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

On 2020-12-11 4:25 p.m., Tyler Hicks wrote:

On 2020-12-11 15:58:03, Tushar Sugandhi wrote:

quoted

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 <redacted>
---
  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

quoted

  	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