IMA: Defined delayed workqueue to free the queued keys

Keys queued for measurement should be freed if a custom IMA policy
was not loaded.  Otherwise, the keys will remain queued forever
consuming kernel memory.

This patch defines a delayed workqueue to handle the above scenario.
The workqueue handler is setup to execute 5 minutes after IMA
initialization is completed.

If a custom IMA policy is loaded before the workqueue handler is
scheduled to execute, the workqueue task is cancelled and any queued keys
are processed for measurement.  But if a custom policy was not loaded then
the queued keys are just freed when the delayed workqueue handler is run.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Reported-by: kernel test robot <rong.a.chen@intel.com> # sleeping
function called from invalid context
Reported-by: kbuild test robot <lkp@intel.com> # redefinition of
ima_init_key_queue() function.
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/ima/ima.h

@@ -215,11 +215,13 @@ struct ima_key_entry {
 	size_t payload_len;
 	char *keyring_name;
 };
+void ima_init_key_queue(void);
 bool ima_should_queue_key(void);
 bool ima_queue_key(struct key *keyring, const void *payload,
 		   size_t payload_len);
 void ima_process_queued_keys(void);
 #else
+static inline void ima_init_key_queue(void) {}
 static inline bool ima_should_queue_key(void) { return false; }
 static inline bool ima_queue_key(struct key *keyring,
 				 const void *payload,

security/integrity/ima/ima_init.c

@@ -131,5 +131,11 @@ int __init ima_init(void)
 
 	ima_init_policy();
 
-	return ima_fs_init();
+	rc = ima_fs_init();
+	if (rc != 0)
+		return rc;
+
+	ima_init_key_queue();
+
+	return rc;
 }

security/integrity/ima/ima_queue_keys.c

@@ -10,6 +10,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/workqueue.h>
 #include <keys/asymmetric-type.h>
 #include "ima.h"
 
@@ -25,6 +26,36 @@ static bool ima_process_keys;
 static DEFINE_MUTEX(ima_keys_lock);
 static LIST_HEAD(ima_keys);
 
+/*
+ * If custom IMA policy is not loaded then keys queued up
+ * for measurement should be freed. This worker is used
+ * for handling this scenario.
+ */
+static long ima_key_queue_timeout = 300000; /* 5 Minutes */
+static void ima_keys_handler(struct work_struct *work);
+static DECLARE_DELAYED_WORK(ima_keys_delayed_work, ima_keys_handler);
+static bool timer_expired;
+
+/*
+ * This worker function frees keys that may still be
+ * queued up in case custom IMA policy was not loaded.
+ */
+static void ima_keys_handler(struct work_struct *work)
+{
+	timer_expired = true;
+	ima_process_queued_keys();
+}
+
+/*
+ * This function sets up a worker to free queued keys in case
+ * custom IMA policy was never loaded.
+ */
+void ima_init_key_queue(void)
+{
+	schedule_delayed_work(&ima_keys_delayed_work,
+			      msecs_to_jiffies(ima_key_queue_timeout));
+}
+
 static void ima_free_key_entry(struct ima_key_entry *entry)
 {
 	if (entry) {
@@ -119,13 +150,16 @@ void ima_process_queued_keys(void)
 	if (!process)
 		return;
 
+	if (!timer_expired)
+		cancel_delayed_work_sync(&ima_keys_delayed_work);
 
 	list_for_each_entry_safe(entry, tmp, &ima_keys, list) {
-		process_buffer_measurement(entry->payload,
-					   entry->payload_len,
-					   entry->keyring_name,
-					   KEY_CHECK, 0,
-					   entry->keyring_name);
+		if (!timer_expired)
+			process_buffer_measurement(entry->payload,
+						   entry->payload_len,
+						   entry->keyring_name,
+						   KEY_CHECK, 0,
+						   entry->keyring_name);
 		list_del(&entry->list);
 		ima_free_key_entry(entry);
 	}