#include <linux/magic.h>
#include <linux/parser.h>
#include <linux/slab.h>
+#include <linux/rculist.h>
#include <linux/genhd.h>
#include "ima.h"
static LIST_HEAD(ima_default_rules);
static LIST_HEAD(ima_policy_rules);
+static LIST_HEAD(ima_temp_rules);
static struct list_head *ima_rules;
-static DEFINE_MUTEX(ima_rules_mutex);
-
static int ima_policy __initdata;
+
static int __init default_measure_policy_setup(char *str)
{
if (ima_policy)
__setup("ima_appraise_tcb", default_appraise_policy_setup);
/*
- * Although the IMA policy does not change, 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 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.
*/
static void ima_lsm_update_rules(void)
{
- struct ima_rule_entry *entry, *tmp;
+ struct ima_rule_entry *entry;
int result;
int i;
- mutex_lock(&ima_rules_mutex);
- list_for_each_entry_safe(entry, tmp, &ima_policy_rules, list) {
+ list_for_each_entry(entry, &ima_policy_rules, list) {
for (i = 0; i < MAX_LSM_RULES; i++) {
if (!entry->lsm[i].rule)
continue;
BUG_ON(!entry->lsm[i].rule);
}
}
- mutex_unlock(&ima_rules_mutex);
}
/**
* Measure decision based on func/mask/fsmagic and LSM(subj/obj/type)
* conditions.
*
- * (There is no need for locking when walking the policy list,
- * as elements in the list are never deleted, nor does the list
- * change.)
+ * Since the IMA policy may be updated multiple times we need to lock the
+ * list when walking it. Reads are many orders of magnitude more numerous
+ * than writes so ima_match_policy() is classical RCU candidate.
*/
int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask,
int flags)
struct ima_rule_entry *entry;
int action = 0, actmask = flags | (flags << 1);
- list_for_each_entry(entry, ima_rules, list) {
+ rcu_read_lock();
+ list_for_each_entry_rcu(entry, ima_rules, list) {
if (!(entry->action & actmask))
continue;
if (!actmask)
break;
}
+ rcu_read_unlock();
return action;
}
{
struct ima_rule_entry *entry;
- ima_policy_flag = 0;
list_for_each_entry(entry, ima_rules, list) {
if (entry->action & IMA_DO_MASK)
ima_policy_flag |= entry->action;
* ima_update_policy - update default_rules with new measure rules
*
* Called on file .release to update the default rules with a complete new
- * policy. Once updated, the policy is locked, no additional rules can be
- * added to the policy.
+ * policy. What we do here is to splice ima_policy_rules and ima_temp_rules so
+ * they make a queue. The policy may be updated multiple times and this is the
+ * RCU updater.
+ *
+ * Policy rules are never deleted so ima_policy_flag gets zeroed only once when
+ * we switch from the default policy to user defined.
*/
void ima_update_policy(void)
{
- ima_rules = &ima_policy_rules;
+ struct list_head *first, *last, *policy;
+
+ /* append current policy with the new rules */
+ first = (&ima_temp_rules)->next;
+ last = (&ima_temp_rules)->prev;
+ policy = &ima_policy_rules;
+
+ synchronize_rcu();
+
+ last->next = policy;
+ rcu_assign_pointer(list_next_rcu(policy->prev), first);
+ first->prev = policy->prev;
+ policy->prev = last;
+
+ /* prepare for the next policy rules addition */
+ INIT_LIST_HEAD(&ima_temp_rules);
+
+ if (ima_rules != policy) {
+ ima_policy_flag = 0;
+ ima_rules = policy;
+ }
ima_update_policy_flag();
}
* ima_parse_add_rule - add a rule to ima_policy_rules
* @rule - ima measurement policy rule
*
- * Uses a mutex to protect the policy list from multiple concurrent writers.
+ * Avoid locking by allowing just one writer at a time in ima_write_policy()
* Returns the length of the rule parsed, an error code on failure
*/
ssize_t ima_parse_add_rule(char *rule)
return result;
}
- mutex_lock(&ima_rules_mutex);
- list_add_tail(&entry->list, &ima_policy_rules);
- mutex_unlock(&ima_rules_mutex);
+ list_add_tail(&entry->list, &ima_temp_rules);
return len;
}
-/* ima_delete_rules called to cleanup invalid policy */
+/**
+ * ima_delete_rules() called to cleanup invalid in-flight policy.
+ * We don't need locking as we operate on the temp list, which is
+ * different from the active one. There is also only one user of
+ * ima_delete_rules() at a time.
+ */
void ima_delete_rules(void)
{
struct ima_rule_entry *entry, *tmp;
int i;
- mutex_lock(&ima_rules_mutex);
- list_for_each_entry_safe(entry, tmp, &ima_policy_rules, list) {
+ list_for_each_entry_safe(entry, tmp, &ima_temp_rules, list) {
for (i = 0; i < MAX_LSM_RULES; i++)
kfree(entry->lsm[i].args_p);
list_del(&entry->list);
kfree(entry);
}
- mutex_unlock(&ima_rules_mutex);
}
projects / GitHub / LineageOS / android_kernel_motorola_exynos9610.git / commitdiff