TPM: integrity fix

Fix to function which is called by IMA, now tpm_chip_find_get() considers the case in which the machine doesn't have a TPM or, if it has, its TPM isn't enabled.
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

drivers/char/tpm/tpm.c

@@ -666,18 +666,20 @@ EXPORT_SYMBOL_GPL(tpm_show_temp_deactivated);
  */
 static struct tpm_chip *tpm_chip_find_get(int chip_num)
 {
-	struct tpm_chip *pos;
+	struct tpm_chip *pos, *chip = NULL;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(pos, &tpm_chip_list, list) {
 		if (chip_num != TPM_ANY_NUM && chip_num != pos->dev_num)
 			continue;
 
-		if (try_module_get(pos->dev->driver->owner))
+		if (try_module_get(pos->dev->driver->owner)) {
+			chip = pos;
 			break;
+		}
 	}
 	rcu_read_unlock();
-	return pos;
+	return chip;
 }
 
 #define TPM_ORDINAL_PCRREAD cpu_to_be32(21)