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

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Message-ID: <ed27351e0574f58ee59a3024554b8b0c7293515f.camel@linux.ibm.com>
Date:   Thu, 19 Aug 2021 09:47:20 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     THOBY Simon <Simon.THOBY@...eris.fr>,
        liqiong <liqiong@...china.com>
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.

On Thu, 2021-08-19 at 12:58 +0000, THOBY Simon wrote:
> Hi Liqiong,
> 
> On 8/19/21 12:15 PM, liqiong wrote:
> > When "ima_match_policy" is looping while "ima_update_policy" changs
> > the variable "ima_rules", then "ima_match_policy" may can't exit loop,
> > and kernel keeps printf "rcu_sched detected stall on CPU ...".
> > 
> > It occurs at boot phase, systemd-services are being checked within
> > "ima_match_policy,at the same time, the variable "ima_rules"
> > is changed by a service.
> 
> First off, thanks for finding and identifying this nasty bug.

Once the initial builtin policy rules have been replaced by a custom
policy, rules may only be appended by splicing the new rules with the
existing rules.  There should never be a problem reading the rules at
that point.   Does this problem occur before the builtin policy rules
have been replaced with a custom policy?

Mimi