linux-kernel - Re: [PATCH] IMA: policy can be updated zero times

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Date:	Wed, 23 Dec 2015 13:47:21 +0200
From:	Petko Manolov <petkan@...-labs.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>, dmitry.kasatkin@...il.com,
	james.l.morris@...cle.com, serge@...lyn.com,
	linux-ima-devel@...ts.sourceforge.net,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IMA: policy can be updated zero times

On 15-12-22 16:50:01, Sasha Levin wrote:
> On 12/22/2015 04:40 PM, Petko Manolov wrote:
> >> Thanks, Sasha.  By the time ima_update_policy() is called
> >> >ima_release_policy() has already output the policy update status
> >> >message.  I guess an empty policy could be considered a valid policy.
> >> >Could you add a msg indicating that the new policy was empty?
> > 
> > As far as I can say we can't get to ima_update_policy() with empty 
> > ima_temp_rules because ima_write_policy() will set valid_policy to 0 in case 
> > of an empty rule.  I'll double check it tomorrow, but please you do that 
> > too.
> 
> This is based on an actual crash rather than code analysis.

I was able to reproduce the crash with: echo "" > /sys/kernel/security/ima/policy

It turns out ima_parse_add_rule() returns 1, even though the string is empty 
This logic may be part of "empty policy is a valid policy" or something else.  
As it is more dangerous to change the behavior at this point i assume your patch 
is the right solution for the problem.

Acked-by: Petko Manolov <petkan@...-labs.com>

Mimi, shall we change ima_parse_add_rule's behavior in the future or it's too 
much work?


cheers,
Petko
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