Re: [PATCH] ima: fix deadlock within RCU list of ima_rules

From: THOBY Simon <Simon.THOBY@viveris.fr>
To: liqiong <liqiong@nfschina.com>, Mimi Zohar <zohar@linux.ibm.com>
Cc: "dmitry.kasatkin@gmail.com" <dmitry.kasatkin@gmail.com>,
	"jmorris@namei.org" <jmorris@namei.org>,
	"serge@hallyn.com" <serge@hallyn.com>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ima: fix deadlock within RCU list of ima_rules
Date: Wed, 25 Aug 2021 12:03:50 +0000	[thread overview]
Message-ID: <eb9921ff-2d4b-136f-b7a7-924e61a0651b@viveris.fr> (raw)
In-Reply-To: <5a032a1b-f763-a0e4-8ea2-803872bd7174@nfschina.com>

Hi Liqiong,

On 8/25/21 1:45 PM, liqiong wrote:
> Hi Mimi,
> 
> This copy may be better.
> 
> 
> subject: ima: fix deadlock when iterating over the init "ima_rules" list.
> 
> 

As Mimi said, consider adding an introducing paragraph, like:
'The current IMA ruleset is identified by the variable "ima_rules",
and the pointer starts pointing at the list "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.'

> 
> 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.

Per the process (see 'Documentation/process/submitting-patches.rst'),
please prefer an imperative style (written in another paragraph):
'Introduce a temporary value for "ima_rules" when iterating over the ruleset.'

Thanks,
Simon