ima: use the lsm policy update notifier

Don't do lazy policy updates while running the rule matching,
run the updates as they happen.

Depends on commit f242064c5df3 ("LSM: switch to blocking policy update notifiers")
Signed-off-by: Janne Karhunen <janne.karhunen@gmail.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/ima/ima.h

@@ -154,6 +154,8 @@ unsigned long ima_get_binary_runtime_size(void);
 int ima_init_template(void);
 void ima_init_template_list(void);
 int __init ima_init_digests(void);
+int ima_lsm_policy_change(struct notifier_block *nb, unsigned long event,
+			  void *lsm_data);
 
 /*
  * used to protect h_table and sha_table

security/integrity/ima/ima_main.c

@@ -43,6 +43,10 @@ int ima_appraise;
 int ima_hash_algo = HASH_ALGO_SHA1;
 static int hash_setup_done;
 
+static struct notifier_block ima_lsm_policy_notifier = {
+	.notifier_call = ima_lsm_policy_change,
+};
+
 static int __init hash_setup(char *str)
 {
 	struct ima_template_desc *template_desc = ima_template_desc_current();
@@ -621,6 +625,10 @@ static int __init init_ima(void)
 		error = ima_init();
 	}
 
+	error = register_blocking_lsm_notifier(&ima_lsm_policy_notifier);
+	if (error)
+		pr_warn("Couldn't register LSM notifier, error %d\n", error);
+
 	if (!error)
 		ima_update_policy_flag();
 

security/integrity/ima/ima_policy.c

@@ -249,31 +249,113 @@ static int __init default_appraise_policy_setup(char *str)
 }
 __setup("ima_appraise_tcb", default_appraise_policy_setup);
 
+static void ima_lsm_free_rule(struct ima_rule_entry *entry)
+{
+	int i;
+
+	for (i = 0; i < MAX_LSM_RULES; i++) {
+		kfree(entry->lsm[i].rule);
+		kfree(entry->lsm[i].args_p);
+	}
+	kfree(entry);
+}
+
+static struct ima_rule_entry *ima_lsm_copy_rule(struct ima_rule_entry *entry)
+{
+	struct ima_rule_entry *nentry;
+	int i, result;
+
+	nentry = kmalloc(sizeof(*nentry), GFP_KERNEL);
+	if (!nentry)
+		return NULL;
+
+	/*
+	 * Immutable elements are copied over as pointers and data; only
+	 * lsm rules can change
+	 */
+	memcpy(nentry, entry, sizeof(*nentry));
+	memset(nentry->lsm, 0, FIELD_SIZEOF(struct ima_rule_entry, lsm));
+
+	for (i = 0; i < MAX_LSM_RULES; i++) {
+		if (!entry->lsm[i].rule)
+			continue;
+
+		nentry->lsm[i].type = entry->lsm[i].type;
+		nentry->lsm[i].args_p = kstrdup(entry->lsm[i].args_p,
+						GFP_KERNEL);
+		if (!nentry->lsm[i].args_p)
+			goto out_err;
+
+		result = security_filter_rule_init(nentry->lsm[i].type,
+						   Audit_equal,
+						   nentry->lsm[i].args_p,
+						   &nentry->lsm[i].rule);
+		if (result == -EINVAL)
+			pr_warn("ima: rule for LSM \'%d\' is undefined\n",
+				entry->lsm[i].type);
+	}
+	return nentry;
+
+out_err:
+	ima_lsm_free_rule(nentry);
+	return NULL;
+}
+
+static int ima_lsm_update_rule(struct ima_rule_entry *entry)
+{
+	struct ima_rule_entry *nentry;
+
+	nentry = ima_lsm_copy_rule(entry);
+	if (!nentry)
+		return -ENOMEM;
+
+	list_replace_rcu(&entry->list, &nentry->list);
+	synchronize_rcu();
+	ima_lsm_free_rule(entry);
+
+	return 0;
+}
+
 /*
  * The LSM policy can be reloaded, leaving the IMA LSM based rules referring
  * to the old, stale LSM policy.  Update the IMA LSM based rules to reflect
- * the reloaded LSM policy.  We assume the rules still exist; and BUG_ON() if
- * they don't.
+ * the reloaded LSM policy.
  */
 static void ima_lsm_update_rules(void)
 {
-	struct ima_rule_entry *entry;
-	int result;
-	int i;
+	struct ima_rule_entry *entry, *e;
+	int i, result, needs_update;
 
-	list_for_each_entry(entry, &ima_policy_rules, list) {
+	list_for_each_entry_safe(entry, e, &ima_policy_rules, list) {
+		needs_update = 0;
 		for (i = 0; i < MAX_LSM_RULES; i++) {
-			if (!entry->lsm[i].rule)
+			if (entry->lsm[i].rule) {
+				needs_update = 1;
+				break;
+			}
+		}
+		if (!needs_update)
 			continue;
-			result = security_filter_rule_init(entry->lsm[i].type,
-							   Audit_equal,
-							   entry->lsm[i].args_p,
-							   &entry->lsm[i].rule);
-			BUG_ON(!entry->lsm[i].rule);
+
+		result = ima_lsm_update_rule(entry);
+		if (result) {
+			pr_err("ima: lsm rule update error %d\n",
+				result);
+			return;
 		}
 	}
 }
 
+int ima_lsm_policy_change(struct notifier_block *nb, unsigned long event,
+			  void *lsm_data)
+{
+	if (event != LSM_POLICY_CHANGE)
+		return NOTIFY_DONE;
+
+	ima_lsm_update_rules();
+	return NOTIFY_OK;
+}
+
 /**
  * ima_match_rules - determine whether an inode matches the measure rule.
  * @rule: a pointer to a rule
@@ -327,11 +409,10 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 	for (i = 0; i < MAX_LSM_RULES; i++) {
 		int rc = 0;
 		u32 osid;
-		int retried = 0;
 
 		if (!rule->lsm[i].rule)
 			continue;
-retry:
+
 		switch (i) {
 		case LSM_OBJ_USER:
 		case LSM_OBJ_ROLE:
@@ -352,11 +433,6 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
 		default:
 			break;
 		}
-		if ((rc < 0) && (!retried)) {
-			retried = 1;
-			ima_lsm_update_rules();
-			goto retry;
-		}
 		if (!rc)
 			return false;
 	}