ima: change integrity cache to store measured pcr

IMA avoids re-measuring files by storing the current state as a flag in
the integrity cache. It will then skip adding a new measurement log entry
if the cache reports the file as already measured.

If a policy measures an already measured file to a new PCR, the measurement
will not be added to the list. This patch implements a new bitfield for
specifying which PCR the file was measured into, rather than if it was
measured.
Signed-off-by: Eric Richter <erichte@linux.vnet.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/ima/ima_api.c

@@ -266,7 +266,7 @@ void ima_store_measurement(struct integrity_iint_cache *iint,
 					    xattr_len, NULL};
 	int violation = 0;
 
-	if (iint->flags & IMA_MEASURED)
+	if (iint->measured_pcrs & (0x1 << pcr))
 		return;
 
 	result = ima_alloc_init_template(&event_data, &entry);
@@ -277,8 +277,10 @@ void ima_store_measurement(struct integrity_iint_cache *iint,
 	}
 
 	result = ima_store_template(entry, violation, inode, filename, pcr);
-	if (!result || result == -EEXIST)
+	if (!result || result == -EEXIST) {
 		iint->flags |= IMA_MEASURED;
+		iint->measured_pcrs |= (0x1 << pcr);
+	}
 	if (result < 0)
 		ima_free_template_entry(entry);
 }

security/integrity/ima/ima_appraise.c

@@ -370,6 +370,7 @@ static void ima_reset_appraise_flags(struct inode *inode, int digsig)
 		return;
 
 	iint->flags &= ~IMA_DONE_MASK;
+	iint->measured_pcrs = 0;
 	if (digsig)
 		iint->flags |= IMA_DIGSIG;
 	return;

security/integrity/ima/ima_main.c

@@ -125,6 +125,7 @@ static void ima_check_last_writer(struct integrity_iint_cache *iint,
 		if ((iint->version != inode->i_version) ||
 		    (iint->flags & IMA_NEW_FILE)) {
 			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
+			iint->measured_pcrs = 0;
 			if (iint->flags & IMA_APPRAISE)
 				ima_update_xattr(iint, file);
 		}
@@ -210,7 +211,11 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
 	 */
 	iint->flags |= action;
 	action &= IMA_DO_MASK;
-	action &= ~((iint->flags & IMA_DONE_MASK) >> 1);
+	action &= ~((iint->flags & (IMA_DONE_MASK ^ IMA_MEASURED)) >> 1);
+
+	/* If target pcr is already measured, unset IMA_MEASURE action */
+	if ((action & IMA_MEASURE) && (iint->measured_pcrs & (0x1 << pcr)))
+		action ^= IMA_MEASURE;
 
 	/* Nothing to do, just return existing appraised status */
 	if (!action) {