linux-kernel - Re: [PATCH v7 4/8] IMA: add policy rule to measure critical data

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Message-ID: <472dc503-295c-1723-b329-c9e08fff4574@linux.microsoft.com>
Date:   Thu, 10 Dec 2020 19:28:15 -0800
From:   Tushar Sugandhi <tusharsu@...ux.microsoft.com>
To:     Tyler Hicks <tyhicks@...ux.microsoft.com>
Cc:     zohar@...ux.ibm.com, stephen.smalley.work@...il.com,
        casey@...aufler-ca.com, agk@...hat.com, snitzer@...hat.com,
        gmazyland@...il.com, paul@...l-moore.com, sashal@...nel.org,
        jmorris@...ei.org, nramas@...ux.microsoft.com,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: [PATCH v7 4/8] IMA: add policy rule to measure critical data



On 2020-12-10 3:10 p.m., Tyler Hicks wrote:
> On 2020-12-09 11:42:08, Tushar Sugandhi wrote:
>> A new IMA policy rule is needed for the IMA hook
>> ima_measure_critical_data() and the corresponding func CRITICAL_DATA for
>> measuring the input buffer. The policy rule should ensure the buffer
>> would get measured only when the policy rule allows the action. The
>> policy rule should also support the necessary constraints (flags etc.)
>> for integrity critical buffer data measurements.
>>
>> Add a policy rule to define the constraints for restricting integrity
>> critical data measurements.
>>
>> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>> ---
>>   security/integrity/ima/ima_policy.c | 35 +++++++++++++++++++++++++----
>>   1 file changed, 31 insertions(+), 4 deletions(-)
>>
>> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
>> index 2a0c0603626e..9a8ee80a3128 100644
>> --- a/security/integrity/ima/ima_policy.c
>> +++ b/security/integrity/ima/ima_policy.c
>> @@ -34,6 +34,7 @@
>>   #define IMA_PCR		0x0100
>>   #define IMA_FSNAME	0x0200
>>   #define IMA_KEYRINGS	0x0400
>> +#define IMA_DATA_SOURCE	0x0800
> 
> You introduce data_source= in the next patch. This macro shouldn't be
> added until the next patch.
> 
Ok I will move IMA_DATA_SOURCE to the next patch.

>>   
>>   #define UNKNOWN		0
>>   #define MEASURE		0x0001	/* same as IMA_MEASURE */
>> @@ -85,6 +86,7 @@ struct ima_rule_entry {
>>   	} lsm[MAX_LSM_RULES];
>>   	char *fsname;
>>   	struct ima_rule_opt_list *keyrings; /* Measure keys added to these keyrings */
>> +	struct ima_rule_opt_list *data_source; /* Measure data from this source */
>>   	struct ima_template_desc *template;
>>   };
>>   
>> @@ -479,6 +481,12 @@ static bool ima_match_rule_data(struct ima_rule_entry *rule,
>>   		else
>>   			opt_list = rule->keyrings;
>>   		break;
>> +	case CRITICAL_DATA:
>> +		if (!rule->data_source)
>> +			return true;
>> +		else
>> +			opt_list = rule->data_source;
> 
> If you take my suggestions on patch #1, remove the else and simply
> assign opt_list here, too.
> 
Yup. Will do.
>> +		break;
>>   	default:
>>   		break;
>>   	}
>> @@ -518,13 +526,19 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
>>   {
>>   	int i;
>>   
>> -	if (func == KEY_CHECK) {
>> -		return (rule->flags & IMA_FUNC) && (rule->func == func) &&
>> -			ima_match_rule_data(rule, func_data, cred);
>> -	}
>>   	if ((rule->flags & IMA_FUNC) &&
>>   	    (rule->func != func && func != POST_SETATTR))
>>   		return false;
>> +
>> +	switch (func) {
>> +	case KEY_CHECK:
>> +	case CRITICAL_DATA:
>> +		return ((rule->func == func) &&
>> +			ima_match_rule_data(rule, func_data, cred));
>> +	default:
>> +		break;
>> +	}
>> +
>>   	if ((rule->flags & IMA_MASK) &&
>>   	    (rule->mask != mask && func != POST_SETATTR))
>>   		return false;
>> @@ -1119,6 +1133,19 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
>>   		if (ima_rule_contains_lsm_cond(entry))
>>   			return false;
>>   
>> +		break;
>> +	case CRITICAL_DATA:
>> +		if (entry->action & ~(MEASURE | DONT_MEASURE))
>> +			return false;
>> +
>> +		if (!(entry->flags & IMA_DATA_SOURCE) ||
>> +		    (entry->flags & ~(IMA_FUNC | IMA_UID | IMA_PCR |
>> +		    IMA_DATA_SOURCE)))
> 
> IMA_DATA_SOURCE shouldn't exist in this patch. This isn't the right
> indentation, either. See how IMA_KEYRINGS is indented in the KEY_CHECK
> case above.
> 
Will do.
~Tushar
> Tyler
> 
>> +			return false;
>> +
>> +		if (ima_rule_contains_lsm_cond(entry))
>> +			return false;
>> +
>>   		break;
>>   	default:
>>   		return false;
>> -- 
>> 2.17.1
>>