Re: [PATCH v8 4/8] IMA: add policy rule to measure critical data

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

On 2020-12-11 4:25 p.m., Tyler Hicks wrote:
> On 2020-12-11 15:58:03, 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@linux.microsoft.com>
>> ---
>>   Documentation/ABI/testing/ima_policy |  2 +-
>>   security/integrity/ima/ima_policy.c  | 34 ++++++++++++++++++++++++----
>>   2 files changed, 31 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
>> index e35263f97fc1..6ec7daa87cba 100644
>> --- a/Documentation/ABI/testing/ima_policy
>> +++ b/Documentation/ABI/testing/ima_policy
>> @@ -32,7 +32,7 @@ Description:
>>   			func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK]MODULE_CHECK]
>>   			        [FIRMWARE_CHECK]
>>   				[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
>> -				[KEXEC_CMDLINE] [KEY_CHECK]
>> +				[KEXEC_CMDLINE] [KEY_CHECK] [CRITICAL_DATA]
>>   			mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
>>   			       [[^]MAY_EXEC]
>>   			fsmagic:= hex value
>> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
>> index a09d1a41a290..07116ff35c25 100644
>> --- a/security/integrity/ima/ima_policy.c
>> +++ b/security/integrity/ima/ima_policy.c
>> @@ -85,6 +85,7 @@ 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 */
> 
> Argh, there are still some more instances of data_source sneaking into
> this patch too early instead of waiting until the next patch.
> 
I kept it purposefully in this patch so that the
"case CRITICAL_DATA:" could be properly defined.

Also, my impression was rule->data_source is not part of the user facing
policy.

Whereas IMA_DATA_SOURCE, Opt_data_source, data_source=%s are.
That's why they are part of Patch #5.

Patch #5 IMA: limit critical data measurement based on a label

>>   	struct ima_template_desc *template;
>>   };
>>   
>> @@ -479,6 +480,12 @@ static bool ima_match_rule_data(struct ima_rule_entry *rule,
>>   
>>   		opt_list = rule->keyrings;
>>   		break;
>> +	case CRITICAL_DATA:
>> +		if (!rule->data_source)
>> +			return true;
>> +
>> +		opt_list = rule->data_source;
>> +		break;
> 
> I guess this case should unconditionally return true in this patch and
> then the include this additional logic in the next patch.
> 
> Sorry, I missed these on my last review.
> 
No worries.

As I mentioned above, I kept it purposefully in this patch since
my impression was rule->data_source is not part of the user facing
policy.

But I can simply return true here as you suggested, and move the logic 
to the next patch.

+	case CRITICAL_DATA:
+		if (!rule->data_source)
+			return true;
+
+		opt_list = rule->data_source;
+		break;


~Tushar