" list can't exit iterating if "ima_rules" has been updated to "ima_policy_rules". It causes soft lockup and RCU stalls. So we can introduce a duplicate of "ima_rules" for each "ima_rules" list loop. Signed-off-by: liqiong --- This problem can happen in practice: updating the IMA policy in the boot process while systemd-services are being checked. 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 Regards, liqiong 在 2021年08月25日 15:05, liqiong 写道: > Hi Mimi, > > Thanks for the advice，maybe i should trim the message, > here is a new copy: > > > subject: ima: fix deadlock when iterating over the init "ima_rules" list. > > The init "ima_rules" list can't traverse back to head, if "ima_rules" > is being updated to "ima_policy_rules". It causes soft lockup and RCU stalls. > So we can introduce a duplicate of "ima_rules" for each "ima_rules" list loop. > > Signed-off-by: liqiong > --- > This problem can happen in practice: updating the IMA policy > in the boot process while systemd-services are being checked. > > 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 > > > Regards, > > liqiong > > 在 2021年08月24日 20:38, Mimi Zohar 写道: >> On Tue, 2021-08-24 at 20:09 +0800, liqiong wrote: >>> Hi Simon : >>> >>> ima: fix deadlock within RCU list of ima_rules. >>> >> Before the following paragraph, an introductory sentence is needed. >> Try adding a sentence to the affect that "ima_rules" initially points >> to the "ima_default_rules", but after loading a custom policy points to >> the "ima_policy_rules". Then describe the bug at a high level, >> something like - transitioning to the "ima_policy_rules" isn't being >> done safely. >> >> Followed by the details. >> >>> ima_match_policy() is looping on the policy ruleset while >>> ima_update_policy() updates the variable "ima_rules". This can >>> lead to a situation where ima_match_policy() can't exit the >>> 'list_for_each_entry_rcu' loop, causing RCU stalls >>> ("rcu_sched detected stall on CPU ..."). >>> >>> This problem can happen in practice: updating the IMA policy >>> in the boot process while systemd-services are being checked. >>> >>> In addition to ima_match_policy(), other function with >>> "list_for_each_entry_rcu" should happen too. Fix locking by >>> introducing a duplicate of "ima_rules" for each >>> "list_for_each_entry_rcu". >>> >>> >>> How about this commit message ? >>> >>> I have tested this patch in lab, we can reproduced this error case, >>> have done reboot test many times. This patch should work. >> The above comment doesn't belong in the commit message, but is a >> message to the reviewers/maintainers and goes after the patch >> descriptions three dashes line. >> >> thanks, >> >> Mimi >> >> >