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

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

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.

Mimi