linux-kernel - Re: [PATCH] ima: fix infinite loop within "ima_match

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Date:   Mon, 23 Aug 2021 07:22:52 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     李力琼 <liqiong@...china.com>,
        THOBY Simon <Simon.THOBY@...eris.fr>
Cc:     "dmitry.kasatkin@...il.com" <dmitry.kasatkin@...il.com>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ima: fix infinite loop within "ima_match_policy"
 function.

Hi Liqiong,

On Mon, 2021-08-23 at 11:04 +0800, 李力琼 wrote:
> Hi Mimi :
> 
> The situation is a little different,'list_splice_init_rcu'
> don't change the list head. If "ima_rules" being changed,
> readers may can't reload the new value in time for cpu cache
> or compiler optimization. Defining "ima_rules" as a volatile 
> variable can fix, but It is inefficient.

After looking at list_splice_tail_init_rcu() some more, it is
actually making sure there aren't any readers traversing
"ima_temp_rules", not "ima_policy_rules".   There aren't any readers
traversing "ima_temp_rules". 

> 
> Maybe using a temporary ima_rules variable for every 
> "list_for_each_entry_rcu(entry, ima_rules, list)" loop is 
> a better solution to fix the "endless loop" bug. 

Agreed

thanks,

Mimi