Message-ID: <1450874832.2774.37.camel@linux.vnet.ibm.com>
Subject: Re: [Linux-ima-devel] [PATCH] IMA: policy can be updated zero times
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Petko Manolov <petkan@mip-labs.com>, Sasha Levin <sasha.levin@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org,
        james.l.morris@oracle.com,
        linux-ima-devel <linux-ima-devel@lists.sourceforge.net>
Date: Wed, 23 Dec 2015 07:47:12 -0500
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On Wed, 2015-12-23 at 07:24 -0500, Mimi Zohar wrote:
> On Wed, 2015-12-23 at 13:47 +0200, Petko Manolov wrote:
> 
> > 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@mip-labs.com>
> > 
> > Mimi, shall we change ima_parse_add_rule's behavior in the future or it's too 
> > much work?
> 
> ima_parse_add_rules() has no way of knowing if the policy as a whole is
> valid.  I would define a new function in ima_policy.c to return the
> number of rules being added and call it at the beginning of
> ima_release_policy() before the status message.  That way the number of
> rules added can be included in the status message.
> 
> For now, the function could just return have rules or no rules, instead
> of the number of rules.

Sasha, could you make your fix a separate function (above
ima_update_policy) and call it from ima_release_policy()?

Thanks!

Mimi

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