[PATCH 3/5] device_cgroup: keep track of local group settings

@@ -39,13 +39,27 @@
 	struct rcu_head rcu;
 };
 
+enum devcg_behavior {
+	DEVCG_DEFAULT_NONE,
+	DEVCG_DEFAULT_ALLOW,
+	DEVCG_DEFAULT_DENY,
+};
+
 struct dev_cgroup {
 	struct cgroup_subsys_state css;
+
+	/* result of merging the parent's rules with local ones */
 	struct list_head exceptions;
-	enum {
-		DEVCG_DEFAULT_ALLOW,
-		DEVCG_DEFAULT_DENY,
-	} behavior;
+	enum devcg_behavior behavior;
+
+	/*
+	 * local set rules, saved so when a parent propagates new rules, the
+	 * local preferences can be preserved
+	 */
+	struct {
+		struct list_head exceptions;
+		enum devcg_behavior behavior;
+	} local;
 };
 
 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)

@@ -104,8 +118,41 @@
 /*
  * called under devcgroup_mutex
  */
-static int dev_exception_add(struct list_head *exceptions,
-			     struct dev_exception_item *ex)
+static void __dev_exception_rm(struct list_head *exceptions,
+			       struct dev_exception_item *ex)
+{
+	struct dev_exception_item *walk, *tmp;
+
+	lockdep_assert_held(&devcgroup_mutex);
+
+	list_for_each_entry_safe(walk, tmp, exceptions, list) {
+		if (walk->type != ex->type)
+			continue;
+		if (walk->major != ex->major)
+			continue;
+		if (walk->minor != ex->minor)
+			continue;
+
+		walk->access &= ~ex->access;
+		if (!walk->access) {
+			list_del_rcu(&walk->list);
+			kfree_rcu(walk, rcu);
+		}
+	}
+}
+
+static void dev_exception_rm(struct dev_cgroup *devcgroup,
+			    struct dev_exception_item *ex)
+{
+	__dev_exception_rm(&devcgroup->local.exceptions, ex);
+	__dev_exception_rm(&devcgroup->exceptions, ex);
+}
+
+/*
+ * called under devcgroup_mutex
+ */
+static int __dev_exception_add(struct list_head *exceptions,
+			       struct dev_exception_item *ex)
 {
 	struct dev_exception_item *excopy, *walk;
 

@@ -133,30 +180,26 @@
 	return 0;
 }
 
-/*
- * called under devcgroup_mutex
- */
-static void dev_exception_rm(struct list_head *exceptions,
+static int dev_exception_add(struct dev_cgroup *devcgroup,
 			     struct dev_exception_item *ex)
 {
-	struct dev_exception_item *walk, *tmp;
+	int rc;
 
 	lockdep_assert_held(&devcgroup_mutex);
 
-	list_for_each_entry_safe(walk, tmp, exceptions, list) {
-		if (walk->type != ex->type)
-			continue;
-		if (walk->major != ex->major)
-			continue;
-		if (walk->minor != ex->minor)
-			continue;
+	/*
+	 * we add to the local list so we can preserve local preferences if
+	 * the parent propagates down new rules
+	 */
+	rc = __dev_exception_add(&devcgroup->local.exceptions, ex);
+	if (rc)
+		return rc;
+
+	rc = __dev_exception_add(&devcgroup->exceptions, ex);
+	if (rc)
+		__dev_exception_rm(&devcgroup->local.exceptions, ex);
 
-		walk->access &= ~ex->access;
-		if (!walk->access) {
-			list_del_rcu(&walk->list);
-			kfree_rcu(walk, rcu);
-		}
-	}
+	return rc;
 }
 
 /**

@@ -175,6 +218,11 @@
 		list_del_rcu(&ex->list);
 		kfree_rcu(ex, rcu);
 	}
+	list_for_each_entry_safe(ex, tmp, &dev_cgroup->local.exceptions,
+				 list) {
+		list_del_rcu(&ex->list);
+		kfree_rcu(ex, rcu);
+	}
 }
 
 /*

@@ -190,6 +238,8 @@
 	if (!dev_cgroup)
 		return ERR_PTR(-ENOMEM);
 	INIT_LIST_HEAD(&dev_cgroup->exceptions);
+	INIT_LIST_HEAD(&dev_cgroup->local.exceptions);
+	dev_cgroup->local.behavior = DEVCG_DEFAULT_NONE;
 	parent_cgroup = cgroup->parent;
 
 	if (parent_cgroup == NULL)

@@ -413,6 +463,7 @@
 				return -EPERM;
 			dev_exception_clean(devcgroup);
 			devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
+			devcgroup->local.behavior = DEVCG_DEFAULT_ALLOW;
 			if (!parent)
 				break;
 

@@ -424,6 +475,7 @@
 		case DEVCG_DENY:
 			dev_exception_clean(devcgroup);
 			devcgroup->behavior = DEVCG_DEFAULT_DENY;
+			devcgroup->local.behavior = DEVCG_DEFAULT_DENY;
 			break;
 		default:
 			return -EINVAL;

@@ -513,10 +565,10 @@
 		 * don't want to break compatibility
 		 */
 		if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
-			dev_exception_rm(&devcgroup->exceptions, &ex);
+			dev_exception_rm(devcgroup, &ex);
 			return 0;
 		}
-		return dev_exception_add(&devcgroup->exceptions, &ex);
+		return dev_exception_add(devcgroup, &ex);
 	case DEVCG_DENY:
 		/*
 		 * If the default policy is to deny by default, try to remove

@@ -524,10 +576,10 @@
 		 * don't want to break compatibility
 		 */
 		if (devcgroup->behavior == DEVCG_DEFAULT_DENY) {
-			dev_exception_rm(&devcgroup->exceptions, &ex);
+			dev_exception_rm(devcgroup, &ex);
 			return 0;
 		}
-		return dev_exception_add(&devcgroup->exceptions, &ex);
+		return dev_exception_add(devcgroup, &ex);
 	default:
 		return -EINVAL;
 	}