linux-kernel - [PATCH v1] IMA: Defined timer to free queued keys

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Message-Id: <20191223032454.2797-1-nramas@linux.microsoft.com>
Date:   Sun, 22 Dec 2019 19:24:54 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     zohar@...ux.ibm.com, James.Bottomley@...senPartnership.com,
        linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: [PATCH v1] IMA: Defined timer to free queued keys

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

This patch defines a timer to handle the above scenario. The timer
is setup to expire 5 minutes after IMA initialization is completed.

If a custom IMA policy is loaded before the timer expires, the timer
is removed and any queued keys are processed for measurement.
But if a custom policy was not loaded, on timer expiration
any queued keys are just freed.

Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
---
 security/integrity/ima/ima.h                 |  2 +
 security/integrity/ima/ima_asymmetric_keys.c | 46 ++++++++++++++++++--
 security/integrity/ima/ima_init.c            |  8 +++-
 3 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 97f8a4078483..c483215a9ee5 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -216,8 +216,10 @@ struct ima_key_entry {
 	char *keyring_name;
 };
 void ima_process_queued_keys(void);
+void ima_init_key_queue(void);
 #else
 static inline void ima_process_queued_keys(void) {}
+static inline void ima_init_key_queue(void) {}
 #endif /* CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE */
 
 /* LIM API function definitions */
diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
index 4124f10ff0c2..e1c4e1e7d9a1 100644
--- a/security/integrity/ima/ima_asymmetric_keys.c
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -11,6 +11,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/timer.h>
 #include <keys/asymmetric-type.h>
 #include "ima.h"
 
@@ -26,6 +27,34 @@ static bool ima_process_keys;
 static DEFINE_MUTEX(ima_keys_mutex);
 static LIST_HEAD(ima_keys);
 
+/*
+ * If custom IMA policy is not loaded then keys queued up
+ * for measurement should be freed. This timer is used
+ * for handling this scenario.
+ */
+static long ima_key_queue_timeout = 300000; /* 5 Minutes */
+static struct timer_list ima_key_queue_timer;
+
+/*
+ * This timer callback function processes keys that may still be
+ * queued up in case custom IMA policy was not loaded.
+ */
+static void ima_timer_handler(struct timer_list *timer)
+{
+	ima_process_queued_keys();
+}
+
+/*
+ * This function sets up a timer to process queued keys in case
+ * custom IMA policy was never loaded.
+ */
+void ima_init_key_queue(void)
+{
+	timer_setup(&ima_key_queue_timer, ima_timer_handler, 0);
+	mod_timer(&ima_key_queue_timer,
+		  jiffies + msecs_to_jiffies(ima_key_queue_timeout));
+}
+
 static void ima_free_key_entry(struct ima_key_entry *entry)
 {
 	if (entry) {
@@ -100,6 +129,7 @@ void ima_process_queued_keys(void)
 {
 	struct ima_key_entry *entry, *tmp;
 	bool process = false;
+	int timer_removed;
 
 	if (ima_process_keys)
 		return;
@@ -120,10 +150,20 @@ void ima_process_queued_keys(void)
 	if (!process)
 		return;
 
+	/*
+	 * Timer is no longer needed. If the timer was removed
+	 * (i.e., the timer had not expired) the queued keys are
+	 * processed for measurement. Else, the keys are just freed.
+	 */
+	timer_removed = del_timer(&ima_key_queue_timer);
+
 	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_removed)
+			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);
 	}
diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index 5d55ade5f3b9..195cb4079b2b 100644
--- a/security/integrity/ima/ima_init.c
+++ b/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;
 }
-- 
2.17.1