Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <7222772aed3bf4651dc4ed580ade3e6bd33b253d.camel@linux.ibm.com>
Subject: Re: [PATCH] ima: fix deadlock when traversing "ima_default_rules".
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     liqiong <liqiong@nfschina.com>, Simon.THOBY@viveris.fr
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
Date:   Thu, 30 Sep 2021 15:46:52 -0400
In-Reply-To: <20210918031139.22674-1-liqiong@nfschina.com>
References: <20210827103536.4149-1-liqiong@nfschina.com>
         <20210918031139.22674-1-liqiong@nfschina.com>
Content-Type: text/plain; charset="ISO-8859-15"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi Liqiong,

On Sat, 2021-09-18 at 11:11 +0800, liqiong wrote:
> 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 <liqiong@nfschina.com>
> Reviewed-by: THOBY Simon <Simon.THOBY@viveris.fr>
> Fixes: 38d859f991f3 ("IMA: policy can now be updated multiple times")
> Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Fix sparse: incompatible types in comparison expression.

The "Fix sparse" line shouldn't be on a separate line.  Either post the
one line fix as a separate patch using the normal "Fixes:" tag or fix
the "Reported-by" line, as previously suggested.

thanks,

Mimi