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

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Message-ID: <31A92AAB-5516-4176-A947-128CB65B6931@mip-labs.com>
Date:	Tue, 22 Dec 2015 23:40:03 +0200
From:	Petko Manolov <petkan@...-labs.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Sasha Levin <sasha.levin@...cle.com>
CC:	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 December 22, 2015 9:56:28 PM GMT+02:00, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
>On Tue, 2015-12-22 at 08:51 -0500, Sasha Levin wrote:
>> Commit "IMA: policy can now be updated multiple times" assumed that
>the
>> policy would be updated at least once.
>> 
>> If there are zero updates, the temporary list head object will get
>added
>> to the policy list, and later dereferenced as an IMA policy object,
>which
>> means that invalid memory will be accessed.
>> 
>> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
>> ---
>>  security/integrity/ima/ima_policy.c |    3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/security/integrity/ima/ima_policy.c
>b/security/integrity/ima/ima_policy.c
>> index ba5d2fc..9b958b8 100644
>> --- a/security/integrity/ima/ima_policy.c
>> +++ b/security/integrity/ima/ima_policy.c
>> @@ -431,6 +431,9 @@ void ima_update_policy(void)
>>  {
>>  	struct list_head *first, *last, *policy;
>> 
>> +	if (list_empty(&ima_temp_rules))
>> +		return;
>> +
>>  	/* append current policy with the new rules */
>>  	first = (&ima_temp_rules)->next;
>>  	last = (&ima_temp_rules)->prev;
>
>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.


cheers,
Petko




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