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 615C4C43214 for ; Fri, 27 Aug 2021 09:11:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47CF36054F for ; Fri, 27 Aug 2021 09:11:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244635AbhH0JMK (ORCPT ); Fri, 27 Aug 2021 05:12:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60906 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244624AbhH0JL7 (ORCPT ); Fri, 27 Aug 2021 05:11:59 -0400 Received: from ha0.nfschina.com (unknown [IPv6:2400:dd01:100f:2:d63d:7eff:fe08:eb3f]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 45C02C061757; Fri, 27 Aug 2021 02:11:10 -0700 (PDT) Received: from localhost (unknown [127.0.0.1]) by ha0.nfschina.com (Postfix) with ESMTP id 2CA2FAE0DE1; Fri, 27 Aug 2021 17:10:13 +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 I55RfApHpAp4; Fri, 27 Aug 2021 17:09:49 +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 D5F44AE0DB0; Fri, 27 Aug 2021 17:09:48 +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: <266c50d0-1efd-dc45-d11f-e8c91bfc8490@nfschina.com> Date: Fri, 27 Aug 2021 17:10:44 +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 Simon, Thanks for your patient, i learn a lot. If the commit message does work, i would resubmit the patch. Here is the whole patch: 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. Indeed, some functions like ima_match_policy() may loop indefinitely when traversing "ima_default_rules" with list_for_each_entry_rcu(). When iterating over the default ruleset back to head, if the list head is "ima_default_rules", and "ima_rules" have been updated to "&ima_policy_rules", the loop condition (&entry->list != ima_rules) stays always true, traversing won't terminate, causing a 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 @@ -662,12 +662,14 @@ int ima_match_policy(struct user_namespace *mnt_userns, struct inode *inode, { struct ima_rule_entry *entry; int action = 0, actmask = flags | (flags << 1); + struct list_head *ima_rules_tmp; if (template_desc && !*template_desc) *template_desc = ima_template_desc_current(); rcu_read_lock(); - list_for_each_entry_rcu(entry, ima_rules, list) { + ima_rules_tmp = rcu_dereference(ima_rules); + list_for_each_entry_rcu(entry, ima_rules_tmp, list) { if (!(entry->action & actmask)) continue; @@ -919,8 +921,8 @@ void ima_update_policy(void) if (ima_rules != policy) { ima_policy_flag = 0; - ima_rules = policy; + rcu_assign_pointer(ima_rules, policy); /* * IMA architecture specific policy rules are specified * as strings and converted to an array of ima_entry_rules @@ -1649,9 +1651,11 @@ void *ima_policy_start(struct seq_file *m, loff_t *pos) { loff_t l = *pos; struct ima_rule_entry *entry; + struct list_head *ima_rules_tmp; rcu_read_lock(); - list_for_each_entry_rcu(entry, ima_rules, list) { + ima_rules_tmp = rcu_dereference(ima_rules); + list_for_each_entry_rcu(entry, ima_rules_tmp, list) { if (!l--) { rcu_read_unlock(); return entry; @@ -1670,7 +1674,8 @@ void *ima_policy_next(struct seq_file *m, void *v, loff_t *pos) rcu_read_unlock(); (*pos)++; - return (&entry->list == ima_rules) ? NULL : entry; + return (&entry->list == &ima_default_rules || + &entry->list == &ima_policy_rules) ? NULL : entry; } void ima_policy_stop(struct seq_file *m, void *v) @@ -1872,6 +1877,7 @@ bool ima_appraise_signature(enum kernel_read_file_id id) struct ima_rule_entry *entry; bool found = false; enum ima_hooks func; + struct list_head *ima_rules_tmp; if (id >= READING_MAX_ID) return false; @@ -1879,7 +1885,8 @@ bool ima_appraise_signature(enum kernel_read_file_id id) func = read_idmap[id] ?: FILE_CHECK; rcu_read_lock(); - list_for_each_entry_rcu(entry, ima_rules, list) { + ima_rules_tmp = rcu_dereference(ima_rules); + list_for_each_entry_rcu(entry, ima_rules_tmp, list) { if (entry->action != APPRAISE) continue; -- 2.11.0 在 2021年08月27日 15:30, THOBY Simon 写道: > Hi liqiong, > > a few nits but nothing significant. This is getting in good shape! > > On 8/27/21 8:41 AM, liqiong wrote: >> 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 > s/Because/Indeed,/ (in english, sentences with a subordinating conjunction > like 'because' are usually written in two parts, and a dependent clause > standing by itself is rarely used except for stylistic effect) > >> over traversing the "ima_default_rules" as list_for_each_entry_rcu(). > s/over traversing the "ima_default_rules" as list_for_each_entry_rcu()/when traversing "ima_default_rules" with 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 > s/value of "&entry->list" is "&ima_default_rules"/if the list head is "ima_default_rules"/ > s/may have been/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 > Don't forget the 's' in "stays" (or "remains") > Ditto for "always" > s/traversing doesn't/traversing won't/ > Also: s/cause/causing a/ > >> 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 >> > Thanks, > Simon